Cranks, Shafts and etc.

Show some teeth

2012-03-10T05:27:00.002-08:00

The dynamics of a bikes power delivery is not as simple as it looks. One of the first things that needs to be done after a modification that improves performance is to choose the right sprocket size, for the target speed and RPMs.

People often assume that going to a bigger sprocket automatically increases top speed, by a simple ratio (I was under this delusion too, which was removed by practical experience and some study of the physics involved)

Let's look at what it takes to go fast...

In a frictionless, vacuum, there is a simple relationship between power, acceleration and mass :

A = P/mv

P = A/mv

v = P/Am

This is why there is no concept of "top speed" for a spacecraft. For a constant power output acceleration will asymptotically reach 0 and velocity will reach infinity (forget relativity for now, were talking Newton-ese)

Once you add gravity and friction to the picture, there is a certain constant frictional force that counters the acceleration, but there is still no limit to the maximum velocity achievable.

For a real world vehicle scenario, the most important factor comes into play next - atmosphere and air resistance.

Somewhere around 35 mph or 50 kph, this factor starts getting significant.

The formula for determining top speed from power including aerodynamic drag is involved - here is one from Mazda :

P = ((A/2 * Cd * D * v^3) + (Cr * m * g * v))

with

A: being the frontal area in m^2

Cd: being the drag coefficient (0.3 for sports cars, 0.5 to 0.75 for motorbikes, 1 for trucks)

D: Density of the air (1.29 kg/m^3)

Cr: roll resistance coefficient (about 0.015)

m: Mass of the vehicle in kilograms

g: The earth's gravitational acceleration (9.81 m/sec^2)

v: Velocity in m/sec (kph/3.6 or mph/2.2374)

P: Wheel power in W (divide by 736 to get hp)

Another common formula that works pretty well is the LRT formula :

hp = (mph / 215.39)^3.3135 x weight (lbs)

The main thing to notice is that power is proportional to the cube of the velocity. Doubling the speed needs roughly eight times the power. The drag formula seems on the button, the LRT is a bit pessimistic.

For a typical motorbike, the frontal area is about 0.5 to 0.75, including a rider. My enfield comes in at 0.75 - How do I know?

I took a head on picture of a Bullet, with fully geared rider, made a silhouette of it and counted the pixels. A few calculations based on the wheel diameter and I got a ballpark calculation.

Fully geared rider on loaded bike

Profile of above picture

Thus what we have is that a certain speed requires a certain power at the wheel. So the next step is to formulate a function for power delivery.

This is quite simple : Take a dyno chart ( I did this for the CL500 and Fireball ) and put a few numbers say every 1000 RPM into a spreadsheet, and make a chart out of it.

Then you can ask Excel to derive a second order order polynomial function F such that P = F(RPM)

The function maps the dyno data quite well, and there is only a few % difference anywhere. The CL500 chart didn't fit well, so I did a linear approximation by filling in straight line approximations between data points.

The next step is to calculate the speed at each RPM for a given sprocket and tire size. We then use the LRT and Drag formulas to determine how much power is required to actually go at that speed. From that we derive the required torque for both formulas.

Thus we now have, for a given speed and a given gearing, how much torque is needed to maintain that speed.

Now we can divide the available torque by the required torque to get a value. If this value is greater than 1.0 then the engine can increase its RPM. At the point it reaches exactly 1.0 the engine will no longer be able to rev any further.

To get a sense of what is the ideal sprocket size, we can multiply the above value by the sprocket teeth to know what is the maximum sprocket size possible to rev out at that RPM. This will obviously not be very accurate for the lower RPMs, but it gives a pretty accurate picture in the later revs.

Plugging in different values into this, we can clearly see that within a certain range, changing the sprocket does not affect top speed much, since the fag end of the power curve is quite flat. But outside that range, the top speed is always reduced.

Here is the chart for the Fireball and CL500 respectively (Google docs link, opens in new window).

The highlighted fields show the RPM range where the required sprocket size goes below the actual sprocket size. That is the rev limit.

You can easily adapt this chart for any bike if you have a dyno chart image (ask me for the Excel sheet if interested)

The main benefit of a taller sprocket is to have a slightly reduced RPM for cruising. In the fireball at 19 teeth 19", the engine will be exactly at around peak power close to 5700 RPM, hitting the "ton". Which means it's geared perfectly right.

The CL500 also hits around 128 kph at 19T, 18" wheel at 4600 revs which is the peak power RPM.

I have chosen 0.6 as the c.o.d. value, but a slight variation in it causes quite a change in the values. But at least, relatively, you can see what happens with different sprockets.

The silence of the bangs

2012-02-17T12:11:00.000-08:00

I never cared much about the exhaust note of my bike, when I initially rode it around. But the stock silencer was an enormously long one and looked totally weird. My mechanic at that time (Jaf from Chennai) swapped it for a shorter one.

I'd never given it much thought after that, but one day as I was ripping down a flyover, the silencer fell right off! Apparently the mounting bracket had cracked, and the secondary bracket bolt loosened due to vibration. I never noticed that and when I rode full speed over a rut in the road, it just fell off. It looked pretty bad, vehicles swerving around avoiding hitting that thick piece of metal on the road. Fortunately there was a traffic cop who held the traffic off as I scrambled to fetch it.

I rigged it back temporarily and then the following day, I went over to Nandan's to find out where to get it fixed. For some reason I couldn't get it done that day and Nandan lent me a silencer to use until I could get mine fixed. It was almost exactly the same as the older one. A few months later, this one broke its bracket too, and this time I went back to Nandan, to retrieve my old one and get it fixed. We could not find that anywhere amongst the huge piles of spare parts, so Nandan said "Hey, I have an experimental glass wool thing, try that out, keep it if you like."

Once I'd hooked that up, I was totally hooked - It had a nice bassy roar and lovely idle beat. It boosted performance enough to notice. But it was a little noisy and since it had been made by chopping and welding, the finish was not quite up to spec and despite my grinding and epoxy filling and painting, it was not possible to make it look aesthetic.

So I decided to build one of my own, and promptly chopped the older silencer I had into two halves, and figured out a way to bolt the two halves together as follows.


The lower half


Upper half


The stuff that was inside, which I knocked out.

The "blueprint"

Two studs made of a copper rod to enable bolting it together

A spacer I cut from a rubberized dumbbell


Close up of the assembly

At this point it was just a hollow bottle shape, and when I put it on, just for kicks, it sounded like a tin can.

Now I had not much idea about how silencers work, all I knew was a certain length would resonate nearby certain RPMs, thus boosting scavenge. I was under the incorrect impression that a certain back pressure was necessary for proper running. Thus I thought I'd need to put in something there that would be slightly restrictive, but yet allow the gas to flow in a more or less straight path.

My first experiment involved getting a number of aluminum tubes of 3/8" diameter and packing them across the length of the silencer. I thought "OK that wont be as restrictive as a baffle, but there will be some smooth restriction of flow, due to the thin tubes".

I put it on, and it still sounded like a tin can, so that was the end of that! But I believed the tinny noise was due to gas entering the wide part of the silencer body. I bought a thick aluminum tube that fitted snugly across the length of it.

Then I remember reading somewhere on some blog about the Brough Superior or some such ancient legendary motorcycle having a spiral baffle and blowing smoke rings. I had no idea what a spiral baffle looks like, but I thought "Aha! I'll put a spiral strip in a tube and the gas will spin around slowing a bit and I shall have a glorious and unique design."

