Grimace

I posted this in a really old thread, but it seems appropriate to bring it up now (edited for brevity). These are different tire sizes, in 16" and 17", that are approximately the same height as the tires we have been told are coming on the car (225/45R18). If you are plus-sizing (or in this case, minus-sizing) your tires/rims, you should stay within 1" of height of the original tires meant for the car, or else handling, braking, ride quality, etc. deteriorates. Ideally, you should keep within 0.5" to stay on the safe side.

Quick_lude

Staggering widths depends on suspension design.. It helps control oversteer afaik.. A lot of rwd sports cars have staggered wheels/tires.. Corvette, Porsches, S2000's..

Sputnik

Ya know, looking at the numbers has made me realize that I was getting caught up in the pictures after all. A 225/45 sidewall height is actually what I've found to be the perfect medium for me. The bigger wheels and quality of the "spy" shots made it look different.

Okay, I'm happy with the 18s again...

---jps

PatrickB

Heh. The Road and Track article has been quoting 18x8 225/45R18s since it came out. A quick check at tirerack.com... tires in this size (besides cheapo continentals) are $187 Bridgestone Potenza Pole Position, $193 Pirelli PZero, $211 Bridgestone Blizzak winter tires, and $251 Michelin Pilots.

-Patrick

Renesis Rex

i have no problem with 18x8 because i'll just be buying Kumho Supra Ecsta 712.... the current price for a Kumho Ecsta Supra 712 235/40-18 is $125 US. and they're such great tires, too...

Quick_lude

The are not as good as the Bridgestone Pole Position, Pirelli P7000Z, Toyo T1-S or Michelin Pilot.
A good tire for the money but not the best.

Renesis Rex

not the best by far, that's agreed. if i was gonna pick my favorite tire in general it would be the Potenza S03's..... yummy tire.

Quick_lude

Yup me too.. expensive though.. I've also heard good things about Pilots and BF KD's.

fuz

I dunno if I can stomach blowing though $800 (+ installation) in tires every 20k...

I guess that'd be funny, either me burning my 325i at every turn, or driving an RX-8 like a granny. :D

R.Cade

I like wider tires myself. I had 245s all the way around on my 3rd gen 7, the orginal Toyo Proxies and they where awsome.

Will 245's fit on an 8 inch rim? I'm hoping the bolt pattern/offest will be the same as the 7, cause I got a nice set of 18x10's waiting for it already :P

Rexman

245's all the way around will be awesome. The original 225's are good tho.

RedRotaryRocket

Rich,

While your discussion of tire pressure / vehicle weight = contact patch is correct, your conclusion that the contact patch is ultimately the same is dependent on the assumption that the tire pressure stays the same when going to a wider tire.

Every tire has an optimum pressure for a given load. We all know that if you put too much air in your tires, you get more wear in the center... this is because the increased pressure has reduced your contact patch and are only riding on the center of the tire. Therefore, it is easy to see that even with the same tire, the contact patch is variable dependent on the pressure you are running.

The reason a wider tire provides a larger contact patch, as I've always understood it, is that the optimum tire pressure for a wider tire is lower than the optimum pressure for a narrower tire. Since the operating pressure will be lower, the tire must have a larger contact patch to support the vehicle weight.

This is how I've always understood it anyway. If this is incorrect, I'd appreciate some enlightenment.

EDIT - Oops! Somehow I missed a whole page of this thread...it looks like you guys have already discussed this....nevermind me.....

wakeech

225's are "good"?? wow... too much rubber for me... if i ever get an 8, or (more probably) an FD, i'd be downsizing the rims a cm or two... maybe... for sure on the winter set though...

Beemer

As for the tire choise, let me help a bit. My dad sells tires so we have quite some experience with some brands and models.
The best tire at the moment is the Michelin pilot sport. And second best very close to the Michelins are the Bridgestone potenza S02-03's. Other brands are more average except Continental because they can make the most kilometers/miles. A brand I sure would dissuade is Pirelli. They have an average grip but excessive wear and they make the car very nervous. I have to say, I don't know about Yokohama's but I've heard they're also pretty good.

About the width issue:
You could compare with skates on ice. The sharper they are, the better they have grip on a skiddy surface. So when it rains, your tires have to keep grip by cutting through the water (thats also why they have ribs, to cut and to guide all the water around the contact surface). When the tire is wider, it also has to process more water, not in the length, because when you're driving, the length is continuously growing, but in the width.
That's why rally cars also use smaller tires in bad weather conditions.

I hope this can help a bit, feel free to correct me

wakeech

exactly my point Beemer...

pelucidor

Spot on anlysis for Pirelli (at least for some models). I got a great deal on a set of Pirelli P7000 Supersport (all-season) - but they are absolutely awful and in hindsight not worth the savings. The original Goodyear Eagle GS-D summer tires (not a well-regarded tire in it's own right) were noticeably better - even my wife can easily tell the difference and is nervous about driving with these new tires in the rain.

Quick_lude

Really? I've got the Pirelli P7000 Summer version and they are great. Dry and wet, not too loud.. Grip like mad at the track, in the rain too! True treadwear is 160 but I got a good deal and unfortunately there is a tradeoff between grip and treadwear usage..

pelucidor

It could be that there is a huge difference between the all-season (which squeal too easily and feel nervous in the rain - the TC kicks in much too often) and the summer versions. Just after I got the new tires I had to move from NJ to Houston, where summer tires all year round would have been fine. Typical.

DakarM

staggered size would suck.

my current car has stagger size. 7.5 front and 9 rear.

The difference in the tire sizes generates too much understeer and my car is 50/50 and weighs ~3100pounds (wet including driver).

I know a few folks who have gone to 235/45 all around to eliminate understeering and be more competitive in autox.


Also Kumhos are good street tires, but for track/autox they are not very good. Many people have commented that they get wayyyyy to greasy and also chunks of tires coming off is not very good either.


18X8 sounds good to me, 17x8 would be even better.