So I recently regeared my TJ with 33/12.50/15 tires & got rid of those terrible 3.07 gears & had 4.56 gears installed along with True Tracks (front & rear), chromoly axles, the correct 39 tooth speedometer gear & new front hubs. It drives wonderful now. I thought I would post some before & after data showing RPMs & indicated vs actual speeds. I used an old Garmin portable dash mounted GPS to get the true speeds.
I will show the actual speed (GPS), speedometer indication & RPM for 55, 60 & 65 mph with 3.07 gears & then I will show the same data with the 4.56 gears.
Here we go:
3.07 gears:
55 mph (GPS), 49 mph ( speedometer), 1,500 RPM
60 mph (GPS), 54 mph (speedometer), 1,625 RPM
65 mph (GPS), 58 mph (speedometer), 1,750 RPM
4.56 gears (& proper 39 tooth speedometer gear):
55 mph (GPS), 55 mph (speedometer), 2,250 RPM
60 mph (GPS), 60 mph (speedometer), 2,450 RPM
65 mph (GPS), 65 mph (speedometer), 2,800 RPM
As you can see, the speedometer is dead on accurate now & the RPMs are now at a usable level; much closer to the peak of the torque band & not lugging all the time. 6th gear is much more usable now.
This is THE BEST thing anyone could do to a Jeep with larger diameter tires!!!
I will show the actual speed (GPS), speedometer indication & RPM for 55, 60 & 65 mph with 3.07 gears & then I will show the same data with the 4.56 gears.
Here we go:
3.07 gears:
55 mph (GPS), 49 mph ( speedometer), 1,500 RPM
60 mph (GPS), 54 mph (speedometer), 1,625 RPM
65 mph (GPS), 58 mph (speedometer), 1,750 RPM
4.56 gears (& proper 39 tooth speedometer gear):
55 mph (GPS), 55 mph (speedometer), 2,250 RPM
60 mph (GPS), 60 mph (speedometer), 2,450 RPM
65 mph (GPS), 65 mph (speedometer), 2,800 RPM
As you can see, the speedometer is dead on accurate now & the RPMs are now at a usable level; much closer to the peak of the torque band & not lugging all the time. 6th gear is much more usable now.
This is THE BEST thing anyone could do to a Jeep with larger diameter tires!!!
