Tire clearance and wheel travel

[Alponcho]

Never set up one of these cars before so I have rookie questions.

Installed wheels and tires on my car and am wondering whether I'll be OK (70 firebird, quadra link, minitub, 18X12 5.5 bs, Rival S 335). I have about .125" clearance from the outside of the lip to the fattest part of the tire, which is about 2" down from the edge of the lip. If I'm thinking about this right, at the lowest ride height setting, 2" of wheel travel will likely result in contact with the lip, even if most of it is trimmed away and rolled (which I will do).



Am I overthinking this and am good now, or will I have to raise the ride height to be OK..and if so how much?

If it's necessary to raise the ride height more than an inch or so, what's the best alternative? I have a little less than an inch all the way around on the inside, so I guess the obvious solution would be to order new wheels with .25" more bs?

Other options...find a 335 that's narrower than the Rival S? have Forgeline rebuild the wheels? shorten the axle housing and axles by .25 on each side?

[Alponcho]

Here's a photo that show's where I'm at.

[andrewb70]

What does it look like at full lock?

Andrew

[Alponcho]

Not sure what you mean by full lock (the issue concerns the rear wheels....I should have been clearer).

[andrewb70]

What's the rear suspension set-up? Does it have good lateral support?

Andrew

[Alponcho]

I'm using a DSE Quadralink, single adjustable rear shocks, rear say bar...I believe the springs are 250# but they are quite stiff...I put 350lbs in the trunk and they hardly budged. In the photo, the coilovers are at the lowest ride height.

[dontlifttoshift]

Remove your coilovers.

Remove the springs from the coilovers.

Reinstall the coilovers and run suspension through travel all the way to the bump stop on the shock. Then you don't have to guess, measure, or interpolate.

How much clearance to the inside? Rehooping can only be done in 1/2" increments, otherwise you need new centers.

At 250# rate on the springs it would take 500# to compress 1".

[stab6902]

I agree with Donny... do as much rolling/trimming on the lip as you're willing to do, and then remove the springs and see how much travel and clearance you really have.

The rule of thumb is that you want about 3" of jounce travel, but I've gotten away with less, especially with springs and shocks on the firm side and modern micro-cellular jounce bumpers. The micro-cellular jounce bumpers act like progressive "helper" springs that gradually add spring rate, and even some extra damping due to the properties of the foam. To me they're imperceptible from the drivers seat, in contrast to the old school rubber bump stops that make it known when you hit them.

[CSG]

Like stated you need to see it at full bump but .125" is not nearly enough clearance.

[Alponcho]

Thank you very much for the input guys.

I have 1.25" on the inside all the way around until the rear corners, and there it tapers to 1". If I go inboard by .375" on each side, I'll have .5625" to the outer edge of the fender. So if I can get the lip down to .25", I should have .3125" between the tire at it's fattest point and lip, and .625" to the nearest point on the inside.

I know the first order of business will be to trim and roll the lips as far as possible, and at that point, I'll definitely run the suspension through it's travel without springs, but just want to know if I'm in the ball park, and whether these gaps would be a good compromise? Would it be better to have more clearance on the inside, or outside, or should it be equal?

[TheJDMan]

Just for the record, the outer edge of the fender is not where you need to be measuring. You need to be concerned with clearance between the tire and the inner fender lip which is where the tire actually needs to clear. Rolling the fender lip or trimming it will help gain some tire clearance. I can almost fit my fingers between my rolled fender lips and the tire sidewall maybe .500". I don't know if you can tell from this pic or not but my tire is not in line with the outside edge of the fender it is in fact clearing the fender lip. Based on the numbers you mentioned above I think your rear axle is too wide for your wheels. I suspect your best option now will be to have the wheels re-hooped to move each one inboard somewhere between .500" to .625" which will put you very close to the inside edge of a rolled or trimmed fender lip while still leaving you sufficient clearance inboard

[Alponcho]

...Based on the numbers you mentioned above I think your rear axle is too wide for your wheels. I suspect your best option now will be to have the wheels re-hooped to move each one inboard somewhere between .500" to .625" which will put you very close to the inside edge of a rolled or trimmed fender lip while still leaving you sufficient clearance inboard

thanks for posting the photo. Rather than re-hooping, what about having the rear end narrowed more? Narrowing it would be less than the cost shipping the wheels back to Forgeline, but maybe there's a downside to this I'm not thinking of?

