The Ford Barn - View Single Post

JSeery · 08-10-2020, 05:18 PM

rpm = (mph x Rear End Ratio x 336) / Tire Diameter

Guessing some numbers, 4:11 rear axle and 28 inch dia tires.

rpm = (60 mph x 4.11 x 336) / 28 = 2,960

Don't see where you are getting the 4000 rpms from, might consider a better tach! Unless you are running very small tires or a rear axle lower than 4.11.

Even with a 4.56 rear axle ratio and 26 inch dia tires you are still only at 3,535 rpm at 60.

It is common to run 29 inch tires if you want to lower you rpms. So, that would work out to 2,857 with a 4.11 rear axle.

08-10-2020, 05:18 PM	#10
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Need your advice for new engine rpm = (mph x Rear End Ratio x 336) / Tire Diameter Guessing some numbers, 4:11 rear axle and 28 inch dia tires. rpm = (60 mph x 4.11 x 336) / 28 = 2,960 Don't see where you are getting the 4000 rpms from, might consider a better tach! Unless you are running very small tires or a rear axle lower than 4.11. Even with a 4.56 rear axle ratio and 26 inch dia tires you are still only at 3,535 rpm at 60. It is common to run 29 inch tires if you want to lower you rpms. So, that would work out to 2,857 with a 4.11 rear axle.