larger tire

anchsatre · December 2, 2004

Hello all, I am new here and new to my truck 95 3\4 ton chevy 4x4. My question is I heard that when you up size tires you must change something on the tranny or in the computer for the shifting to be right and the speedo to read right . My truck has the 4l80e trans, 5.7 engine. Thanks for any help on this subject.

Mike

Wingnut · December 2, 2004

Yes, you need to have the computer adjusted to match your tire size. It affects your shift points and speedo, among other things.

As to who can make this adjustment, well...It kind of depends on what size tires you are going to.

I'm not sure about your model year, but the 99 and newer 3/4 tons can only be adjusted up to a 265/75/r16, not up to the 285/75/r16 that a lot of folks upgrade to...At least that's all that a dealer can correct the computer to. Custom chip programmers can adjust it to just about any tire you want to put on there.

This may or may not be true for a 95, I'm sure that somebody with a little more knowledge in this area will chime in...At least I hope they would.

Welcome to the forums, by the way

Stick around, there's a big enough knowledge base here to make your head spin if you care to ask the questions.

anchsatre · December 3, 2004

Thanks for the info, and for the welcome. I have been looking into a hot chip from TBI Chips who does these chips custom, and they cost less then the others I have see the guy is a one man show so no overhead, anyway I will talk to the chip guy about tire size. I'll let you all know.

Mike

Stryker · December 4, 2004

Hey Mike, welcome.

I have a 95 Z71 and when I upsized my tires to 285, I calculated a 4 Km/h change at 100 Km/h. Is changing the shift points that important to you? I didn't to save me a couple of bucks but if I am doing something wrong please tell me. Anyways, just my two cents.

citydriver · December 6, 2004

On a '95 you will need a new DRAC (Digital Ration Adapter Controller) or ERA (Electronic Ratio Adapter) to get your speedo. to read correctly. If you go up several tire sizes it will also affect your torque converter lock-up AND your ABS. You can use THIS CALCULATOR to see how much the tire size you want to use will affect your speedo..Unfortunately the correction could not be made thru the ECM til '96.

You can order one of these units thru your local GM dealer, or even better(cheaper) they are available thru some of the Pref Vendors on this web site.

Or you can order one from SUMMIT RACING, or several other vendors on the internet....hope this helps