Tires
 

New to Rennlist. I have a 2007 911 Cabriolet with 18's. Can I replace with 19's on the same rims or is there more to it. Thanks

uh, 19" tires won't fit 18" rims. If you visit TireRack, they have some educational areas where you can learn what tire sizes mean.
New rims and tires required.

They won't seal real well along the bead.

The outer diameter of tires mounted on 18" rims or 19" rims is the same. The tire's inner diameter is different - 18" in 18" rims and 19" in 19" rims.

If you mount tires for your car on your 18" rims they would not seal, showing a gap of about 1".

The difference between 18" rim/tire and 19" rim/tire is sidewall size - smaller on 19" rims.

Technically the gap would be about 1/2" but yeah. You can go slightly wider or narrower on the same width rim but you cannot choose a different circumference.

mike

FIFY

As of others have said, not a good idea. And, Tire Rack is a good resource for knowledge. Welcome to Rennlist, and post up some pics of your sweet new ride! Remember the RL Motto "Pics, or it didn't happen!" Cheers...T

Interestingly, been driving on 18s Winter tires for a few weeks now and I am now wondering whether or not our 997.1 suspension was actually optimized on 18s instead of 19s? Obviously my winter tires have softer sidewalls than 19s summer, BUT the car just rides and feels so much nicer on the street it makes me wonder if 18s work better in all cases? Obviously, I am losing ultimate performance, but oh boy does it feel amazing driving on the street, going through bumps, potholes, rain, snow, slush, etc... Basically on bumpy roads my tires are more in contact with the road than 19s hard sidewall tires that just bounce off bums on the road.

More sidewall.:)

not really. Not to get all 3rd grade geometry on you but when you try and put a 19in tire on an 18 inch wheel you're dealing with a larger circumference because circumference is directly proportional to diameter. So you cany put a larger circumference Tire on a smaller circumference wheel.

maybe you are thinking the outer circumferecs or diameter. you can change the outer diameter or outer circumference (rolling) but I don't think thats what the original poster is discussing.

Mike

Sorry, we agree - but your initial post confuses the matter. The tire is spec'd with an 18" or 19" mounting diameter! They are not spec'd as 56.5" circumference ( pi x 18"), or 59.6" circumference ( pi x 19") - which is exactly what your initial post was inferring.

There's always gonna be a compromise somewhere.

Are you still running factory width 235/265? I have 235/265/r18 Potenza S-04 on my car, I like them for the lower noise and comfort but they are only ok for fast stuff. In the rears; too much air and the contact patch isn't enough on power track out, not enough air and it flexes taking away some spring rate leading to vague transitions. They are missing some feedback and are mismatched to the factory non-sport suspension, and don't have that much bite but that's a compound issue not a diameter one. I had RE050's previously, they did have better bite on brakes and a little better hold in corners.

How do you like the pro-kit springs? I'm interested in the Pro-Kit package.

Biggest fault I find with factory 235/r18 front is the lack of turn-in feel. I've driven a 996 that had 19's with 245 front and it had a much crisper and direct turn-in feel off dead-center in the steering wheel and the butt of the pants, same experience with the 997 911C2S cars. ATSR, you notice any difference on turn-in with 18's vs 19's?

Original Poster - you need 19" wheels to safely have 19" tires mounted. When doing tires consider changing out the tire pressure monitoring system (TPMS) as the batteries are good for about 7-10 years, once they go you'll have a warning in the dash until they are either coded out (potentially illegal, do at your own discretion) or you replace them which requires breaking the bead of the tire. If you're unsure the age of the batteries it's prudent to get a set 'while you're in there' and have them swapped with new wheels/tires free of charge. You can buy a TPMS set for about $140 online on Amazon from a Chinese supplier or spend 3x for official Porsche units. Also, be aware of load rating - our rear tires need to be at least 101 rated to handle all that weight back there, it significantly cuts down on potential tires you can buy. Some folks will argue you should get Porsche approved tires, but there's enough folks running non-approved tires happily and without fault that suggests that's more aggressive marketing than anything else. As long as they are rated appropriately, you'll be fine.

Popular options for both 18" and 19" wheels are:

Michelin Pilot Sport PS2 (pricier - better)
Potenza RE050A (OEM - good)
Potenza S-04 Pole Positions (cheaper - ok)
Michelin Pilot Super Sports (great, if you can find them)
Hankook Ventus V12 Evo2 (generally cheapest $$)

You should look on your gas cap door on on your door jamb and see the tire sizes that are recommended for the car. Then check to see if they match whats on the car, then make sure you are buying the ones that are listed on the decals so you are getting the correct size.