So i bought a hypertech programmer to adjust for my tire size. It wants to to enter my tires in inches. Currently I have 295/60/20. So what I can find, it's 33.9" or 33.75" in my hypertech programmer.

I entered that and now it says I'm going 3 MPH faster than what my GPS is telling me. Previously before I adjusted I was going roughly 3 MPH slower than what my GPS says.

What gives? Am I entering my tire size wrong?

 

Try 32.75.

I have 34.6" tires and 33 is the magic number on the hypertech for that sized tire. I read that from somebody on here so when I got mine I set it at 33 and sure as shootin it was bang on, handheld Garmin GPS verfied, on flat level highway.

 

If you know what the old setting was, try half way. As tires wear, they will change, you will not have a perfect setting from a spec sheet. You could also figure the percentage error and reduce the 33.75" by that percentage and reprogram with that new number and likely get it right on.

 

What's this programmer for out of curiosity?

 

So I ended up using 32.5". It's pretty close now, I could possibly do 32.25" and be dead on. Maybe try it tomorrow.

I guess I was thinking this would be a little more exact based on tire size. My tires only have like 3.5k miles on them.

 

Hypertech

 

I mean, what's it for... im guessing to program the trucks computer so the speedo reads right with bigger tires???

 

Correct, adjust for larger tire size

 

What do these things go for? Are they expensive... i'm trying to do a level maybe on my truck and doing a lot of sourcing myself... TPMS/programming... so trying to get everything setup so I know what i need.

Expensive? Easy to use?

 

I'm not very mechanical savvy, oil changes and brakes are about it for me. This is straight forward. Roughly $229, I think pretty expensive for what I'm doing with it. But I wanted it done. You could spend a little more money and get a tuner that could do the same thing and still tune now or whenever you're ready.