I'm wondering- I HAD Dunlop SP8000's on my car on 16" rims- 225/50/16 & 245/45/16- I JUST bought new Michelin Pilot Sport PS2's & for 17" rims- 225/45/17 & 255/40/17- the profile for these tires, is OBVIOULSY shorter, BUT, the sidewalls feel weeaker than my Dunlops- this would REALLY surprise me- Porsche recommends 36psi front AND rear- I always kept my SP8000's at 35psi all the way around- the Pilots, at 36psi felt really wiggly- like the car was a boat or something- I've increased the pressure to 38psi, & it feels a little better- I also noticed- the SP's had a MAX pressure level of 40psi & the Pilots show 51psi- should I be running the Pilots a lot higher? Maybe 40psi? What do other's here run? Especially those of you w/Pilots? I ALSO noticed the Pilot's are narrower than the SP8000's- this was rather upsetting- the 225 Dunlop was wider than the 225 Pilot & the 245 Dunlop was a hair wider than the 255 Pilot.... oh well- too late now... Starting to wish I'd bought S03's, but.... any input? Sorry for X-posting, but, I really need some quick input & would like as many responses as possible....

Thanks

 

Robby - I told you so :>)

Seriously, what you are feeling is the difference in the tread block height. New tires have deeper tread blocks and you are feeling what is called, tread squirm.

The difference in width varies by manufacturer. Michelin is one of the smaller tires. I.e. their 225 is the most narrow of most of the popular 225s.
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I PROBABLY deserve that...

It's a LONG story, really, but, I actually ordered the S03's originally....

Anyway, that's what it FEELS like- some sort of tread squirm or something- but, w/a tire like the Sport PS2 &/or the S03, etc, I would NEVER expect that- especially since the SP8000's NEVER had that prob, even when new & THEY were taller profile too- 101.25mm & 102mm vs 110.25mm & 112.5mm... I also ran all sorts of tires on my Integra & NEVER had a prob w/any of them- 117mm profile- best tires it ever had were AVS Intermediates- Pilot PS2's should be MUCH better than those too... Anyway, when I ran the pressure up slightly, it DID feel a little better- I just don't want to OVERFILL- I'm hoping that they don't HAVE to BE overfilled to feel right- wouldn't make sense, but, I was just hoping some people would chim in w/some of their pressures, etc & maybe SOMEONE would have had a similar prob w/the Sports & confirm that they need more pressure than other's, or something ...

Oh yeah, Matt- can you look up the weights on the S03's in 225/45/17 & 255/40/17- Just out of curiosity? Doesn't matter at all now, but, I'm just curious- the Michelins were sent to the guy who refinished my wheels & he had them mounted already, so, I couldn't weigh them seperately- I weighed the wheel/tire combo & had weighed the wheels when I got them, so, I can do the math- I was surprised to find that the combo weight was actually a HAIR lighter than the 16" club Sports w/SP8000's- the SP8000's were ALSO lighter than the Bridgestone RE950's (I THINK they were 950's) that the PO had had on the car... No big deal either way- just kind of interesting IMO...

Thanks

 

IIRC, Porsche specs a different pressure for 17s than they do for 16s, I don't have it in front of me but I think it's in the infamous TSB. Also in the TSB is the proper alignment specs for 17" wheels, it's not the same as for 16" wheels and will probably make a bit of a difference. I think the 968 caster block upgrade is due to a problem with adjusting the alignment to the spec for 17" wheels so you may need to do that upgrade if you haven't already.
Sidewall stiffness is inconsistant from one manufacturer to the next and even from one tire model to the next. reduced sidewall height does not equal increased stiffness. As much as I don't doubt that you are feeling the tread squirm that Matt mentioned, that is probably not the only difference. Get the pressure and alignment set up right or you're comparing apples to oranges.

 

I'm curious to know the tire pressure specs also. On 15" (NA cars) they spec 32 front and 36psi for the rear. Is it different for 16" wheels, and does the alignment need to be changed?

 

225/45/17 25.32 lbs
255/40/17 28.31 lbs

It doesnt matter what tire you buy, there will be some squirm at first. It is the difference between new soft rubber that is 8mm taller (tread block not overall diameter) and rubber that has hardened and worn down to the base of the tire. A good example is to take a pencil eraser from a new pencil and one that is worn down, see how much easier one moves than the other.
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Thanks for the input guys- I DO have the 968 caster blocks already & had the alignment done last week, BUT, had the 16" Turbo S wheels on it at the time- not sure what dif that will make- HOPEFULLY none, but....

As for tread squirm- I do understand the concept, but, the only reason it's strange to me is, that I NEVER felt that from any other tires before, even when they were BRAND NEW, so, it's straqnge that I would feel it on such a high end tire- I threw in the shorter profile part b/c I would THINK, that if ANYTHING, the shorter profile would help slightly, not hurt... oh well- thanks for all the input- I'm going to play w/tire pressures a little & keep a CLOSE eye on tread wear- we'll see what happens...