How much rubber is too much?

[911teo]

Hi all
I am about to order some Lindsay Racing Fuchs. I need to decide wether to go 9 and 11 (with 255/265 front and 315 rear) or 10 and 12 (275 and 335).

Fitting the wheels will not be a problem as we are going to weld steel flares to my fenders so we can play a little...

My biggest concer is actually overdoing it and making the car feel less nimble and heavy, especially at the front.

I have seen some beautiful 930s with 275 and 315 combos and I know some of the RSR replicas are running different combinations of those measures...

Any thoughts? Also how about tires avaliability? I checked Tirerack and they are all there... Will it be the case in the future?
Thanks

[doozer]

911teo - I am running these on the street / limited track with no problems.

Front: 11 x 18 K58's on 275/35/18 Pilot Sports
Rear : 13 x 18 K58's on 335/30/18 Pilot Sports


Tires are a Dodge Viper OEM size and thus are much cheaper than the exact same tire of the exact same size without the ViperOEM stamp... Go Figure...


http://hypertec.ws/todd_porsche/photos/wheels/wheels.html





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[911teo]

the Fuchs will be 17s.... This limits the tire choice a little

[IROC]

I think to answer your question in a somewhat subjective manner - it depends. I have 245s/275s on my 2400lb '76 and at parking lot speeds and even sometimes "around town", I feel like my car is "over-tired".

Going thru turn 12 at Road Atlanta at full tilt, they feel just about right.

Mike

[Jack Olsen]

Will Lindsey make 2-piece 12-inch wheels, or are you going with 3-piece? As I understood it, 11 was as wide as they'd do for 2-piece wheels.

I think you'll be happy with either 255/315 or 275/335, with a Vram 3.6.

[911teo]

Nope would have to go 3 piece for the 12 inches... Maybe I just stick to 255/315...

[RarlyL8]

The 17 inch 335s are a bit tall. They look awkward to me.
Width must conform to the application. A nimble street car needs more narrow tires than a high HP track car.

[doozer]

Originally posted by RarlyL8
The 17 inch 335s are a bit tall. They look awkward to me.
Width must conform to the application. A nimble street car needs more narrow tires than a high HP track car.

My 335's are 26.22" on 18x13 rims and the 275's are 25.85" on 11x18 rims

[Bill Verburg]

Biggest down side to really big rubber is that it will take longer to get heat into them, this can be a good thing or bad. depends.

[Bill Verburg]

Oh bigger is also heavier, weight for a reason is acceptable otherwise not.

[kaisen]

The 275-40-17 is a VERY common size (Camaro SS/Firebird WS6/Mustang Cobra/C4 Corvette) and will undoubtedly be available for a LONG time.

The 315/35-17 was the stock Corvette ZR1 tire, and is also popular for the GM crowd as F-body updates.

Those tires are 'comfortable' with 9.5" fr and 11" rr wheels and they are exactly the same diameter (25.7") front and rear. Being taller than the stock 911 Turbo's 24.7-25.0". Standard 911 Carrera G50 gearing for 1988 puts you at 6500 rpm at 160mph in 5th.... a little taller tire might not be a bad thing for the track if you have the motor to reach those speeds at the end of the straights.

There are several choices for brand and compound, and even price.

In 18's 265/35-18 and 315/30-18 (Porsche oe sizes BTW) understeers a little more but give a little steering effort/feel back and they're a little shorter in front (25.1" fr/25.5" rr) and closer to stock 88 Carrera diameter.

E

[kaisen]

Oh, almost forgot....

245/45-17 is also 25.7", exactly the same as the 275/40 and 315/35.

265/40 = 25.4"
255/45 = 26.0"
245/40 = 24.7"

I'd do the 275 because it is a much more common size (more choice, lower pricing, be around longer).

E

[Grady Clay]

It isn’t the amount of rubber; it’s the amount of grip.

Grip is a combination of tire, suspension, and driving technique. Of course all sorts of other factors come into play. Weight, ratio of un-sprung weight, and height of center of gravity all play a huge factor. There is much more.

Tires are the most important, certainly the least expensive for the maximum performance gain. Generally speaking, the bigger the better. However, they must sit on the pavement when called upon. You can have huge tires and just wear the insides, centers, or outsides off (depending on suspension settings) with loss of grip. Tire size is just part of the equation.

If you bolt huge tires on stock suspension, guess what, they work less well than the original stock set-up that Porsche delivered on the new car.

In our 911 realm, we are limited to changing the spring rate (larger torsion bars), changing the shock rate (HD, Sport, or custom valveing in the shocks), adjusting the rate for the sway bars, and lowering the center of gravity (lowering the car.) Of course there are lots of tricks to accomplish this. 911 racers use all sorts of other means, including repositioning the suspension mounts and custom suspension components.

Use and driving technique effects the way a 911 is set up. The same 911 would be set dramatically different for an auto-X compared to the Rolex 24 hour. Some drivers are perfectly comfortable with a 911 that is loose, others want some push. Everyone wants consistency and predictability.

Above all, everyone wants GRIP.

Best,
Grady

[450knotOffice]

Thank you for that informative lesson Grady.

-Scott

[bigrubberjeep]

Just curious, since 911's have so much understear, why doesnt anyone go, say.....9's and 9's all the way around? Is it because it would look funny?

[Jack Olsen]

911's have low-speed understeer built in as part of the attempt to counteract oversteer at higher speeds. It's a balancing act.

[Bill Verburg]

Just curious, since 911's have so much understear, why doesnt anyone go, say.....9's and 9's all the way around? Is it because it would look funny?

Like Jack said SLOW SPEED at speed tis seemlessly changes to oversteer

[911teo]

Thank you everybody. I think I will go 9.5 and 11 with 275/40 and 315/35. Thanks again.

[rattlsnak]

Im running 245/315sx17s.. 275 in front seems a bit much.

[banjomike]

Originally posted by bigrubberjeep
Just curious, since 911's have so much understear, why doesnt anyone go, say.....9's and 9's all the way around? Is it because it would look funny?

UNDERSTEER?!?!
same size wheels/tires all the way around...