Tire Settings?

[TJake]

Hello,

 

Haven't posted in quite awhile but I need a little advice. I just got new tires for the 03 Z and I replaced the P265/75/16 Bridgestones with some Sport King AT 285/75/16's. My question is, my speedometer is a little slow (GPS) now by about 0.5-0.7 miles per hour. Before this it was about 1-1.2 MPH fast (worn out tires). Its actually closer to being correct now. I found a HPIII for pretty reasonable so I bought it for reading codes, changing tire size, shift firmness, etc. I don't know what to set the tire size at. The tire unmounted has a diameter of 32.5" and mounted on the truck about 31.8. The unmounted Bridgestones have a spec of 31.6" and mounted less than that. I wonder what GM sets theirs at, the unmounted spec or mounted spec. Sorry for the ramble and thanks.

 

TJake

[Bish]

Hello,

 

Haven't posted in quite awhile but I need a little advice.  I just got new tires for the 03 Z and I replaced the P265/75/16 Bridgestones with some Sport King AT 285/75/16's.  My question is, my speedometer is a little slow (GPS) now by about 0.5-0.7 miles per hour.  Before this it was about 1-1.2 MPH fast (worn out tires).  Its actually closer to being correct now.  I found a HPIII for pretty reasonable so I bought it for reading codes, changing tire size, shift firmness, etc.  I don't know what to set the tire size at.  The tire unmounted has a diameter of 32.5" and mounted on the truck about 31.8.  The unmounted Bridgestones have a spec of 31.6" and mounted less than that.  I wonder what GM sets theirs at, the unmounted spec or mounted spec.  Sorry for the ramble and thanks.

 

TJake

 

<{POST_SNAPBACK}>

 

 

 

Simplest way IMO is the chaulk on the driveway method. Park vehicle, draw chaulk line on tire and ground at center of contact patch. Roll vehicle backwards until the chaulk line is again pointing at the ground and draw chaulk line on driveway. Measure the distance between the two chaulk lines on the driveway and divide by 3.1415 and that is the number you plug into HPPIII.

[wreedZ71]

What HPIII tuner did you get to reporgram tire size?

[Bish]

What HPIII tuner did you get to reporgram tire size?

 

<{POST_SNAPBACK}>

 

 

 

I had a Hypertech Power Programmer II. It was great for changing tire size, shift points, rev limiter, and top speed limiter. I'm not convinced I got any significant HP gains out of it. My custom tune was cheaper and performs way better.

[TJake]

Thanks Bish! WreedZ71, I got the HPPIII part number 30019 for 2003 GM trucks. I didn't get it to improve performance, just for tire size , trans firmness, and to have a code reader for my truck. Thanks again.

 

TJake