Sidewall flex under cornering

Judging by the picture here, I've got a bit of a sidewall flex problem on the front end of the Jeep (gee, what a surprise!) The front tires show a little evidence of insufficient camber by looking at the outer tread blocks, but nothing too severe. Oddly enough, the rear tires don't show this, despite having 0 camber (fronts are around -0.75* plus whatever it gains from caster). In the picture, there's clearly negative camber at the front wheel, but not enough to keep the tire from ending up with a little positive camber as it flexes.

So I clearly need to add some more camber up front (conveniently, I'm going to be swapping upper ball joints soon anyway, so I'll kick it up to around 1.3* while I'm doing it). But the real question is, how much sidewall flex / roll is acceptable before I have to worry about actually de-beading a tire? Or is that within the realm of "don't worry about it"? Of course, it doesn't get pushed this hard very often, but it's good to know I can use most/all of the grip the tires have without having to worry about E36 M3 hitting the fan.

Your jeep is defying the laws of truck suspension! Where have you hidden the body roll?!?

Have you tried simply bumping the cold pressure up a pound or two?

I wouldn't worry about it. Unless you're running super low tire pressure (offroading). A properly inflated tire shouldn't de-bead even on a track.

Did you out brake the Cayman to take the corner fist?

The suspension under there isn't exactly stock, so not a ton body roll to be had. As a reference point, stock, it had 190lb front springs, 160 rear and a 26mm front sway, 16mm rear. Currently, it has 280lb front springs, progressive rears (around 320lb at ride height, around 600lb by full squish) and a 29mm front sway (no rear sway). So it's a lot stiffer than stock, but still rides pretty well. There's definitely some body roll present, looks like about an inch or 2 of wheel gap difference between the sides in the picture. Fortunately, in terms of body roll vs camber, I have a theoretically perfect camber curve, as solid axles can't lose camber to body roll (it's solid front and rear, parallel-ish 4 link with panhard at both ends).

Pressure wise, I was running about 40 psi cold in the fronts when that picture was taken. I'll play with pressure again once I swap the ball joints for more camber (might do that tonight), but I have a feeling I'll end up in the 40 - 42 psi range to keep the tires sitting well on the ground and not have them wear to the center.

trucke wrote: Did you out brake the Cayman to take the corner fist?

It was opening weekend at Watkins Glen, so the laps were "paced" and theoretically no passing (although the Ferarri behind the Porsche did pass him at one point and then stayed behind me).

Oh, and for anyone curious, the tires in question are a set of 255/60R17 Goodyear Eagle F1 Asymmetric SUV-4x4 mounted on a set of 17x8 wheels (+10 offset with a 3/4" spacer, stock offset is +13).

rslifkin wrote: The suspension under there isn't exactly stock, so not a ton body roll to be had. As a reference point, stock, it had 190lb Fortunately, in terms of body roll vs camber, I have a theoretically perfect camber curve, as solid axles can't lose camber to body roll (it's solid front and rear, parallel-ish 4 link with panhard at both ends).

Unfortunately, in practice, the tire on the outside of the turn will squish down while the one on the inside will expand slightly, causing your axle to lean toward the outside of the turn, leaving you with unfavorable camber changes in corners

So the best way to make a solid axle handle well is similar to what you'd do with macstrut suspension - set your static camber to what you'd like to have in a hard corner, and then make the suspension so hard that it can't move much (see famous Colin Chapman quote)

rslifkin wrote: Judging by the picture here, I've got a bit of a sidewall flex problem on the front end of the Jeep

That isn't a problem, that's normal.

GameboyRMH wrote: Unfortunately, in practice, the tire on the outside of the turn will squish down while the one on the inside will expand slightly, causing your axle to lean toward the outside of the turn, leaving you with unfavorable camber changes in corners So the best way to make a solid axle handle well is similar to what you'd do with macstrut suspension - set your static camber to what you'd like to have in a hard corner, and then make the suspension so hard that it can't move much (see famous Colin Chapman quote)

Now that's something I had never thought of! Although unlike a Mcstrut setup, making the springs stiffer won't do anything to help that. Only making the tires stiffer (via more pressure or different tires) to reduce their squishiness will help. But judging by the amount of camber still visible on the outside front wheel, this effect probably isn't costing me a whole lot of camber. I'm curious to see how different it feels / behaves with an extra half-degree in there though.

