Question About Changing Rim Sizes.

[RVJ]

I'm looking to save my 18 inch rims and want to install 17 inch rims till spring. I'm sure that will change speedometer a little. Does anyone know how much that would throw it off at 30 mph and 60 mph?

[5829BMG]

There are several tire and wheel calculators on the web Google is you friend. Cant remember the links right now you might have to do MPH calculations your self but they give you the +- diffs

[zozmanGMC]

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

[MikeNH]

Rim size means nothing, the overall diameter is what you need to keep in mind using the calculator linked above.

[RVJ]

Thanks very much, love the link to the mph calculator. Excellent.

[GPSilverado]

I had a nice informative reply all typed out, but the topic got moved while I was typing it, so when I hit reply, I lost the info.

 

Bottom line (I don't feel like typing it all out again) is to go to tirerack.com, decide which size 17" tire you want to run, compare the overall height to you current tires, and try to stay within a 1/2" or so in height and you will be fine.

 

A 1 inch difference is approx 3% on the speedo. Not exact, but enough to give you an idea.

 

 

edit: The tire size calculator is a great tool.

[RVJ]

I really don't know what I will buy for winter tires and rims yet. I'll probably go as cheap as possible. I have stock 18's now and figured I'd go stock 17's steel if I could find some.

[blackout07]

Rim size means nothing, the overall diameter is what you need to keep in mind using the calculator linked above.

 

This. Just get tires that are equal in diameter to your others and you'll be good to go.

[RVJ]

I'm looking at a set from a 2008 Suburban. They are 2.65 x 70 x 17 and mine are 2.65 x 65 x 18. According to the speedometer calculator the Speedo will read 60 mph but my actual speed will be 60.1 mph. That would probably not even be noticable. Only problem I see is the Bowtie emblem on a GMC. Would there be any other issues I'm missing?

[Matt_]

There's effectively NO difference between a 265/70/17 and a 265/65/18. Tread wear and manufacturing differences more than consume any calculated "nominal" tire diameter difference. In other words, no tires measures exactly true to size... so what you calculated to be your difference in speed isn't going to be the actual difference (if there is any at all). That method is really meant for getting an idea of speed differences when jumping a few tire sizes, not replacing with the same "overall" size.

[RVJ]

OK, thanks everyone. I really learned some things about tires today, now it's time to syart finding some.