upstate bob

OK gents, I'm awondering why some 928 owners feel the need for rears wider than fronts. Seems counter to logic: when you make a sudden direction change the fronts take a greater side load than the rears. Please don't offer the juvenile reason, "it looks cool". I can understand it in a muscle car built for straight line acceleration. (an old 69 302 Camaro will kick a 928's *** at the stoplight). Having all four tires the same has too many advantages to abandon. -let the sniping begin.......

hacker-pschorr

Not unless you have an ultra rare ZL1 Camaro. The rest are the 6-7 second mark for 0-60.
Any stock 32V 928 will do better.

Those old muscle cars are not as fast as most people think they are.

Way too many factors to make such a static statement for all vehicles.

Put the same size tires as the front on the rear of a ZO6 Corvette you will gain nothing in any performance category, except maybe fuel mileage.
The Corvette racing team I'm a part of in NASA, we cannot put enough tire on the back of our ZO6's (with stock engines). The wider we go, the faster the cars are around the track. If we could fit a 385 series tire on there, we would.

Install wider rear tires on a BRZ you will probably make it slower by upsetting the balance of the chassis.

As for the 928, which year? Putting monster tires on a stock 78 isn't going to gain much other than looks.
Put 235's on the back of a GT it's going to be a rubber burner which isn't going to help performance any.

upstate bob

I'm referring to boulevard holeshots which the old camaros and mustangs were superb at. I used to watch the fun on Hawthorne blvd back in the 70s. No 1/4 mile times, all from light to light. weight to hp and gummy slicks. A category we should not entertain. Then at night we went to Orange county or Lions.

Fsharp9

Corner grip and traction in and out of corners , remember, when the front gets heavy the rear gets light and will want to rotate mid corner, essentially more rubber compensates for weight transfer

upstate bob

BTW I love my cherry old 79 928 and wouldn't trade it for a barn full of awkward muskle cars.

hacker-pschorr

The 302 Camaro's had less than 300hp (I've seen more than a few on the dyno) and weight over 3200lbs.
My friend who owns the Vette team I'm on also has a Corvette performance shop. He tries to persuade any vintage Vette owners from joining in on Dyno days, especially the big block owners. The numbers rated back then were Gross HP, by the time you get a net rear wheel number, the results are usually rather embarrassing.

My friends fully restored Road Runner put down 170rwhp on the same dyno day as stock 928's putting down over 270. IIRC the "rated" factory HP of that Road Runner is over 300hp.

The average 1/4 mile time for your typical muscle car is 15+ seconds.

You did throw "slicks" into the mix, well that changes things. Let's grab a GT 928 with sticky tires, headers and a custom engine tune......

.....and now we reach the silliness of these threads.

James Bailey

more tire is more tire better lateral traction...the only reason the rears end up wider is the front will not take much wider rubber...ideally they too would be wide And the wider rear tires give better traction as you accelerate out of the corners. But for normal everyday putting around town it makes little difference. Like so what if the car goes 150 MPH if you never exceed 70 MPH.

rnixon

Isn't that what Porsche specified? The GTS is 225 on the front and 255 on the rear. (S4 is 225, 245 IIRC)

I do agree that you have to be careful when putting different sizes on though - the suspension geometry is designed for the standard tyres.

James Bailey

all the early cars used 7 inch rims front and back.....then 83-84 added rear wheel spacers as option to "fill out" the wheel wells. 85-86 all got rear spacers. then 1987 S-4 got the 8 inch rear wheels 245x45x16 tires which eliminated the spacers until CS, GT, and GTS again used them

123quattro

Why wouldn't you?

RKD in OKC

Tires the same diameter and pressure have the same contact patch area. Narrower tires have a longer contact patch front to back which provide better acceleration and braking. Wider tires have a wider side to side contact patch which provides higher cornering G's but at the cost of acceleration. Most of the weight is transferred to the front under braking so narrow tires in the front provide better braking. When accelerating out of a corner the rears will break loose laterally before spinning so wider rear tires help accelerate out of turns. Also wider rear tires and a wider rear track help to steer or turn the front tires laterally when the Weissach rear end turns increasing the front tires effective lateral grip.

Did NOT sleep in a Holiday In Express, have only done enough reading and have enough experience with suspension setup to sound good making things up.

James Bailey

Ah yes contact patch , good to hear that term again. Was the cause of many a discussion in years past.

RKD in OKC

It's just that some thing wider rear tires provide better acceleration grip, and it is just not true. The reason drag racer separate themselves by small tires and tall tires. Larger diameter makes a longer contact patch for better acceleration grip.

mark kibort

wider tires in front works, as it helps with the natural understeer of the 928 platform. (as with most undertired cars from the factory) the 911 seems to work best with small front tires (cup cars have had 245s /305s) , due to the engine in the back.

From racing all combos...... the "4 square" concept works at the cost of higher front ride hight and a heavier steering feel. (as well as steering limits and fit concerns)

there is really no real significant acceleration lost.... if you are talking about more weight up front. On a dyno, it wouldnt even appear as a rounding errror (if you could spin up the different front sized tires) the reason being, is that the relative acceleration in say 2nd 3rd gear, is pretty slow , and that longer time to accelerate, means that extra weight is less of a factor than you might think...... in other words, adding 5-10lbs of tire and wheel weight , might only be like having 2x that if it was sitting in the car as an effect on acceleration. the gains on braking and cornering is significant with a larger tire.
mk

rnixon

Could you explain why? I don't see how the orientation of the contact patch changes the force it can exert.

Narrow tyres are going to need a higher pressure to keep the load deformation reasonable, so comparing at the same pressure doesn't seem useful. Am I misisng something?