Beleive it or not I cant find much answers about this after searching all over the net.

I would think they do this so the drive wheels get much more traction, and there is less Coeffiencicy of drag with the fronts.

Porsches, Ferrari's, Lamborgini's all come like this.

Ive seen FWD cars with much larger fw tires, set for drag mainly.

My question is why do they not have wide tires all the way around?

Like if a car had 295's or 315's all the way around would it not handle the road like a vice grip? orr does it create over/under steer issues?

I know that wider front tires will slow the car to a point, but it would well make up for it in handling right?

I know this is a Noob question, thanks for being tolerant.

 

generally in a powerful rwd car the rear tires will break loose under hard accel. i'm sure you know this. i'm also 99% sure thats why manufacturers include staggered tire sizes on stock performance cars; and in fact the car may come from factory to take advantage of the stagger.

that being said, in a diy context, it depends on awful lot on car set up and driver preference. a local autocrosser off the forums swears by staggered setups. i on the other hand dislike it... i had 225F 245R and i recently changed it to 245 all around.... much more neutral; and who knows... maybe even slower. but thats the way i like it, and our cars may be the same model, but they are definitely not setup the same... so take it as you will.

 

Porsches, Ferraris and Lamborginis all have a rear biased weight distrobution, so they need the wider rear tires to handle the extra weight back there. On some cars it's partly for style and partly to make the car understeer, which is safer for the average driver.

You can make any combination of tire widths handle in a balanced way, but that'll be done by reducing the grip of the one end untill it reaches the (lower) grip level of the other end. You're better off increasing the grip of the other end.

On a powerful RWD car the wider rears do help to combat power on oversteer, but it's often at the expense of steady state understeer.

 

I don't think the drag from the rolling mass of the front wheels is much of an issue in a Lambo. I think it's all about traction and trying to do something about oversteer without making the car so stiff that it knocks out your fillings...While still cornering like it's on rails.

More traction in the rear = friendly understeer. At least that's what happened when I staggered the wheel and tire width on my FD.

 

car manufacturers wont produce a car that only oversteers. if enough average joes with money buy a sports car, and they keep spinning them into walls, there would be a lawsuit.
its a general rule that the better a car handles (both grip and balance) the harder is is to control once sliding. to add a margin of safety, all production cars hint towards understeer.
on another note, its much more difficult to fit really wide tires over the front suspension, due to the fact that they have to turn. the wheel well also has to contend with the engine bay for space.

 

rwd.
corner exit is where you mash the throttle.
to get the power down you need a wider tire.
but to match that tire to the front you end up with limitations.
usually with the weight transfer to the rear during acceleration, you want more tire out back on a rwd so it wont lose grip exiting a corner with the throttle being floored. you only need so much tire up front, not massive tire, because at corner entry the car should be well balanced, but at corner exit the chassis is much more rear heavy and you need a wide tire to control that extra weight and the extra force of acceleration on those drive-wheels.

 

Correct me if Im wrong, but if all 4's were equally as wide (assuming no clearance issues), exiting a corner with the throttle being floored might lose a little grip in the rear due to the extra traction in the front?

I would think that in this situation the tires in the front would provide better cornering g's and perhaps promote oversteer. Also that the rear would hold almost if not just as well.

Thanks for your input, Im still trying to understand this concept

 

Is that going from a 9 to a 9.5" front wheel?
What did you mainly notice other than feeling more neuteral? Like it grips better? can hold more g's in a corner? perhaps feels more like a mid engine?

 

wheels did not change. still 9" all around. i have no idea if it holds more g's in the corner. nor do i have any experience driving a mid engined car.

i do know that when i push it too hard mid corner the car will start to slip a bit more evenly, instead of front end telling me it refuses to turn harder. i like that more. again, it depends alot on how the driver actually drives, and the rest of the car.

 

Naturally with a car that understeers you'll be able to be more violent with the gas because you have excess grip back there.

With a weight distribution close to 50/50, having equal tire sizes front and rear will help promote balanced handling in steady state cornering because the loads on each end will be more or less balanced. If you try to accelerate at that point you will oversteer because the car cannot give you any more grip. If you reduce your turning then there's more grip available for accel (familiar with the friction circle concept?). When you accelerate weight trasnfers to the rear which helps give you more grip for acceleration and takes grip away from the front.

With big power it's often desirable to get as much grip as possible back there and put up with a little understeer in order to make it easier to get on the gas sooner to get out of the corner faster for faster times.

 

The interplay between the distribution of weight and f/r contact patch size in the context of high hp cars is something I have been thinking about a lot recently.

I hope that the motor in my car will produce in excess of 400lbft of torque at the wheels when everything is sorted out and the weight distribution should be around 50/50 at best and 55/45 F/R at worst.

