Ok, Thanks for taking a look.

I am not the best with transmission gear ratios and such, I know what they are but trying to figure out what the rpm would be of the drive shaft at a given speed is making my head hurt.

Ok

S5 TII Rear end
S5 TII Trans
S4 Vert Rims
205/50/R15 Tires

Just need a good rough number of drive shaft RPM @

@50mph
@75mph
@100mph
@125mph



If you are wondering we are working on a Hybrid Electric setup, with regenerated braking.

 

5280 feet in a mile (63360in)

The rolling diameter of your tires gives you a certain number of revolutions per mile. The ratio of your rear end will change that to driveshaft revolutions per mile.

(Driveshaft rev's per mile) x (miles per hour) = driveshaft rev's per hour

(Driveshaft rev's per hour) divided by 60 (60min in a hour) will give you driveshaft RPM.

You should be able to take it from here.


Isaac

 

Driveshaft RPM = ((Vehicle MPH * Gear Ratio * 336) / Tire Diameter in Inches)

 

your doing it the hard way, just look at your tachometer while driving and divide by the current gear ratio.
S5 turbo trans:
1s- 3.483
2nd- 2.015
3rd- 1.391
4th- 1
5th- .719

 

how is that the hard way if he doesn't even have to get into the car to calculate it?