# rough guess on bike gearing for no tire spin?



## Tomdb (Jan 28, 2013)

With you on it? 450kg? 1000Lb?

you will need more then about a 20:1 reduction, if you were to get almost all the weight shifted rear. This would limit you alot in top speed.

A 10:1 would give you an alright topspeed of around 130 km/h and 7 seconds to 100 km/h.


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## dcb (Dec 5, 2009)

Thanks! 1000 is just a swag, I didn't even consider the engine removal so probably less. less. So you mean I would need the torque of 20:1 sprocket to break the tire loose (at 1000 lbs)? 


Any hints how you did the figuring though? Is there a rule of thumb for the tire coefficient of friction for weight?


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## Duncan (Dec 8, 2008)

Hi

1000lbs weight on the rear wheel
Road tires have a coefficient of friction of about 0.8 (80%)

So 800lbs at what 2ft diameter?
is 800 ftlbs
90Nm is 66 ftlbs
800/66 = 12:1

replace my 2ft with the actual size of the tire!

80% is a good estimate for normal "high performance" tires, tires for racing go a lot higher


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## dcb (Dec 5, 2009)

excellent! thanks guys, I think I'm on the right path here (roughly speaking).

will refine a bit with some measurements and better estimates. Just looking at the original motor and gearing, ~10:1 would deliver the same peak torque as the gasser in first (though it will be a bit heavier).

Not sure where to find a 12-1 sprocket, though they aren't impossible to make. Otherwise I need shed some more weight or find some more motor torque before I worry about the low end tire spinning side of it.

http://papers.sae.org/2010-01-0054/
"Generally, on the dry surfaces peak friction coefficients of around 1.2 were found, with locked wheel coefficients of around 0.7-0.9. The exception was in the measurement of the peak friction on dry hot rolled asphalt, where the coefficient of friction of the car tire was about 0.2 less than that of the motorcycle tires. The same difference was not found in the locked-wheel friction on the dry hot rolled asphalt."


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## RIPPERTON (Jan 26, 2010)

Motorcycles don't just spin the wheels they loop out ie do a wheelie and flip. All depends where you put your body weight.
If you sit in a normal upright position, the tire will bite and it will flip.
If you put your upper body weight over the handle bars it will spin regardless of what chain ratio you have.
So I think you should forget about that all important cloud of smoke and base you gearing choice around something more sensible like cruising speed.
An AC24 on 240v should give you plenty of torque. don't worry be happy


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## dcb (Dec 5, 2009)

well it won't flip with the 15:41 stock sprockets, even if I'm standing on the license plate, I'm pretty sure about that  It is worth at least thinking about it before shopping for sprockets solutions. Setting the wheel torque gearing to no more than the tires can handle can help on the high speed end of it too.


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## dcb (Dec 5, 2009)

Ah well, I scoured jt for a bolt on, found a 52 tooth 530 for $35 (12 tooth on front). No where near 10:1, and probably the biggest that would fit the swingarm is ~7:1. Will revisit custom sprocket if not happy w/performance but should get it rolling ok.

edit: looks like 3800 rpm @ 60mph (motor peaks at [email protected], 10k+ redline). It is gonna be weak on accel, have a top speed I'd never use in practice (even 60mph would be rare around here). will probably be needing a custom sprocket, but a $35 experiment isn't too awful. Might try 425/#40 sized with a .343 thick sprocket narrowed at the teeth.

edit2: blech, torque-wise it is going to be like starting in 4th...


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## Karter2 (Nov 17, 2011)

dcb said:


> Ah well, I scoured jt for a bolt on, found a 52 tooth 530 for $35 (12 tooth on front). No where near 10:1, and probably the biggest that would fit the swingarm is ~7:1. ...


So, why don't you install a primary reduction Jackshaft . ?.
That would give you all the gearing options you like.


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## jwiger (Oct 18, 2014)

If you could provide a few numbers I can give you a better guess. 
1. I need the wheel base and the total weight.
2. I need the size of the rear tire (diameter if nothing else).
3. The front and rear wheel weights with the bike completely level, and rider on it. 
4. Elevate the front wheel on a sturdy box to a reasonable wheelie height (12 inches or 30 cm), then re-weigh the front and rear wheel weights.

With this info I can approximate the fore/aft x height of the center of gravity for the bike, and help you learn how much weight transfer you will have. I do this on four wheel cars and karts so I can get it pretty good for you.

For both level and wheelie positions I recommend the rider sit in the best "launch" position he/she would be in during a hard acceleration. Of course the position should be the same for both, relative the bike.


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