8 replies to this topic

[mtl'78]

Alright, I know what it is, I'm just unclear as to how it is used. Logic dictates that they would want to set camber so that the angle is zero in the corners, right? But then I've read that they sometimes want "camber thrust". Does that mean that they actually want a negative camber in the corners? Is that how camber thrust works? Is camber very important to grip or is it mostly for tyre wear? thanks!

[Ben]

When a wheel is cambered the tread is pulled sideways as it enters the contact patch. The reaction of this creates a lateral force in addition to the normal cornering force due to the slip angle. This is camber thrust.

If you set up a car with lots of negative camber (all F1 cars) the outside front wheel will still be in negative camber dispite roll in a corner. The camber thrust acts in the direction that the wheel is leaning so this adds to the car's cornering force.

Obviously the inside wheel goes to an even greater negative camber angle, so you might say that this should create more camber thrust that would pull the car in the opposite direction. In reality the camber thrust from the inside wheel is much less due to the lower normal load on it due to weight transfer.

When the car doesn't need to be symetrical (oval racing) you will see all the wheels leaning in one direction (i.e. positive camber on one side and negative on the other.)

Ben

[mtl'78]

OK, thanks Ben, I think I get it. So they would want to put on as much (negative) camber as tyre wear allows then?

I find it very interesting that camber thrust forces are strong enough to be given more consideration than having the maximum contact patch...

[desmo]

Just to complicate matters further, the cross section of the tire in the shoulder area as well as the construction of the tire will affect the camber thrust effect. From close-ups of run tires as well as their evident shapes, I'd guess that Bridgestone's front tires make more use of camber thrust and that the Michelins are more biased toward contact area.

[imaginesix]

I think it is misleading to say that cars are set up with camber in order to allow them to take advantage of camber thrust. This is my take on the subject:

The effect that Ben described of lateral distortion of the tread is very true as long as the tire is travelling mostly in a straight line. However once you start to include lateral loading on the tire, this lateral tread distortion starts to get mixed up with all the other changes that affect grip.

When the tire is horizontal and providing maximum grip, the carcass distorts enough to cause the centre of pressure on the tread to move outboard from the centre of the tire, meaning the outer edge of the tire is mostly at or past the point of maximum grip, while the inner edge is mostly below that maximum.

Inclining the tire moves the tread's CofP back inboard, allowing the inner edge to work harder while relieving the outer edge of it's burden somewhat. So from that perspective, the benefit of camber is acheived through the improvement in contact patch loading.

Looking at it from the other angle, if camber thrust were the only consequence of inclining the tire at peak lateral loading, the tire would actually lose grip due to the increased tread distortion, past the point where maximum grip is achieved.

I don't believe camber thrust is a set-up consideration at all. One simply determines the ideal camber and pressure to achieve maximum grip, and aims for those targets in the set-up. Whatever contribution camber thrust may or may not make is irrelevant.

[MattPete]

I'm with ImagineSix on this one. My general understanding was that camber was generally set such that the tire pyrometer readings were roughly equal across the tread width. Too hot on the outside? Add some negative camber the relieve the burden on the outside of the tire. Too hot in the middle? Lower the air pressure.

[Ross Stonefeld]

Have they made Tech for Dummies yet?

[mtl'78]

one more question: Does tyre pressure have an effect on camber thrust? and Why is rear camber almost always less than front camber?

Thanks guys, I've been here two years and I'm just starting to realize how fantastic a forum this is. No flaming, just intelligent discussion . Plus since the raqcing is not so hot these days, it really helps to get interested in the technical side.

[Ben]

Point taken about camber thrust being predomiantly a factor at zero or low slip angles.

I've done a bit of digging and while the effect of camber thrust is less at high slip angles it still has an effect.

If you add the camber thrust directly to the side force vs. slip angle curve you get a theoretical curve for the cambered wheel through the slip angle range. In practice this curve gets closer to the curve for zero camber so the improvement in lateral force due to the camber reduces as the slip angle increases. This phenmenon is called 'camber roll off'.

The important point though is that camber thrust still gives a measurable increase in lateral force even at higher slip angles.

I suspect that you see less negative camber at the rear because keeping the contact patch flat is much more important from a traction point of view.

Ben