Hey all,

I have 17 inch moto metal wheels and 33 inch pro comp tires. I am planning on getting an edge and was wondering if i had to change the tire size when i do get the edge. I think the 35 inch tires require you to make changes but I'm not sure.

 

I have 305/65/18's (which comes to a little bigger than 33's) and I changed mine. It seems to have helped. Especially with the noise going down the highway w/ my exhaust...nowhere near as loud as it was when I didnt recal. for the tires.

 

You guys have lost me, not sure what is being asked or what the answer is. But, If you make any change in the height of the tire (the circumference), then the computer needs to be told. Otherwise, your speedometer, your odemeter and the transmission will be out od sync. You can get a recalibration at the dealer, or you may use a tuner, such as the Edge to make the change.

 

I was under the impression that 33 inch tires were the biggest you could go and not have to change anything in the computer, anything higher than that and you had to make changes.

 

Ok. But here is what I know. My truck came with 255/6517s. As I recall, they are about 31 inches tall. I replaced them with 265/70/17s which I am remembering to be about 32 inches tall, a difference of about an inch. This made my speedometer and odemeter off just over 5%. If I had put 33s on the difference would have been even more. So, I went into my Edge and reprogrammed from 2398mm to 2521mm. and I am back in calibration. Now as to the transmission, that may not have been enough difference in height to require a recalibration, I do not know. That may be where you get the idea that 33s will be close enough. But I know for sure I do not want to be doing 75 when I think I am doing 70, and I want my mileage to be accurate. Any change in height/circumference will change yor speedometer and odemeter readings. It is just a mathematical fact and they do not self adjust.

I think the key here is in the word HAVE to adjust and it probably just refers to the tranny. The tranny shift points may be ok with 33's but everything will be off. I would still WANT to recalibrate.

 

For what its worth, even after updating for my tire size my speedo and what the edge says my speed is, is 2 mph off.

 

How much mileage would it be off by? anyway to tell? I have had the 33 inch tires for a couple years now.........

 

It's called the sqish factor. You can play with the number to get it correct or you can do a rollout and get an actual measurement. There is a formula you use and I forget the formula. Even from the factory, they are off 1 or 2 mph.

 

Go to Discount Tire site and compare the size of your original tire with what you have now. Take the difference and divide that by the size of the original tire. That will gize you a percentage difference. Multiply that times your speed and that is about how far off you are. Or, multply times how many miles you have driven and that is how much the mileage is off.

NEW TIRE SIZE minus OLD TIRE SIZE = PERCENT OFF
OLD TIRE SIZE