I spent the better part of a day hacksawing a 1.75" strip of thick stainless steel from a sheet I had. Then I decided I'd twist it into a strip that would fit in the aluminum tube. It was an exercise in frustration - That piece of Al was completely stubborn and all the kings men and wild horses could not have twisted it into the tight, even spiral that I wanted. I tried hammer and vise, and vise-grip and bare hands, and gloved hands and I finally gave up after some bruised knuckles and bleeding heart. So the whole spiral idea spun away into oblivion.

Then I thought "OK, while I'm at it, maybe I'll go back to my initial idea, but this time I'll put the thin tubes in the thick tube, and no gas will leak into the main silencer body - It will be like a long, straight through pipe, except for appearance."

Instead of putting long tubes through and through, i inserted small (3") pieces of 3/8" tube on either end of the bigger Al tube, wedging in enough of them to pack tightly. Some I hammered into a slightly flat shape so that I'd get a denser packing. This should work!!

But this was again not to be... Same old leaky tin-can noise... Arrrrrgh!

Then I decided I'll go ahead and use the tried and trusted design, use a perforated tube and pack the gap between with glass wool. After much study on the intertubes, I realized that the ideal silencer was no silencer, and all the stuff was there to muffle the sound (obviously! it's called a muffler/silencer, not a "gas flow constrictor"). I also learned that the tinny sound was not so much due to the gas flowing incorrectly, but simply the effect of a loud bang happening within a hollow pipe.

So I started drilling holes in the tube, and got tired after about 40.

Then I thought I ought to try with something more easy to prototype, before committing to this design. Suddenly, I remembered I had this old rolled up aluminum sheet with holes (that I had originally made for this very purpose many many months ago, and relegated to a junk box while I dallied with all the unworkable ideas.

The shiny thing in the corner is the down tube using which I rolled this aluminum sheet into a tube.

Glass wool, however, from what I had heard of it, was a nasty substance, just ready to get into your skin and lungs and eyes, I wanted no part of it. I looked on the net and some people were using wire meshes and stuff for silencer packing with good results, so I decided I'll use steel wool - the maximum danger seems to be tetanus, and that's avoidable, as opposed to silicosis or some such horrible ailment you may get from inhaling microscopic glass.

Trying to buy a small amount of steel wool was a challenge. I ended up buying 5 KG, which is a lot of it! Finally, today, I stuffed about a kilo and a half in the gap, with the reverence of a Christmas ritual, and rammed it in tight. I fitted the silencer with bated breath and fired the beast up, and SILENCE! Finally it was doing what it was meant to! A silent silencer, with nothing that is obstructing the gas flow. So silent, that now the valve train noise is unbearable! Something quite charming about a muted thump that's barely heard at idle, yet without the whiny sound associated with the stock Enfield silencers.

So this week I'll drill the remaining 360 odd holes in my thick gauge tube, and replace the thin rolled sheet tube with this.

My calculations seem to point to a resonance frequency of about 3300 RPM - They say a glass pack is like a very long collector pipe, and I have about 67 inches from exhaust valve till the end of the silencer.

So that would put the ideal scavenging RPM range somewhere close to peak torque ate about 3000-3500 revs. This would be very good, as the major portion of my riding is done at between 2800 and 4000 revs, and a boost there would make it more relaxed.

I might go a bit easy with the steel wool now, maybe I like a little more of ze what you call - "Ze thump"

Remains to be seen if the hard rubber spacer thingummy withstands the heat. If it starts burning, I'll have to make that piece with metal somehow.

Altogether cost me about the equivalent of 25 US$, including the value of the silencer that I cut up. This is what you can do with an Enfield!

Throttle wide open at Kari race track

2012-02-13T14:34:00.000-08:00

Racing bikes...

On the one hand, the sheer excitement of being able to actually ride on a race track, and be trained by experts, all at a very affordable price!
On the other hand, the awareness of one's own meager riding experience and skills, and the fear of possible failure, injury to flesh and steel, and humiliation.

But the former won the day, and I rode down to Coimbatore, to attend the indiMotard T.W.O. track school event.
On the ride down, my ride buddies found it quaint that I'd wanted to bring a Bullet of all the things - One expressed surprise that I'd often out braked him at the speed breakers on the highway.

Somewhere along the way the bike suddenly dies and I coast to a halt... I forget the cardinal rule with my bike - "If it stops without any reason, it's a fuel problem, it's probably in reserve".

I cranked it like a donkey, checked the spark plug, tapped the carb to free the float if stuck, but nothing. Then i checked the fuel flow and saw it was in reserve - As far as I can remember, the only time my bike ever gave out mid-journey was due to either lack of fuel or a stuck carb float... And each time I'd done all crazy things trying to start it (including once pushing it uphill on a steep flyover in Chennai to try to get a rolling start, thinking the battery was dead) except the most simple thing - to check the petrol!

So much for the famed unreliability of Bullets.

We climbed to Ooty, all of 36 hairpin bends, lovely road, lovely weather, but nowhere near as scary or difficult as the Himalayas. On the downhill section, at some point I suddenly found my front brakes going spongy. I quickly stopped, using the very inadequate and worn out rear, and looked for any damage, lost brake fluid etc. All seemed fine, then i touched the brake caliper unit and it was burning hot. Seemed like the brake fluid had boiled due to aggressive use over the entire descent. After a 15 minute break waiting for it to cool, we set off and my buddies graciously agreed to ride slowly for a while, just to be on the safe side. We soon hit the plains and the brakes worked just fine. Then a lot of traffic, all the way into Coimbatore city.

In the morning, I taped the headlight and indicators, and took off the main stand for safety reasons, as advised. Then we set out for the track about 15-20 KM away.

I had no idea what to expect there, but no sooner than I saw the instructors however, that I knew things were gonna be great - you can just see it - there are people who have things and do things and there are people who be things - These guys were not the guys who "have bikes" and "do racing" - they "were racers".

There were lots of R15s and P220s, hordes of CBR 250s, some Ninjas, the odd R6 and Duke 795 monster.
We started off with a classroom and much of it was familiar to me as theory - Apex points, no rear brakes, throttle modulation, slow entry, fast exit - but I'd never given it much thought, since I never ever expected to ever apply that theory on a track.

Then we got on the first track drill, by following the instructors on the track for a couple of laps, slowly, first on the outer line, then the inner, then the middle, to get a feel for the track and identify any markers. Then came the single gear drill... We were supposed to ride the track in one gear without any brakes. It wasn't that hard for me, because I decided beforehand(wisely), that I would concentrate less on going fast and more on doing what had been told. Besides my 3rd gear is good for anywhere between 20 and 90 kph, so that was that. I was disappointed by the fact that many of the guys were not following the no-brakes rule, coming too fast into corners and correcting with the brake. Even more scarier was the sight of seeing the brake lights glowing mid corner.

After a couple of drills, at some point they said, OK just ride around the track now, any which way - and then everyone went nuts, and even so did I foolishly, rather than trying to apply what had been taught in the drill, everyone, including me started just gunning like crazy and taking totally incorrect lines - I was stupidly chasing down the bike ahead of me, rather than concentrate on the track. That's when I saw the first guy deck his bike - it was a blue R6 and it went down at the "bowl" - a relentlessly long sweeping curve, which I personally felt was the most difficult part of the track to drive fast.

