Camber (Page 2 of 2)

Thanx, Erik.  I didn't want to get too technical.  All I was doing was answering the question of how to heat the coil to collapse it, lower the car and create some additional camber.  Anyway, with all of this information, there should be question on how and why... and it should remove any excuse for putting $300 Eibach's on a Lemons car.

John

WHAT?

Well --- that sure shut down that topic!  I ought to try out my poetry more often...

Let's see -- The once was a man from Nantucket...

To Troubleonwheels,

We have around 3.0 degrees of static camber.  From what I understand, the point isn't to maintain negative camber the whole time.  The static negative camber approaches 0 or even positive (bad) camber in a turn like you said. 

The point is to keep the tire as close to flat, Zero camber, with the ground in a turn.

We have increased our inner tire wear with the additional camber while almost eliminating the cupped wear on the outside of our tires.  There are both advantages and drawbacks here.

Not only has tire wear been changed on our car from the first to second race, so has the cars turning ability.  With a welded rear diff and whatever camber we had in the first race, the car pushed really bad in the turns.  We could not get on the gas much coming out of the turns.  Our car now corners much better.  I think the car will always push some with a welded diff since it's like driving a sled.

You're basically exactly right.  You want the individual tire tread surfaces flat when you're at the maximum traction need.   Due to differences in tires,  this isn't necessarily at zero camber....  It's at the full load or full cornering camber where the tire is properly dynamically deflected to maintain the best road contact.

===>Technical boring stuff if you're not a car geek<===.  I love this stuff so I'm going to ramble a bit.  If I mess something up please point it out, I finished these classes a long time ago

The camber profile and final 'full corner' camber a car needs depends entirely on the tire design and inflation.  Besides compound, there are three basic parts:

Tread design:  When the tire is experiencing lateral forces, each individual  tread block will deform, each individual tread block will slip on the pavement, and the edge of each tread will 'grip' the pavement.  If you have lots of little tread blocks (i.e. all-season tires) at moderate speeds all the little tread edges will grip well and handle uneven surfaces well, as well as 'push' water off the pavement for good wet weather traction.  Unfortunately, at high cornering loads the little and thus *weak* tread blocks deform greatly, the flat surface of the tread has little contact with the road, and so they have very little traction.  You also see this in heavily scalloped tread edges and cupping from where only part of the tread block is making contact with the pavement.  Think of the results of autox on regular street tires - tears em up.  If you have large tread blocks, particularly shallow large tread blocks, then the tread doesn't deform as much under cornering and you end up with good road contact and better traction.  Unfortunately, these kind of tires don't handle water or rough surfaces well at all (and are usually a soft compound) so are not good for every day use. 

Sidewall height and strength:  Under cornering forces, sidewalls deform.  The taller and softer your sidewall is, the more it deforms.  As it deforms it changes the way the tread contacts the pavement.  I'm not even going to get into tire slip angles and contact patch dynamics, but suffice to say if your sidewall rolls over, it affects how the tread contacts the surface, usually negatively.

Pressure: Clearly this affects how the tire behaves.  It's also the one thing we can adjust easily, thus it gets a lot of attention.  Lower pressure softens the sidewall (which is usually negative) but also changes the way the slip angles at the contact patch behave, which can be positive.  It's complicated.

So the result is that if you have a tall sidewall all season tire, you're going to need a lot of camber at full cornering to counteract the sidewall rolling over and the tread blocks trying to pull up on edge.  If you have a low profile traction tire with large tread blocks you'll need less camber in the corner because if the wheel is actually perpendicular to the pavement, the tire will also be making good contact.

One last thing to consider:  as you enter a corner and begin to load up your outside tire, if you have a large amount of static camber the inner tread blocks should be on the 'flat' of the tread and bite, creating good traction prior to the maximum cornering load, this has the effect of causing increased weight transfer, increased suspension compression, and in 90% of suspension geometry lost negative camber.  At this point that's a good thing, as the tire will roll up onto the flat of the tire providing maximum traction at maximum cornering need.  If you have too little camber the  tire will reach its 'flat' point too early and roll onto the outside edge.  Conversely, if you have too much camber (fantasy junction I'm thinking of you guys you will always be trying to corner on the inside of the tire and it will never roll over enough to reach maximum contact AND you will wear out  the inside of your tire very fast.

So how do we use all this do our advantage.  Examine your tires.  If the inside edge is totally worn out but the rest of the tread blocks don't show much or any scalloping, too much camber.  If the outside edge is rounded and worn bald, or your outside sidewall is very, very clean , you have too little camber and/or inappropriate tires.  If you're showing rounding on both  the inner and outer tread blocks and the middle ones have some sign of scalloping, you're probably pretty close.  At that point play with pressures to find the best feel for the car.

As for compound, a softer compound allows those little tread blocks to deform to and  grip the bumpy road surface better (at the minute level you are creating more contact area as the tire can deform over little bumps) and the rubber physically has a higher coefficient of friction (stickier).  This means the tire grips better, will cause greater cornering forces and thus greater weight transfer, body roll, and loss of camber at maximum cornering (for the 90% of McPherson strut cars), thus requiring more initial static camber.

Now, if slicks are in the equation all the tread talk basically goes out the door and all you're worried about is slip angles....but that doesn't affect us budget racers.

Or I could compose some more poetry...

You have room on your team for Buttonwillow?  I'm tired of listing to Erik "nerd out"

Either one

If you're into limericks, boy do I have a suggestion for you... [Hint: Exoskeleton Jag...:-)]

Team Blue Goose came up with a unique solution to the camber problem on its CRX. We took a cutting torch, cut out the driver's side strut tower mounting area, grabbed the top with a gloved hand, yanked it inward a couple inches, and welded the whole thing back in place with lots of scrap metal. Then we did the same thing on the passenger side.

We've never measured it, but just looking at it you can tell it's at least 5 deg neg on each side. The sides are a bit uneven, but it works fine. We've done five or six events (several not really "run" though due other difficulties) and never had a problem with it.

Here's a track specific camber question:

We dialed in -2 degrees on our FWD VW GTI for our first race at CMP this September.
Pictures of our car show the driver-side front keeping a pretty good contact patch.  The passenger front was really up on it's inside edge.

Since CMP is almost exclusively right turns, does it make sense to keep the -2 for the driver front, and go to +2 for the passenger front?
I'm thinking this would maximize the contact patch for both tires during cornering on all but the one left turn.

I don't think *any* camber setting will improve the passenger rear contact patch. (but we are actively haggling for a set of stiffer springs to keep the front from diving so much)