Hey guys I have a blazer with p205/75/r15 tires that look like they should be on a honda civic. I'm going with the LT235/75/r15 tires. Now I did some research and it said earlier gm's had a DRAC and the newer ones used a VSS buffer I have only been able to find a vehicle speed sensor on the parts websites. Any info on what controls the speedometer and how to calibrate it for larger tires. I calculated a 6 mph difference. Thanks i think this will help a few ppl and I did use the search function.

Also will the larger tires wear out my engine/tranny and brakes faster?

 

Your tire size (circumference) and gear ratio are programmed into the PCM. The truck uses this calibration along with speed sensor readings (how often is the driveshaft turning) to give you a speed reading. The dealership can recalibrate for different tires and I know they make re-programmers capable of it. I can't see that size tire having any negative effect on brakes & driveline. Monster truck tires on the other hand.........

 

What year is your blazer if it is old enough to have a drac module I can tell you how to recalibrate it for anything, although I am to lazy to actually do mine lol. Bigger tires wear out front end parts a lot faster but 235/75/15 aren't that big so it shouldn't affect it much.

 

Thanks alot XM mine is a 97 2-dr 4wd Thanks.! if I dont have the drac will I need to go to the dealership? Any idea on what that costs? I saw the link to the DRAC calibration and will probably get a used one and modify it incase I f it up lol

I think this thread will help alot of people!

 

You do not have a DRAC unit in your truck. It is all handled by the PCM. The dealer, a pcm tune by PCMforLess or equivalent, or a hand held programmer is your only choice. This has been covered a few times in the past.