Can someone help me calculate the rpm range for a given tire size? I have the drive ratio's but not sure how to input them.

05 5mt wrx with these parameters
65mph
tire dia-24.87
front final- 3.900
Rear final- 3.545
Transfer- 1.100
Q: what is the rpm at 65mph? I want to see how much tire diameter affects rpm at a given speed (65)
I have the drive ratios from the tranny if needed.

 

(65miles/hr)(5280ft/mile)(12inches/ft)(hr/60min)(1rev/pi*24.87inches)= 879(rev/min)

...but this is for the wheels- I believe you use the drive ratios from there to find the rpm you see on your tach.

 

Whoa! quick reply! For the stock 205/55/16 tire it comes out to 24.87 in diameter and has 836.3 revs per MILE. I looked at several tire/gear calculators out there and most are asking for the same info.
Axle ratio-
Transmission ratio-
Transfer case ratio-
MPH-
Tire size-
I guess I need to add 5th gear at 65mph which has a 0.738 ratio.

 

if you're going close to a mile a minitue (65mph), that seems to agree with my figure...

I don't know what rpm the tach reads, and how many or which gear transfers (ratios) you need to factor in... but using the right ratios, you should be able to get it from the rpm at the wheels.