im currently running 295/75r16's on my 97 and i noticed a chance in mileage, not gas mileage but trip meter mileage. with stock tires it was exactly 35 miles from my house to the college. now with the bigger tires, it says its about 32-33 if i remember right. i was just wondering if besides having an incorrect odometer reading if this will mess with anything. also, does this mean that im getting slightly better gas mileage than im averaging out? last tank i got 360 miles, 95% freeway. with the odometer being off, that means im getting more miles to the tank than it says right?

 

theres another post floating around here. that guy has almost the same problem, except his mileage jumps 200 and something miles in a 2 mile span. he has an 08. you might wanna try looking for that post.

 

what did you use to get out of a tank of gas before the new tires?

 

what is the stock tire size? if the new tire size if much bigger then it could throw off the odometer over a 40 mile trip.

 

stock tires came out to 31.5", these are 33".

 

It stands to reason that the taller tires will turn fewer times to go a mile than smaller tires. Your speedometer is also off by the same amount. You are actually traveling faster than the indicated speed. I would estimate 9.5% faster than you are actually traveling.

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i was hoping my edge programmer would be able to fix the speedometer but it turns out mine can only be changed by changing the gear in the transmission.

 

This site, scroll down to comapre A to B, will show you the odometer, AND, speedometer differences between 2 different sizes. It will also show the height and circumference diffs too.

As well as your odometer being off, your speedo is as well!! Watch that.

A Scan tool (a proper one) can be used to reprogram your BCM/PCM for the new sizes and it will adjust the speedo. Go to a garage, slip the guy $10 and he will do it for you, out the back door usually.

 

FYI, Speed info is first sent to the instrument cluster and from there the PCM gets it. In 1999 this chaned to the PCM getting it first and then sending it to the instrument cluster. This is why you cannot reprogram the tire size nor the axle ratio in 1997-98 models. You are limited to the gear change at the transmission or t-case if 4x4.

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