[joes455]

76 rally 2 15x10 4 1/2 bs with 275/60 stock 10 bolt ,love the look and stability around turns,hooks from a slight dig full throttle thanks to the 273 gear

[chuckies76ta]

Originally Posted by joes455

76 rally 2 15x10 4 1/2 bs with 275/60 stock 10 bolt ,love the look and stability around turns,hooks from a slight dig full throttle thanks to the 273 gear

This is what you want. ^ 15x10" rim. The 275 tire will look suck in on the sides with an 8" rim. They fit much nicer on a 10" rim. I have the BF Goodrich T/A on a 15x10 " rim with 4.5" B.S. IMO
Like Bart says, you almost need to do some measuring. I do run a Moser 12 bolt rear-end. I did run the same tire on my 10 bolt rear-end with 8" rims and then moved up to 10" rim, same back space.

[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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[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.

.

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.

[R 70 Judge]

Originally Posted by R 70 Judge

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.

I pulled the Weld drag lites and measured the backspace. They appear to be a 15x8 4.5” BS. I also discovered the inner part of the 30x12.5 MT tire was rubbing against the tailpipes. If you are thinking of trying this tire size you may want to consider something a little smaller.

[zippy]

Originally Posted by HWYSTR455

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.


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You meaning Hub flange to wheel opening lip? My TA, the drivers side sticks out further from the wheel lip than the pass. 275/4518. But have had to roll the DS rear inner fender to minimze tire rubing Pass side fine. Is that common for them (axles) to not be centered in firebirds?

[HWYSTR455]

Originally Posted by zippy

You meaning Hub flange to wheel opening lip? My TA, the drivers side sticks out further from the wheel lip than the pass. 275/4518. But have had to roll the DS rear inner fender to minimze tire rubing Pass side fine. Is that common for them (axles) to not be centered in firebirds?

My understanding is in order to maintain the same axle length on both sides the housing was offset to the passenger side, but maybe I have the side mixed up?

The reason it needs to be offset is due to the pinion to ring gear relationship. The offset allows the centerline of the pinion to be on the same plane/centerline as the rest of the driveline.

So the side the ring gear is on the housing is further to the outside the body.

The choice GM had to make was, make 2 diff length axles ($$$) or offset the housing.

Others may have more detailed info on this than I do, but i came across this at one point trying to fit the largest wheel/tire combo as possible (in the early 80s).


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[HWYSTR455]

Yup, I got the sides mixed up...


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[Steve C.]

Very common with 2nd generation Camaro and firebird where the rear-end is offset to one side.

Ride height topic for 2nd Gen if interested....

https://forums.maxperformanceinc.com...ht=ride+height

( AMA Specifications in my post #10 )

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