Any issues running 7x16 all around?

[Swoboda]

Are there any issues with using 7's on all four corners?

My car is a 1985, and I currently have 6'a on the front and 7'a on the rear.

Thanks.

Lawrence

[IROC]

Technically, no. From an maximum performance standpoint, you're giving up a little if you plan on running the same tires on all four. Personally, I would probably use a spacer in the rear for aesthetics, but you can do it.

I ran 7x15s on all four corners on my '76 for a while.

[diverdan]

Oversteer! Until you have had the backend snap out on you, you don't understand. If you have experienced this phenonomon and are comfortable with it then enjoy. Its happened to me ...... I planted my right foot, compensated very quickly on the steering wheel and prayed. Luckily I never lost it long enough to go too far off the paved road. Great to have that experience under my belt. Modern tire technology with the extra grip in the back changed forever the way your 911 handles. The wider rear wheel is a big part of that formula. Lots of weight way in the back was extremely bad geometry. Just don't try to hang with a Corvette on a mountain road. (Don't ask me how I know. It was real scary.)

Dan

[naparsei]

For street cars in general I agree you'd like to have a little more rubber in the rear. However, 911s driven hard tend to understeer more than oversteer (except for the obvious), so I like having equal tire sizes all around.

[ben parrish]

Nope..no problem at all. I run 1" spacers in the rear and normal 205 front 225 rear. It does handle slightly differnt than before but I went back to Fuchs after running 17" Cups for 10 years.

[IROC]

Originally Posted by diverdan

Oversteer! Until you have had the backend snap out on you, you don't understand.

I ran 225/50s front and rear at DEs/time trials and never had a problem with oversteer. I've seen club racers running 245s all around. Is the ultimate traction set-up? Probably not, but there's really nothing wrong with the same size front and rear.

For the kind of oversteer you mention, I don't think wider tires in the rear would have made a difference. I've got 275s in the rear now (with 245s in the front) and if I make a mistake, the rear end will come around. BTDT got the flat spots.

[stlrj]

Originally Posted by IROC

... but there's really nothing wrong with the same size front and rear.

That's the way they came from the factory for almost all 911s until '77, so it must be OK.

[diverdan]

If there is nothing wrong with that, why did Porsche change? And why do the still do it? Why don't they go back to it? Why is it even more so on competition cars?

Dan

[IROC]

Originally Posted by diverdan

If there is nothing wrong with that, why did Porsche change? And why do the still do it? Why don't they go back to it? Why is it even more so on competition cars?

Dan

I think that as the engines got bigger and more powerful (and tire technology evolved) it made sense from a performance standpoint to widen the rear tires relative to the fronts. There's a difference between "nothing wrong" and "better". Is there anything wrong with driving a Porsche on the track with street tires? Not really. Are r-compound track tires better? Sure.

If the original question was "what is the optimal tire width stagger front and rear", the answer would be different than what was actually asked - namely: "are there any issues with running the same size front and rear"...

[sc_rufctr]

Don't mean to hijack but WOW that's a great looking car.

Originally Posted by ben parrish

Nope..no problem at all. I run 1" spacers in the rear and normal 205 front 225 rear. It does handle slightly differnt than before but I went back to Fuchs after running 17" Cups for 10 years.

[Grady Clay]

Lawrence (Swoboda),

Mike (IROC) and Dan (driverdan) are giving you good advice.

For ‘normal’ street driving there is “nothing wrong” with equal tires.
However, the lack of balanced tire size can become an issue if you get to a limit-of-traction situation while ‘normally’ driving.
This can be something as critically simple as avoiding a child chasing a ball into the street.
Proper balance may prevent you losing control in some critical situation.

I’ll strongly disagree with this statement for our pre-1989 911s:

Originally Posted by naparsei

For street cars in general I agree you'd like to have a little more rubber in the rear. However, 911s driven hard tend to understeer more than oversteer (except for the obvious), so I like having equal tire sizes all around.

Porsche has gone to a great deal of effort to have the 911 not have any oversteer.
Larger rear tires are part of that effort.

‘Recovering’ from understeer is easy and usually a safe outcome returning to ‘neutral’ conditions.
In an oversteer situation, it takes great skill and experience to regain control.

Porsche has gone to great lengths to ‘engineer out’ the inherent rear-weight-bias oversteer with the 993, 996, 997 and later cars.
With our ‘early’ technology, we have more limited means to minimize oversteer.

So…
Given the choice (fender clearance, etc.), the more rear tire relatively to the front the better – to a point.

The difficult balance is to not reduce the front tire grip as its primary functions are turning and braking grip.
Engineering a car (like our 911s) is an exercise in ‘balancing’ competing (often conflicting) aspects.
Porsche has gone to a lot of engineering effort (and expense) to try and find that ‘balance’ with the historic 911.
Wider rear tires are one.
Look to the later suspension design for the extended effort.


You haven’t lived until you have had your 911 backwards at speed and both survived.
Too many don’t.

Best,
Grady
(Author of the “Grady Clay School of Sideways Driving.”)

[diverdan]

Well said Gardy. Several times a week while in the UAE I did a 10km run that many call the best road in the world for sports cars. Its Jebel Hafeet near Al Ain. Would have been a world class mountain climb. The 265mm wide rear meats on the 3.2 allowed me to do some very spirited driving with a very secure feeling that I wouldn't experience the crush of the wall one side nor the fear of flying over the "nothing" on the other. My swimming workout greeted me near the top so there was more to it than just a drive. Often I took the Ducati which put the Gs straight through the axis of my body instead of laterally. I think that the bike did more to improve my skills than the car but it was close. Occasionally, I drove the Alfa RZ which was even more incredible in the curves. (1.2 - 1.4 Gs on stock rubber.)

Dan

[diverdan]

I'd also like to add that in the 911 its not just oversteer, but often a sudden violent break away. I wish I could call it skill that saved me, but I have to admit that the lightning like reactions were helped with good luck or something out of this world.

Dan

[Swoboda]

Thank you all for the great advice and comments!

Lawrence