"practical limit" for camber gain

Not all tires have the max grip for cornering at the same camber angles and IIRC it usually isn't a zero degrees camber.

If you want to maximize your camber gain, you will have to design to the intended tire. Since every tires' contact patch and carcass deflects differently under load, the engineers have to design to a "good enough" curve. This can also be affected by packaging limitations in small cars as well.

This should do.

iadr wrote: Ok, tell me why cars never come from the factory with aggressive camber curves,

Look at the back of a pre-65 Corvair, or a pre-68 VWAC, or the front of any Ford with the TTB, and tell me that nothing ever came from the factory with an aggressive camber curve.

(Yes, those were evil cars. That's what aggressive camber curves do)

Hey sorry never saw it. Look up camber curves, VSAL, and string computers. Those should start you down the path you seek. What you are describing is not practically possible without moving inner ball joints. I mean ones that dynamically move with the suspension.
Very simply your camber curve is linear with the length of you virtual swing ARM(vsal).

I think the reason you haven't gotten a lot of response is because it is a VERY long answer that requires you to have a fairly high level understanding of suspension design theory to grasp.

All suspension designs are a big compromise there is no 1 correct answer. The miata may look like its not working how you expect but that's just because the decisions made by its designers are different than those of other designers.

If you have any specific questions or need anything cleared up as you reaserch ill be glad to help. It's just not an answer I can really type up in a paragraph to any satisfaction. There are literally 200 page books on this subject.

Wrong kind of camber, he's talking negative, not positive like the Vair in the picture has.

Since the cars are designed for road use mostly that's probably the reason why no more aggressive negative camber, plus it would promote tire wear. They already get grief over tire wear.

Now if you are talking a track only car then WHY NOT?!

Keep in mind that the stiffer the suspension is the less movement you get and therefore the less camber gain. So are you wanting more camber gain over the whole range of soft suspension movement or more gain over a small range of motion that comes from the stiffer springs and big sway bars?

I see no reason why you couldn't do it on your car to fit your particular purpose, but for the general public - nay.

iadr wrote: Here's what it looks like when you set up with the required static negative..and you can see where it leaves the inside front. Ok, I am not sure what the inside front can really do...but it just looks wrong.

I would focus much more on the outside front tire. It delivers most of your front traction. And it looks pretty good, just eyeballing it. Tire wear and tire temperatures would be the real test but I think they would be pretty good.

David

nocones is on the money. Other quick points to note include the observation that the suspension doesn't know whether it's compressing because of roll, heave, or dive. Having your front tires camber way in when the nose dives under braking isn't going to help your braking distances one bit, nor will having the rears camber on squat help your corner exits. Everything affects everything else.

Scrub and jacking (not from caster, but from the virtual swing arm) under suspension motion are, I think, the other biggest arguments against going crazy with negative camber gain on compression.

I also agree with DWNSHFT that the camber on the inside wheel is relatively inconsequential.

carguy123 wrote: Wrong kind of camber, he's talking negative, not positive like the Vair in the picture has.

No, that's the right kind of camber. On suspension compression travel, a swingaxle design will gain a lot of negative camber.

The problem is, with a geometry that can be packaged into a car, the roll center ends up so high that the car will jack up, extending the suspension instead of compressing it.

An easier way to perceive it is to think of the track change on the outside wheel. With a really aggressive camber curve, the effective swingarm must necessarily be short. When that happens, unless you put the suspension links below ground level, the track will widen under compression and the track will narrow under droop. Cornering forces are trying to narrow the track, driving the bottom of the tire towards the inside of the car. When the effective swingarm is short enough, cornering forces will win and jack the suspension up. Since the CG is above ground, the vehicle will still lean to the outside of the corner.

The reason there is so much positive camber is because the rear suspension is almost TOPPED out!

You can fix this, sort of, by stiffening up the suspension so much that it barely moves at all, but at that point the suspension geometry is merely a piece of trivia.

iadr wrote: Ok, tell me why cars never come from the factory with aggressive camber curves, even when the hardware is there to do so? I'm lookin' at you, Mr Miata.

One word: Understeer. Factories are more interested in idiot control. 99.9% of their buyers are numb-witted drivers who couldn't control a car if their lives depended on it.

Kind of tangential but...

Here's a youtube video of an old MB concept with active camber. Benz claimed 1.3 lateral G's, but it used special hybrid car/motorcycle tires.

Mercedes Benz F400 concept

Skip to 1:00 for the meat.

I heart caster. More negative caster improves turn-in response and increases dynamic negative camber, which means negative camber while the car is steering. It increases the negative camber on the outside wheel (where it's needed) and decreases the negative camber on the inside wheel (improving the contact patch on that side as well). Another upside to this is caster does not increase tire wear, as it only affects camber when actually turning the steering wheel.

The downside is that you can only get so much caster on a particular architecture without radically redesigning the front end.

On my ZX2SR, when I tracked it, my tire temperatures were pretty even with 3 derees negative static camber and 4 degrees positive caster. I had very little roll with a stiff rear say bar and I had increased the caster with a stock adjustment and offset bushings in the control arm. I ran Hoosier R tires. on 7" wide rims.

