[R 70 Judge]

Originally Posted by HWYSTR455

If you run a wider tire on a narrow(er) wheel, that 'bulge' takes away from what you can fit, not to mention it's not safe. It is possible for the tire to roll off the wheel. Also, on a dip or bump as the suspension compresses, the bulge can contact the lip and blow a tire.

If you run a 'bulge', you actually can only fit a narrower tire than without a bulge.

An option that helps is you can roll the lips, but more prefer not to do that.

Several things need to be known before trying to fit the widest possible tire on a 2nd gen F:

The 'baseline' wheel size on a 2nd gen F is 15x8 with zero offset. Or, in other terms, 4" back space. (EDIT: or 4.5")

Some wheel manufacturers measure width differently, so it's important to know that.

The distance to the wheel lip from the rear end flange is closer to the lip on the passenger side than the driver's side. So measure both sides.

When doing offset calculations, understand it's not just the fender lip that you need to watch, it's also the leaf. In some cases, the leaf buckle.

Tire 'squirm' can make contact even though they clear at stand still. Like around turns.

In general, you can't go more than 4" outboard on the wheel due to fender lip contact. That accounts for squirm/tire roll. (and no bulge). So when going to an aftermarket wheel, changes to width should be made towards the inside.

On like 74-up, there's also the seat belt bulge that can make contact. Might be '75-up or so.

b-man is correct, 'section widths' do vary, and you have to check/take into account. Keep in mind that measurement does not take into account for bulge when running a tire on 'unapproved' widths.

You should be able to do a 275/60-15 on a 15x8 wheel with 4.5 backspacing. A 15x9 with 5 or so backspacing would be a better choice though. And, it will depend more so on the tire.

That is not taking into account if you added disc brakes to an OE width rear.

The Herb Adams VSE catalog (should be able to find one) outlines much of this and is a good reference.

Just to say, it is possible to go too wide on a tire. As the contact patch increases, the corner weight gets distributed over a larger area and will not have as much downforce.

Just look how 10.5 cars can hook so well.

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Great info here

It’s surprising how big of a tire you can cram into a f-body. This is a 30x12.5 ET Street biasply tire.