Speedometer Calibration

[gtolvr]

Just found out the 2006 silvy i just purchased has 18" wheels vs. stock 17". Guess i wasn't too concerned about it until i went to look at getting stock P25 wheels.

 

Is there any speedo calibration needed when switching wheel sizes or is it automatic from where the speedo connects on rig? Where ever that is.

 

Thanks

[Jim67]

Wheel size has nothing to do with it, tire diameter does.

 

And there is no speedo cable on modern trucks. They are all electronic and can be re-programmed for diferent tire sizes.

[wcortesi]

Wheel size has nothing to do with it, tire diameter does.

 

And there is no speedo cable on modern trucks. They are all electronic and can be re-programmed for diferent tire sizes.

That's exactly right. The circumference is all that matters. Try this out to check: http://www.tiresizecalculator.info/

[Jim67]

The circumference is all that matters.

 

That's what she said.

[gtolvr]

so if i change from the after market 18" to stock 17" would i have to calibrate the speedometer to get accurate readings on speed or will that automatically take care of itself?

[Zembonez]

so if i change from the after market 18" to stock 17" would i have to calibrate the speedometer to get accurate readings on speed or will that automatically take care of itself?

Think about it. If the overall diameter of the tire is the same It doesn't matter if the wheel is 4 inches or 20. Your vehicle wouldn';t know the difference. Want an easy way to know how accurate your speedo is? Plug in a Garmin GPS unit (somebody you know has one for sure) and go see what it reads when you are traveling 60. Mine says about 62. Yours should be close. No speedometer is 100% accurate.

[dewfpo]

so if i change from the after market 18" to stock 17" would i have to calibrate the speedometer to get accurate readings on speed or will that automatically take care of itself?

 

If you change the overall diameter of the tire/wheel then your odometer and your speedometer may be off. On my '05 2500HD Silverado they read fast and more miles. I switched from 245 to 265 and they read dead on accurate. I didn't have to change the calibration of the unit at all. You can check it with a radar gun or an accurate GPS.

 

DEWFPO

[sabre364]

When you switch go back to 265 70/17..its better anyways, more sidewall. the diameter is all that matters.

 

a good calculator to use is this, just give it a second to load the java

 

http://www.miata.net/garage/tirecalc.html

[amtz.zero]

What if you have a Black Bear tune? If you get your speedo recalibrated, is it still recommended to have Justin do a re-tune?

[brims]

What if you have a Black Bear tune? If you get your speedo recalibrated, is it still recommended to have Justin do a re-tune?

 

I don't think there's anything he'd do differently to the tune for different size tires other than changing the tire calibration.

[usmc3529]

if you go to a bigger wheel and different tire size your speedo will be off. You have a couple options, get a handheld tuner or get a black bear tune. The ecm does not "calibrate itself" for larger wheel/tire combos.

[gtolvr]

So what i am reading is it is better to go with the stock size than getting the larger size tire?

 

Will the truck ride a little smother on road if 17" tires are on vs. 18"? That is why it came out stock with 17.

[FarmerDave]

These trucks come with stock 17's cause of the brakes, 16's dont fit. Also, more sidewall = better ride quality, large diameter tires ride better, smaller rim sizes ride better.