Then we were given more "track-gyaan" in the classroom, and did drills for entry and exit of each curve - there were little blue X marks on the track at the good entry and exit points and we were supposed to ride as close to them as possible... One drill for entries, one drill for exits, and each time to attempt getting the apexes correct. It wasn't at all going well for me... I touched my crash guard down and got a bit jittery, so I started taking more lazy and invalid lines. The instructors were eagle eyed and they hailed us down to talk to us and correct our mistakes - I loved the fact that they had great patience, and very objectively encouraged us to get it right - not at all a "school" kind of sternness or reprimanding. Once in a while they led us around the track, pointing and signalling at us as to, where the markers were, when to open the throttle and so on.

There was Anand, really experienced, who raced extensively in club events in the US, and Joshua who led my drills (who's also a pilot), and Daniel 'Dodo' - who I'd met in 2004, at the Madras Bulls group, and 'Schumi' from Overdrive, and of course, Prashanth who had done all kinds of crazy things on the track with Bullets and Yezdis, back in the day.

They seemed to know every kind of bike on a first name basis...

Obviously my noisy old beast of a clunker attracted some attention, and enough good natured ribbing about the only three tools ever needed to fix a Royal Enfield...
A small hammer, a bigger hammer, and a matchbox to set it on fire. They forgot about the 4th tool, the nice guy who usually rides on one!
Dodo especially, hid his pain as Bullets were joked about, since he himself owns and rides several, but then again all the indiMotard guys own an Enfield in some form or other, and ride them, so LOL!

During the drills when we were allowed to use all gears, and brakes, people were falling left and right, every which way. I was once in a while gouging my crash guard into the ground and it wasn't doing much for my confidence.I was glad I didn't fully lose it though. My (biased?) opinion was that the drills were actually quite simple, and there was absolutely no reason to fall if you followed instructions and didn't act too gung-ho. This was later vindicated when I took a joy ride with Anand on day 2 at a blistering pace on a Ninja - at times the horizon seemed almost vertical from my view, I had the tank in a white knuckled death grip, and as he snapped the bike to and fro across the chicanes, the G forces made me feel like my liver and pancreas were doing a little dance inside. I daresay he could have easily maxed out the capabilities of the lil' green Ninja 250 if he'd wanted to. All our level 1 guys speeds were nothing compared to this.

At the speeds at which all of us Level 1 guys were riding, the only reason to fall during the drills, would have been rider ineptness or panic reactions. There was no way anyone could have been approaching the traction limits of the bikes, if they rode on the right lines as instructed.

I took the policy of easing off if I took the wrong line, and trying to do better the next time around, rather than try to gun it when it's clearly going way outside the proper path. I was very wary of falling, for fear of damaging the bike, which may have been either a good or bad thing - good because I didn't get shaken up and lose my nerve, bad because perhaps at points I didn't push my limits, especially on Day 1.

After lunch we had the brake drills, where we had to start off from about 10 meters away and brake smoothly to stop exactly at a given line. I did the first drill and heard some "chak chak" noise from the rear - braked a little too much and stopped short. Second time round I noticed while waiting for my turn that some of my rear sprocket teeth were broken off... I was like "Oh hell! Of all the times!". I did the second drill anyway, managed to stop on the line, and then took a break to inspect the damage...

Prashanth of "Let-me-tell-you-about-the-time-when-we-completely-destroyed-RD350s-on-the-track-with-our-bullets" fame, tells me "If less than 7 teeth in a row are broken, just tighten the chain and keep going! It will work just fine".

Inspection showed however that about 12 or 13 consecutive teeth had been sheared of, and a couple of them right at the roots. It seemed that the chain had been quite loose and the hard ride down had caused the damage. Prashanth told me where to go get it fixed, and I had to skip the rest of day , since it was about 4:30 PM and a Saturday, and I needed to get it done before the garage folks closed.

I tightened the chain by several notches, and set off to the city again - Even with the busted sprocket, I could not tell there was anything wrong now! Such is the nature of the beast.

I spent the rest of the evening getting the parts, and holding a torch for the mechanic guy when the power failed. Very decent chap, he had gotten word from the track guys that my bike needed a sprocket job, and he worked fast and hard, in the poor light to get it done for me.

Got back to the hotel, had dinner, and then joined a friend and hung out with the instructors for a while... Everyone called it a night and then it was just me and Shriram, a young chappie who'd just joined indiMotard and we got along really famously, and kept blabbering on till almost 2:30 AM.

The next day dawned, and I was feeling a bit nervous, since I'd not ridden to the level I'd be satisfied with, the previous day.
We did a couple of sessions and though I did better on the chicanes, I was completely inconsistent and totally off on the first corner and the bowl curve. We were supposed to do the whole combination - everything we did in all drills combined - brake smoothly, enter on the blue X, apex it, exit on the blue X, throttle wide open...

I consulted with Schumi, about the right line for my troublesome areas, and tried to make sense of the shape of the track. He emphasized that the point was to get the line properly, and that speed was the side effect of correct riding, not vice versa.

Anand advised to concentrate on just one of the troublesome points per lap, rather than stress out, trying to ride the whole thing perfectly, and to relax.

After lunch, I walked down to C1 and did a sighting from several points, as to where the X marks were (each time before when I rode, I'd been hunting for the second X and found it way too late)

Then it was time for the final session of the day, and somehow things just started to fall into place for me. I did these things...

I braked slowly and smoothly, way way before the bend, so I'd not use an aggressive downshift to control speed.
I realized I needed to swing the bike deliberately at the S and Z bends - Earlier, I had been leaning it in fast, but letting it straighten on its own, which made it take too long to lean in the other direction.
I turned in a little later consciously - this helped me judge the right apex point
I looked far far ahead on the track.
I taped over the rev counter as advised (speedos had been taped over on drill 1 itself)
I sang (in a very ad hoc nursery rhyme like tune) to myself, telling me what to do - something like "Now take the first X, cross the oil patch, take the second X, look at the ape-X... Swing it right and, hit the apex, gun the throttle, swing it left now.... when its the 100, press the brake-ed, when its 50, you down-shifty...."

After a couple of laps, I was feeling really good, I managed in many places to up shift before I even hit the second X, coming out of the apexes. I still did have to take a slightly easier line at the curve where my crash guard would bottom, but at least I got some consistent line there. Next time I'll get a higher one!

Each time around, I eased off on the main straight, relaxed a bit - I was totally unconcerned about lap times - straight line top speeds were hardly the point of the whole exercise - as one of the instructors said, even a monkey can top out any bike on a straight line!

It was a glorious 10 laps or so, I think, until the red flags waved, and in the last one, I managed to actually keep throttle fully wide open coming out of the bowl. I was really grinning when i got back to the pit. I probably made a horrible lap time, even discounting the straights, but I was happy because I had learned something.

After that there was some open session time, and Dodo took my bike out (while I rode pillion with Anand on a Ninja) - Dodo was able to ride the hell out of it, leaning motocross style, avoiding the crash guard scraping, putting the toe out under it to gauge when it would touch. He managed to outdo many of the nimbler bikes on the track, with my ponderous lumbering beast.

There was one particular guy, with a Splendor... He was doing an amazing job, of course the bike was not quite up to ripping down the straights, but on the curves, he had a perfect consistent line, and was a treat to watch. Then there was this souped up screaming Shaolin that would hold a CBR all around the track, lose on the straight, and then catch up again in a couple of bends.

