Bigger Wheels And Tires Affect Spedo?

yfzrider · May 9, 2011

I have a 2010 silverado and im going to put oversized wheels and tires on it. Wont this make my spedo off? and if so can you recalibrate it?

SouthCo · May 9, 2011

If the outside diameter is bigger, than yes the speedo will be off. A few inches taller tire wont be a big difference. Your speedo can be recalibrated.

700 sportsman · May 9, 2011

Yes, it will certainly affect your speedo. It all depends on how much larger you are going, but if your going an inch or two it would probably be about 3-4 mph.

Big Whiskey · May 9, 2011

Check this out: http://www.miata.net/garage/tirecalc.html

NWI_#73 · May 12, 2011

Can the dealership recalibrate the speedo for free?

Doug_Scott · May 12, 2011

Can the dealership recalibrate the speedo for free?

They can, provided the new tires are a size the the truck comes with. For example, if you put 265-70-17 on in place of 245-70-17, the dealer can change the ECM to allow for that. As for them doing it for free? Depends on the dealer and your relationship with them. Mechanics are paid flat rate, they get paid by someone, either you, GM or the owner of the dealership must pay them for their work.

ETMegabyte · May 23, 2011

I have a quick question on this. I bought my truck a couple years ago. An '03 Sierra 2500HD. Came with LT245/75R16s on them, which from my understanding is the stock size that came on it... But my speedo has always been a few MPH off... The same 4-5mph mentioned earlier in this thread (which is what sparked my current question). Does this mean that my speedo was calibrated for slightly larger tires previously? If so, how much bigger?

mhenshaw · May 23, 2011

I have a quick question on this. I bought my truck a couple years ago. An '03 Sierra 2500HD. Came with LT245/75R16s on them, which from my understanding is the stock size that came on it... But my speedo has always been a few MPH off... The same 4-5mph mentioned earlier in this thread (which is what sparked my current question). Does this mean that my speedo was calibrated for slightly larger tires previously? If so, how much bigger?

Is the speedo reading faster than you are actually going? If the truck was calibrated with 265/75/16 and now you have 245/75/16 then your speedo would be 2.6 mph high at 70 mph. So your actual mph would be 67.4

Tire Size Cal Just enter the tire sizes and see what the speedo would be off by.

ETMegabyte · May 24, 2011

Is the speedo reading faster than you are actually going? If the truck was calibrated with 265/75/16 and now you have 245/75/16 then your speedo would be 2.6 mph high at 70 mph. So your actual mph would be 67.4

Tire Size Cal Just enter the tire sizes and see what the speedo would be off by.

Yes, the speedo is reading high... The truck currently has LT245/75/16s on it. I never really noticed the speedo being off until I got my android phone, which has GPS. The car mode for it has a digital speedo and at ~40mph (gps speed), the truck's speedo is ~43mph... At ~75mph GPS speed, the truck's speedo is right around 80mph... This is all from memory, so I might be slightly off, but those numbers are pretty close...

wages999 · May 25, 2011

Yes, the speedo is reading high... The truck currently has LT245/75/16s on it. I never really noticed the speedo being off until I got my android phone, which has GPS. The car mode for it has a digital speedo and at ~40mph (gps speed), the truck's speedo is ~43mph... At ~75mph GPS speed, the truck's speedo is right around 80mph... This is all from memory, so I might be slightly off, but those numbers are pretty close...

My truck was the same way from the factory. With the stock 265/70/17's it was slow, which I didn't realize it until I got a GPS. Putting 275/70/17's on it makes the speed of the truck match the speedometer. I think my brother's old 2500HD was the same way. Must be a common problem.

Doug_Scott · May 25, 2011

Most speedos are off from the factory, but, it is almost always reading faster than you are going. It is common knowledge around the motorcycle crowd that honda motorcycle speedos are up to 8% off on the speedo. Odometer is usually spot on though. Guess they don't want to get nailed for running the mileage faster than it is.