Tire performance versus lateral load and camber. 1

[ksw100]

I'm looking to deepen my understanding of tire engineering, specifically regarding how to determine the optimum camber angle versus lateral force to achieve the highest levels of traction and tire life. I've come across the term 'Mx' in my readings but am unclear on its meaning in relation to tire dynamics. Can anyone recommend resources or explain this concept in more detail?

Also, what is the topic of tire performance called? Is it something like tire dynamics or others?... So I can Google it or buy the right books to learn more.

 

[cibachrome]

As a general statement, more camber generates more lateral force. You need the characteristics of YOUR tires to know what the gain is. While you may imagine that the center of vertical load is in the center of the wheel, it is most likely not. As a result, there is an offsetting moment (Mx) which is this lateral distance times the net Fz (vertical) force. You can see this in videos of tires being tested and from cameras watching tire tread movement while cornering. If your car has "roll-camber" compliance (camber due to roll), it also responds to this moment by increasing the body roll angle (generally by about 10%).
Even though you hear all the blather about scrub radius needed for braking/traction stability, the Mx gets involved with what is called "pneumatic scrub" which can increase OR decrease the static scrub radius, even to the point that it can change the sign. Very important in FWD cars because this effect has been found to be tire brand dependent, and if the effective scrub radius goes positive, you will have your hands full when this sign change occurs while going with throttle up.

If it's max-lat improvements you are looking for, the goal is usually to keep Mx to a minimum in order to maximize the full tread patch contact pressure.

Here's the caveat: Just like "optimizing" Ackermann turning geometry for the pair of front steered tires, if you don't also improve the rear lateral capability, your car looses understeer and will loosen up, to the point where it's unstable without massive timely corrections. Anti-Ackermann (more toe-in with steer) can greatly improve front lateral grip, but can kill the car because the rear can't keep up. So it gets a black eye. This ALSO depends on the tire properties because it takes advantage of the slip angle at peak Fy location increasing with load. Not all tires do this. Some have their slip angle at peak Fy decrease with load, so you need +Ackermann (toe-out with steering) to gain an advantage.

Search for "Tire Force & Moment Properties" literature. Not a lot of specific facts usually, but a huge diet of bullshit awaits you !

 

[cibachrome]

Here's a sample of Mx brand characteristics at the same Fz load for a commonly used size. Yes the pair of tires needs to be taken into account during turning, but you can see what could happen to your braking/traction ratings if you chose the wrong one... Did I mention that a rotation direction can come into play too ? These are all mounted as a right front.

https://imgur.com/HXoCfBq

You can imagine why 'Tires' are considered a religion in most parts of the Vehicle Dynamics World because of so few facts, depending only on Faith. (Not a good idea). Lots of smoke, mirrors, and hand-waving. You should know what they say about opinions.....