[Bandini]

I've taken my car to a couple of track days recently, and I loved it. For next season, I thought I'd get r-spec tires and I need some advice.



The car is fine on my S03's, and I'm not chasing tenths. I'd just rather get a set of purpose built tires and some extra grip, than burning up my street tires.



One thing I've noticed about the car is that the gearing is too tall for the kind of tracks we use, as I barely get to use sixth gear. I don't want to touch the gear train, but I was thinking smaller diameter tires just might help a little bit.



I can get Toyo Trampio R888's in 225/45-16, which I believe would work well in the rear. That's the only available size in 16 inch, however. Could I possibly use those on all four corners? A little extra grip up front couldn't hurt, but maybe this would be more than just a little.



Another option would be Bridgestone RE740's. These come in 225/45-16 and 205/50-16. They are more expensive, though, and those sizes would do nothing to counter understeer.



I also thought about 15 inch rims. Would those even fit on our cars?



And finally, I also thought about forgetting about gearing and go for the Michelin Pilot Sport Cup's in stock sizes, or possibly 225/50 front and 245/45 rear.



Grateful for any advice. Remember, this is for track use only.

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[flash]

you can answer the question of size by looking at the track you run, figuring out what speed you think you might be doing at different places on the track, and then calculating, via outside diameter, what rpm that would put you at



we frequently would change the tire size based on the track we were running - autocrosses got the smallest OD we could put on, and the longer tracks got taller tires



as or matching all 4 corners, the desision to go with wider stuff on the rear of this car was really more of a "follow the leader" thing from the 911 marketing team - that car needed it, the public got used to seeing it, so ......- the car certainly doesn't need bigger stuff in the rear that it does in the front



you will defintely get more life from a matched set, since you can rotate them



you will get better handling from the larger tires in lower profiles, as long as you don't go too big on any given rim



it's really about how you want to car to act and where you are driving it (twisty track, big open straights and sweepers, tight autocrosses, yada yada)

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[Lemming]

I'm not sure why you should care if you hit 6th gear or not?

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[BruceWard]

If Kuhmo Victoracers are available in Sweden then you should be able to get them in a 225 front & 245 rear combination. This is what I use for Autocross and really like them.



I do not believe 15" wheels will fit over our calipers.



You could change the ratio slightly by using lower diameter tires. Any significant change would result in more frequent gear changes that I suspect would slow you down.

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[Bandini]

[quote name='flash' date='Sep 13 2005, 10:47 PM']the car certainly doesn't need bigger stuff in the rear that it does in the front



you will defintely get more life from a matched set, since you can rotate them



you will get better handling from the larger tires in lower profiles, as long as you don't go too big on any given rim[right][post="9811"]<{POST_SNAPBACK}>[/post][/right][/quote]

I was thinking about getting new 17" rims and street tires, and using my stock 16" rims for the track tires, but maybe that would create fitting problems? The Toyo's are meant to work on 7"-8½" rims, but I'm sure they would be happier on the 8" rears than on the 7" fronts. Perhaps I need to find a set of four 7½" or 8" rims. That way I could also rotate them every time.

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[Bandini]

[quote name='Lemming' date='Sep 13 2005, 10:57 PM']I'm not sure why you should care if you hit 6th gear or not?[right][post="9812"]<{POST_SNAPBACK}>[/post][/right][/quote]

I do hit sixth gear briefly on the longest straights[color="red"]*[/color], but I'm still accelerating when I reach my braking point, which tells me that I could use shorter gears.



I'm aware that larger wheels and wider tires would provide more grip, but compared to the others - mainly 996's - I'm quicker in the corners than I am on the straights.



[color="red"]*[/color] See corrective post below.

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[Bandini]

[quote name='BruceWard' date='Sep 13 2005, 11:25 PM']If Kuhmo Victoracers are available in Sweden then you should be able to get them in a 225 front & 245 rear combination.  This is what I use for Autocross and really like them.[right][post="9814"]<{POST_SNAPBACK}>[/post][/right][/quote]

As far as I know, I can only get Ecsta V70A's, which look identical to Ecsta V700's (not Victoracers). They're more expensive than they are over there, and also the 245 isn't available yet. I can get Michelin Pilot Sport Cup's in those sizes at a discount. Still not cheap, though.

Any significant change would result in more frequent gear changes that I suspect would slow you down.

That's probably true, but there are corners where I think I could stay in third instead of dropping to second, so it depends on the track I guess.

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[Eric_K]

I haven't been on a track yet that has needed 6th gear. It must be a real long fast straight to get to sixth. You would have to be going around 140mph/225kph+, which takes a bit of a run in a stock 968. I would just get some stock size r-spec tires and enjoy it. A 996 is always going to be faster on the straights. The fun is in the corners anyways.



Eric

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[Clem]

Running 8x16s all around is a nice setup since it will allow you swap wheels front to back and left to right. This should get you some more life out of your rubber. Plus, staying with 16s should be easier on your wallet.

If you went to 17s, I would suggest getting 7.5 inch fronts.



I run 7.5/9 x 17 with MPSCs on the track and am very happy with them.



