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Apex Selection And Lines For Smaller Bikes


laverda
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Are there some rules of thumb or guidelines for choosing an apex or picking a line when riding something like an RS 125 as opposed to a 600 or a liter bike? It seems to be universally accepted that smaller bikes carry more speed in the corners compared to the bigger bikes. Is it the case that they are capable of higher corner speeds or is it just that they have to because they can't rely on horsepower to launch them off of the apex? Do the small bikes use entirely different lines and apexes than the larger bikes?

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Good question. I'm going to pay attention at the upcoming gp's see what can be observed that way.

 

We used to do 125 gp schools, and they are capable of amazing corner speeds. The ones we used weighed 150 lbs., and are less now I'm sure (10 years ago when we did those schools). There is also the fact they don't have the acceleration that a 250 would have (they are fast), much less a MOTO GP bike, so yes, there is going to be some difference in the lines due to that.

 

Here's the question: what do you think the difference would be?

 

Cobie

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I would have said that as a general rule of thumb, the less drive you have, the closer you should be to the 'classic' line (nice wide arc).

 

If you have a big powerful engine (as a MotoGP bike would have), I expect that you'd be wanting to use as much of that power as you can (otherwise what's the point in having it), so you'd be looking to pick the bike up early so you can get as much drive as you can, as early as you can.

 

The basic theory would be that a powerful engine can make up any shortfall in mid corner speed by going faster at the corner exit (which also leads to greater speeds on the straight bits)...

 

I expect that the rider's weight distribution will also have a greater effect on corner speed for smaller bikes. To corner faster, the rider positions their weight more to the inside of the corner. The lighter the bike, I expect the greater effect this will have, allowing you to pick the bike up further than you would a heavier bike (or, allowing you to go faster for a given lean of the bike).

 

Also, 125 GP bikes are a bit slimmer than MotoGP bikes, so you probably gain a little extra clearance there too.

 

What is it that ultimately limits corner speed? Lean angle!

 

Don't mind me, I'm just thinking out loud...

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What's the chance that the Superbike School will have any more 125 GP schools? I would love to attend one of those. It seems like the "mini gp" concept is gaining in popularity and a 125 school would be helpful for those folks. Especially to help some of the young riders getting started without having to unlearn bad habits when they are older.

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I would have said that as a general rule of thumb, the less drive you have, the closer you should be to the 'classic' line (nice wide arc).

 

If you have a big powerful engine (as a MotoGP bike would have), I expect that you'd be wanting to use as much of that power as you can (otherwise what's the point in having it), so you'd be looking to pick the bike up early so you can get as much drive as you can, as early as you can.

 

The basic theory would be that a powerful engine can make up any shortfall in mid corner speed by going faster at the corner exit (which also leads to greater speeds on the straight bits)...

 

I expect that the rider's weight distribution will also have a greater effect on corner speed for smaller bikes. To corner faster, the rider positions their weight more to the inside of the corner. The lighter the bike, I expect the greater effect this will have, allowing you to pick the bike up further than you would a heavier bike (or, allowing you to go faster for a given lean of the bike).

 

Also, 125 GP bikes are a bit slimmer than MotoGP bikes, so you probably gain a little extra clearance there too.

 

What is it that ultimately limits corner speed? Lean angle!

 

 

 

Don't mind me, I'm just thinking out loud...

 

On the 125, it is all about the entrance speed, at least as far as I can tell. Now when I go to the school, I'm hoping to learn more about the lean angle.

 

 

Good question. I'm going to pay attention at the upcoming gp's see what can be observed that way.

 

We used to do 125 gp schools, and they are capable of amazing corner speeds. The ones we used weighed 150 lbs., and are less now I'm sure (10 years ago when we did those schools). There is also the fact they don't have the acceleration that a 250 would have (they are fast), much less a MOTO GP bike, so yes, there is going to be some difference in the lines due to that.

 

Here's the question: what do you think the difference would be?

 

Cobie

 

There's a little bit of Honda propoganda going on there! My '95 RS weighed right around 190 lbs. with half a tank of gas. Tha manual claims 156 lbs. with half a tank. They are a hoot to ride either way!

