PCA SDR

My wife's car has 17" rims with 205/35/17 tires. I measured them the other day and they are within a 1/2" in overall size as the tires on my 1971 911. Those are 205/50/15's. Is ther an advantage to running bigger rims if the overall size of the tire remains basically the same? Would it affect unsprung weight( the extra rim weight canceled by less tire)? Just curious.

I am sorry the tire size is 205/40/17.

Gary Burch wrote:Is ther an advantage to running bigger rims if the overall size of the tire remains basically the same? Would it affect unsprung weight( the extra rim weight canceled by less tire)?

You would have to weigh the two different tire-and-wheel packages to know if the unsprung weight would be affected, Gary. The larger rim weight may be offset by less tire weight, but until you measure, you won't know. Many of the cast 17" rims are fairly heavy, compared to a forged 15" Fuchs wheel, though, so I would be surprised if they were lighter. There can be a big weight difference in tires between different manufacturers, too. There is also a difference in rotational inertia to be considered (more weight distributed towards the outside diameter of the wheel requires more energy to spin up.) If the diameter is the same, your gearing won't be affected, though, and if the weight difference is only a couple of pounds, you might be hard pressed to notice it.

There are advantages in the performance characteristics of the 17" wheels also, as the lower profile tires used generally have better sidewall support, helping with that crisp turn-in feel. They can also be more harsh over bumps, though. Another big advantage is the availability of different tires in the larger diameter. Aesthetically, I don't like the look on an early street 911, myself. Unless it is a race car, with big wide wheels, the low-profile "ricer" look isn't happening for me on a classic 911.

YMMV,
TT

Gary Burch wrote:My wife's car has 17" rims with 205/35/17 tires. I measured them the other day and they are within a 1/2" in overall size as the tires on my 1971 911. Those are 205/50/15's. Is ther an advantage to running bigger rims if the overall size of the tire remains basically the same? Would it affect unsprung weight( the extra rim weight canceled by less tire)? Just curious.

Gary,

I experimented with tire size this year with just your reasoning in mind. Last year, I competed quite successfully with 17" wheels and wider tires. There was a bit of roll-out difference with the 17's, changing the shifting points (reducing shifts at A-X's and using a lot of 2nd gear). The traction from the 225/245 Azenis was really predictable and manageable ... with a little push. The power seemed a bit lacking, but the ability to carry speed through the corners was Awesome .

This year, I tried 15" rims with itsy bitsy dinky little 205/50/15 Azenis. Result: CRAP! I had much better punch and sprint .... more apparent torque and power-to-wheels. However, the car broke loose very early .... I found myself drifting when I used to just hold through a corner with the larger 225/245's. Additionally, my shifting points were shortened and the frequency increased quite a bit. I saw a lot of 3rd gear at a-x's this year while my competition on 16's and/or bigger, taller tires shifted less. Lots of shifting means less time on the throttle .

Now, Carl Scragg will tell you the 15's he drives on his Carrera are the only way to go. That's what he preferes for power, and lowering the car a bit. Seeing as how he drives a 911, like you, and Mr. TT also drives a 911 with 15's, it raises an interesting counter-point to my experience. Of course, if there were 15" Azenis that were 225/50's, or 225/45's I'd think about staying on the 15's for the power issue.

So, 2005 will likely see me on 17's with 225/45's Azenis all around. I won't catch the venerable Mr. Tweed, but I'll give John Kinkaid and Jerry Mize a little something to think about.

That's my story (and I'm sticking with it) for what it's worth.

Dan,

Are you trying to tell us that an experienced ax chair wasn't able to come up with track designs that were compatible with his own shift points? What nonsense! The most fun thing about being ax chair was trying to design tracks that drive the 951's crazy.

And what's this story you're trying to spread about my use of 15 inch wheels? I use them because. . . well, just because. I strongly recommend that all my competitors run on 16 inch wheels because they will help you get through the swales so much better.

Tom,

I don't like the big wheel look myself. Especially on early 911's. I guess the next step is to weigh the 2 different wheels. I was just wondering if there was a real competition advantage.

Dan, too bad it took you a year to figure out the 15/17 thing. I thought you liked the 15's.

Gary Burch wrote: I thought you liked the 15's.

Dan said above: "if there were 15" Azenis that were 225/50's, or 225/45's I'd think about staying on the 15's...." That points out the availability issue that I mentioned. 15" tires are just not being made in wide sizes any more except for racing slicks. Hoosier does make a 225, 245 and 275 in the 15" DOT radial (R3S04), but only the 225/45-15 comes in the autox compound (A3S04), and since they are not streetable and fairly expensive, only the deep-of-pocket can afford to run them. You might as well run slicks.

In the street tire department, you are SOL on 245+ sizes without going to bigger diameter wheels, at least until the long-rumored, second-gen Azenis come out (I'm not holding my breath.)

TT

Carl Scragg wrote:Dan,

Are you trying to tell us that an experienced ax chair wasn't able to come up with track designs that were compatible with his own shift points? What nonsense! The most fun thing about being ax chair was trying to design tracks that drive the 951's crazy.

And what's this story you're trying to spread about my use of 15 inch wheels? I use them because. . . well, just because. I strongly recommend that all my competitors run on 16 inch wheels because they will help you get through the swales so much better.

As to point#1: In all honesty, I never thought of designing a track for my specific car set-up (DANG IT! You forgot to tell me that when I was in training ). I always designed the tracks based on safety (ZZZZ ) and what the loudest complainers wanted. I'm sure I designed quite a few tracks that drove the 951's crazy, but that was the nature of the parking lot. I'm sure a modified oval would have suited the 951's just fine for spool-up .... the rest of us would nod off during our runs .

As to point#2: Ooops! Did I divulge a secret when I shouldn't have ?

The correct tire/wheel package for one driver and/or one car will not be the ticket for another. Dont overlook the fact that the tire is a spring. The stiffness and size of the sidewall (and pressures) dramatically change the effective spring rate of the car; therefore, they must be chosen with an eye to the overall setup.

I knew it would be posted quickly....

Please note Mr. Marguglio's reference to "personal driving coach to Maria Sherapova". I can confirm it. But at the end of their final lap of the day, security guards blocked his exit from the parking lot (with passenger that is).

And he kept using the patented Dente "hand on the knee" technique (I think it was the knee, anyway).

My "student" (Elena Dementieva - just as cute as Sharapova) didn't have a driver's license and didn't know how to drive, so I had to drive all the laps for her (darn the luck). Thus, she seemed very confused as to why I had to use the hand on the knee teaching technique also.

Not to hijack the thread completely, but somebody please do a write up on the day with the tennis players. I guess Dave can tell us about his experience as a boy toy, errrr driving instructor. Note that Ms. Sherpova is 17 years old.

I will let Timmy "the mouth of the west" Comeau handle all my media inquiries.

Pete Millikin wrote:Not to hijack the thread completely, but somebody please do a write up on the day with the tennis players. I guess Dave can tell us about his experience as a boy toy, errrr driving instructor. Note that Ms. Sherpova is 17 years old.

Duly noted.....David is my hero...

Duly noted.....David is my hero... [/quote]

He should only be your hero IF he got past the security guard. You'd think he would be good enough to escape a parkinglot in a turbo Cayenne against an old security guard on foot, but I guess not

PS My tennis pro can beat your tennis pro...nah nah (does the slalom count?)