Good luck,

Jim

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[BruceWard]

At one time Bob Blackwell had 16x8s on all four corners with either 225s or 245s on them. He has posted how he liked that setup. And I believe they were the tires he was using when he won an award for best autocross and time trial performance in his PCA Region for either 2003 or 2004.

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[coloradocab]

[quote name='BruceWard' date='Sep 14 2005, 12:13 PM']At one time Bob Blackwell had 16x8s on all four corners with either 225s or 245s on them.  He has posted how he liked that setup.  And I believe they were the tires he was using when he won an award for best autocross and time trial performance in his PCA Region for either 2003 or 2004.

[right][post="9862"]<{POST_SNAPBACK}>[/post][/right][/quote]



This year, I ran 245s all around and it worked well, although I'm going to 225s in the front and 245s now, hoping to improve my times on some slower speed auto-x courses we have. I use the same setup on the track as on auto-x. I think you're right about Bob, but their autocrosses are mostly on tracks as I recall, but he certainly had a great deal of success. Of course, it helps that he's a very good driver!

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[flash]

and so we get back to doing some math, figuring out the rpms at given places on the track, then figuring out tire diameters that give you what you want for that track



you may well find that you need different size stuff for different tracks - feel lucky - with the mgb, we had to go so far as to not only change tires and wheels, but to change rear end gear ratios as well in order to get the most performance for different tracks

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[EEZATOY]

Has anyone tried going with the stock Rear 17x9's all round (255/40/17) - Thats what I was thinking about - thoughts on how it might work, fittment problems in the front?

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[flash]

ET is an issue - to get a 9" rim under there, i had to go to a 57mm ET - there is very little clearance - a millimeter either way and it would rub - it would be worse with 17s because the tire would get closer to the spring, due to the angle of the spring



now if you changed to 2.5" diameter springs..............

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[Bandini]

[quote name='Eric_K' date='Sep 14 2005, 03:41 PM']I haven't been on a track yet that has needed 6th gear. It must be a real long fast straight to get to sixth.[right][post="9845"]<{POST_SNAPBACK}>[/post][/right][/quote]

My bad, Eric and Tim. Looking at the acceleration curve below, I realize that I was really thinking about fifth. <img src="/forum/images/smilies/968/wacko.gif" class="smilie" alt="" /> I've only just touched 200 km/h, but I don't think this rather embarrassing detail knocks enormous holes in my argument; with shorter gearing, I should hit fifth a bit earlier and go a bit faster at the end of the straight.

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[Clem]

[quote name='EEZATOY' date='Sep 14 2005, 02:54 PM']Has anyone tried going with the stock Rear 17x9's all round (255/40/17) - Thats what I was thinking about - thoughts on how it might work, fittment problems in the front?

[right][post="9870"]<{POST_SNAPBACK}>[/post][/right][/quote]



Can be done - though you will need to put longer studs on in the front.

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[Lemming]

[quote name='EEZATOY' date='Sep 14 2005, 01:54 PM']Has anyone tried going with the stock Rear 17x9's all round (255/40/17) - Thats what I was thinking about - thoughts on how it might work, fittment problems in the front?

[right][post="9870"]<{POST_SNAPBACK}>[/post][/right][/quote]



For the 924S3 that I'm building I plan on buying another set of cup wheels (17x7 and 17x9). I plan to run the 9's on all four corners with 255 in dry conditions and run the 7's with 225 in the rain. Now, lets talk about some serious fender rolling on my 924S body <img src="/forum/images/smilies/968/huh.gif" class="smilie" alt="" />

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[Bandini]

[quote name='flash' date='Sep 14 2005, 07:46 PM']and so we get back to doing some math, figuring out the rpms at given places on the track, then figuring out tire diameters that give you what you want for that track[right][post="9869"]<{POST_SNAPBACK}>[/post][/right][/quote]

I don't have the gearing numbers, but if my thinking is correct, going from 225/50-16 to 225/45-16 would mean a 3.56% drop in tire circumference, and consequently 3.56% higher rpm at any given speed and gear. Or put another way; if I'm hitting fifth at say 190 km/h now, I would hit it 7 km/h earlier with the smaller tires. Not a huge difference, but not completely negligible either.

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[bibbetson]

[quote name='EEZATOY' date='Sep 14 2005, 11:54 AM']Has anyone tried going with the stock Rear 17x9's all round (255/40/17) - Thats what I was thinking about - thoughts on how it might work, fittment problems in the front?

[right][post="9870"]<{POST_SNAPBACK}>[/post][/right][/quote]



That's the setup that I run, however to get it to work you need some extra camber adjustability up front. If you can get -2.7 degrees, you can make it work. I run -2.7 to -3.5 depending on the track using camber plates - no rubbing. I am able to do this with the stock ET55 17x9 wheels w/o any special studs. I do use steel lug nuts for safety however. I have found that this setup works really well with 250 lb front springs to get quicker turn-in and grip through tight AX corners.

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[mikew968]

Just keep in mind anytime you change wheels/tires/etc the car is going to handle differently. I t might be easier to stick with something and get the car really dialed in. In the end you might just be faster than doing a lot of changing around.



Mike

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