ideal contact patch

[aither]

What would an ideal contact patch shape look like for the purposes of maximum grip? What about for a drift set up? Also, what effect does the total area have on these two set ups? I've been doing a lot of research on slip angles and different set up theories, but no one has described this. I remember that a wide contact patch does a better job at resisting lateral loads, and narrow contact patches, "cut through," rain puddles. That's the extent of my knowledge on this.

[Q45tech]

There is no ideal tire patch shape it depends on the way the slipping forces are applied vectorially.

There is no area change in that 1000 pounds on a tire divided by inflation pressure is the contact area 1000/32psi= 31.25 square inches no matter what shape the tire is. Tread patterns [void ratio] get in the way of this calculation..........so say 95% true even under extreme widths 6"-12".

[Mayhem_J30]

There is no ideal tire patch shape it depends on the way the slipping forces are applied vectorially.

There is no area change in that 1000 pounds on a tire divided by inflation pressure is the contact area 1000/32psi= 31.25 square inches no matter what shape the tire is. Tread patterns [void ratio] get in the way of this calculation..........so say 95% true even under extreme widths 6"-12".

Are you saying that no matter what the camber, if the tire pressure is constant the contact area is the same no matter what under constant load? Load divided by tire pressure makes sense, but then it seems to throw out the point of camber adjustment. Unless camber just controls WHERE on the tire that 1000 lbs is distributed within 31.25 in^2.

Seems in this case the easiest way to set up for drift is to find a smaller tire/wheel combo that does not meet the load/psi requirements, thus giving way to the lateral vectors sooner. This of course isn't even taking in consideration to CoF of the tire and pavement/concrete/gravel/dirt/debris/grass/water....

[Q45tech]

"camber just controls WHERE on the tire that 1000 lbs is distributed within 31.25 in^2." EXACTLY...........the static vertical force vector is angled [the camber].

The problem is the effective camber decreases as the tire slips sideways and quickly goes from negative 1.5 to flat to positive to very positive brcause the sidewall is not rigid!

Tires with lots of negative camber wear the inside going straight, the same set up will wear the outside edges if the vehicles is driven constantly in curves................wear shows where the force concentrations lie!

[aither]

thanks for the replies. Here is another question, what effect does a change in the contact shape/size have. For instance, under heavy cornering loads, the outside tire's contact patch should grow slightly, and its shape might change slightly, depending on the tire's construction, right? The opposite should happen to the inside tire, right? Basically, I am trying to understand what is happening to the tire in a corner, when slip angles turn into slide angles. I am curious what the contact patch shape/relation with the tire is doing in this situation, in order to understand WHY certain wheel/tire set ups are better for drifting and why others are better for grip driving. Does anyone have any suggestions on books, links, direction to give me on this? (btw, this isn't for a physics class or anything, this is just to expand my knowledge. I also realize that these questions may require several years of physics, etc, to answer with a lot of depth.) Thanks!

[Q45tech]

The coefficient of friction and thus the total friction increases as weight is applied to the contact patch.............in a somewhat linear graph to a point then it starts to roll over and become more than parabolic in shape...........the curve would be cornering stiffness [Newton/degree] vs. Load [KiloNewtons].

Lateral forces vs slip angle at a constant load is another good thing to know.

Generally the higher the maximum load rating of a tire the lower the slip angles with the same applied forces.

The shape of the contact patch in a rear slide means wider is better if the slide forces are 90 degrees to foward motion. Also shorter sidewalls [aspect ratio 65>60>50>45] mean less deformation in the tire patch as the loads shift.....stiffer sidewalls holding the patch more constant.

Mostly the compound and the temperature of the tire road interface controls the friction. As different compounds have differing optimum temperatures and the curve falls very rapidly beyond the too hot point which is just past the perfecet point of maximum friction.The more "racing" a tire is, the closer the points are.

Tires have to slip to roll and turn. The problem is when you try to add forces together. Turning, acceleration, and deceleration [braking] at the same time.

Your question points out that the weight on each tire [static plus load shifted] changes the instantaneous friction on each tire.

http://www.presspley.com/racec...e.htm

[Q45tech]

The problem is the important or any curves/graphs are not available from the tire manufacturers for each tire to use in Pacejka Equations. Search goole for this key word and read the 100's of sources.

[MrFox]

I am trying to understand what is happening to the tire in a corner, when slip angles turn into slide angles. I am curious what the contact patch shape/relation with the tire is doing in this situation

http://home.tiscali.be/be067749/58/c1/c11.gif

The effect of the contact patch shape (along w/ sidewall stiffness, compound, etc...) is to change the shape of the above curve - a stiffer wider tire, I believe, should move the peak to the left. The transistion from slipping to sliding is gradual. A popular school of thought theorizes that the contact patch is divided up into sections of static and dynamic contact. As the slip angles increase, the region of dynamic contact grows, and the static region skrinks.

[Q45tech]

Much of it depends on the molecular structure of the road as there is a tremendous variation in the friction of compounds and water drainage designs [roughness/void ratio of the road] and the temperature of the road/tire. Speed of rotation [for the heat to be released]

http://www.fest.tuwien.ac.at/I...r.pdf

http://scholar.lib.vt.edu/thes...0920/

http://scholar.lib.vt.edu/thes...s.pdf

http://www.insideracingtechnol...n.htm

[aither]

cool. Thanks a lot. Now I have plans for the weekend! (research)

[Mayhem_J30]

cool. Thanks a lot. Now I have plans for the weekend! (research)

Haha, never thought homework was cool until I got interested in cars. :ylsuper

[C-Kwik]

yeah, but too bad you don't get college credits for it, huh?

I will add my two cents. The mathmatical and scientific understanding is important to know, but some amount of trial and error is necesssary when properly setting up a suspension and tire pressures. A good pyrometer along with an accurate tire presure gauge can work wonders in the field. It's hard to predict exactly what the car will do and can vary with road surfaces as well. Even race car engineers make adjustments at the track. The math and science of it just helps you to understand how to best deal with tuning problems to maximize grip.

[aither]

I agree. Driving is what makes you a better driver. However, my car was recently totaled, and now all I can do is think about this stuff and play Gran Turismo. Hopefully, I'll be able to apply some new knowledge to my next 240, plus, its just good to be able to explain what your car is doing.

[Q45tech]

If you use a negative 1.5 degree static camber and have a camber gain of 0.8 degree per inch you really want to limit body roll to 2 degrees to have a squarish/rectanglish pattern under load.This is the design challage in a street car.

If you have a coil over with no camber gain you must further limit body roll. Stiffer springs. ..........or find tires that can take the stress.

Many race tires have camber build into their carcass and street tires [radials] like at least 0.5 degrees negative to maximize grip.