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Interesting, I had thought that 150 lb number was real, they seemed so light to move around.

 

As for the weight of the rider, we found that moving around too much, hanging off too much made them harder to ride. The bikes we had were the '94 and 96 RS-125's. Moto-Liberty supplied them, and I think at the time they were the sole importers. That later changed, and other guys were able to bring them in, and that's when we stopped doing those schools.

 

Ask Will about chasing the guys that were trying out for the national team. They were on the '96's (for sure faster) and he was on a '94--and caught them.

 

Don't have plans to do any more at this point, but who knows what the future might bring!

 

Cobie

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Interesting, I had thought that 150 lb number was real, they seemed so light to move around.

 

As for the weight of the rider, we found that moving around too much, hanging off too much made them harder to ride. The bikes we had were the '94 and 96 RS-125's. Moto-Liberty supplied them, and I think at the time they were the sole importers. That later changed, and other guys were able to bring them in, and that's when we stopped doing those schools.

 

Ask Will about chasing the guys that were trying out for the national team. They were on the '96's (for sure faster) and he was on a '94--and caught them.

 

Don't have plans to do any more at this point, but who knows what the future might bring!

 

Cobie

 

They're still very light! I can pick the bike up with my left hand on the left grip and my right hand on the right footpeg, and turn it around.

 

I've gotten to where I can move around on the bike pretty well without upsetting it too much, but it took a while. Hanging off can also slow the bike down just from wind resistance, so it pays to stay tucked in as much as you can.

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Are there some rules of thumb or guidelines for choosing an apex or picking a line when riding something like an RS 125 as opposed to a 600 or a liter bike? It seems to be universally accepted that smaller bikes carry more speed in the corners compared to the bigger bikes. Is it the case that they are capable of higher corner speeds or is it just that they have to because they can't rely on horsepower to launch them off of the apex? Do the small bikes use entirely different lines and apexes than the larger bikes?

 

 

A 125 does not have much horsepower, hence, to make a fast lap, the less powerful machine must maintain as much entry speed as possible and choose a line to maintain as much speed as possible through the corner. To that end your turn point will be 1/4" off the paint stripe or curb. (Or perhaps up on the curb if you are Pierce Duchene passing someone on the brakes.)

 

The fact that a 125 can corner faster than bigger HEAVIER bikes is a separate issue and mostly due to the light weight of the machine creating less stress on the contact patch of the tire.

 

The dry weight of a pre-2004 box stock RS125 is about 70 kg or 154 lbs. Throw in three gallons of fuel/oil mix, transmission oil and water in the radiator and that goes up to circa 190 lbs. Add an airbox and other black box goodies like electronic shifter, detonation counter, data aquisition, telemetry or other electronic modules for kit options like adjustable power jet or rigging for variable exhaust port valve timing and you might get upward of 195 lbs. (Of course, Marchesini wheels, carbon fibre bodywork and a bag of Ti fasteners will cure that.)

 

A well tuned box stock 1996 RS125 running avgas on dry fat air made circa 39-40 bhp at the rear wheel. A kitted and modified machine running oxygenated fuel could make over 50 bhp at the rear wheel. World GP 125's of that era were making about 53 bhp at the rear wheel. The fastest bike in the US was undoubtedly RodFee's which dyno'd around 51 bhp. The only thing his engine had that mine didn't was a D-bore powerjet carb, stuffed cases, modified reed block and the kit igniter box which altogether was probably worth about 3 bhp. (To be fair, Ben Solis and Vicky Jackson-Bell were right about there as well.)

 

That may not seem like a big deal but that's a 20-25% (or more) increase in raw power and brings the horsepower to weight ratio down to circa 5:1 with a small rider. Which is about the same or better than a modern 600 with a big rider. Back then, at 120 lbs, I could easily motor past older 600's on the front straight at Putnam Park. And more than one 250 rider came searching for me in the pits to find out just what the heck I was riding after they had to stay in my draft to keep up. I was also able to roll up power wheelies coming onto the front straight at Laguna Seca by scooching back in the seat a bit.

 

Hee hee hee...thank you Rodney Fee...whatever third world prison you may inhabit today....you madman.

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