I think the main thing is to limit roll. Then camber is controlable.

I'll second the love for caster. On my Volvo Amazons, the factory set them up with positive caster, probably for easier maneuverability. But at higher speeds, the steering wheel will actually "rock" back and forth if you let go of it. In 10 minutes you can swap shims around on the front subframe and get a couple of degrees of negative caster, which makes things nice and stable. Not to mention the camber improvements Sky_Render mentions.

As for camber...the MB active camber car was a cool concept, but William Milliken came up with the idea of motorcycle-turning type levels of camber even earlier:

Check out his book, "Equations of Motion", sometime. Its a really fascinating read. Milliken himself is over 100 years old, and still active.

volvoclearinghouse wrote: William Milliken came up with the idea of motorcycle-turning type levels of camber even earlier:

Interesting car. Wonder how he dealt with camber thrust; maybe not an issue on a race track?? I once put extreme neg camber into one of my Saab 900s (wishbones up front) and you had to keep both hands on the wheel due to thrust issues.

In reply to procainestart:

I believe the fact that the tires were motorcycle tires, with a round tread face rather than flat, mostly eliminates the issues associated with camber thrust.

There's a group building an MX-2, sort of a modern-day version of Milliken's MX-1, apparently with his input.

volvoclearinghouse wrote: I'll second the love for caster. On my Volvo Amazons, the factory set them up with positive caster, probably for easier maneuverability. But at higher speeds, the steering wheel will actually "rock" back and forth if you let go of it. In 10 minutes you can swap shims around on the front subframe and get a couple of degrees of negative caster, which makes things nice and stable. Not to mention the camber improvements Sky_Render mentions. As for camber...the MB active camber car was a cool concept, but William Milliken came up with the idea of motorcycle-turning type levels of camber even earlier: Check out his book, "Equations of Motion", sometime. Its a really fascinating read. Milliken himself is over 100 years old, and still active.

Umm. I think you have positive and negative reversed.

iceracer wrote: Umm. I think you have positive and negative reversed.

He does. So does SkyRender above.

volvoclearinghouse wrote: I believe the fact that the tires were motorcycle tires, with a round tread face rather than flat, mostly eliminates the issues associated with camber thrust.

Somebody better tell the motorcycle guys! They keep going around corners by leaning those things over!

Less hyperbolically, according to Tony Foale's "Motorcycle Handling and Chassis Design", "this force [camber thrust] will likely be the major contributor to the total cornering force, and the steering effects will just make up for the difference between the required cornering force and that provided by the lean."

I thought positive caster was like a shopping cart, and negative caster was like a chopper? It's possible I had them confused.

I know negative camber is the tops of the tires closer together than the bottoms.

Perhaps I misunderstood "camber thrust". At any rate, with both tires cambered negative equally side to side, the net thrust would be zero, until a disruptive input from the steering system was introduced. The High Negative Camber Car was explained in some detail in his book. It's worth a read.

volvoclearinghouse wrote: I thought positive caster was like a shopping cart, and negative caster was like a chopper? It's possible I had them confused.

Well, both a shopping cart and a chopper have positive caster, in that the contact patch of the tire is behind the point where the steering axis intersects the ground.

It's possible that I'm abusing the word "caster" there. They both have positive trail, the distance from the steering axis' intersection with the ground back to the tire's contact patch. Obviously, the chopper will lean the tire like crazy while steering, while the shopping cart won't lean it at all.

EDIT: Etymologically, I would think my use of caster was okay. After all, the small wheels on a piece of furniture which use the shopping-cart model of construction are called casters.

In the simpler-to-visualize automotive version, simplified to a steering knuckle with upper and lower ball joints and no axle offset (so the axle is smack between the ball joints when viewed from the side): Positive caster is when the upper ball joint is further back than the lower ball joint. The steering axis is then inclined so that it runs forward as it goes down through the upper and lower ball joints and intersects the ground ahead of the contact patch. Negative caster would be the opposite, with the upper ball joint ahead, and the steering axis going rearward as it runs down through the upper and lower ball joints, intersecting the ground behind the contact patch.

I know negative camber is the tops of the tires closer together than the bottoms. Perhaps I misunderstood "camber thrust". At any rate, with both tires cambered negative equally side to side, the net thrust would be zero, until a disruptive input from the steering system was introduced. The High Negative Camber Car was explained in some detail in his book. It's worth a read.

I really should read his book.

I would observe this: A car with three inches of toe in should also have a net cornering force of zero, but it's sure going to act funny, and the tires won't like it very well.

That being said, I'm not going to suggest that I'm qualified to do the reconciliation of Milliken and Foale; either of them knows more about their arenas than I could ever hope to. Not sure what I'm failing to understand about Milliken's camber thrust car, but I'm pretty sure the failing is more likely to be with me than his car

ProDarwin wrote:

iceracer wrote: Umm. I think you have positive and negative reversed.

He does. So does SkyRender above.

You're right. I said "negative" when I meant "positive." Quite sorry.

http://www.motoiq.com/magazine_articles/articletype/articleview/articleid/1982/the-ultimate-handling-guide-part-8-understanding-your-caster-king-pin-inclination-and-scrub.aspx