All this convinces me that it takes a huge amount of skill to get the maximum out of a bike. I was told (and I am convinced), that I should try a more nimbler bike, so that I could learn faster with less effort. I will probably do that, but I will definitely stick to my Enfield primarily until such time that my skill reaches a much higher level - of course, by then, I'll do a Fireball conversion, so it will once again be way beyond my skill to max it out.

I hung around till the end, hobnobbing with all the chaps, and we went back to the hotel. Spent a couple of hours with the indiMotard guys and Karthik from TopGear India. Had dinner and went to bed, deciding on a relaxed start the next day for the ride back home.

Next morning me and Karthik rode back together to Bangalore, we started at 11:30 or so, and he maintained a perfect consistent pace on his CBR, just at the cruising speed of my bike, and we maintained approximately 115 to 120 kph for about two hours non-stop on the nice Salem - Krishnagiri route. Bike was roaring beautifully, a very relaxed and non-tiring ride, we hardly knew by the time we were in Bangalore city, and despite the slow progress through the messy traffic at Coimbatore and Bangalore city limits, we'd reached the forum mall by around 4:15 PM.

Altogther a really wonderful experience, I'm certainly going to try to make it for the Level 2 course next month, and I am bringing my black, noisy, hunk of cast iron too!

Counter strike out!

2012-01-27T13:30:00.000-08:00

So yesterday, me and a bunch of friends went out to this paintball range and while we waited for our turn, we decided to go check out a small ATV ride in the same place.

I was all excited, since I'd never driven one before and I assumed I'd be able to really throw it around since I consider myself a pretty decent bike rider (I've never driven a car BTW).

However, no sooner than I got on the ATV and set off, did I realize that something was wrong - I was totally unable to steer the vehicle in the direction I wished - The total steering movement of the handlebars was way, way more than what a motorbike would have and for some reason (simple physics and the fact that this was a 4-wheeler), all my attempts at correcting steering using lean were totally in vain. I seemed to be counter steering - My brain was saying "turn right" but my hands were causing the vehicle to turn left.

I had three attempts and each time I ended up a few meters ahead plowed into the median on the left edge of the track. Each time my foot ended up on the ground as if I were driving a motorbike and needed to keep it standing.

My friends had no issues driving around the track at all, and while they are not self-professed bikers, they do ride motorbikes to varying extents.

It was embarassing and weird, and my only consolation was to convince myself that my bike riding instincts are so strong that they cannot be over-ridden, meaning I must have some skill at least!

This whole episode convinces me that counter-steering input is used at all speeds on a motorbike, contrary to my earlier beliefs about this.

It seems to be true that at any speed, one initiates lean by a counter steer, and then uses body position to fix the lean angle of the bike. In my case with the ATV, every steering attempt of mine resulted in the vehicle going a bit more in the wrong direction. Since it did not respond as my instincts expected, I apparently increased my steering input magnitude to compensate... until I ended up with steering fully locked, to the left and left front tire pressed hard against the extreme left of the track and with my right leg down, as if I was wrestling the machine to lean to the right.

Much humbled, a bit confused, but now wiser....

What I built this weekend

2011-10-10T11:22:00.000-07:00

Ever since we did a rebuild of my bikes on a new frame in 2005, the meter console had never been quite right - We'd replaced the original wiring and console of the Lightning with the Thunderbirds.

The chromed plastic bowls had been quite scratched and the mounting stubs broke, and so we ended up taping the meters together with duct tape. In time I replaced the tape with a strip made out of two red bull cans. Skillfully disguised, but still tacky...

So this week I had Thursday and Friday off, so I decided to build a new console - I started with this :

A 87mm inner dia copper pipe (funny that my bikes piston is exactly this size! )

I'd looked for aluminum or brass, but no one was selling me a piece shorter than 12 foot. Steel and SS is just too painful to work by hand.

First sawed it with a hacksaw, filed and deburred the edges, made a three inch piece for each meter

The pipe pieces were slit lengthwise to allow the meters to fit in.

Another segment cut and drilled to join the two together - Phew! Sawing this 3 mm pipe by hand is a real bitch.

Bolted together with some SS fasteners salvaged from an old motherboard.

Added two more bolts, threaded into the copper - The screws are tough enough to cut their own thread. A slot was cut in both sides and the bolts washer slots into it.

A spacer is bolted across the two pieces and the thick SS bolt holds the entire thing stable. It's well below the bottom of the meter innards.

An L shaped bracket made from some scrap I had lying and a aluminum thingamajig to fit the ignition key switch.I had to drill that hole with a Stanley power bore bit, it managed quite well in aluminum. Not the most sturdy thing, but it will do.

Spray painted the whole thing matte black.

Found a part of the old console and cut the piece of it, drilled holes for LEDs and wired them up, replacing the old bulb based indicators.

It took me three days to build this, I used a hacksaw, files, a drill machine, and a Dremel moto tool. It's not the most perfect thing with sub millimeter accuracy, but it works and looks good!!

Back and forth, left and right

2011-09-23T10:41:00.000-07:00

There's a lot of riding folklore out there, passed on from the mists of time... Not all of it is accurate or logical.

One of the most common myths is about the use of the front brake - Indeed as a kid, when I first rode a bicycle, I was told by my friends "Never use the front brake! The bicycle will somersault!"

I was too dumb then to realize that physics does not bear this out. Indeed I never ever did use the front brakes on my bicycle ever, for the brief time that I did ride one!

When I graduated to a motorbike, however, I had read enough at msgroup.org and various other locations on the internet to realize that the front brake is where it's at.

My first motorbike was an Enfield Bullet Lightning 535 as seen here (this is not my bike)

It's essentially a beefed up 500 bullet with :

535 cc's - Bore 87mm vs the 84 mm of a 500, producing a claimed 26 crank HP, and bigger oil rocker feed lines.
Fritz Egli design "high speed" forged piston - a real lemon - this piston is prone to seize or become very loose and clattery - also they cost a fortune. Thankfully I never had one seize, although the first one cracked - I've since "downgraded" to a solid UK made cast piston, cheap and robust..
Disc brakes
"Cruiser" styling

When I first rode the bike, I fell several times, almost always by locking the front wheel on sandy patches. For some reason the cruiser style handlebars and the seating made for a vague front end, similar to the Bullet Thunderbird, and totally unlike the way an old Standard 350 Bullet handles.

The default Dunlop ribbed front tyre didn't help the cause much - for a while I doubted my ability to ride, and was chided by several (non-biking) peers about my "incorrect" braking technique.

After a big T-bone accident I had at about 50MPH (which bent the frame down tube by sheer impact force), we rebuilt the bike onto a standard 350 frame, while retaining the original handle tee.

Since then the bike handles perfectly, and last year, after the addition of a Pirelli MT60 front tyre, I have never been able to get the front wheel to skid, even under relentless braking. Meanwhile the rear wheel can break traction even under over-aggressive down shifting.

So the whole "use front brakes unless you are in a curve" theory is vindicated.

What I've never been able to figure out completely is why the Thunderbird style seating and handlebars give rise to front end instability.

Here's an interesting observation though - If you trace the paths of ends of the handlebar from lock to lock, you will find a big difference between that of the Thunderbird and the Standard Bullet and how my bike is set up :

Figures are not very accurate and a bit exaggerated since the handlebar is a complex shape, but the idea is pretty clear.

