Angle of Control arms (Suspension theory thread) - Page 2 - Mazda3 Forums : The #1 Mazda 3 Forum
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post #11 of 512 (permalink) Old 06-11-2013, 10:22 AM
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Nuse, can you post up a pic of your front suspension shot at ground level (if your LCA's are even visible based on your ride height?) With an angle finder and tape measure, I could probably help to find out if your camber is moving in a positive direction at some point in your suspension travel. That's something I dealt with in my 96 Miata track car when it was lowered WAY too much, and like you my front grip would all of a sudden just go completely away. This is why I always tune suspension on low grip street tires as track tires can mask a lot of these bad behaviors.

I'll have to dust off my suspension theory books (haven't done any number crunching for suspension mod/design since I quit racing when family and finances pushed it to the back burner) but if you'd like the help I'm more than willing to get involved and see if we can figure it out together. This, of course, would be a Hell of a lot easier if I didn't live several hundred miles from you but I'm sure we can figure it out.

My gut instinct based on your symptoms (and not doing the math or taking measurements, just an educated guess) is that your front suspension geometry is compromised due to ride height, and that you are correct in wanting to raise the suspension back up to correct. Not knowing more about your setup, that's all guesswork but at least it's not an uneducated guess.

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post #12 of 512 (permalink) Old 06-11-2013, 10:23 AM
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Yeah there isn't really a good way to fix it. Best you can do is stiff-as-hell springs.
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post #13 of 512 (permalink) Old 06-11-2013, 10:32 AM Thread Starter
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My suspension setup right now is set up to be solid, but positive gain and awkward roll in front is ruining it as far as I can look into it and research I've done.

BC coilovers (dampening is set at/near critical; hard to really know without having them dynoed though).
10k front springs
8k rear springs (will likely be pushing these to 12k later this year)
hotchkiss front and rear sway bars (soft front, stiff rear).

When I had my front bar at full stiff I semi had more grip (and it makes sense due to body roll); BUT thanks to open diff the inside would lift and spin freely (no good of course).

I might be able to get pictures but it's rather useless lol; they're absolutely pointed down, not severely but going the wrong way nonetheless.

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post #14 of 512 (permalink) Old 06-11-2013, 11:00 AM
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Phil: tuning suspension on street tires for use with race tires isn't ideal. You're right that race tires can cover a lot of mistakes, but they are also very different. A setup that gets 100% out of street tires will always get less than peak performance out of slicks.

Just as one example, consider camber gain versus body roll. Ideally, you adjust things so that in a maximum lateral acceleration turn, the body roll and camber gain cancel each other, leaving the tire square to the ground for maximum grip. Then you swap race tires on, and suddenly you have more grip, therefore more body roll, and you go beyond the sweet spot of the camber curve. You could be getting more out of the race tire with more spring rate, so you keep the body roll the same, and the camber happy.

Btw, you mentioned finding your suspension theory books. I think I happen to know what you're looking for so I can save you the headache. Mcstruts begin to gain +camber when the lca is perpendicular to the line from the strut top to the lower ball joint.

Last edited by ckingsley; 06-11-2013 at 11:03 AM.
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post #15 of 512 (permalink) Old 06-11-2013, 11:08 AM Thread Starter
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For the sake of simplification and the fact none of us here are turning their cars into full time racecars.. street tires for reference are the way to go.

Besides, NT05s are hardly slicks lol (but when those go I'll definitely be going with a stickier compound most likely)
But.. I do want to keep this conversation alive as it's a very important topic that NEVER happens on this forum. Rarely on the MSF forum; but still majority of those guys just want to go fast in a straight line.

My question though is; IS there a negative camber gain somewhere in the arc of the control arm motion?
If not; then for a mcstrut setup.. wouldn't theoretically on a flat surface having a solid rock hard suspension and a shitload of negative camber be the best thing for it?

