i found this
http://www.offroaders.com/info ... orner/reading/mph-rpm.htm

and was wondering if someone could make a maths equation to make it more simple and in following this. RPM, GEAR RATIO, DIFF RATIO, TYRE SIZE

example
at 5000 RPM with a ratio of .900 and 3.45 diff gears and 17x45 tyres what speed would the car be running? i need it in KPH if anyone can help

The one at the bottom.

RPM = (1000*Speed*Gear Ratio*Diff Ratio) / (2*pi*60*Radius of Tyre)

rearranging gives

Speed = (RPM*2*pi*60*Radius of Tyre) / (1000*Gear Ratio*Diff Ratio)

Simplifying constants

RPM = (2.653*Speed*Gear Ratio*Diff Ratio) / Radius of Tyre
Speed = (0.377*RPM*Radius of Tyre) / (Gear Ratio*Diff Ratio)

Radius of Tyre = metres
Speed = km/h

Your problem:
Speed = (0.377*5000*Radius of Tyre) / (0.900*3.450)
You need to specify more tyre data I think. Unless that's the sidewall height rather than the ratio, or perhaps the diameter in centimetres.
If it was the sidewall height in millimetres - speed = 158km/h = 98.4mph
If it was the rolling diameter in centimeters - speed = 136km/h = 84.9mph

Hope this helps.

thanks man i didnt exactly understand (grade 9 maths lvl only) but im sure if i study a little ill get it


this is as far as i got

RPM gear ratio diff ratio tyre size in mm
1 1.00 3.45 4,76.8mm = 1644,96mm pm <wrong i think



100 kp = 27.7778 mps
1666.668 mpm x.06 = KPH



17x45 is the rim size and side wall size so its 17 inchs and 45mm