Something radically good in terms of control seems to happen when the handlebar ends are between 9 o' clock and 3 o' clock positions. Gets progressively bad as they come towards 6 o'clock, as evidenced by the better handling of the Standard as compared to the Thunderbird and even better handling on my bike which has the Standard handlebar mounted in the Thunderbird tee yoke.

Perhaps is as simple as the fact that the further ahead the bars are, the more forward the rider weight goes, or maybe its the arc that the arms trace - consider driving a car with the hands on top of the wheel vs. hands at the bottom.

It could be the fact that close to 9 and 3 o clock, lateral movement of the hands is almost nil, only forward backward motion is involved.

Whatever it is, it's quite surprising that mild change in seating position and handlebars alone can affect the feel of a bike so much!

Comparing bananas and lemons - Part 1 : Power

2011-08-27T04:14:00.000-07:00

When it comes to motorbikes, there is a lot of partisan attitude, some fanboyism and cliquishness…

Right here we have the Bullet chaps (moi included), the Yezdi/Jawa fans (me included), the RD350 lovers, and the RX boys – Inevitably, there is debate about the relative merits of each and much bragging about top speeds and ¼ mile times.

But, the problem is: How would you go about comparing say a 100cc Hero Honda Splendor with a 1300cc Suzuki Hayabusa? It’s all very well to say that they’re made with different aims and can’t be compared, but actually they can – even though the only common thing about the two is the fact that they’re Japanese designs and 4 strokers.

Looking at the fundamental aspect of a motorbike – the engine – we can define certain parameters that let us place a bike as a point in some multidimensional space and see how it compares to others along different dimensions.

Power

The scientific definition of power is “Work performed per unit time” – no doubt this is the absolute measure of a bike, but then things are also relative – Which is more impressive? An elephant lifting a quarter of its weight, or a slim weightlifter hoisting four times his own weight overhead?

Thus, to measure different classes of bikes we need to normalize the power values.

An engine produces a certain amount of power at a certain RPM with a certain displacement – Ideally, (and this is true to a large extent as you will see later) we should assume that if you double an engines displacement, and maintain the same RPM, you should expect twice the power. The same applies to doubling RPM while keeping the displacement same.
The reason is simply because an engine is essentially an air pump, and the power it produces is purely dependent on how much air flows through it.

Thus, the correct way to measure relative power output is to divide the actual value by RPM and displacement.

For example: If a 100cc engine makes 7.5 HP @ 6000 RPM, we should expect a 200cc engine of similar design to develop 15 HP at the same RPM, since it displaces twice the volume as the former in a given interval of time.

Thus one of the first variables we can derive (in no meaningful SI units) is HP/Liter-KRevs - Namely, how many peak horsepower are developed per liter of engine per 1000 RPM – We will call this the K - factor

Let’s look at some famous (mostly from the Indian market) 4 stroke bikes past and present and see where they fare… Note that this data is gleaned from manufactures specs and some of it from reading wheel dyno charts, and adjusting upwards by around 15% to get crankshaft figures.

Japanese bikes

Model`	CC	RPM	HP	K
Hero Honda CD100	100	7500	7.5	10.00
Bajaj Pulsar DTSI 220	220	8500	21	11.23
Honda Karizma ZMR	223	7000	17.6	11.27
Yamaha R 15	150	8500	17	13.33
Honda CBR 250	250	8500	26.4	12.42
Honda CB750	750	8000	67	11.17
Suzuki Hayabusa	1300	12000	190	12.18
HD Sportster 883	883	6000	50	9.45

What can we read from this?

The ubiquitous Hero Honda, seen as the epitome of efficiency in India, is actually close to the bottom of the list – The CBR 250 does 24% better. If you metaphorically grafted 2.5 CD100 engines together and revved it up to 8500 RPM, you would get 7.5 * 2.5 * (8500/7500) = 21.5 HP – The CBR makes 5 HP more! So either more fuel is being burnt, or fuel is being burnt better.

In fact, the Hayabusa is quite astounding! If you grafted 5.2 CBR250 engines together and revved it to 12000 RPM, you would get 26.4 * 5.2 * (12000/8500) = 193.8 HP – Just about 2% more than what the Hayabusa makes on paper – Getting 1300cc to rev at 12000 RPM is no joke, it’s hard rocket science to be able to scale up an engine so well! The Hayabusa is an engineering marvel.

The R15 seems quite amazing, with only 150 cc, it makes almost as much as the 220 Pulsar – Seems like the most advanced engine amongst its peers.

The Harley is nowhere near the rest, even though it is a highly engineered design, but then again it’s a pushrod engine with an extremely under-square design, built for an almost flat torque-curve.

Let’s look at the two popular mid level bikes Pulsar and Karizma – Isn’t it startling that despite all the state of the art technology, fuel injection and what not, a 1970s CB750 of much larger capacity comes within 1% of the figures in terms of our metric?

I tell you sir! They don’t make ‘em like they used to! They just hype ‘em louder.

Of course, we aren’t looking at fuel efficiency (yet), so perhaps this conclusion is flawed; perhaps the bikes that have higher K are burning much more fuel. But nevertheless, if the question is: “How much power can you get out of a liter of engine regardless of fuel consumption?” then the above table shows the answer.

Royal Enfield’s

Model	CC	RPM	HP	K
Diesel bullet	435	3600	7.5	4.79
Std 500	500	4750	22	9.26
Std 350	350	5000	18	10.29
Lightning 535	535	4750	26	10.23
Enfield CL500	500	4750	27.2	11.45
ACE Fireball bullet	535	5750	42	13.65
Hitchcocks 612 stroker	612	5750	45	12.79
Enfield Constellation	700	6250	51	11.66
Enfield Interceptor	750	6750	56	11.06

This had to be in a separate table!

Not much to say here, except that Tom Lyons’ (aka ACE) Fireball kit can take a Bullet well beyond Jap bike territory: The dyno charts for the Fireball charts show about 36 wheel HP, so 42 engine HP is a reasonable estimate.

The Hitchcocks stroker 612 does great too, despite having an even longer stroke, and the CL500 is much better than the old Enfield’s, even considering it has to contend with Euro 4 emissions norms.

Quite surprising that the Connie and the Interceptor of yore do so well for air-cooled long stroke parallel twins.

These numbers are derived from observing several wheel dyno charts, rather than manufacturers specs (which are quite off), 6 HP added to get crankshaft horsepower estimate.

Legendary Classic Brit bikes

Model	CC	RPM	HP	K
BSA Goldstar	500	7000	42	12.00
Velocette Venom	500	6500	41	12.62
Triumph 650 twin	650	6500	46	10.89
Norton 650SS	650	6800	49	11.09
Vincent 1000	998	5500	55	10.02

Just astounding! These were mostly OHV pushrod bikes (except the Norton which was an OHC), ranging from the 40s to the 60s.

The Velocette even beats the Hayabusa in this metric! No doubt it ran on “real gas” but even so – this is a 50s bike with 8.75:1 compression! It still holds the 500 cc 24 hour endurance record at an average of 100 mph+, that too with a stock engine. All the employees of Velocette rode these bikes themselves and the build quality was so good that a stock bike was race ready. A few years after this record, they attempted it again with a souped up 350cc bike, which was going great for hours, unfortunately after 6 hours averaging > 105 mph, the piston blew ( this was not a Velocette manufactured one, but sourced from elsewhere) and the record attempt was thwarted.

