Why do my tire sidewalls bulge on aftermarket wheels?

SSTJ

SSTJ

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Hi all,

So why is it that my 30" tires on stock Jeep wheels have a straight/flat sidewall, but then my same tires on aftermarket steelies have a bit of an outward curve/bulge sidewall? Is it something about the depth of the wheel? Wish I had pictures to show the difference, and hope the description makes sense.

Don't get me wrong, I like the look (the tire looks bigger), and I'm shopping for new 31s soon.
 
It's very popular in the off road community to run the narrowest rim a tire will allow for. So a 35X12.5R15 tire is typically run on a 15x8, though it could also be run on a 15x10.

The purpose is to allow the tire to protect the rim from damage, and also to give the tire more grip on the rim at very low tire pressures.

Sports car enthusiasts often do the opposite, or they stretch the tire onto as wide a rim as possible. This is intended to give better cornering response. More often than not, it is also done for looks. You'll notice even some mall crawling jeeps and trucks have stretched tires. It's highly impractical off the road, but people do it for looks regardless.
 
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Thanks both, this is good to know.

So, my first wheels were the stock SE wheels, which Chris lists here as being 15x7. I guess I'm surprised, because if I didn't have the bulge on those rims, but I do on the current ones, that would mean my current ones are even narrower than 15x7? I'll measure when I'm home.
 
Thanks Jerry,

A good question. I can check when I get home, but the actual wheel-swap was a while back, and I can't remember what I was running at the time. I suppose that may be it.

Anyway, what's behind all this is that I'm shopping for new 31s, and wanted to know if this difference should inform my decision at all. Sounds like as long as I have 15x7s or 15x8s I should be ok with 31x10.5s, and should see some of the same bulge too, if not more, since the new tires will be wider.
 
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