Same size tires, yet different dimensions

I know that different manufacturers have different actual dimensions, but even I was surprised when I went from the Sumi HTRZIIs that came on the car to PS2 N3s. The Sumis are/were the cheapest tire that could be found to fit the car, and the PO acted like he did me a huge favor letting me know he put new tires on the car less than a year ago. They are horrible, greasy, flat spotting, soft sidewall crap, and despite 2 rebalances, still shook like vibrator, and the ONLY reason I left them on for so long, was I was waiting until I had installed the PSS9s, new TREs, etc before putting on good tires. They still had a ton of tread, in fact, even worn (only 14k miles on them), they had as much tread as the new PS2s. The PS2s, even without an alignment yet, are smooth and quiet, and even before the mold release is gone, a better feel by far. As well they should be at 3 times the price. What shocked me though was, the huge difference in width and height between them! The PS2, in 285/30-18 goes way past the rim edge on both sides (providing rim protection, and a much fuller filled in look) whereas the Sumis, looked like they were stretched to fit the rim, and there is at least 20mm more actual tread width on the ground! They are also about 0.25" taller. Yet, the front 225/40-18s are only a little wider, maybe 10 mm, and are actually 0.125" or so shorter. Also wierd, is I had measured the tread depths on the Sumi's when I got the car, and found pretty even wear, side to side and the fronts and rears matched in tread depth. Yet the PS2s in front have solid 1/32 more tread depth than the rears. The end result, was when measuring the factory ride height points front and rear, the car went from around 123F/119R to about 120F/122R, so the stance has actually visually changed (for the better) ANyone else notice such huge differences? I think I may not have noticed it so much on other cars, because normally I wait until the tires or worn (duh!), but I HAD to toss those Sumis..it was embarrassing to take a turn in them with any HINT of moisture on the road, and watch the PSM kick in

Check the specs page on the Tire Rack site - such size variations are relatively common.

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The aforementioned is VERY true. We've had numerous discussions about this on the Jag list and there are so many instances where size "x" of one brand is very different a far as actual measurements go, to brand "y" Buyer beware!

I've had several different brands of tire on my C4S, including Pirellis, Michelins and Sumis. I went from Sumis back to PS2s and I couldn't be happier. They are vastly superior in terms of handling - it's even noticable to be in daily driving. I won't buy Sumis again. I think I'll stick with PS2s, at least until they make the Michelin Pilot Super Sport in the proper size for the C4S! The SS got fantastic reviews in the last C&D.

Major brand tires often are wider because they are made in what's called a premium mold & you get a truer size. Think about it , if you are trying to cut the cost of a tire, you put less into it.

Yes as others have said this is very common, that is why it is recommended to never mix and match tire brands. Yes sure you can find two different brands with identical dimensions but best not to risk it.

Ii bought sumis and after driving on them for 6 month i will not purchase another set. Agreed, my 295s looked stretched compared to the previous tires i had. Also forget about tracking with sumis they give up after 3 sessions of abuse. I wouldve bought the Yoko Ad08 if they were in stock. 180 tread wear rating shouldve made a good all purpose track/rain/daily tire. Still pissed that michelin is leaving a lot of us 996 guys out of the super sports.

Yes, I agree, PSSs were my first choice too, regardless of N rating, but until they know they have a ton of sales in that size, I don't think it's gonna happen. I have 7mm FVD spacers on the car, and putting the PS2 N3s on the rear, makes it look like I put on 15mm ones. You would THINK that it wouldn't be that hard to design a tire to actually BE 285mm wide, when that is the stated size. I wonder if that is also a reason to stick with N rated tires? Verification of true dimensions.

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More on this by a Popular Mechanics writer here: http://autos.yahoo.com/news/6-common...-debunked.html

Hi there.. I just switched from PS2's to the Sumis, albeit less than a 1k miles on them I feel you get what you pay for.. They don't compare in every respect to the quality of the Michelins, ride performance, and my biggest disappointment is the noise they make. I'm running my third set of Michelin sports cups for track and love them.. I should have not cheaped out and bought the Sumi's, but I wanted to try myself these myself and base my own opinion. I have a very aggressive suspension set up that loves to consume tires. My street rear tires don't last as the inside of the tire gets chewed up with all the negative camber.. The good news is these Sumis won't live long on my car,

i should have mentioned another important observation with the Sumis, was the vibration in the steering wheel has subsided from the time they were installed, but still makes me crazy and doesn't compare to the feel of the michelins.. Good luck..

Yes, and I'd bet you put on HTZ IIIs..these were HTZ IIs, which is a far worse tire, IMHO. I didn't even mention the huge difference in road impact rolling noise. I acknowledge that 6-7 year old tires will be a lot harder than new ones, but I disliked them from the first time I got in the car 4 years ago, and I had to really convince myself that I knew I was going to make tire and suspension changes, anyway, so not to judge the cars handling from that aspect when considering the purchase. Most every other one I drove had worn PS2s on it and the road feel was better by far.