Hi,I'm fairly new to this forum and was looking for info on how to recalibrate my trucks speedo and tcm if i was to run larger tires ie 285/75/16 and i know you can use a programer to correct the speedo but i was more interested in correcting for abs and tcm and was wondering if anyone had experience using a superlift tru-speed and if it corrected the transmission shift points due to the larger tire.
thanks in advance

This may not help you but this is my experience- I put 285's on 70k miles ago. The speedo is off so little that it must have been off the other way with the 245's. I never recalibrated the ABS because the error factor is so little I didn't think the expense and hassle would be worth it. The transmission seemed to acclimate on it's own and works fine. I have towed 11k routinely with the cruise set on 70 without problems. I have heard that the Superlift calibrater works but I think it only corrects the speedo- I don't think the ABS gets any data from the speedo but I am not sure on this point. Good luck.

I attempted to have installed Superlift's Tru-speeds ( there is one for speedo, one for ABS ), however, to date they do not have a model out for the LLY yet. The Computer plugs changed with the "up-grade" to LLY in 2004.5 so if this is your problem as well if this is your truck. I you really wish to pursue this matter further, on Superlift's message board there is a thread concerning this very matter. A shop has been making modifications to the Tru-speed that reportedly works. There are some instructions posted there. The thread is dated back on May 12 2004. Hope this is some help.

thanks for the input and sorry i didnt post it but my trucks an lb7 and im mostly concerned about the allison shift quality for example i've been told it will shift earlier with a larger tire and was wondering if the truspeed would correct that
thanks again

If you correct the VSS signal with the Tru-Speed, the dealer can program tire diameters up up 34" or so into the EBCM with a Tech 2. This corrects the front speed sensor signal input to match the new "modified" rear wheel speed (VSS). If you don't do this, it will set an ABS/BRAKE warning light if the speed difference between front and rear is more than 10%. (Not an issue with 285's but it is with 315's)

my dealer told me they couldn't change to 265 and they called they gm tech line while i was there and gm said they didn't support that tire size. Is there any way i can do this without going to the dealer such as using a programer like diablo sport or hypetech. I'm just looking for the best/right way to do this and still keep the factory shift points with the larger tire
thanks for everyones input

They can ONLY correct the tire size in the EBCM(which calibrates only the front speed sensor inputs), not the rest of the modules. Yes, a Bully Dog/Predator will correct the tire size, and you won't have to screw with the Tru-Speed. Do not worry about the shift points, you will not notice the change. The shift will occur at the same MPH, which will be slightly later with a larger tire. Not enough to really feel when only going up 2 sizes.

Just for reference, Dean Patterson Chevrolet in Altoona, Pa said they could re-calibrate for 285's. Not sure how big they can go.

I just put 275 60 20's on and the Service Mgr I know said they couldn't help me.