100% Camber Recovery

[johnc]

Is it a good idea when designing a suspension to shoot for 100% camber recovery in roll? What is camber recovery you ask?:

 

Camber recovery is the percentage of the roll angle that is recovered at the wheel when the car rolls. If the wheel leans the same amount as the body, that’s zero camber recovery. If the wheel leans half as much as the body, that’s 50% camber recovery. If it doesn’t lean at all, that’s 100% recovery.

 

Talk amongst yourselves...

[jeffp]

Myself I am looking for 100% recovery going strait line. Cornering the car is a little different. What I like is a 1 Degree camber static, and about 2 degrees when the car is cornering hard.

[cygnusx1]

OK, talking amongst ourselves...

 

When the Z rolls, the imaginary line between the strut top and the inner LCA pivot leans by the same degree as the body. If the LCA was fixed, imagine welded, then the angle of the strut and wheel would lean by the exact same angle as the body. Fortunately, the LCA is not "welded" and it is allowed to swing a radius. As that radius is swung, it changes the angle of the strut relative to the body angle. The ideal, as JohnC quotes, would be that for every angle of body lean, the wheel would be "corrected" back to it's desired camber angle through geometry. The only mechanism that our Z's have to do this, are the LCA's.

 

What can we do to control or at least limit the angularity of the tire to the road?

 

-Initial Angle of the strut tower (camber plates)

-Initial angle, length, and position of the LCA and bushing.

-spring stiffness

-roll bar stiffness

-to lesser extent, wheel/tire widths and offsets.

 

Anything else to add to this or correct me if I am mistaking?

[JMortensen]

Is it a good idea when designing a suspension to shoot for 100% camber recovery in roll? What is camber recovery you ask?:

 

 

 

Talk amongst yourselves...

What kind of tires?

[johnc]

The question is more fundamental then what you guys are asking about. Is designing a suspension to achieve 100% camber recovery in roll a good idea? Is so, why? If not, why?

 

For example: if the car rolls 3 degrees in a corner and uses 2.5" of bump travel, is having the suspension gain 3 degrees of negative camber in 2.5" of bump travel (100% camber recovery) a good thing?

[JMortensen]

When you put it that way, I'd say no. That amount of camber change would require a really short control arm and would put some weird camber thrust on the tires. It would probably be really hard to drive in a straight line on anything but a glassy smooth road.

 

If you have a car that only rolls one degree at max lateral acceleration (formula car, etc), then I'd say the answer is more likely to be yes.

 

I think the modern idea with radial tires is to minimize the amount of camber change and then set static camber to where it works best around corners, and hopefully that doesn't screw you too badly in the longitudinal acceleration department, hence touring cars running 5+ degrees of negative camber. With the old bias ply slicks you can get away with a lot less camber and so I think they'd be less sensitive to camber recovery.

 

Then you have that Mercedes F400. If you're leaning BOTH sets of tires into the turn, it appears that you want them leaning at different angles, and that would make sense given weight transfer and the relative loading on each tire.

http://www.seriouswheels.com/cars/top-2002-Mercedes-Benz-F400-Carving-Concept.htm

[JMortensen]

Here's an interesting conversation on a part that increases camber recovery on the back of a 911:

EDIT-FIXED LINK: http://forums.pelicanparts.com/showthread.php?t=321152

 

I think CLE has it right when he says:

I’ve had a few people ask me to comment on this thread to help eliminate some apparent misconceptions of racing radial tires. My intention is not to blast but, rather to pass on some vital information that has been documented.

 

However, I first have to say, using the reasoning that street cars from the early 90’s (and on) have more camber to come to this conclusion is no more valid saying you need to put MORE bumpsteer in the car because Porsches has more of that now too.

 

There are several reasons that there is built in bumpersteer, camber gain and tons of rubber mounts and bushings on a street car but, the sole reason of a functional street car is NOT to maximize lateral grip. Remember, you are talking about STREET CARS, the same cars they took the dry sumps out of as well.

 

Radial tires are a four dimensional spring and they are very sensitive to active changes i.e., bumpsteer or camber change. This means Radial race tires DO NOT LIKE camber change. This is the reason you see 1500 pound spring rates and higher becoming so common. It’s done because the newer cars have TOO much camber gain and the only way (by the rules) to eliminate it is to limit the travel of the suspension and let the tire do the work.

 

Over the past 10 years or so, we’ve started to hear more about this new term called SNAP OVERSTEER … primarily in the new cars. Spending countless hours looking through data logs there is always one common denominator when this occurs. The cars are under heavy loads in a turn and the surface isn’t totally smooth, right at that point it hits the slightest bump and there is damper movement causing a quick camber change (gain). This causes something to the occur in the tire itself know as CAMBER THRUST and it will change the tire patch for on instant upsetting the car causing it to lose grip. The correct term is Camber Thrust but, you may also hear it called Tire Kick Back.

 

Easily adjustable camber plates are good. …. Camber gain is NOT.

 

Everything is based upon the tire because it’s a fixed given. Trying to reason and guess what the tire wants is NOT always what you might think.

