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jolee
11-15-2010, 07:30 PM
I am thinking of installing new gears in my 97 LC. Can anyone tell me what their RPMs are at 65 to 70 mph with 315 size tires.

Thanks

coax
11-15-2010, 08:25 PM
my brain won't do math, but I think these numbers (if correct) should help figure it out for you.

The gear ratios are: 1st 2.95:1, 2nd 1.53:1, 3rd 1:1, 4th .765:1, reverse 2.678:1
The differential ratio is 4.11:1.
Circumference of 35" tire: ~110"


http://www.marks4wd.com/vehicle-information/lc-80-series-info.htm

corsair23
11-16-2010, 03:13 AM
I am thinking of installing new gears in my 97 LC. Can anyone tell me what their RPMs are at 65 to 70 mph with 315 size tires.

Thanks

From this thread (post #63)

http://forum.ih8mud.com/80-series-tech/408513-4-88-gearing-will-i-glad-regret-2.html#post6041809

Just putting this here for future reference since I finally found the napkins on which I wrote the info down :rolleyes:

285s w/ Stock Gears | 285s w/ 4.88 Gears | 315s w/ 4.88 Gears (guesstimate)
60 mph = 2050 RPM ..| 60 mph = 2400 RPM .| 60 mph = 2200 RPM
65 mph = 2200 RPM ..| 65 mph = 2600 RPM .| 65 mph = 2400 RPM
70 mph = 2350 RPM ..| 70 mph = 2800 RPM .| 70 mph = 2600 RPM
75 mph = 2500 RPM ..| 75 mph = 3000 RPM .| 75 mph = 2800 RPM

Rig setup: 285/75/16 Toyo MTs with about 1/2 tread and OD on. YRMV

Based on this and Romer's numbers running 315s w/ 4.88s, bumping up to 315s will bring the RPM down about 200 or so from my numbers listed for 4.88s w/ the 285s. Added this above as a best guesstimate.