Picking New Tires, Trying To Get More Front Grip

Red__Zed

People always say things like this because the Physics 101 equations (F.friction = mu * F.normal) say friction isn't dependent on surface area, but the Coulomb model has a couple of holes in practice, especially in regards to car tires.

Increasing contact patch does help with a tire for a couple of reasons, especially because we are concerned with traction, rather than just friction.

One element is maintaining stability over rough surfaces. A wider tire gives you more opportunity to have rubber in contact with the road, as the tire deforms over imperfections. If you've ever cornered on a road bicycle and hit something mid corner, you'll understand why this is important.

Adhesion plays a role in traction as well. If you slap a piece of tape on your desk and try to slide it, you can see this. It will be very difficult to slide, despite a very minimal normal force acting on it. Adhesion comes into play on car tires as well - there are dozens of SAE papers out there on it, and the Wikipedia page on friction has some links for you as well.

If you really want to get into the weeds on cornering performance, a wider tire also tends to help with slip angle. And of course heat management comes into play.

Other reading:
https://en.wikipedia.org/wiki/Tire_load_sensitivity

ScottOmatic

Thanks,

I was just searching most of the points you have made here a half hour ago, lot's of things going on here.

Another interesting factor that I saw brought up was viscoelasticity. Tires are not simple creatures.

MacCool

Slip angle, rough surface traction, heat management, and therefore cornering performance, assuming you're pushing it hard enough to generate that much heat that it matters, are absolutely valid points in the discussion of traction vs friction. The OP is contemplating differing tires sizes to manage understeer/oversteer. Those factors don't come into play. He want's to "loosen it up" and "free it up a little more by getting more contact with the road with the front tires". We're back to high school physics.

Red__Zed

You're neglecting adhesion in your response. And oversteer/under steer is just f/r management of traction...

That basic equation assumes minimally elastic solids. Surface area matters more as the material becomes more elastic.

There are a lot of good resources to school up on traction out there. I'd recommend taking a look.

MacCool

The basic equation accounts for adhesion as part of the coefficient of friction. Surface area doesn't matter.

JARblue

Thank you for the enlightening response

Let me get this straight. You acknowledge those factors are all part of cornering performance, then proceed to state that since the OP wants to manage under/oversteer those factors don't come into play.

Want to try that again?

Or maybe you can explain how to induce understeer or oversteer without turning the steering wheel

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dP3NGU1N

Typical troll responses. Plenty of "you're wrong because I said so" with zero usable information pertaining to the OPs original question. Please stop wasting everyone's time. The rest of us are here for answers.

If you have a solution, state it. Otherwise, kindly feel free to fu[k right off.

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MacCool

The solution, obvious solution, to oversteering or understeering is suspension, not tires. I can't help it if your grasp of rudimentary physics is so lacking that these concepts are beyond your ability to understand. Public education apparently isn't what it used to be.

Red__Zed

Simply not true. What you are describing is the Coulomb model of Physics, not Physics. If you had any background in physics you would know that adhesion and deformation are two of the most standard cases to break you out of the Coulomb model. Your 7th grade Physics equation assumes "hard" solids - it's a terrible approximation of a tire, especially on a performance car, where you are using "sticky" tires and air pressures that allow for a good bit of deformation.


That's for sure - now they explain the limitations of basic models to junior high students. Go do some research on the adhesion and deformative components - you can find a start on Wikipedia, but any modern Physics textbook will get you up to speed here.

Here's a relevant quote to get you started:

Points are true in general, but the Z tends to have more issues with stiffness up front (depending on tire selection), and not need a whole lot of help in the rear. The additional camber up front is very important. The Z runs best with 3+* of camber and a bigass bar up front from what I've seen - all the really fast guys have a Hotchkis bar and as much tire as they can get up front, preferably with a stiff sidewall. There's already a ton of stiffness out back on the Z, and a stiffer rear bar doesn't do as much for you.

Rusty

Here I am of thinking on going with 305's in the front to go with my 345's in the rear in search for more grip. Now I'm going to have to rethink everything. Maybe I'll start a new trend by going with 145's in the front and 155's in the rear.

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