Does a 20 inch rim make that BIG a difference???

Bear · Jan 2, 2007

Here's my story, I ordered a Yukon with Autoride and the factory 17's. I got a wild bug up my ass about 20's and Autoride so I ordered some from GMC. Now the dealership is trying to tell me they have to reprogram the speedometer to compensate for the bigger wheels. Is it really that big a difference between the two wheel sizes???? Cause I was planning on switching between the two sizes in winter and summer, does this mean that I also have to reprogram the speedometer if I change them on the Yukon???

Hawstly · Jan 2, 2007

You ONLY need to reprogram IF you are going to an "overall" larger tire diameter. It doesnt matter the wheel size. Its all about how tall your tires are. If you are more than 1" taller than stock then yes you "could" need it reprogrammed but most people dont because its really not off by that much.

Bear · Jan 2, 2007

Hawstly said:
You ONLY need to reprogram IF you are going to an "overall" larger tire diameter. It doesnt matter the wheel size. Its all about how tall your tires are. If you are more than 1" taller than stock then yes you "could" need it reprogrammed but most people dont because its really not off by that much.

Fantastic, thanks for the info brother, now the question that wil prove I am a novice. How do I interpret the tire "height" of a P265/70R17 and P275/55R20?

bparker · Jan 3, 2007

Just go to tirerack.com and lookup your tire and it will show you the overall diameter to compare them. Like I said, if its within 2 inches from factory most dont jack with it. If you want it "dead on" you can have it fixed. You will just be the 1 in 500 that does it.

Bear · Jan 4, 2007

Bear said:
Fantastic, thanks for the info brother, now the question that wil prove I am a novice. How do I interpret the tire "height" of a P265/70R17 and P275/55R20?

Okay, went to tire rack and verified the difference is a grand total of 1.3" and I think I WILL be the 1 in 5 gazillion to get the speedometer reprogrammed. the P275/55R20 is 33" in diameter and the P265/70R17 is 31.7" around.

bparker · Jan 4, 2007

But you cant put a dollar ammount on peace of mind -

smoothfrc · Jan 11, 2007

You could just get the powerprogrammer - which will let you modify the tire size yourself - so you can just change it between winter and summer.

The 33" tires would make your speedometer read lower then what you are actually going - there are calculators all over that can tell you what kind of mph difference you are talking about between the two sized.

Bear · Jan 11, 2007

Okay, I found a site on the web to get the numbers crunched.

Bear · Jan 11, 2007

I also found this website that allows you to immediately compare two different sizes. Thanks for the help everyone, learning HAS occured and I appreciate the input.

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

diehrd · Jan 12, 2007

The tranny shift points will be early making a slight gas mileage loss and some performance loss.Although you can argue it may be slight shifting from first to second at 15.something, instead of 18 will alter driving a little.

I would let the dealer recalibrate the computer to compensate for this difference

smoothfrc · Jan 12, 2007

just get a programmer - they are like $300 or something, and if you are going to be switching them back and forth - the dealer cost's will add up i am sure.

Plus you may be able to get a bit more power from the programmer to make up for the larger wheel weight and height.

Does a 20 inch rim make that BIG a difference???

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