rusnak

13mm is what, a quarter inch? On 7" wheels? You're worried about "over tire"ing the car?

And you say you want to push oversteer while not making it on-off?

Trust, me your 3.2 911 will never be "on off" or have snap inertia oversteer. With the engine hanging out the back, that will never be a problem, and with those skinny little wheels, it won't matter if they are a half inch total spacing further apart.

Please re-read my first post where I tell you to put some 9" wheels on there. Actually forget that advice, just go take a two day long driving course. You'll have a fun time, and learn a ton about how to get the most out of the car.

Ed Hughes

13mm is just over 1/2 inch. 7mm is closer to a 1/4".

Yoram

Thank you, Iceman! I will very soon...

Dear Ed,

I am a PCA member and have been for many years. I have dozens of DE events in my past (not only with PCA) as well as years of chassis development driving and vehicle dynamics analysis... I am well aware of trailing throttle oversteer in the 911 as well as in the 944TS and many other cars, especially older designs like semi-trailing arms, full trailing arms and twist beams lacking proper compliance steer characteristics...

I am also very well aware that you will not fix a throttle-off oversteer with widening the rear track... however you will raise the cornering limit (especially in a car whose limit is oversteer) due to a reduction in vertical load transfer between the rear tires.

Please let us give each other some credit and not talk down to each other....

Thanks and cheers,

Yoram

Yoram

P.S....

Rusnak, I missed your post (did not page to P.2)

Clarifying: I want to increase the cornering limit without increasing tire size... the apparently feasible track increase with spacers (or wheels with less offset) is ~2", or nearly 4%. This is not huge, but not negligible either.

I may work my way to increase tire size down the road if I convince myself that the car can benefit from it on public roads. For sure I will track the car in the Fall to "calibrate" myself, however I am looking for different things in track vs. road use (just for example, steering on-center friction and feel are critical for highway use, but completely insignificant on the track) and will ultimately use different wheels for either.
To quote loosely a German chassis development leader: "Anyone pulling 0.8G on a public road is about to crash..."

Cheers.

Yoram

race911

Wow, this has gone off the rails. I used to put bolt on spacers on the rear of plenty of customer cars. And that was when we could pick up 8" wheels for $250/ea!

I find it pretty laughable that there's been mention made of running a 245 tire on a 7" wheel. Will it physically fit? Yeah. Does it work better than a 225? Doubtful. (I won't say "no" because I've never done any back-to-back testing.)

As far as "handling" or "cornering"? I can't imagine it making the least bit of difference outside of instrumented analysis. This car is said to be stock. ~25 year old suspension bushings, torsion bars that are suffering from their form of ED, shocks past their prime, tire pressure, etc. will all make more of a difference to ultimate handling characteristics/roadholding than widening the track 1/2 inch. (I can't say I've ever run faster on a similar engine/weight widebody v. an RS/SC/Carrera body running similar tires, and I've competed with enough of pretty much everything you can cobble together.) Not to mention if the tire had 8/32 v. 4/32 of tread, or if it is one year old v. 5 years old.

Ed Hughes

Talking down to you? You come on here with like no posts stating you want to improve your handling by increasing the rear track. That isn't going to happen. One can only assume you have no experience with a 911 and are either timid about having the end come around, or have already been scared by it. How in the heck do I know what you've done and what clubs to you belong to? If Porsche could have taken this chassis and made it handle better with a wider track, I'm pretty sure they would have made that discovery.

Lastly, please speak in clearer terms. Your phrases in parenthesis aren't totally clear or commonly used.

Ken has also stated the truth that you should spend some time and attention on your suspension. Then go to wider wheels and tires if you want more grip.

You haven't even taken the time to even put your location or any other info in your signature.

whalebird

I think what your after Yoram will have a detrimental effect. Stock wheels/tires with the correct offset(no spacers etc) can be made to far exceed any positive effect by track-widening. Modestly improved/renewed suspension components with a good alignment and corner balance will yeild a highly capable chassis both on the track and street.

rusnak

Yoram, I think I get it now...you're a masochist!! Just kidding. All I can tell you from my own experience is that the rear will let you know that it's going to slide, unless you transfer weight off the rear suddenly toward the front. Then you'll have snap oversteer (throttle lift or suddenly jumping on the brakes in a turn), which is not fatal so long as you don't over-correct. Give it the right learned amount of steering correction and wait for it to come back to you, and you'll save it. It helps if you've done some dirt track racing in a previous life.....

As far as your question, I guess you found your answer. For some people, oversteer is terrifying. For others, its a way to set up for the straight. Why you would intentionally settle for a lower limit of adhesion or maximum grip is a question only you can answer. Why you want to stick to 225s instead of 245s is also beyond me. My own opinion (just mine) is that the tires seem to grip better if the sidewalls are straight up and down. What that means is that 205s work well on 7s, and 245s work well on 8s. Your existing 225s at the rear might work better on 8s. It's been awhile since I ran 225s at the rear, but I THINK they were rolled inward on 7" wheels. I like 9s because they push the 245s outward at the bead.

rfloz

FWIW, we ran 275 tires on an 8" wide rims while auto-crossing a Mustang Cobra. The rules allowed any tire, but stock wheel width. It was a bit quicker back to back on the 275s (245s stock). Silly for the street, though. Not to mention it looks dumb.

Well, Porsche did make the Turbo/Turbo-Look/RSR cars with considerably wider track and the RSR, at least, agruably handles better than a standard 911.

That said, I've had 14mm spacers on my 911 and felt to discernable difference when auto-crossing. For the street, this is a "looks" only proposition.

Viz-a-vis the dread oversteer, I've had to work a lot harder to cure the inherent understeer in slow speed corners with my 911, than dealing with oversteer. You have to be pretty ham-fisted, er, -footed, to encounter uncontrollable oversteeer, at least in a Carrera.

Ed Hughes

Indeed they did. Good thing the pit crew screwed up and put the wide wheels/tires on too!

whalebird

yea^^^the wider fenders was to fit enough tire for the car. The track didn't really increase. Turbos have an entirely different suspension. I have replace dozens of wheel bearings on the turbo-look cars with spacers.

Ed Hughes

That's another point about spacers. Artificially filling the fenders with spacers puts more wear on the wheel bearings.

racer

iirc, Porsche by either '88 or '89, likely in response to still lawyerly concerns, offered Fuchs in 6" front with 8" rear on the 911. 205 front/245 rear. This would certainly help quell the oversteering tendencies and make it understeer much easier. Since you seem set on your 6/7 rim combo, perhaps try a narrower front (195/60-65 ??) and a 225 rear (although I can't really imagine anyone making a matching set of tires in those sizes these days.)

whalebird

Ed, I could go on for paragraphs explaining why this is a bad idea. There would be a thread-division over the merits and failings of the myriad of different wheels blah blah blah. Changing track on one axle is foolish. Both axles is twice as foolish. Wheel offset, scrub radius, and roll center should not be tampered with. This is one of those things where it's all been done. The book was written on this decades ago and there is a good solution. A 911 is really a pleasant and easily tuned chassis.

rusnak

This is a pretty good point. I think of driving the 911, which responds wonderfully to throttle and wheel input, to balancing the car on the head of a pin. It's about balancing weight and maximizing traction.

I think the OP is probably after the experience of chasing the balance and feeling that head of a pin experience more than ultimate speed. Personally I think more grip is inherently safer, but there is a lot of room for debate here still.