The Ford Barn

jrvariel48 · 11-26-2020, 09:13 AM

Is there a calculation to find out how a rear ratio affects transmission gearing?
Let's say my 1st gear is a 4.03 and my rear ratio is a 3.25. If I were to change the rear ratio to a 3.50, how would that affect the 4.03 number? I have a T5 behind my flathead. My most notable problem is 3rd gear. The following comments for 1st, 2nd and 3rd would be at WOT. 1st gear revs up very fast(4.03), 2nd gear is perfect at 2.37, but 3rd gear (1.49) is really slow bringing up the rpm. By the time I hit 5000 rpm, I'm doing 85 mph! When I back off the throttle, 4th gear is good at 1.00. I can't really get into 5th gear (.76) without going 80 mph which I have no desire to do. So now I wondering if changing the rear ratio will do me any good. Open to suggestions.
Happy Thanksgiving!
Joe

11-26-2020, 09:13 AM	#1
jrvariel48 Senior Member Join Date: Jan 2012 Location: New Jersey Posts: 1,425	Gear ratio's and final drives Is there a calculation to find out how a rear ratio affects transmission gearing? Let's say my 1st gear is a 4.03 and my rear ratio is a 3.25. If I were to change the rear ratio to a 3.50, how would that affect the 4.03 number? I have a T5 behind my flathead. My most notable problem is 3rd gear. The following comments for 1st, 2nd and 3rd would be at WOT. 1st gear revs up very fast(4.03), 2nd gear is perfect at 2.37, but 3rd gear (1.49) is really slow bringing up the rpm. By the time I hit 5000 rpm, I'm doing 85 mph! When I back off the throttle, 4th gear is good at 1.00. I can't really get into 5th gear (.76) without going 80 mph which I have no desire to do. So now I wondering if changing the rear ratio will do me any good. Open to suggestions. Happy Thanksgiving! Joe