Speed

[gibbs114]

How much will my speedometer be off if I go up in tire size 265 to a 275.

[Zembonez]

How much will my speedometer be off if I go up in tire size 265 to a 275.

Almost none. 1.5 mph at 60 or so. Not enough to affect anything.

[iscsidude]

You can use the following web site to determine the speed change.

 

Tire Size Calculator

 

As Zembonez points out, it is minimal, but it may come in handy if you are looking for something more drastic.

[pm26]

The speed difference is directly proportional to the increase in the new tire diameter.

If you install a taller tire, the speedometer will indicate lower than actual speed, if you install a smaller diameter tire, the speedometer will indicate higher than actual speed.

 

And because typically speedometers are calibrated to read about 3 to 5 % higher than the actual speed, installing a slightly wider (and taller if the aspect ratio is the same) tire will get your speedometer to read closer to the actual speed.

[fbachman]

IF you have, or can borrow, a GPS, you can gauge the speedo error off the GPS reported speed.

 

 

On my 07 Sierra (900), with the 20" factory wheels and tires, the speedo was dead-nuts accurate at all speeds up to 85, relative to the TomTom reported speed.

 

 

Just a thought.

[Nick The Great]

IF you have, or can borrow, a GPS, you can gauge the speedo error off the GPS reported speed.

 

 

On my 07 Sierra (900), with the 20" factory wheels and tires, the speedo was dead-nuts accurate at all speeds up to 85, relative to the TomTom reported speed.

 

 

Just a thought.

 

No offense, but any idiot knows that Big GPS and Big Auto are in cohoots with Big Oil. Your TomTom is off the same as your truck. It's the easy way to get around CAFE.

 

 

Seriously though, Justin at BlackBear told me during my tune that a lot of factory speedometers are off. Mine seems ok, but I've never messed with my tires either.

[VMax2007]

IF you have, or can borrow, a GPS, you can gauge the speedo error off the GPS reported speed.

 

 

On my 07 Sierra (900), with the 20" factory wheels and tires, the speedo was dead-nuts accurate at all speeds up to 85, relative to the TomTom reported speed.

 

 

Just a thought.

 

No offense, but any idiot knows that Big GPS and Big Auto are in cohoots with Big Oil. Your TomTom is off the same as your truck. It's the easy way to get around CAFE.

 

 

Seriously though, Justin at BlackBear told me during my tune that a lot of factory speedometers are off. Mine seems ok, but I've never messed with my tires either.

 

 

Mine was off with the stock wheels/tires and was dead on when I went to the new wheels/tires (larger OD tire). Justin set my ECM based on my tire size and now it's off again. No biggie though, it's reading slightly slower than actual, which explains why my mileage "appears" to have dropped slightly.

 

I do think that GM errs on the side of MPGs with their speedo/DIC.

[TN_Z71]

How much will my speedometer be off if I go up in tire size 265 to a 275.

 

I went from a 265 to a 285 and according to the Garmin my speedometer's ~ 3mph off.