GP964

Hi Everyone,

Time for new tires for my 964 C2, just wondering what is the largest size tire I can put on the rears. I currently have 255/40/17 on a 17x10 ruf rim with .5 inch spacers.
Reason I'm looking for a wider tires is that the lip of the rim sticks out farther than the sidewall of the tire.
I'm thinking either a 265/40/17 or 275/40/17.
One concern though is the oil line on the right rear fender well.

Has anyone used anything larger than the 255/40/17.

Btw the car is lowered and setup for street agressive.

Thanks in advance

GP

joey bagadonuts

I think folks are reluctant to chime in because not a lot of people go higher than 255. Now, I KNOW there are people who've experimented with 275's but they went to great lengths to ensure there was no interior rubbing and that the offsets were just right, approx. 48mm. That being said, I'm not sure anyone here can assure you that you will not have some fitment issue since none of these cars are exactly alike.

At the very least, you might want to provide offset information so that someone can provide a recommendation. Good luck!

buckdr1

GP, I'm running new pilot sport cups in 265/18's in the rear. No problem there, but the 225's in the front required the "shovel handle" roll in the front!(both sides). FYI my C2 is mainly a track car that I'd like to take to work etc every now & then. If it would only Stop SNooowing!
Bill

Jim Michaels

What width would you put on the front? If you have 225s on the front and anything wider than 255s in the rear, you will very likey have more understeer than you now have (which is probably already plenty enough). I ran 275s in the rear with 235s in front, and that worked well. You should be careful trying to fit those sizes, however.

J richard

GP964,

I'm running both 993 and C2 turbo wheels, (55mm offset) 235/40-17 front, 275/40-17 rear, with a 10 mm spacer on the rear, My car is lowered, has rolled rear fender lips and H&R springs, It dosen't rub even on the track, but I would be a bit nervous if I was running softer spring rates. It might not be a problem if you don't lower it too much. A common problem is the right rear rubbing on the inside Oil line and the trailing arm. The spacer will solve this problem. Also some tires have the wider sidwall such as S02's, for some reason they seem to have less of a shoulder and fit easier.

The tires fill the whole well, in fact you'd swear on a bump the fender would ride down on the tread at the top rear, but no problem. DO check the top inside of the wheel arch about 2" up from the edge of the fender, If you have ANY evidence of rubbing, I would thin up the spacer or raise the car. You can blister the paint easy. (found out about this one back on my first car, it really sucked...)

Hope this helps.

oldtimer

Hi, just a comment on what you want the result to look like, and possible effects. I've got a German spec 964RS with 17x9 inch original rear wheels and 255x40 ZR17 tyres - Bridgestone S02 pole positions. These tyres have a fat lip that stands well proud of the rim, and all looks fine. I've also got a 996C2 with 18x10 inch turbo look wheels and 265x35 ZR18 tyres - Continental Contisport 2's. The wheel rim stands well proud of these tyres, they do not have the fat lip of the Bridgestones, and yeah they dont look so good. Which is your point. So my guess is that if you go to 265x40 on a 10 inch wheel it will look better than 255 but still not quite right. You'd need the 275 for the 'look'.

OK now for the twist in the tail. I go to track with both cars, the 964RS was made just for that reason by Porsche, hardly any suspension give, very direct steering, no power assist, comes lowered 'out of the box'. Raw and scary. The 996 by comparison is soft, but those 18 inch wheels work very well, the car turns in fast and the 265 rear on the 10 inch wheel ( and 225x40 on 8 inch fronts) gives good handling balance between understeer and oversteer...yup it can oversteer!
So I've left the 'narrow' tyres on !
I remember reading somewhere that the wheel width and the tyre width should be about same, not a benefit to 'overtyre' the wheel.....HTH

joey bagadonuts

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by oldtimer:
<strong>I remember reading somewhere that the wheel width and the tyre width should be about same, not a benefit to 'overtyre' the wheel.....HTH</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Jeez Oldtimer, you write like an American expat. Am I warm?

