gears ?

If you go to the Corral I belive they have a calculator that will tell u this. There are some other sites as well, but I can't remember all of them.

tkareno said:

i was wondering if i got 4.10s where would my rpms be at

Click to expand...

At what speed?

What transmission do you have?


Here are some easy formulas I have recently worked out for some of the most common rear end gear ratio and speedo gear questions (remember that * means multiply, and / means divide):

What will my RPMs be at x mph ?

Engine RPM = 336.1352 / Tire Height * Axle Ratio * Transmission Gear Ratio * MPH

Example: T-5 tranny (0.68:1 5th gear), with 4.10s, and 225/60R15s (25.6" height) @75 mph
336.1352 / 25.6 * 4.10 * 0.68 * 75 = 2746 rpm


How fast should I be going at x rpm, with these gears ?

MPH = Tire Height * 0.0000496 * Engine RPM / Transmission Gear Ratio / Axle Ratio * 60

Example: 2500rpm, AOD tranny (0.67:1 4th gear), with 3.73s, and 215/65R15s (26.0")
26.0 * 0.0000496 * 2500 / 0.67 / 3.73 * 60 = 77.4 mph


What speedo gear do I need for these rear end gears ?

# of Driven Gear Teeth = 20.168114 / Tire Height * Axle Ratio * # of Drive Gear Teeth

Example: 3.55 gears with a 1988 5-Speed (7-tooth drive gear), and 225/60R15s
20.168114 / 25.6 * 3.55 * 7 = 19.6 (a 20-tooth gear)


I'm doing x mph at y rpm, what gears do I have?

Gear Ratio = Tire height * 0.0000496 * RPM / Trans. Gear Ratio * 60 / MPH

Example: 80 mph @ 2500 rpm, with an AOD and 215/65R15s
26 * 0.0000496 * 2500 / 0.67 * 60 / 80 = 3.6 (3.55 gears)


What is my tire height ?

Tire Height (inches) = Tread Width * Aspect Ratio / 1270 + Wheel Diameter

Example: 225/60R15s 225=Tread Width (milimeters), 60=Aspect Ratio, 15= Wheel Diameter (inches).
225 * 60 / 1270 + 15 = 25.63"


For these to be accurate, it requires accurate data. It is possible for your tach to be off be several hundred RPM. The formulas assume your speedometer is reasonably correct. If rear gears have been changed, and the speedometer not corrected your results will be way off.

My answer would be: It depends on how hard you push on the gas pedal

This should help you, with all the different gears. 1-5.

http://www.allfordmustangs.com/Detailed/608.shtml