Chevy & GMC Vans

The transfer case shift control module uses the VIN information for calculations that are required for the different calibrations used based on axle ratio, transmission, tire size, and engine. The system does not know which calibration to use without this information. This information is provided to the transfer case shift control module via Class 2 data bus from the powertrain control module (PCM). The transfer case shift control module monitors front and rear propshaft speed as well as controlling the operation of the transfer case encoder motor assembly.

What effect does installing larger diameter tires have on the behaviour of the transfer case?

First and foremost you MUST be sure both front and rear tires are the same diameter. This also only affects the 1999 - 2005 AWD vans.

Now, in theory the TCCM could be screwed up with different diameter tires. You may get the front wheels engaged too early or too late. What you will feel if the t-case engage too late is a banging into AWD when the rear wheels slip. We used to feel this when running our 2005 TrailBlazer in AWD mode. It was an abrupt slam into 4WD and we elected to run 4HI when the roads were slippery. If the t-case engages too easily, you could be engaged in tight turns I suppose.

So far anyone I know who have run larger diameter tires have had no issues with the t-case locking in.

The tire size really shouldnt affect anything other than the speedo speed and your actual real speed.(I suppose it can affect the engines performance with a differnt sped in relation to RPM, but thats a differnt subject) As far as I know the AWD transfercases sence wheel slip so it shouldnt matter what the tire size is really. It allows for a fair amount of slip for going around corners and such once that limit is exceeded it engauges the AWD. I suppose if you drastically changed tire size it could mess it up and try to engauge while cornering and such but it once you go so big your money would be better spent on swapping to a part time system anyway.

With larger tires, you're actually moving/slipping faster than what the vehicle is sensing, causing the AWD to engage less, making it less effective. Same with the G80 diff. I don't think the amount would be very noticeable though.

I'm pretty sure you would have the opposite effect, the larger the wheel the longer the rotation so if there is anything which senses anything based on tire rotation it would sense it quicker with a smaller tire (I think :-k ) yea, I'll go with that

That's what I said. Quicker with smaller tires, slower with larger ones.

timelessbeing wrote:That's what I said. Quicker with smaller tires, slower with larger ones.

You're messin with my mind brother

Hehe I know.

With larger tires, you are MOVING faster right? The circumference is larger. But the sensing and AWD engagement is slower.

Sorry for the confusion.