The ACE fireball is on par with the Goldie on paper, and that speaks a lot about its potential performance!

I ask you!

Two strokes and four strokes

A four stroke has one power stroke for every two revolutions of the crank, whereas a two stroke has one. That means that a two stoke will (ideally) pump twice as much air as a four stroke of the same displacement at a given RPM.

Thus if we want to measure using the above metric then we need to include a factor of two – This is unfair because usually a 2 stroke of a given displacement makes only about 30 to 50% more than a 4 stroke cousin of the same volume – For e.g. take the Yamaha RX100: It makes 11.5 HP vs. 7.5 for a CD100 – that’s 53% more power, which is impressive, but still not double, even though it displaces twice as much air per unit time!

But fair or not, that’s the metric so let’s look at 2 strokes of all kinds:

Legendary two-strokes from India

Model	CC	RPM	HP	K
Jawa 250	250	4750	12	5.05
Yezdi Roadking	250	4750	16	6.74
Jawa 350	350	5000	23	6.57
Yamaha RX100	100	7500	11.5	7.67
Yamaha RX135	135	7500	14	6.91
Suzuki Shogun	108	8500	13.8	7.52
Yamaha RD350	350	6750	30.5	6.46

The RX 100 is the absolute champ here! Squeezes out every ounce of power from that 100cc, the Shogun does quite similarly. The Roadking has its reputation as a rally and motocross bike and for a 70s design, it is quite impressive.

None come anywhere close to the four stroke bikes, so it’s obvious that if you ride a two stroke, you are throwing a lot of fuel down the exhaust chute…. But then again a two stroke has an exhilarating, almost linearly increasing torque curve all the way up to the top, and who can not be enchanted by the coarse whine of the RX, the scream of the RD350 or the burbling purr of a Jawa?

Really amazing bikes

Model	CC	RPM	HP	K
Maico 760	760	4000	43	7.07
Maico 760 @ peak torque	760	1200	26	14.25
Suzuki RS67	124	16500	41	10.02
Honda Rc 165	250	10500	60	11.43
NSR500	500	19000	240	12.63

Yes, all those numbers are correct! The Maico 760 was a two stroke single, the largest ever made, and perhaps the most “gruntiest” of any bike that I have ever heard of… It makes even a thumper like a Bullet look like a revvy whiner. Stomach churning torque, I say! Look at the K factor at peak torque! That is true “bang” for the buck! Only 6 were ever made…

The other Japanese race bikes are again crazy - the RS67 had 4 cylinders, 12 gears and hit 137 mph – unbelievable!

The NSR 500 is probably the most powerful two-stroke made anytime, anywhere and needs just about 2cc to make a HP!

One thing that’s quite clear to me from real life experience is that manufacturers’ figures are way off reality; we all know how optimistic our speedos are… Dyno results are the most believable, and even they have some contradictions.

Read on to the next part where we talk about power to weight ratios…

Comparing bananas and lemons - Part 2 : Torque

2011-08-27T03:43:00.000-07:00

What happens in the hills?

While we have been harping on power all along, some of us are accustomed to grunt and scoff at high revs – which brings us to another metric – torque – To put it very simply, think of your engine connected to a pulley of one meter diameter : The amount of weight it can hoist is the torque.

Torque is the value which can tell you what maximum grade of hill a motorbike can climb – The road is essentially a rope and the rear wheel like a pulley that your bike pulls itself up on.

Most engines have the following power/torque characteristics –

High revving four strokes – make negligible torque at the lower 1/3^rd of their RPM range, and the difference between peak power and peak torque RPM is less than 25%

Low revving four strokes – make decent torque starting from the 1/4^th of the RPM range and the difference in peak power and torque RPMs can be up to 50%, at the expense of peak power values

Two strokes – Rarely make good torque at low end, and peak power and peak torque RPMs are very close – The Maico 760 is an exception here

Torque defines instantaneous acceleration based on the current gear ratio: Climbing a hill at constant speed is equivalent to accelerating steadily on a plain.

With an engine that has a narrow power band, the gears have to be shifted much more often to ensure that the engine keeps within that range. For a given gearing, a wide power band engine has an overlap of speeds across gears, allowing a climb to happen with less shifting and use of the clutch. There will come a point for a peaky engine, where close to maximum revs in a certain gear are required, but the resulting vehicle speed is too much to handle on the twisties. The low revving bikes have the option of modulating speed with the throttle in the same gear since torque does not fall off too rapidly below peak torque RPM.

Think of the shape of the torque curve, if you are riding at an RPM after the peak, the slope of the curve is downwards, that means a reduction in engine RPM makes the engine push harder – it is a negative feedback effect - and there is an equilibrium found as the bike climbs steeper or flatter slopes. If you drop below peak torque, there is now positive slope in the torque curve and speed falls off rapidly, forcing either a downshift, or wider throttle.

The ratio between peak power RPM and peak torque RPM gives a range of “cruising” speeds for each gear that are in the same proportion – My own thumper for example has 5250/3000 ratio – In practice the peak RPM is closer to 5000, so that’s a 5:3 ratio meaning in 4^th gear, I can range from 75 to 125 KPH with full acceleration potential. If I were on an extremely steep hill where 1^st gear was the only possible option, I could go from around 30 to 50 without needing to up-shift. This is what the definition of drivability is – the engine can pull away cleanly at a range of RPMs

Not to take anything away from the way two-strokes and high revvers deliver torque – They generally have this effect of ever increasing acceleration until peak, and that’s one of the highs of riding such bikes – on the plains!

What makes an engine produce power? Essentially airflow – pump enough air through the engine and you are done – the carb or fuel injector will ensure (mostly) that there is enough fuel in that air, and when all of it combusts you have glorious horse power.

The trouble is that airflow cannot easily optimized across all the RPM ranges – it’s almost as though you can change the power curve, but must preserve the area under it. So you can make it peaky at one end, or flatten it out and reduce the peak.

I do not have enough data, otherwise we could have looked at the integral of the power curve as a real metric of overall performance – An electric motor or steam engine comes to mind as the ideal maximum: Full torque at all RPMs for a motor, and torque descending from peak value to zero linearly across the rev range for a steam engine. That means for both of these, the peak power/peak torque rev range is the entire rev range, so gearing is entirely unnecessary, except for final drive!

Once again torque should be normalized according to weight, so we have a torque to weight ratio, and again one normalized based on RPM such that making peak torque at lower RPMs gives a higher metric.