I'd think spring stiffness would have an effect as well - it doesn't affect weight transfer but I'd think having more body roll would give the axle more motivation to follow along due to the effects of suspension bind, which are more prominent with a solid axle.

GameboyRMH wrote: I'd think spring stiffness would have an effect as well - it doesn't affect weight transfer but I'd think having more body roll would give the axle more motivation to follow along due to the effects of suspension bind, which are more prominent with a solid axle.

True, binding could have some effect. Binding issues are part of why the rear sway bar is deleted. The stock end links had horrible binding problems, so the suspension ended up working better (both ride quality and handling) with the bar removed and stiffer springs in its place.

You're on a track in a Grand Cherokee and you're in front of a Cayman and you want to fix something?!

Go pour yourself a cold one. You win trackdays!

LuxInterior wrote: You're on a track in a *Grand Cherokee and* you're in front of a Cayman *and* you want to fix something?! Go pour yourself a cold one. You win trackdays!

After a guy in an F430 swapped places with the Cayman and got behind me, I did have a proud moment when I shook him for a few seconds at one point. Of course, I'm sure that was entirely his doing and not mine...

In reply to rslifkin:

I'm really enjoying the grin on your face in the pic.

My hoosiers flex over an inch and a half (since they will just rub the frame, and i have that much clearance at rest), and they're low profile 275/35/15 tires. I wouldn't worry.

In reply to rslifkin:

Around here, it's common to see exotic drivers with very un-exotic skills.

Alright, so it sounds like I'm just gonna fix the camber issue, play with the pressures again and then call it a non-problem.

LuxInterior wrote: In reply to rslifkin: Around here, it's common to see exotic drivers with very un-exotic skills.

I have a picture of my ZX2SR passing a 911 on the front straight at Lime Rock

Watch this video, then stop worrying.

https://www.youtube.com/watch?v=phwyk7zJ68A

Streetwiseguy wrote: Watch this video, then stop worrying. https://www.youtube.com/watch?v=phwyk7zJ68A

Got it Considering how much more sidewall height I have, mine definitely looks like a non-problem with that for perspective.

I get more deflection than that just autocrossing the V. Hell, I think I get more deflection than that rallycrossing. I'd love to see the shoulder/sidewall of the tire after a session to truly judge, but my guess is that you can drive quite lot harder than you were without any ill effects. Were you pushing the tires hard enough for them to make noise?

mazdeuce wrote: I get more deflection than that just autocrossing the V. Hell, I think I get more deflection than that rallycrossing. I'd love to see the shoulder/sidewall of the tire after a session to truly judge, but my guess is that you can drive quite lot harder than you were without any ill effects. Were you pushing the tires hard enough for them to make noise?

No, I wasn't sitting on their limits, as I haven't had them on all that long and am still getting a feel for them. But even when I've chirped one under power on the street, they don't seem to make much noise. They just kinda quietly slip a bit when pushed too far, it seems.

Opening weekend is probably the hardest they'll really get pushed all summer beyond a random corner here and there (unless we happen to end up on a rallycross surface where these would be better than my M/Ts).

As a reference for deflection distance, the bottom edge of the tire that appears about even with the lip of the wheel is deflected a good 1.5 inches. These tires run on the narrower tread, bulgy sidewalls end of the spectrum in terms of size / shape.

The tread on a radial moves around laterally under the bead. That is a lot of why radials are better than bias-plies, and in a broader sense why pneumatic tires are better than solid rubber.

If the tire isn't moving, it isn't working, in other words.

Now a really interesting thing is, if you could get a picture from above, the wheel will not be on the same axis as the tread, either.

Big tall tires deflect, it's just what they do. Check the shoulder when you come off track and bump pressure or back off a bit if you see them rolling more than you're comfortable.
Very cool taking it on track, that's awesome.