Sarathesahara

So I have a 09 sahara stock tires ect. And I know it has the stock 4.10s, but my rpms tell me differently, at 70mph I run 1950rpms can anyone help me in understanding whats going on.

No1AP

The chart assumes a 1-1 drive ratio, which for an auto is 3rd gear and the manual is 5th. Run down the highway in 5th or your OD off and see what it says then.

Sarathesahara

Ah that makes better since, thanks! ?

Sarathesahara

That's what I thought at first too, but my VIN report sheet tells me differently.

nthinuf

Remember to use the actual measured tire height. Not the mfg's spec or a conversion from what's on the sidewall.

Just looking at the chart in the faq's:
auto, 3.73, stock 32" sahara 18's (31" actual measured height) = 1953 rpm @ 70




If you want to double check that the build sheet is correct (or incorrect) - put a mark on rear tire and the ground, another mark across the end of the driveshaft onto the pinion. Then jack up that corner, and rotate the tire two full revolutions while counting the driveshaft rotations.

Just from what you stated in the original post, I would guess that you actually have 3.73's and not the 4.10s your build sheet shows.

Sarathesahara

Hmmm, how would I fully check? Just rip out the gears? :eek:

nthinuf

Pop the covers and count teeth?

But counting driveshaft revs is pretty accurate, and easier. (unless it is oil change time and you are opening the axles anyway.)