Let’s look at the figures:

I have no peak torque data for many of the classic bikes, only the current bikes are shown here

Japanese Bikes

Model	PTQ RPM	KGM	KGM/ton	(KGM/ton)/KRPM
Hero Honda CD100	6000	0.75	4.05	0.68
Pulsar DTSI 220	7000	1.9	8.52	1.22
Karizma ZMR	6000	1.83	7.82	1.30
CBR 250	7000	2.2	9.28	1.33
Suzuki Hayabusa	7000	13.5	42.59	6.08

Enfield’s

Model	PTQ RPM	KGM	KGM/ton	(KGM/Ton)/KRPM
Diesel bullet	2500	1.5	5.77	2.31
Std 500	3000	3.8	14.62	4.87
Std 350	2800	3.2	12.55	4.48
Lightning 535	3000	3.8	14.62	4.87
Enfield CL500	4000	4.1	15.77	3.94
ACE Fireball bullet	3000	5.7	21.92	7.31

Two Strokes (again RPM is factored by 2)

Model	PTQ RPM	KGM	KGM/ton	(KgM/Ton)/2KR
Jawa 250	4500	1.8	8.57	0.95
Yezdi Roadking	4500	2	9.52	1.06
Jawa 350	5000	3.1	12.76	1.28
Yamaha RX100	6500	0.9	5.06	0.39
Yamaha RX135	6500	1	5.62	0.43
Suzuki Shogun	7500	1	5.59	0.37
Yamaha RD350	6500	3.3	15.14	1.16
Maico 760	3600	8.2	43.16	5.99

Look at the figures! Is it a wonder that thumper fans scoff at crotch rockets? Even the ‘busa, though having great torque, is outdone by the Fireball here.

The Fireball is off the charts, it could do great things off the road, probably has enough torque to hoist itself vertically on a rope at a good speed!

The new age 4 strokers are just not made for relaxed riding – They barely tract as well as the antiquated Jawas, while revving much higher – makes for a whiny washing machine like sound.

The CL500 needs to be ridden in a different style from the older bullets, same goes for the other twin spark and AVL engine ones which also have 4000 RPM peak torque, which is why probably many feel these are not “real” bullets.

The RD 350 is pretty decent, reaching almost to the level of the modern 4 strokers, although nowhere near the Enfield’s.

The Maico looks mighty impressive for a two-stroker, Pity only six of them were ever made.

Next let’s look at the RPM spread metric:

We would like the ideal spread to be 100% like a choo-choo train – So let’s say the percentage of the RPM range between peak power and torque. We’d also like the difference in actual torque at those two points to be as little as possible, so the ratio between the torque values at peak power and peak torque is another thing we can multiply with the above.

Let’s look at RPM ratios ( The column titled RR ) - A steam engine would have a value of 1.0
PP - Peak power
PTQ - Peak torque

Model	CC	PP RPM	PTQ RPM	RR	HP	KGM	PP KGM
Hero Honda CD100	100	7500	6000	0.20	7.5	0.75	0.70
Pulsar DTSI 220	220	8500	7000	0.18	21	1.9	1.72
Karizma ZMR	223	7000	6000	0.14	17.6	1.83	1.75
CBR 250	250	8500	7000	0.18	26.4	2.2	2.16
Honda CB750	750	8000	7000	0.13	67	6	5.83
Suzuki Hayabusa	1300	12000	7000	0.42	190	13.5	11.03

Model	CC	PP RPM	PTQ RPM	RR	HP	KGM	PP KGM
Diesel bullet	435	3600	2500	0.31	7.5	1.5	1.45
Std 500	500	5250	3000	0.43	22	3.8	2.92
Std 350	350	5650	2800	0.50	18	3.2	2.22
Lightning 535	535	5250	3000	0.43	26	3.8	3.45
Enfield CL500	500	5250	4000	0.24	27.2	4.1	3.61
ACE Fireball bullet	535	6000	3000	0.50	37	5.7	4.30

Model	CC	PP RPM	PTQ RPM	RR	HP	KGM	PP KGM
Jawa 250	250	4750	4500	0.05	12	1.8	1.76
Yezdi Roadking	250	4750	4500	0.05	16	2	2.35
Jawa 350	350	5250	5000	0.05	23	3.1	3.05
Yamaha RX100	100	7500	6500	0.13	11.5	0.9	1.07
Yamaha RX135	135	7500	6500	0.13	14	1	1.30
Suzuki Shogun	108	8500	7500	0.12	13.8	1	1.13
Yamaha RD350	350	6750	6500	0.04	30.5	3.3	3.15
Maico 760	760	4000	3600	0.10	43	8.2	7.49

The numbers speak for themselves – no doubt all these engines have usable torque for well below peak, but the fact remains that below that RPM the torque curve slopes upwards, so the ability to cruise is absent in that lower rev range.

The Hayabusa impresses again, with almost 50% of the rev range spread out between PTQ and PP!

The Enfield’s are all superlative when compared to the commuter bikes, and the Std 350 is still the king in terms of tractability! The fireball does as good on account of spreading the rev range upwards to 6000 revs

The CL500 (and all AVL and UCE engined bullets), have opted for a more rev happy engine, sacrificing that thumpy nature, by tuning it towards a later peak torque and better higher end breathing – most likely with higher valve overlap.

Here’s a simple test to determine true peak torque RPM on a bike : On a straight road, accelerate well past the estimated PTQ RPM, and then slowly back off the throttle - the RPM keeps dropping until there’s a point where the speed of the bike stabilizes. If you go below the actual PTQ RPM, the bike will slow rapidly and ask for more throttle to maintain speed. So essentially find the slowest “cruising” RPM – you can feel the top of the torque curve.

It’s not quite that you cannot cruise at any given speed on any given bike, it’s just that if you are on the downward sloping part of the torque curve, the engine governs itself due to a negative feedback effect – if it encounters more load, the revs drop and there is more torque, and vice versa. This happens without any throttle change. Having as large a range as possible where this happens makes the ride “relaxed”.

Let’s now incorporate the ratios between the two torque values and see what we get - we get the ratio between the torque values at peak torque and peak power and multiply it by the previous RPM ratio value.

Model	Torque metric
Hero Honda CD100	0.19
Pulsar DTSI 220	0.16
Karizma ZMR	0.14
CBR 250	0.17
Honda CB750	0.12
Suzuki Hayabusa	0.34

Model	Torque metric
Diesel bullet	0.30
Std 500	0.33
Std 350	0.35
Lightning 535	0.39
Enfield CL500	0.21
ACE Fireball bullet	0.38

Model	Torque metric
Jawa 250	0.05
Yezdi Roadking	0.06
Jawa 350	0.05
Yamaha RX100	0.16
Yamaha RX135	0.17
Suzuki Shogun	0.13
Yamaha RD350	0.04
Maico 760	0.09

The metric here is

(KGM@PP / KGM@PTQ) * ((PP – PTQ) / PP)

Meaning the RPM spread times the ratio between the torques – sort of describes how flat the curve is and how wide the “plateau” is.

All said and done, the Hayabusa is more or less like an Enfield in this metric! Eminently rideable.

The UCE bullet will do fine as long as you ride at revs, and not in “Uncle” mode.

I’m a bit surprised that the L535 tops this metric – I’m sure both the CL 500 and the Fireball have a torque curve well above it in most areas, but it’s all about the plateau shape…

Among the two strokes, the RX’s are pretty awesome, figuring higher than the DTSI and the ZMR – Who said two strokes are always twitchy and peaky?

The whole point is unless you are racing and have umpteen gears, and are willing to shift every time your speed increases by 10% to 15%, having extremely peaky power curves does not make for easy riding.

I’ve seen with my own eyes a few days back, ZMRs, DTSIs, CBRs spinning wheels and stopping on an off road track. They have to be revved high in 1^st to get the torque to climb, but that needs 80% or more or so of the 1^st gear top speed. That is surely not a slow enough wheel speed to start off up a slippery slope smoothly, so the wheels spin hopelessly and much use of the clutch is necessary.

I shudder to think how a two stroke would have fared!

