I recently changed my rims from the stock 02 wheels to some 2004 wheels. I am wondering if it would be a good idea to calibrate my speedo for the size change? and if so how would you go about doing this correctly. Thanks for the info, hope all you had a good new year

 

How do you plan to calibrate it? Also, wheel size is not important... overall tire diameter is.

 

Tire dimensions can easily be calculated and new sized can be selected.

The formula is:
Outer Diameter-Rim Diameter/Tire width=Profile

Since the width comes in milimeter and rim diameter comes in inch one of them needs to be converted.

 

Ok, but how does that help him calibrate his speedo? Fact is, he can't unless he uses a "yellow box."

 

There is a shop in Culpeper, Va that does speedo calibration. They pretty good from what I hear, the state send anyone who claims their speedo is off there to get checked. Plus the 4x4 guys go there to get the adjustments needed.

 

Chris, how do they do that? Calibrate it?

 

I have not watched it, but they use a computer tool and something like a dyno. Basically they can plug into the cars comp and change the wheel and tire settings. Then the cars comp will change the speedo. On older cars its done with the cable that feeds to the transmission.

I know with my Impala I had wider/lower profile tires and the hypertech programmer let me change those settings.

 

I used a Hypertech Power Programmer on my GMC. Aren't those ecu's flashable? The S's(pre-'06) is not.

 

Just purchase a Yellow jacket and borrow a GPS, the YJ is pretty easy to instal, then get on the highway, set your cruise 70+ and use the dials to match the GPS speed.

 

It a secret