 

One last thing to consider, if you look at most 88 and earlier cars even with slicks they generally don’t go much beyond 4 degree’s negative….. I was just working on one of the fastest IMSA CUP cars about a week ago (with more camber gain) we had to go to 6 degree’s!!! to make it fast.. now that’s sick… Why is it that all the new cars use more camber rather than less?

 

I hope you find this helpful

[cygnusx1]

The wider and stiffer the tire, the more critical this becomes. I like to run tires with slightly rounded edges to make up for my lack of "full-race" geometry. The rounded edge tires will tolerate more camber + or - and still keep a decent contact patch. I think a more modern suspension that has better camber management can benefit more greatly from a stiffer, squared- off tire.

[johnc]

Think about what a 100% camber recovery suspension would do in ride, not roll.

[cygnusx1]

I really need to take the next Solidworks course so I can model suspensions. A few more months and I go off for more training.

[260DET]

If the car is in roll then its turning in a corner. My simple mind tells me that ideally in a turn both wheels should lean into the corner ie the inner wheel should have positive camber the outer negative.

 

So my answer to the question is 'no', or perhaps more accurately, the question is irrelevant.

[cygnusx1]

I think assuming that the wheels need to lean in any direction for better traction is an error. First you need to understand what the contact patch is doing and what it does under different loading vectors. Then you need to find out at different loads, the optimum angle for the best contact patch. Then you need to design the suspension and car so that it produces that optimal angle for every load condition.

 

Oooh, I just had a vision of variable geometry active link suspension tied back to load sensors! Imagine a suspension that set the proper contact patch for EVERY possible condition. High Tech!

[johnc]

The big issue with 100% camber recovery is when the suspension moves in bump when the car is not in a corner. Huge camber gains in ride led to directional instability and really crappy braking. Imaging braking in a straight line at 1G and then hitting a bump with one wheel that uses 1" of available travel. In my example above that would be 1 degree of negative camber gain and would instantly lock up that wheel. If its a rear wheel, you're going sideways.

 

Adding anti-dive to control this increases bind in the suspension and is a catch 22. Do we increase anti-dive (and reduce bump compliance) to reduce gamber gain in bump so we can get better braking?

[cygnusx1]

Ahhh, I see where you are going now. Since the Z suspension is basically a giant compromise no matter how you look at it, your question is, "where to compromise?" The answer is going to be different for every track. I am a fan of braking potential. I don't feel confident in a car unless I can brake very hard. In racing, on some tracks, the winner is the car with the best brakes. At a track day where corner entry passing is a no-no, set up for lateral handling, but for competition, definitely give up some lateral g's for braking strength. You still want to leave some adjustment for rear grip, for corner exit speeds. It is very complex.

[Flexicoker]

I don't understand how anti-dive increases 'bind' in the suspension. Its the same effect as raising your roll-center and producing a jacking force. You're raising your 'pitch-center'. In a properly designed racecar suspension with spherical bearings there should be no bind. It will reduce your bump compliance, but thats also a function of the geometry and not of bind.

[johnc]

Anti-dive adds bind (resistance) to load transfer under braking. This resistance is primarily through suspension arm geometry (on street cars) when there's a torque rotating through the suspension arms.

 

http://www.circletrack.com/techarticles/antidive_suspension_tech_parameters/index.html

[S30 SPL]

Anti-dive geometry is a plus and minus. For example, in my WRX, the car has "anti-dive". This is great because the front tires keep planted when I brake hard, but under some situations, because there is not dive and weight transfer, the nose just doesn't bite hard enough... the feeling is like trying to stop yourself on a swing with just your heels. For this, there are many kits that get rid of some of the "anti-dive" in that car.

 

I think that it is really hard to answer the question definitively since everyone has a different goal when setting up their car. I think that some camber recovery is needed, but I don't have the number of how much. For example, if you do not have enough recovery, then the outside tire can roll over on it's sidewall. If you have too much, then your patch changes too quickly and too much if you hit a bump going straight...

[johnc]

That's exactly the point of this question: compromise, compromise, compromise. Suspension design and development is the art of compromise.

[S30 SPL]

There is one thing about camber recovery that I reeeeaaalllly like, but it's not for performance. Huge camber recovery is great to tuck neat looking sizes of wheels into the body work. For example, Miata's tucking 10" into stock fenders...

 

Like I said, I am not a suspension pro, so I can only say camber recovery is necessary, but I don't know how much.

[260DET]

I think assuming that the wheels need to lean in any direction for better traction is an error. First you need to understand what the contact patch is doing and what it does under different loading vectors. Then you need to find out at different loads, the optimum angle for the best contact patch. Then you need to design the suspension and car so that it produces that optimal angle for every load condition.

 

Oooh, I just had a vision of variable geometry active link suspension tied back to load sensors! Imagine a suspension that set the proper contact patch for EVERY possible condition. High Tech!

 

I was thinking, but did not say, front suspension. Can't recall seeing any tarmac competition car including F1 without some negative camber on the front.

 

Of course F1 did allow active suspension for a while which varied all sorts of things. High tech yes