My own beast had enough low end to chug up along that slope at 1200 to 2000 RPM, barely above idle in 1^st gear, at almost fully closed throttle.

Now let's move on to everyone's favorite yarn - speed

Comparing bananas and lemons - Part 3 : Speed

2011-08-27T03:16:00.000-07:00

Yes I know, I seem to be plugging Enfield’s in the previous posts (and the ‘busa) but hey, you do the math and see for yourself!

Anyway, I found this “speed trap” formula, given weight and power, for estimating quarter mile times and speeds - It’s surprisingly accurate:

http://www.stealth316.com/2-calc-hp-et-mph.htm

I used the Patrick Hale formulas and the numbers come to within a few percent of real world test reports that are found on the net.

Speeds in KM/h

Model	HP	Dry wt	Wt+75KG	RWHP	QM spd	QM time
Hero Honda CD100	7.5	110	185	6.225	94.24	24.73
Pulsar DTSI 220	21	148	223	17.43	124.46	18.68
Karizma ZMR	17.6	159	234	14.608	115.56	20.13
CBR 250	26.4	162	237	21.912	131.55	17.66
Honda CB750	67	218	293	55.61	166.79	13.89
Suzuki Hayabusa	190	242	317	157.7	229.23	10.08

Model	HP	Dry wt	Wt+75KG	RWHP	QM spd	QM time
Diesel bullet	7.5	185	260	5.625	81.46	28.66
Std 500	22	185	260	16	115.02	20.23
Std 350	18	180	255	12	105.27	22.12
Lightning 535	26	185	260	20	123.80	18.78
Enfield CL500	27.2	185	260	21.2	126.21	18.41
ACE Fireball	42	185	260	36	150.31	15.44
Constellation	51	190	265	45	160.78	14.42
Interceptor	56	190	265	50	166.47	13.92

Model	HP	Dry wt	Wt+75KG	RWHP	QM spd	QM time
BSA Goldstar	42	175	250	36	152.26	15.23
Velocette Venom	41	177	252	35	150.46	15.42
Triumph 650 twin	46	180	255	40	156.62	14.81
Norton 650SS	49	198	273	43	156.84	14.79
Vincent 1000	55	227	302	49	158.38	14.64

Model	HP	Dry wt	Wt+75KG	RWHP	QM spd	QM time
Jawa 250	12	135	210	9	102.07	22.82
Yezdi Roadking	16	135	210	13	115.24	20.19
Jawa 350	23	168	243	20	126.60	18.36
Yamaha RX100	11.5	103	178	8.5	105.78	22.01
Yamaha RX135	14	103	178	11	115.17	20.20
Suzuki Shogun	13.8	104	179	10.8	114.27	20.36
Yamaha RD350	30.5	143	218	26.5	143.98	16.12
Maico 760	43	115	190	34.4	164.21	14.12

Conclusions?

Most bikes will top out after ¼ mile, so common claims of top speeds are greatly exaggerated.

These formulas seem to bear out real world experience -from personal experience, I know that my L 535 tops out at around 125 kph, and Jawa 250 at 100 kph or so, and the figures for the RX100 and DTSI 220 also seem to be on the money. Some also agree with gearing and tire-circumference calculations as seen on www.gearingcommander.com

It is well likely that some of the more powerful bikes with continue to accelerate beyond the quarter mile mark, since they are not yet at peak power RPM, but most of the smaller bikes are maxed out here.

Claims of 144 km/h for the DTSI 220 as per the advertisements (as the worlds fastest Indian) and excess of 160 km/h for the CBR 250R are quite unbelievable.

One key point is that a bike has to be geared such that it hits the top speed at peak power RPM in top gear.Peak power RPM and peak RPM are two different things entirely.

On the road, in top gear, no bike will cross its peak power RPM - it stands to reason - If the bike is geared to reach top speed after or before peak power, the engine it rotating too fast or too slow, and producing less power than it could. Neither is ideal.

Bikes like the Hayabusa may differ in this regard because they are often rev limited and under geared - Meaning if it were allowed, it could rev higher than the limit and produce more power.

Many manufacturers will slyly use redline RPMs, calculate top speed based on the gearing, and put that in the specifications. Speedometers are notoriously inaccurate, even digital ones. Civilian GPS units seem to have anecdotal evidence of gross inaccuracy. Radar guns are also suspect.

The only accurate way to measure top speed that I can think of, is to record a video while driving full tilt, between two milestones. Road milestones will probably be accurate to within a couple of meters, and the timer in handy cams is digital, and has no measurable timing error.

So take that "How fast does your bike go?" thread on your motorcycle forum with a tablespoon or two of salt. Even a camera shot of a speedometer is not valid evidence.

Let's go on and look at efficiencies in the next part of this series

Comparing bananas and lemons - Part 4 : Efficiency

2011-08-27T02:52:00.000-07:00

Lets look at mileage figures now – We will use kmpl * hp as the metric for both engine and wheel horsepower values respectively, so we have engine efficiency and vehicle efficiency

Model	HP	RWHP	KMPL	Wheel Eff	Eng Eff
Hero Honda CD100	7.5	6.225	75.00	0.466	0.562
Pulsar DTSI 220	21	17.43	40.00	0.697	0.84
Karizma ZMR	17.6	14.608	45.00	0.657	0.792
CBR 250	26.4	21.912	30.00	0.657	0.792
Honda CB750	67	55.61	14.36	0.798	0.962
Suzuki Hayabusa	190	157.7	13.6	2.144	2.58

Model	HP	RWHP	KMPL	Wheel Eff	Eng Eff
Diesel bullet	7.5	5.625	40.00	0.225	0.3
Std 500	22	16	28.00	0.448	0.616
Std 350	18	12	35.00	0.42	0.63
Lightning 535	26	20	24.00	0.48	0.624
Enfield CL500	27.2	21.2	28.00	0.593	0.761
ACE Fireball bullet	37	31	28.72	0.890	1.062
Enfield Interceptor	56	50	16.41	0.820	0.918

Model	HP	RWHP	KMPL	Wheel Eff	Eng Eff
Jawa 250	12	9	35.00	0.315	0.42
Yezdi Roadking	16	13	35.00	0.455	0.56
Yamaha RX100	11.5	8.5	35.00	0.297	0.40
Yamaha RX135	14	11	35.00	0.385	0.49
Suzuki Shogun	13.8	10.8	35.00	0.378	0.48
Yamaha RD350	30.5	26.5	16.00	0.424	0.49
Maico 760	43	34.4	8.00	0.275	0.34

These numbers are self explanatory – no doubt it’s a meaningless metric because km/l is not measured while running at peak power, but the relative numbers between bikes will remain more or less similar.

The Hayabusa makes amazing amounts of power for a liter of petrol, and the Fireball impresses too, despite being based on an antiquated OHV Enfield engine

Summary

New technology is not always better, whatever metric you choose - except for real…
…rocket science (Hayabusa class bikes) , which will win hands down on any contest, except where rockets cannot be ridden.
The legendary Brit super bikes are still way ahead of today's "hoi polloi" bikes.
Two strokes are generally very bad on almost all metric.
There is no substitute for wheel horsepower, raw displacement, or a skinny rider!
The RD350 is a winner when it comes to two strokes, but even it pales in front of the Maico 760
Enfield's are a class apart on what they do best - pull like a tractor.
If you ride Enfield's, get a Fireball, it's as close to rocket science as you can get while maintaining its pedigree.