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post #16 of 512 (permalink) Old 06-11-2013, 11:13 AM
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Quote:
Originally Posted by ckingsley View Post
Phil: tuning suspension on street tires for use with race tires isn't ideal. You're right that race tires can cover a lot of mistakes, but they are also very different. A setup that gets 100% out of street tires will always get less than peak performance out of slicks.

Just as one example, consider camber gain versus body roll. Ideally, you adjust things so that in a maximum lateral acceleration turn, the body roll and camber gain cancel each other, leaving the tire square to the ground for maximum grip. Then you swap race tires on, and suddenly you have more grip, therefore more body roll, and you go beyond the sweet spot of the camber curve. You could be getting more out of the race tire with more spring rate, so you keep the body roll the same, and the camber happy.

Btw, you mentioned finding your suspension theory books. I think I happen to know what you're looking for so I can save you the headache. Mcstruts begin to gain +camber when the lca is perpendicular to the line from the strut top to the lower ball joint.
I wasn't advocating tuning suspension for race tires using street tires, only that I prefer to baseline on street tires before progressing to stickier tires. That helps you figure out if you have a geometry issue (as seams to be the issue here) that race tires will tend to cover up. As grip levels rise, so must spring rates and by extension damping rates/roll stiffness, but at least you're working from a good foundation.

I need to dust off my books, and my own memory. Coming from a double wishbone car (Miata) to a Mcstrut car the theories still apply, but some of the measuring points are different. I used to build spreadsheets to quickly figure wheel travel taking into account spring rate and roll stiffness to help us figure out if we were exceeding the amount of travel we had between static ride height and the point at which we compromised out geometry by the control arms moving beyond their normal range. That, and a bit of stopwatch trial and error, was how I figured out that I was killing my front end grip with by overlowering. I raised my car up 1.5" and increased the spring rate about 40% over what I was already running(already plenty stiffer than stock, but Miatas have pretty mild spring rates in stock form) and found a whole world of grip on street tires I hadn't found before.

Sometimes a set of fresh eyes helpe point things out that are being missed, but it sounds like XCNuse has things well under control. I was initially offering a stock pic/angles/measurements if he needed a control to compare his care and a Pro Kit lowered car.

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post #17 of 512 (permalink) Old 06-11-2013, 11:22 AM
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Oh I see what you mean. That makes sense. Both about street tires and your suspension setup.

If you guys figure out some of the suspension geometry, I'd definitely be interested. I'd love to know the actual position of the cg, and the instant roll centers at stock height.

If it will be any use I can get you pictures and measurements off my car. It's on Koni yellows and stock springs.
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post #18 of 512 (permalink) Old 06-11-2013, 11:26 AM Thread Starter
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I mean I guess what I'm curious about (because I dont' know), is like I said there a point where the arc decreases camber and if so, where (within reason of course).

Otherwise, is the height of stock going to allow the best movement (not that I have much to begin with), vs a slight lowering as in say Prokit drop area.

Obviously (well.. I think to us in this conversation at least) decreasing the amount of arc will only be helpful (obviously soft springs out; reason I say prokit is for height, not spring rates).

That said when I drove a 2.0 sedan on prokits in the mountains (Nitto Neogens.. awful loud things) I guess it had to of been how weak the tires were because even that felt like I had no grip.

But I KNOW my Toyo Proxes 4 should have plenty more grip than they seem to produce (more-so in the rain).

I'm happy and comfortable with my setup as is, but I know I'm losing a lot in some spots. But I say I'm happy and comfortable otherwise because if I do find grip; I've put my car into 4 wheel slides before controllably with no issue. But I run in to understeer more often than I feel like I should be.

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post #19 of 512 (permalink) Old 06-11-2013, 11:27 AM Thread Starter
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I think we all wish we knew where the CG was haha; even the guys over at MSF are dogging around trying to figure it out; but personally I don't think we'll ever get it.

I also don't have access to a stock 3 to get measurements from

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post #20 of 512 (permalink) Old 06-11-2013, 12:40 PM Thread Starter
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Another good question we should look for is scrub radius; I don't know if the stock setup was zero or not. But it would be nice to figure out where it is and find the optimum wheel setup for that.

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