[CSG]

Narrowing the rear is a fine option. Remember that when leaving space on the inside be sure to fully articulate the suspension when doing your measuring. What seems like good clearance dries up quickly when one wheel hits full bump and the other side does not.

[TheJDMan]

Either approach would work equally well. It just seems to me that narrowing the rear axle would be more work and expense than sending the wheels back to be re-hooped. BTW, you don't necessarily need to send them to Forgeline, this place can also change wheel offsets. http://billetwheelrepair.com/ Also take a closer look at rolling the fender lip to move as much of it out of the way as you can. 2" of vertical clearance will limit your ability to lower the overall stance of the car. In this shot you can see I don't have anywhere near 2" of vertical clearance but the tires still clear the fender lips, which are rolled, without any rubbing. But before you do anything, follow Donny's recommendation to remove the springs and cycle the suspension and check for actual clearance/interference.

[dontlifttoshift]

Has this happened yet?

Remove your coilovers.

Remove the springs from the coilovers.

Reinstall the coilovers and run suspension through travel all the way to the bump stop on the shock. Then you don't have to guess, measure, or interpolate.

To touch on what CSG said regarding roll angle, from full compression, I drop one side until there is a 5 degree difference between the axle and the body/frame. You will never see a bigger angle than that at full compression unless you are landing.......at which point tire rub becomes irrelevant.

[Alponcho]

Has this happened yet?



To touch on what CSG said regarding roll angle, from full compression, I drop one side until there is a 5 degree difference between the axle and the body/frame. You will never see a bigger angle than that at full compression unless you are landing.......at which point tire rub becomes irrelevant.

I won’t be able to fully articulate the suspension until the lips are trimmed and rolled, and this won’t happen for a couple/few weeks. I do have a question though, are the bump stops to which several of you have referred built into the shocks (JRi single adjustable) or is this something I should add to the shocks or somewhere else?

[stab6902]

There are two kinds of bump stops. Some go right over the shock shafts like this: https://www.speedwaymotors.com/shop/...14-16-566-7564. They are typically used on coilovers and struts.

The other type is used between the control arm (or axle) and the frame of the vehicle, like the popular S-10 ZQ8 bump stops: https://www.amazon.com/Dorman-31064-.../dp/B0026M9BDC.

Some shocks have internal bump stops as well. Unfortunately I don't know any specifics about the JRI shocks you have.

[dontlifttoshift]

The JRi have them on the shaft, you may not have seen them as they are usually tucked up into the spring cup.

[Alponcho]

The JRi have them on the shaft, you may not have seen them as they are usually tucked up into the spring cup.

You're right! Thank you. I just walked out to the shop and checked, I just never noticed them for some reason.

Here's something else I just noticed. It looks like the when the springs are set for the lowest ride height, the shock is basically bottomed out on the bumpstop...it can only go down maybe .125" more. If this is the case--and assuming I have everything set up correctly--then I should not have to worry about the tire contacting the lip at all... Is that right?

But what about all the Camaros I see with the tires tucked in under the lip? Why can't I get there? Then it hit me....

I've been looking at how rear wheels & tires fit on second gen Camaros because there are tons more Camaro examples, and of course, we all know that Camaros and Firebirds are essentially the same in most ways. So implicitly I've been shooting for the tire tucked in under the lip look. But now that I think about it, the shape of the rear wheel openings are actually different. The arch seem more rounded and goes up higher on a Firebird, so the tire will never tuck in like on a Camaro. So maybe I'll be OK after all?

[dontlifttoshift]

That's why this is the first step.

Remove your coilovers.

Remove the springs from the coilovers.

Reinstall the coilovers and run suspension through travel all the way to the bump stop on the shock. Then you don't have to guess, measure, or interpolate.