speed(MPH) = (RPM x tire diameter) / (gear ratio x 336)

I did not know the gear ratio so I used the following formula to find it.

Gear Ratio = (RPM x tire diameter) / (mph x 336)

I got these formulas from:PreStage.com Car Math Formulas

Gear Ratio = (RPM x tire diameter) / (mph x 336)

Gear Ratio = (3000 x 22.6) / (60 X 336)

Gear Ratio = (67800) / (20160)

Gear Ratio = 3.36

3000 being the rpms shown on my gauge at 60 Mph

19 being the overall diameter of the wheel and tire together....15 inch wheel with 4 inches of total sidewall(counting both sides together)

Speed (MPH) = (RPM x tire diameter) / (gear ratio x 336)

Speed (MPH) = (7000 x 22.6) / (3.36 x 336)

Speed (MPH) = (158,200) / (1128.96)

Speed (MPH) = 140.1289683 MPH

There is the math, I used the actual measurements from my car and figured it out....now I want to hear comments on my estimation of my speed made in an earlier post. I know that I will hear people saying I should not drive my car at the redline...but it´s my car and my decision. I based my original estimation on that when my car turns 3000 rpms at 60 mph and 4000 rpms at 80 mph, when my car was turning 7000 rpms and my speedo was down near the trip meter it was an easy estimation of 140 mph. I had figured that when I did the math I would come up around 2 mph or so off so this was a bit closer than I had even thought. I hope this clarifies things for the young ignorant people who think that just because they haven´t done it or that because the speedo reads only a certain speed that the car cannot outperform the norm. I would also like to state at this time that when I did this my car was not bone stock, I have never said it was, I have not done what I would consider any major work to the car though and if you would like a rundown of what I have done to it feel free to visit my page.

Mike´s GT

Livin la vida Escort

[ This message was edited by: 93EGTinLR on 07-04-2003 06:52 ]