.......
.....??????????

 

This is great!
But to simplify what (I think) Peejay is saying, and to tie it in with Marques's thoughts, rubber is one of those substances that probably has a non linear friction/per square inch/per lb coefficient because it can squish.
Air, too!
The friction from air filled rubber and pavement simply can't be compared to the friction of asbestos to steel, because niether of the latter are very forgiving like rubber.

So I propose the following, and I'm sure you brainiacs will correct me, but it's really just a question;

There must be an increase in stop-ability as the tire-to-asphalt patch grows in size...until the growth of the combined artea begins to lessen the stopability due to the lessening mass/per inch squared.
For the Peejays and Marios and fatboys out there; concider pressure / temp / compound to be givens on a stock brake equiped 2400 lb rex.

...What is that combined contact patch area that is the best it can be (largest) before it begins to be counter-productive?

Am I even right? If I am, then let's toss a monkey (chimp) into it all and say that 205s @ 60% front braking is also a given. What then would be the ideal rear tire size?

How does this pertain to acceleration?

I ask all this because I have SUPER wide tires on the back, and 185s up front (what I could do at the moment-not the best set-up, I know). I thought I would spin right thru 3rd gear shifts with them because more area meant the wieght was dispersed, effectively making the car "lighter" in the rear. These things are 265s! Third does'nt happen like that with them, but it does with 185s of identical diameter.
So I had it backwards?
I know you cant compare the compound of old Goodyear GTs to the new Toyos that were on there, but still....

 

so we are the result of something that deformed?


but what happens when you heat up the brakes and cause severe brake fade.... then you know you need a better setup

 

Wow, pretty technical, complex, well though out, clever answers to a pretty basic question - "What stops a car"
Is it ok to lighten it up a bit now and inject some humor? Come on. .. can I ?
Ok. . .
This is the story of a man with NO brakes. He uses a parachute to stop in an emergency and the police to stop him in illeagal situations. He's just a regular shmo, who knows 'stuff all' about physics and just drives his seven for the pure pleasure of it. Driving fast around corners he tends to use his gears to the advantage of himself to slow down, rather than jammimg on those brakes. We all know that most passing moves in racing are done "Under brakes" with the winner generally being the one that held out the longest - in other words - the one that used his brakes LESS.
There is also the Hollywood style of stopping your car - ram it into dirt mounds and trees to scrub off excess speed as you hastily decline that mountainside. Seriously though, a turn of the ignition key into the off position would stop a car, as would a hot panted beauty with car troubles on the side of the road. But when it all boils down to it - I STOP MY CAR. So, while there are many many many answers to carls bloody good post, you now may choose the one that suits you best.
Just my $3,50 worth. . . sorry.

I seriously didnt know all that stuff Mar3 and all you other wiz dudes were talking about. . . Nice to know the Seven community not only has GREAT taste in fine cars, but have quite a few brains too!!!!
Refreshing.

 

No, we are the result of mutations in our DNA that didn't get eaten or die before the propagation of said genetic mutations via uninhibited wild hominid sex...next....

 

Theoretically really is no limit looking at purely contact patch size, bigger will always stick better than small. Pressure really has nothing to do with friction, because the force holding the tires against the road is always constant. The only thing a bigger contact patch does is change the effective coefficent of friction (remember this holds true only for materals such as rubber which display elastic deformation). The simple equation for friction is: F_road/tire = F_weight * Coeff_friction. The greater the Coeffient of friction the greater accelation. For 1g-force accleration or deceleration, or even lateral acceleration the coefficient has to be 1. The larger the contact patch at any given time, the larger that coefficent will be. Of course there naturally is a point of diminishing returns, especially in the real world where the suspension has to hold down that larger heavier tire, and the tire itself has structual limits before larger doesn't mean better traction. The limit itself is dependant on so many things, expirimentation is really the best way to detirmine the optimum tire width. I honestly don't have any idea what is optimum on a first gen, but certainly larger than anything you can stick under the stock fenders.

Ideal from what perspective? Supposing you have identical braking systems front and rear, and valving isn't biased, the largest tire you would want is one where the contact patch is roughly 2/3 the size of the front tires contact patch (not that simple really, but...). Any larger and the rear would lock up before the front. Obviously this would be silly, noone biases their braking system by shrinking their rear tires. Brake proportioning/valving is a very important part of a well rounded brake system. And 60% front brake bias is unusually back heavy. I'd expect that even a stock braking system that the wieght transfer to be over 70% front biased. A good brake system (lots of wieght transfer) would be closer to 85% front bias. This is why front brakes are almost always larger than the rears, they do the majority of the heat transfer.

Yea, you had it backwards. If you're building a drag car, you're set up is perfect. If you expect it to handle the twisties well, think again. Those larger rear tires will stick better than the skinnies you've got up front. That thing will likely push in the corners. You're braking shouldn't be affected, so long as your rear brake bias is too great, causing your rear brakes to lock before the front ones.

 

Are wheels? Because if tires are more complex then wheels, why should I not reinvent the wheel? Its not like im reinventing the tire!

 

To simplify all of this, what stops the car is adequate traction. Tire and brake size don't mean a damned thing if you're doing 100kph and hit a patch of black ice. One could argue (and justifiably so) that a certain contact patch will give you a better chance at maintaining adequate traction, but with good traction your car will stop and with little to no traction it won't.

Anyone who's ever attempted a panick stop on ice or on a road after a quick rainfall can testify to this.

 

...Nope. Don't know anyone who's done that! ( )

 

yep - in some cases the answer to 'what stops a car' is 'the roof hitting a bunch of jagged rocks'

 

Does this mean that the tendency for the oversteer in our cars can be corrected with wider rear rubber?

 

ask Mario

 

Yes, it is something that you can tweek to adjust handling. But realize that the suspension is often the culprit. Binding on our cars for instance causes the car to unload a tire and the other rear one's slip angle to go wild. This has little to do with tires, in fact larger tires will most likely cause that point of snap oversteer to be that much more abrupt. But if everthing was equal except the tires, increasing the size of the rear tires will decrease oversteer or increase understeer.

 

Larger tires won't do as much for you unless you are using the proper *air pressure*.

 

Reverse thrusters.

 

So will a fatter front swaybar.

 

or "some 17 year old kid in a Corsica's rear bumper"

 

You see why STOPPING is not important, just SLOWING DOWN CONTROLLABLY.

The most I've ever used to "stop" has been a chainlink fence, maybe a tree... once an Integra. I think I used a curb to slow down once but I bounced back off and kept going...

 

I highly reccomend a bag of shingle evenly poured into the intake to stop an RX7

If the engine stops instantly, then ALL drivtrain components instantly sieze.

Would electro-gravitics suffice?

I'm guessing you would need approx 5 Million-ish Watts to stop an RX7 instantly using electrogravitics, plus the entire internals of the car would need to be filled with Dielectric to make a big enough capacitance effect

 

Hey, I won't question your methods, as long as the car stops. I'm all about that.

 

Dude, you're gonna make me start crying again...