Larger wheels on WH - pinion factor fix

[Finners]

With my recent build-up - the larger diameter 265/70-17 tyres caused a 9% speedo error (gearing now taller of course) and poor tranny shift points (shifting before getting into peak torque band). My dealer was able to reset the pinion factor (software fix), though only part way. i.e. There was no option to reset for 265/70-17 size - so a partial fix only

Have yet to GPS test the pinion factor re-set to see how much it fixed the speedo error by. However the gear shifts are significantly better (though still not perfect).

I know some folks have gone for the AEV speedo healer, though to my knowledge that does not resolve poor (early) shift point selection by the ECU?

Finally - does anyone have experience with dropping the QDII diff internals from the Hemi into the CRD? (And if yes - does the change in final drive ratio offset the impact of fitting larger tyres to the CRD?)

- Finners

[vk2jdh]

I believe they have to change the tyre rotation per (km|mile) in 2 spots , the BCM and the Power Train Module. Could be wrong though.

[glend]

You maybe right VK2, when changing the tyre diametre in the KJ Cherokee you have to make the change in both the BCM and the ABS modules, in fact if you don't do it in the correct order it will revert to the old settings. In some models tyre sizes can be set either by specifiying the tyre size or by the tyre diametre (if known). Speedos (set in the factory) always show about 4% over the real speed (this is done on purpose BTW), and its easy to check that with your GPS. Sometimes a tyre upsize will take you to exact parity between speedo and GPS, and you would think that would be a good thing, but the ABS system needs to know the correct tyre diametre so that it can 'see' what the tyre is doing through its sensor.

[turbomart]

There are a couple of aftermarket electronic speedo correction boxes avail, like marks adapter one which allows you to adjust to suit any tyre diameter.

[jamesjoseph]

Yes I have installed one of these,, in my 06 Grand crd.
It was supplied by AEV and developed in conjunction with Superlift for their 4" lift kits for the Grand Cherokee.
Works perfect, and is easily adjustable as often as you want to change you wheels.
Simple to Unplug a connection behind drop down panel under dash, and plug in both ends of EGR module.

Resets the Speedo.
Resets the ESP, stops premature engagement.
Installs one touch lane change indication.
Installs reverse mirror tilt on the limited models.

It is included in the Superlift 4" suspension system, (part no's K829 & K829r)
Suits Jeep WK,XK,WH,XH.

I run a 265/70/17 on a 5.5" backspaced rim