Get a cluster with a tach...I see them all the time for around $50

I have a DX, that's what I did

 

...one update on this. I tested the formula above on my way home from work, by recording various engine speeds and vehicle speeds, and checking them against the formula. The formula consistantly calculated speeds 3-5mph higher than what I had measured. I think this is a small margin of error, best explained by:

1) The effective diameter of the tire is smaller than math would indicate. This is because the portion that is between the road and rim becomes compressed. Therefore, I assume the formula is a lot more accurate for low-profile tires (with their stiffer sidewalls) than it would be for higher profile tires. Figure that air pressure makes a difference in what the effective diameter is as well.
2) Using an analog tach and speedo is not 100% accurate either. For one, there are not enough gradations for accurate interpretation. For another, each has a slight built-in error margin.

I will say that given these normal error margins, the formula does seem to work well, and is quite good at ballparking what the projected vehicle speed would be. Just thought you would like to know.

 

MPH = RPM(wheel dia., inches x Pi x no. of minutes in one hour)/overall gear ratio x no. of inches in one mile

MPH = RPM(wheel dia., inches x 3.14 x 60)/overall gear ratio x 63360

3.14 x 60 = 188.4
63360/188.4 = 336.31

MPH = RPM(wheel dia., inches)/overall gear ratio x 336.31

 

1st--------33-35mph rough estimate everytime i've bounced off the rev limiter i was racing and forgot to look at the speed but its some where around there
2nd-------60mph bounces off rev limiter if you go any higher
3rd--------80mphsee above
4th--------110mph? not confirmed thats just when i shifted
5th--------***mph? still no clue fastest i've gone is like 117-120 i really stopped looking when i was going that fast needle was close to 120 tho
peace
dante