Anyone out there have the issue when they went to change the tire size that the Tuner said stock was 31.5? I have the stock 20's so my stock tire size should be 33. So I called Superchips and they told me just to enter the new tire size and that was it. I did this and then went on an interstate run and now the Speedo is 2mph over. I stopped and backed it down from 34 to 33.5 and no change. Since I only went up 1 inch in size the only thing I an think of is to set the tire size to 32.5 and see what happens. Does this sound right to anyone?

 

They go by what the height of your tire measured with vehicle weight on it. So if its 33" by its self, when install it on the truck its going to squish down some.

 

Well the one inch thing worked. I set it to 32.5 and it is right on. Kind of weird how that worked but oh well.

 

Is the 33" your actual measurement? Or is that the diameter based on tire specs? Best thing is to fill the tire to your normal psi and then measure from ground to centerline of wheel/hub and double the number. That is your real effective diameter. Anything else (calcing based on specs or measuring from ground to top of tire) is just an approximation.

Rob

 

Agreed, I never measured the old tire when it was on the truck. I was going to measure the new one but since I've got it I probably won't measure it now. I went off the website info( I know rule number one, get out there and get and actual measurement) Anyway if I do measure it I will post the measurement.

 

I'm using the Procomp Acu Pro tuner which is actually made by Hypertech.
I went off the actual measurement from the ground to the top of the tire. First attempt I'm about 2.2 miles per hour under what it should be.