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I am buying tires and rims for my 99 forester. I have decided to go with GY ultra ice grips as I have run them on my other car for 3 winters and am very satisfied with them...I want to go to 15" for the snows and the manual suggestd 205 70R 15's while all the tire stores suggest 215 65R 15...are they comparable???

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Just go to the Dunlop website, or other tire manugfacturer to check outside diameter of each size. Typically changing the aspect ratio by 5% equates to 10mm in tread width hence they will be close in diameter.

 

The 205's being a bit narrower will get you a bit more bite in deep snow as they have less floatation. Just look at the pro rally cars and the skinny tires they run in winter events. Trade-off should be good dry performance while getting a bit better deep snow performance. The 205/70-15 is also a more common size and should be easy to find for less money.

 

Glenn

 

I am buying tires and rims for my 99 forester. I have decided to go with GY ultra ice grips as I have run them on my other car for 3 winters and am very satisfied with them...I want to go to 15" for the snows and the manual suggestd 205 70R 15's while all the tire stores suggest 215 65R 15...are they comparable???

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Per the tire calculator here:

 

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

 

You are reducing rolling circumference by about 1% going to the shorter sidewall tire. If you plug your numbers into the tire calculator you'll see all the particulars. IMHO I'd stick with the stock size, unless you can't find it or it's a lot more expensive for some strange reason. But, either should work pretty well.

 

Steve

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The first thing you need to check is load rating. In PA tire dealers are forced to put on a tire that has the same of higher load rating as the factory tire. (You can thank Bridgestone and Ford for that) Other than that the next rule is rim width vs tire width. That small of a change is no problem, they will fit the rims just fine.

 

Then it comes to performance, and that's where staying with the stock size for a winter only tires will give you worse snow/ice performance than going skinnier. Going to a skinnier tire gives you more PSI on the contact patch and allows the tire to Bite through the loose surface to the packed or hard surface below. This will give you better traction and better performance in the snow and ice. When given a choice I'd go smaller. While the differences in lost dry performance and gained snow/ice performance are minimal, most people don't drive on the limits of their tires in the dry and routinely over drive their tires in the snow. That means having every extra bit of traction helps.

 

Keith

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