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Tire Spacing, the ET specifically

Oct 10, 2019
I've always been annoyed that my snow tires rub my wheel well when I turn, in reverse only.

I run 255/40/21 for my snow tires and run 245/35/21 and 265/35/21 for summer tires. Seemed logical to get 255 as snow tires so the total amount of tread with all around is the same patch size. And putting 245 on the rear seemed like it would be too small for the snow.

I bought my snow rims some years ago and never paid attention to it because they were relatively cheap and I didn't really know about offsets and *sugar*. The ones I got are 20x9 with an ET of 30, which I now know Teslas are am ET of 40.
I always chalk it up to the tires being 255 instead of the 245 but now I'm pretty sure that 10 difference is where the rubbing problem comes from.

I only just noticed this when the tires I have bought 3 sets of over the years now have a note when I go to buy them that says they should be installed on ET40 rims, which is why I checked mine and found out they were ET30.
But whatever I've been using thise combo for ages now and it's all good.

Why would tires care about the ET of a rim though? Like what does the spacing have to do with mounting a tire to the rim? Since the spacing more so applies to how far in or out the wheel sits from the hub. Am I missing something here?

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