Re: Wiki Questions/Suggestions
For those of us that don't use a tachometer on their EVs, could you post a formula for figuring RPMs, off of the gear ratios at these speeds of the car?
I have been working on it and I think this is it.
My 13" tires turn 946 rpms in one mile. They go 5.58' in one turn.
The motor is rated @ 3000 rpm.
Final drive ratiosActual road speeds, that I run in these gears.
1st gear 15.00010 mph (not very often)
2nd gear 8.25025 mph
3rd gear 6.50038 mph
4th gear 4.00045 mph
5th gear 3.25048/50 mph (just under 200 amp draw)
Using 2800 rpms for motor speed, I worked this up.
Motor rpm in each gear @ road speed.
1st gear @ 11.84 mph is 2800 rpm
2nd gear @ 21.53 mph is 2800 rpm
3rd gear @ 27.33 mph is 2800 rpm
4th gear @ 44.41 mph is 2800 rpm
5th gear @ 54.66 mph is 2800 rpm
MPH Formula is what I used. This will get you close.
RPM divided by final gear ratio 2800 divided by 3.25 = 861.54 (5th gear used)
X tire circumfenrence 76 X = 57723.07
X 60 57723.07 X 60 =3463385
divided by 12 3463385 =288615.37
divided by 5280 288615.37 div 5280 =54.66 mph
To figure RPM just change the gear ratio.
Last edited by Coley; 03272008 at 12:00 PM.
Reason: added info