As for your comment above, in the Puhn book, How to Make Your Car Handle, he points out that an overly wide tire will result in reduced sidewall stiffness. In fact he suggests selecting tread widths which are a little narrower than the wheels would be optimal. Here's what the 996 GT1 setup looks like (photo courtesy of <a href="http://www.flat-6.net/index.php" target="_blank">Flat 6</a>).
<img src="http://boards.rennlist.com/upload/996gt1reduced.jpg" alt=" - " />

Of course you don't get the look with narrow tires and the point of Puhn's book is to help enthusiasts realize optimal performance, so I believe it comes down to your intended use.

oldtimer

Joey, I am not an American expat but thanks for the compliment ! Have done most of my business with US companies so I guess something rubbed off, but I am a Brit - your chums in arms.
Going back to the wheel/tyre thing ( 'tire' ) , for serious cornering you stick the biggest wheel with the lowest profile tyre that fits in the hole, the ride is awful but the car goes more precisely where you point it. The 964RS Cup cars had 18 inch wheels I'm told, but I'm not a hot driver , so the standard RS 17 inchers are fine. BTW enjoy reading your contributions to the art of 'Porschering'.. <img border="0" title="" alt="[Wink]" src="wink.gif" />

joey bagadonuts

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by oldtimer:
<strong>enjoy reading your contributions to the art of 'Porschering'.. <img border="0" title="" alt="[Wink]" src="wink.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Same here!
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Jeff Curtis

GP964, I'm going to go back to a point I started making quite awhile back...check what tire you would like to use and compare it to other manufacturers models and their widths as well.

You may find quite the difference when comparing the width of say a Bridgestone Potenza RE-730 to another popular tire. You may find out that tire "B", when compared to the skinniest tires on Tire Rack (the RE-730) will be considerably wider, forget a good example at the moment. <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />

A Bridgestone RE-730 in the 275/40 - 17" size is considerably "thinner" than most of it's competitors widths.

SO, you can fit a 275, just go on TireRack.com and compare widths between some of your favorite choices.

For the interested party who wants to run 275 series tires on the rear of their 964, the difference between the Kumho ECSTA and the Hoosier R3so3 (did I get that one right??) is phenomenal!! There is about a 12mm difference with the Kumho being the "skinnier" one.

I didn't have much issue with running the Kumho tires, once I put 6mm spacers on the rear...but with the Hoosiers and 12mm of spacing, I still had rubbing on the inner fenderwell.

Even with -2.5 deg. camber!! <img border="0" alt="[grrrrrrr]" title="" src="graemlins/cussing.gif" />

You can also use 245s up front, but again, that will present it's issues with a lowered 964 and -2deg. camber.

MY opinion, and what I use on MY 964 is 255s in the rear, 215s in front. The 215 tire size is about4mm "shorter" than a 205 or 225 should wind up being...but think about it...it's only a 2mm difference in height for the front end!!

SO, I use the conservative 255s in the rear and a little wider tire up front, the 215, in an attempt to eliminate some understeer when attending autocrosses with my street tires.

The wheel rubbing risks aren't worth it, I have gone to using 245 and 225 Hoosiers on the track, 17" wheel with wonderful results...the 255 series Hoosier is a bit too tall for the profile and the car would "lug" coming out of sharp turns and being in a higher gear.

I intend to change over to the Michelin Pilot Sport Cups after I wear my inventory of Hoosiers out, then I will use the 225/255 sizes as my friends that have done so are reporting GREAT results with that combo!

I don't agree that a 10mm difference (225 to 235 series) in tire width up front will induce too much oversteer, if anything, these cars could use anything that will take them out of the world of UNDERsteer. <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />

Mr. C4

Listers,

Any idea what can be done to modify the bracket in the front wheelwells, where the front bumper mounts to the front wings. There seems to be a very sharp object that just slightly cuts in to the very edge of the tire.

Ciao,

Johannes E.

buckdr1

Mr C4, W/ 225/18 Pilot sport cups(as mentioned) I rolled the innner ff's w/ a shovel handle(no paint problems) & also had to use a 1/2 round file to smooth out one side of which U speak.
Bill