dave721

So, I have a '01 A4 2.8Q. The tire size is 205/55R16, so the effective radius of the tire is 12.439 inches, I think (16 inch wheel diameter, tire height is 55% of a 205 mm width)?

In doing some simple unit conversion between engine rpm and gear ratios (as posted on the Tech Data section of AW), I came up with about 122 MPH in 1st gear at 5800 RPM (sample calculation); observed data would show this prediction to be WAY OFF!

Obviously, I'm missing an important concept. I think I'm missing one or two other gear conversions, other than the gearbox.

How do I take the gear ratio, for each gear, and use it to calculate speed vs. engine RPM?

dB

Did you forget the final drive ratio?

Hokie_Audi

Depending on the driveline and transmission the final drive can vary quite a bit. I think for a manual quattro equipped car the final drive ratio is something like 3.49:1, so divide your number by 3.49 and you'll get about 35 miles an hour, which is about right.

Bryans12v

The most I ever learned about gear ratio was playing Gran Turismo 1! I adjusted the gear ratio of the Castro Supra for months and months till I found the perfect setup for me.. It was really cool.. Taking the car to 270mph!! Its amazing how advanced that game is..I love it..

CryptoTurbo

You've got mail.

dave721

Excellent! Thanks, everybody

dB

I'm still trying to set up the S3 as a good rally car! It's tough.

dave721

Top speed would be 168 MPH @ 6800 RPM (stock).

dB

Oops! Meant to put this in the post below. Bet you were wondering what is he talking about?

Hokie_Audi

I do the stream of consciousness thing pretty well...