different gear question
Thread Starter
JK Freak
Joined: Feb 2008
Posts: 501
Likes: 0
From: cleveland,
different gear question
I dont want to start another 5.13vs.5.38'svs4.88 vs 3.73 discussion. What I am asking is what gear set will take my unlimited automatic and put the engine around 2k rpms at 60mph. I have 3.73's now, and I am spinning a mind blowing 1300rpm at 60mph. Its no wonder why OD hates me.
JK Enthusiast
Joined: Jan 2007
Posts: 112
Likes: 0
From: Beckley, WV
Actual formula to explain all of this would look something like this:
Engine rpm= E
Transmission ratio = R
Drive shaft rpm = S
Diff ratio = D
Tire rpm = R
Tire circumference = C
Vehicle MPH = M
E / R = S
S / D = T
(T x C) / 88 = M ( you divide by 88 to go from fpm to mph)
Or
(((E / R) / D) x C) / 88 = mph
Ex
2500 rpm 6th gear 4.11gears and 32" tire would be
2500 / .84 / 4.11 x 8.37' / 88 = 68.8mph
If you change to 37's and 5.13's it would be
2500 / .84 / 5.13 x 9.6' / 88 = 63 mph
Now if you kept the mph the same and change the tires and diff gears it would be this:
65mph x .84 x 4.11 / 8.37 x 88 = 2359 rpm for 32's and 4.11
65 x .84 x 5.13 / 9.6 x 88 = 2567rpm for 37's and 5.13's
Engine rpm= E
Transmission ratio = R
Drive shaft rpm = S
Diff ratio = D
Tire rpm = R
Tire circumference = C
Vehicle MPH = M
E / R = S
S / D = T
(T x C) / 88 = M ( you divide by 88 to go from fpm to mph)
Or
(((E / R) / D) x C) / 88 = mph
Ex
2500 rpm 6th gear 4.11gears and 32" tire would be
2500 / .84 / 4.11 x 8.37' / 88 = 68.8mph
If you change to 37's and 5.13's it would be
2500 / .84 / 5.13 x 9.6' / 88 = 63 mph
Now if you kept the mph the same and change the tires and diff gears it would be this:
65mph x .84 x 4.11 / 8.37 x 88 = 2359 rpm for 32's and 4.11
65 x .84 x 5.13 / 9.6 x 88 = 2567rpm for 37's and 5.13's