It may just be cause I'm retarded but I cant figure out what I'm doing wrong, I do the formula shown in the item comments section and come up with 25574.76.

My gear ratio is 3.73 and my tire diameter is 25.1"

Please help me

 

Here's some help.
http://www.thundersgarage.com/rpmcalc.html

 

Thanks I'll check it out, I found I was using diameter when I should have used radius but still I think I may have at one time accidentally deleted part of the equation from the comments.

 

There is a thread here someplace where I went though all the gory details of the math.

However, it is much easier then that. Use a data log and divide the RPM by the MPH, the result is the N/V ratio. Example:

2250 RPM at 70 MPH: 2250 / 70 = 32.1, which is the N/V ratio for the current transmission gear.

Say if in 1st gear at 35 MPH and the RPM is 4000 RPM the N/V ratio is: 4000 / 35 = 114.3

Much easier then all the math. And it takes into account tire growth and measurement inaccuracies and so on.

RBob.

 

It but wouldn't the speed in the log be off since the ratio is off?

The max I can enter is 62.778

 

The highest number I can enter into the RPM/VSS ratio constant is 62.177 or something like that, plus how would the speed be correct with it set up for the old tires and gear ratio?

Okay a lotta searching and a little math and I got it, 49.973.

Thanks!

Ah I still need help, its at least 10 mph to high with 49.