Calculating Top speeds

[Broderick]

Stupid question, but whats the formula for calculating top speed in each gear? I have the ratios and tire size but I can't get reasonable numbers. Any suggestions?

[Broderick]

Stupid question, but whats the formula for calculating top speed in each gear? I have the ratios and tire size but I can't get reasonable numbers. Any suggestions?

[MattG]

I'll see if I can help on this (I work in SI units so if you're using US units you'll have to do a conversion) All the numbers below assume you are using chain (or belt) drive to an axle which is in a locked state.

Wheel speed = Engine speed(rpm) / Primary reduction / gear ratio * drive ratio * tyre circumference * (60/1000)

Example

Engine at 10,000rpm
Primary reduction 1.822 (Crank to clutch ratio on a CBR600F4)
Gear ratio 2.833 (CBR 600F4 1st gear)
Drive ratio 0.267 (12/45 sprockets)
Tyre circumference 1.6m (20" diameter)
The (60/1000) term converts m/min to km/h

Plug all the numbers in and you get 49.6 km/h (or 31 mph)

[Frank]

try this

http://www.uq.edu.au/fsae/Frank/Gearing.xls

[Broderick]

Thanks alot guys, that's what I need to know.