Abman

I apologise if this topic has been thrashed to death over the years, but each tyre and and wheel question seems to need different and specific criteria and I cannot find info on what I intend to do and need direction please.

OK, I am running standard 18" wheels with 225/4/R18 front and 285/35/R18 rear at present.
I intend to go to a set of 19"wheels with either 295/30 or 305/30onthe rear, and either 235/40 or 245/35 on the front.

My questions .....1) on the 993TT are there any dramas in running 19" wheels
2)could I run 305/30 on the rear and say 245 on the front safely without rubbing on the liner.
3) I intend using monoblok HRE mags which the manufacture says will be quite OK for the 993, using 8.5 front and 11 rear.
4)I am concerned that I don't damage the 4wd diff by using this new configuration.

Any help would be appreciated.
Thanks

Rob

Felix

Rennlister sfbanchs is running 997 turbo wheels without issue but no idea what tire sizes he's running,

Stock rear size on a 993tt is 285/30 18 which is a slightly smaller diameter than the fronts (628 vs 637 mm). 285/35 18s are 657 mm so appreciably larger than the fronts. Not sure if it really matters but I would try to keep the front rear diameter ratios like what the factory ships the cars with.

Abman

Thanks for your ideas on that Phelix, but not quite sure how you work out the ratios........stock for the 993 TT is 225/40 front and 285/35 rear

I am looking at say 245/35front and 305/30 rear......not sure whether these aspects would be OK..

Felix

Umm, check your owners manual about those rear sizes; 99% sure they should be 285 30 18.

And the diameters are simple math: wheel size + 2*aspect ratio*width/100

Full Boost

Hey Rob!

Long time no speak! Hows the car going?

Since my brake upgrade - I can no longer use my Champion Motorports 19's - with NEW (never driven on) tyres....

I am runnig 245/35 and 295/30 rear - no issues with rubbing - and no fender issues - (but i do run a LOT of -ve camber) and there seems tobe no issues.

IIRC there is also an "allowance" of i think 5%. Depending on what BRAND of tyres - Tirerack.com will help with the overall diameter. I hope this helps?

Gratutious shot of wheels about to be for sale:

Simon.

Abman

Hi Simon mate..........car's purring like a kitten thanks and what would you think about running 305/30s on the rear and say 245/35 front.....any idea if the wheel arch would accomodate that on 19" wheels.

Cheers

Rob

ca993twin

My car (19" Ruf wheels 9"/11") came with 245x35x19 and 295x30x19 rear. While this F/R ratio is OK, my car rubbed at the rear of the tires where they would touch the rear bumper. This is a DIAMETER problem, not a WIDTH problem, as those tires were about 1" diameter larger than the factory 18" sizes. I have since switched to 255x30x19 and 315x25x19, and have no rubbing issues. These tires are almost the exact same diameter as the factory 18"

You can check tire diameters at the tire rack web site... it is the best source, as you can't be too accurate just knowing the sizes... each manufacturer is different.

sfbanchs

i am running pirelli p zero 235 35 19 front 305 30 19 rear no problems pair of spacers in the rear also to puch them out a bit worked fine without spacers as well may i add another rennlister hewre in miami just put 997tt wheels on his car i ll leave up to him if he wants to post pics car looks sweet

Abman

Hey, thanks Steve and sfbanchs.......most helpful and along with tyre rack website I am sure I will sort something.

Simon........nice set of wheels and I would have been very interested but have seen and sorted a set that I am keen on.

JDHertz11

Here you go...

I have the same sizes as Sebastian's car.... very slight unknown rubbing on drivers rear over bumps I shouldn't be going near anyway.... I do not have any spacers, but may try some 10 or 15MM in the future....

Sebastian maybe we can meet up this weekend to show you my C2... Call me....

OldGuy

I get flamed for this but be aware going to 19" is going to make your handling suffer. if your not concerned as much with your ride or handling and going for looks go ahead. The HRE wheel is a stunning looking wheel, and probably one of the lightest wheels you can get. But going 19" and bigger wheels and tires
than the original design is going to increase unsprung mass and add weight at the worst possible place for ride and handling. But your purpose for this is your choice. I just think its more important to point that this is the way they were designed (18") than be concerced about a couple flames. I am not even convinced my 19" wheels from the factory are a great idea and in fact alot of GT3 guys are moving to 18" for that reason.
RUF has worked their wheels to be the same diameter of the stock 18inchers

ca993twin

Hi Paul, Long time.

Paul is correct... adding unsprung weight is not ideal, and that's why track guys go to great lengths to get the lightest possible wheels/tires. 19" wheels will weigh more than the equivilent 18" wheels (although there are some lightweight 19" wheels out there... for a hefty price). My Ruf 19" wheels are among the heaviest. But here's the tricky part... if you use tires withn a smaller section aspect ratio so that the TOTAL wheel/tire diameter is the same as the 18" wheel/tire combo, then the tires will actually weigh less than the 18" tires with their larger section ratios. The total wheel/tire package will probably still weigh more than the equivelent wheel/tire in an 18" size... but maybe not by too much.

Paul will know more about this than me, but aren't the GT3 guys changing to 18" wheels because the R compounds that are currently available much stickier in 18" than 19"? I know the Mich Sport Cups in 19" are not nearly as well regarded as their 18" counterparts.

The handling of Rufus with 19" wheels is better than my previous turbo with 18" wheels. But there are many other variables, including different tires and Ruf suspension Vs PSS-9. But there is no denying the basic facts... adding unsprung weight is not a great plan. Thanks for pointing that out.

OldGuy

Stevey!!! How are you??!!

Two reasons the GT3 guys are moving Price but nobodys talking about that a MSPC is 530 for one rear
and the 3s were having a terrible push on the track with the 19". They switched back to the 18" and got
rid of the push. You could say that is because the 18" are stickier. Also could be geometry.
Also at the debut of the 997 GT3 other 18 inch tires were more available than the 19" version. More and more 19" tires in the 305 size are coming out.

I was gonna say too your RUF should be better in the 19' version because your whole suspension is RUF tuned. The stock TT has monroe stock shocks that arent the best and the stock sways are unadjustable so your car is more tunable than the stock 18 setup. Thats the other reason that the TT 18" setup is sensitive to the 19" move is the suspension is not adjustable. When you go to 19s the stock design is upset. The RUF setup just adjusts as needed and off you go!
If one were to put on PSS9s and RS sways some of the push can be dialed out. There is nothing you can do about the weight.

ca993twin

Paul,

I think you're right about the geometery, and that's why I was so careful to keep the stock overall diameter when I changed tires on the Ruf wheels. BTW, Ruf delivers the package with the taller tires, which raises the center of gravity. I think you would run into this same issue even staying with 18" wheels, if you went with a taller tire. I think this is a bigger issue than the unsprung weight, assuming that the shorter tire on the 19" wheel did not weigh much more than the taller tire on the 18" wheel. But I haven't looked up the specs on this, so I'm only guessing.

But... the main reason to use 19" wheels (besides looks, some like 'em, some don't) is that I can't get an 18" wheel to fit over my 15" Ruf brakes! Of course, between you, me, and the lampost, the brakes are purely cosmetic... I'll never drive hard enough to need those larger brakes. But I'll deny ever saying that.

OldGuy

DOH!! I forgot about the brakes which is the VERY reason I havent moved yet either
DANG PCCBs are too big. I have a limited choice of wheels.