Tire recalibration--The summary

[pushpole]

I've tried to piece together all the discussions regarding recalibration of 1. Anti-lock brake sensors 2. Speedometer 3. Transmission Shift Points. There are some differences of opinion out there, so I'd like to get all the info in one post. What can we adjust via a plug in programmer? what does the after market offer AND what does it really do for the truck?

[typecast]

Great idea... I'd also like to know the effect on the '03 trip computer of products like the Superlift Truespeed speed signal calibrator.

-- Galen

[LA DMAX]

I would like to know the full scoop also. Seems that some people think larger than stock tires will or does change shift points, ABS, down shifts and 5th gear shifts; some people don't think that. Some feel you loose power, some don't; some feel you loose MPG's, some don't. Hard to say what the clear cut answer is here. I would like to run a 285/75/16 or a 33/12.5/16.5 but I don't want to ruin this precious Allison tranny or drop MPG's or have a gutless truck if I put a tire this size on. Why don't the CTD or PSD guys I talk to complain about this tranny business? I know, they don't have an allison in their truck. Most guys I know are running 285's or bigger without much complaint, but none of them own DMAX's. Can anybody nutshell this tire thing? Thanks.

LA DMAX

[conradv]

Me too! I want to get these firestones off of my new GMC...

As for the Allison, has anyone else seen the Allison VHS that you can get from the dealer? They talk about every clunk, clank and whine that the tranny puts out, and I think they say "This is normal" about 25 times... ;) Kind of funny.

[GMC-2002-Dmax]

285's = NO PROBLEM!!!!!

I am running 16x8 wheels with 285's. I have had them on for over a month now and after factoring the speedo being off I may have lost 1 mpg.

I am sur the SUPER JUICE has something to do with the mileage drop :D

Anyway I have tied back the wheel well in 3 spots for extra clearance and the ABS has worked great. Allison does not seem to mind it either.

Go Ahead and swap the tires and rims, it will be more $$$$$, but if you run into trouble put the stockers on and goto the dealer.

GMC ;)

[Kennedy]

For shift points, the transmission uses OSS (output shaft speed) which is more or less not vehicle speed sensor related.

[pushpole]

If I'm understanding John correctly then the Transmission shift points are independent of tire size. Based on that information, and the Truspeed ad information, that gizmo should input to both the Anti-lock circuitry and the speedometer. A little help with my observation please!