Hardback

Hey guys, Im getting to the point where I am out driving my street tires at the track. Im planning to purchase a set of OZ Alleggerita 18" wheels. The wheels for C4S that are on tire rack have different widths than OEM for the rears I believe. (stock 11" I think?) They offer 10" and 12". I assume if I go with the 12" rears I should match them with 8.5" front wheels. Currently with the stock wheel package my car has predictable understeer, which is fine for now.

Does anyone use these wheels on their 4S? Any tire recommendations would be appreciated as well...

Cheers,
Carey

redridge

you should change to R compounds.

himself

What do you mean by out driving your tires? What are your goals and skill level? Hoe often do you get to the track? And do you trailer or drive?

-td.

Sneaky Pete

Why not get another set of OEM wheels (used) and put some track tires on them. The wheels don't need to look pretty.

Hardback

I run in intermediate group presently. I'm driving an event each month.. Street tires and screetching and loosing grip by end of day. I'd like to mount michelin pilot sport cups but can drive with them daily in south florida with wet roads... I would like to have a seperate wheel package for the track.

Hardback

Sorry, edit: Cannot use mpsc as my only tires...

Ray S

You might also ask the 996TT guys what they typically run. I think there are quite a few guys on the Turbo board that track their cars.

V225

I have Alleggerita 18's on my 4S. I'm running 8.5 up front and 10 rear, with 295 rears and 235 fronts, street tires. Upgrading wheels is a good idea, especially since the stock wheels are horrendously heavy(26 lbs front and 30 rear).

But just fyi, changing the wheels isn't going to do anything for understeer. It sounds like you might want to change the suspension if you're fighting understeer. I've found that removing the mufflers and doing other weight reduction really helps to get the rear end playful.

I run in the advanced groups on most tracks I run at, having done about 30 track days in this car, and I'm still on street tires.

Hardback

V225, thx for responding.. So far the understeer I'm able to work with. The low speed corners I'm losing too much grip but in high speed corners the car drives great. More specifically what I want to feel is confidence. I've looked into x74 suspension, which I will most likey purchase along wih RS motor mounts but this post is really to learn about tire widths for OZ wheels. Your running 235s up front and 295 on 10" rear and still feel understeer? Interesting... I realize these cars are heavy and awd but there has to be a sweet spot in the way of suspension and tire package that will deliver a neutral handling 4S! You agree?

V225

I should clarify. I did the weight reduction before putting the wheels on, and the weight reduction by itself got rid of the understeer completely. The wheels made the car feel more alive in corners and acceleration, and helped shave a few tenths off my lap times.

I was worried about their strength initially, but they've held up well on track as well as on street. I think you'll like them.

himself

Street tires screech, that's just what they do. And that is where you want to be. In fact, if they aren't screeching all the way through a corner, you're leaving time on the table.

There are plenty of medium to high-grip street tires out there that you should use. And, if you are in the intermediate group, I strongly suggest NOT going to MPS-cups (or other R-comp) for a number of reasons. But the most important is: your car is a system, when you switch to R-comps, you should really upgrade the entire system. That is, at a minimum, you need to upgrade your brake pads and brake fluid at a minimum. You should also consider new alignment, lower control arms, sway bars, and possibly upgraded suspension parts. AND, be sure to address oiling issues that come with higher Gs [perhaps X51 baffles, deep sump with extended oil pickup, etc]. For example, if you put on MPS-cups and they are up to temp, if you have stock pads and fluid, you might chew through your pads in under a day and likely boil your fluid every session. A second reason is that many/most drivers that switch to R-comps too early never learn to drive on slip, and remain slow drivers. Their lap times may go down because the car is faster, but the driver never gets better. Driving on slip really needs to be learned on street tires, IMO.

Also, your driving style may dictate what type of tires you need to use. If you like slip angle, you probably should stay with street tires a bit longer. FWIW, most AWD Porsche drivers I've coached like way too much slip angle because the AWD can take it. But it's definitely not the fastest way around a track.

Where are you experiencing understeer? Turn-in? Mid-corner? or Exit? Your description sounds like corner entry. If so, a likely culprit is driving style rather than car setup. If you have any video, we can do a quick analysis. I would bet that it's braking technique and release that is causing entry understeer.

If you don't have adjustable suspension and sway bars, there's really not much you can do to address the built in understeer via setup (wheels or tires). You can change alignment and tire pressures, but you're pretty much stuck with it. If you could trail brake, it really wouldn't matter, since you would be rotating the car with your feet and not the steering wheel anyway.

-td

Hardback

Himself, thanks for your detailed response. Im completely aware that upgrading one system of the car will in turn uncover other issues such as brakes body roll etc etc. If I wasn't on a limited budget I would change a number of suspension parts, sways, control arms, oil pan etc. As far as grip and understeer are concerned my issue comes as I roll on the gas exiting low speed corners. The car pushes the front end. I keep track of tires pressures and have found that my current tires, kumho ecsta, drive really well at 30/34 fr/ rear hot. Varun is saying to put the car on a diet, which won't cost me anything. Good advice for any street car of course. He seems to understand my original question.
So, at what point would you advise your student to run stickier rubber along with suspension and brake mods? I feel I could be quicker and safer if I trusted my tires more.

V225

Actually those modifications will be less trustworthy than your street setup. R Compounds have much more drastic breakaway characteristics than street tires. Also their limits are far higher, so you'll be carrying much more speed when they do break away, and unlike street tires they don't give you much audible warning when they approach their limit.

A track suspension will have a much faster return rate, which means that when you induce oversteer, your counter-steer input will need to be extremely fast in order to catch the slide.

As for the weight reduction, I have my car at 3110 pounds with a full tank of fuel and a 45 pound roll bar, so about 3065 without a bar... which is about the same as a '7 gt3 I believe. It's helped a lot with pretty much everything, and as you mention I didn't pay much(except for the seats), but my car is far from a street car for most people. Here's a list of what I've done:

Racing Seats, muffler bypass, complete interior strip, lightweight wheels, spare tire removal

It is extremely loud without any insulation and with the muffler bypass, but if you don't mind the sound, there's significant performance to be had. Have fun ripping things out of your P-car!

Edit: Here's the graph from Skip Barber's going Faster! that shows racing tire limit behavior. What you want to look for is the range of optimal grip of a street vs a racing tire. The racing slick peaks between 3 to 6 degrees of slip angle, but if you let the car go any more than that (ie if you start to lose control), you lose significant traction, making the problem worse. The street tire is much more rounded, and has consistent behavior until about 10 degrees of slip angle, giving you a lot more leeway to correct your mistakes.

Hardback

Cmon Varun... Any pics of that beast? Not sure I'm ready to strip my daily driver but I'm intrigued by your enthusiasm.

V225

Well it's a Sunday morning and I have nothing better to do, so here you go

If you're interested, here's a running log of my modification travails:
http://picasaweb.google.com/PlorgThe...eat=directlink