I just changed gears from 3.21s to 5.13s. I put 35"s on the JK a month ago, and had the dealershp reset the computer after installing the 35s.

Does anyone know if the dealership needs to update the JK computer again after changing gears? also, any idea what all is updated?

Thanks.
Rick

 

I would say yes since your tires are now turning faster I'm sure your spedo is off again.

The dealer can reset (program) a jeep for larger tires? I thought you needed an aftermarket programmer for this....asking a question because I don't know.

 

The answer really depends. Though your tires are 35", their real size is most likely not exactly 35". If you take it to the dealer, they are not going to know what setting to adjust the computer to. What I would do is take a GPS on a your next long drive, and measure the difference between the mileage on your speedo, compared to actual. If the dealer has already set the computer for 32" tires (largest avail. on the computer), and your actual mileage reads greater than your speedo, then there is not anything more that the dealer can do. If vice versa, then you can have dealer try different settings.

 

The dealers can only re-flash your computer for the largest factory tire size. That would be a 32" tire. The re-gear will not effect your spedo, because the speed sensor is on the axle. The speed difference would only be between the 32" vs. 35" tire. This means your spedo will read 9.4% low. IOW, if your spedo reads 70MPH, then you will be really going 76.5MPH.

So, you in love with those 5.13 gears? I would be, because that will be one of my first mods when she gets here.

 

Has anyone found an after market unit to re-program the computer for tires larger than 35" or for changing gearing?

 

my rubi is pretty much dead on after i put 35's and 4.88's in it its maybe off by 2mph max, not enough to worry about

 

That would mean the speed sensor is more than just in the axle, correct? It'd be affected by both the gears and the tire size... I would think... otherwise, you'd be more than 2mph off... anyone else w/experience... I should have some input sometime after this week... my gears (5.13's) are getting installed this week with my lift and 35's.

 

off course

i only only its accurate as my navigation system has a speedometer guage in it and i compare it with my speedo

 

I had 35's on mine with the stock 4.10's, and 35's when I installed my 5.13's. The speedo readings are the same with the 5.13's as they were with the 4.10's. My speedo reads about 9.3-9.4% slow.
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That is weird that reads slow. I would think that it would read faster? Mine reads 3-6mph slow (depending on speed) as compared to the gps. I have 4:10's, 6sp, and 35's and want to go to 4:88's. I think the spedo is off from the start.