For straight line acceleration 345 rear tires would be a good choice. The biggest contact patch I think I can reasonably match them to in the front is 285. Although, 255s look better (thanks to lower ride height) and probably have less kick-back through the wheel. With this setup I believe the car would have a natural tendency to push while cornering.

In comparison I think a chassis with 35/65 weight distribution has a few inherent advantages. First, more weight is over the drive wheels, so forward grip should be better with all other things being equal. Second, since the weight distribution better corresponds to the staggered tire sizes the chassis should be more neutral while cornering.

I have been told by people with experience playing around with this stuff that under/oversteer can be dialed out by adjusting the sway bars and alignment. Can it really make up for such a fundamental difference? Obviously this is less of a problem for lower hp cars where the forward and lateral traction needs are not so disproportionate.

 

You could probably make a car with 50/50 weight and 335 rears and 225 fronts balanced, but in the end you're just taking grip away from the wider tires untill they match that provided by the smaller tires, so why bother having them be so big in the first place?

 

driving style has a lot to do with the cars handling. i have staggered tires, and no problem with understeer. probably because im so used to instigating oversteer, that its incorporated in my driving.
mid engined cars do have the most traction under hard acceleration, and therefore can apply throttle earlier, yielding higher exit speeds. when they approach a corner however, they are much more difficult to drive. a mid engined car hard on the brakes is no joke, and once the back starts to slide, you cant do much about it. oh, and never lift mid corner.
*** heavy cars are the fastest, but require the most amount of commitment if you wanna stay off the wall. a front heavy car is easy to drive fast, but is inherintly limited in ability. its all trade offs. 50/50 is not ideal under any circumstance, but it is a great compromise between the advantages/disadvantages of front heavy and *** heavy.

 

When I'm talking about neutral handling I mean steady state cornering balance, not turn in or turn out type of balance, which is more dependant on things like brakes, power and driver. Neutral is when you're on a skidpad and going faster has the effect of making all 4 tires loose grip all at once, rather than making it understeer or oversteer, hence the grip is even and no one end is dominant, so neutral.

It's not neutral if the car has grinding understeer but the driver can overpower the rears and get it to powerslide, not the same thing. It's not neutral if the only way to get it to oversteer is to do something to induce it (Scandanavian flick, etc)

 

unfortunately, no race track is a skid pad (besides nascar... barf). corner exit speed is the name of the game, so ideally, your car should be nuetral on full throttle while turning.

 

It's not that simple. If it was neutral under full throttle then it'd have terrible understeer and would be really slow in the corners, making you loose more time slowing down and getting through, and it'll hurt your exit speed too because of having a lower corner speed.

Having a car that's reasonably well balanced will be faster.

 

But wouldnt grip increase, with a balance of 50/50 evenly distributed over the wheels, having the same contact patch front and rear? So that one end is not overly dominant?

 

you really can't make sweeping generalizations about ideal setup or general grip increase. it depends on the corner, it depends on the track, it depends on the driver and it depends on the car.

if you can make such generalizations, then you have a masterful command of race car physics, you model that **** on computer simulation, and you are probably professionally employed in the industry

just drive what you like and set your car so you it feels better and/or you go faster.

 

This guy knows whats going on. Its all about weight transfer. Having massive rear tires and transfering all that weight to them will sure help you come out of a corner.
Better yet, move the weight bias of the car more rear to help it plant even more.
wait hold up, keep moving that weight rear and put a big wing over it so it presses it into the ground even harder! And tune the suspension so it still handles in a neutral fashion. holy crap! now that the rear of the car is doing so much work, the front tires really arn't doing much even under breaking! now its just a waste to have such big front tires.. lets make them small! OMG now we don't even need power steering!

wow, we made an old F-1 car!
http://www.historicracecars.net/carp...003_ALFA03.jpg

 

In F1 in that era, the small front tires were partially to reduce drag and reduce unwanted aero concequences for the rest of the body that tires have. Hence the 6 wheel Tyrrell.

http://en.wikipedia.org/wiki/Image:S...ll-FordP34.jpg

 

yes, the theory was 'air penetration', notice that cars of that era dont even have front wings, but sloped fronts, covering the tires. But i'm pretty sure 'penetration' was not the reason they had skinny font tires, they could have had wide ones and just made the front splitter cover them. Its just how these cars are set up, the rear tires do most of the work!

The 6 wheeled car was rather pointless, since the rear tires were just as huge leaving the frontal area the same, and they would be easily disturbed by anything other less than a perfectly smooth track.

 

pretty much.

i just wanted to add, it is easier to control car that's set to understeer, because all you need is, let off the gas.

car thats tuned to handle and grip..., once you loose control, it is much harder to recover than car thats tuned to understeer. will always carry more speed thru the corner, than car that undersreers.

 

Yes the big rears create drag and all, but their influence on the aerodynamics of the rest of the car are minimal, whereas the fronts will disrupt the air that goes over the rest of the body and that can have much bigger impacts overall, so they're more important aerodynamically.