Yoshimura

I was really excited to install my new 20" wheelset. However, it seems that 255 tires don't have all the same width!!! New tires are a lot more thinner. :-(

I decided to keep my 19". What do you think?

Front: 255/50R19. Rear: 255/45R20.

tgt

That's quite a tread width difference. What brand/model are each?

-tgt

Yoshimura

19" are Bridgestone Dueler H/P Sport
Section Width: 10.4", Tread Width: 9.8"

20" are Michelin Pilot Sport A/S 3
Section Width: 10", Tread Width: 9.2"

It seems that it's my Dueler that are very large.

spijun

Very strange

gk1

Same wheel width?
Per Tirerack...Tread width between brands is not standardized, so disregard.
The michelin's 10" section is on an 8.5" measuring rim.
The bridgestone's 10.4" on an 8" rim.
So if you bridgestone's are on 8.5" rim and the michelins are 8" then that should be 0.8" difference that you see, but you tell me. Best bet would have been if Bridgestone was originally on 7.5" and new Michelin on 9", then section should be same at 10.2".
Either way it stinks that they don't match up.

Yoshimura

Yes, both are 8.5"

spijun

Not important wheel width:
Width 255mm tires must always be 255mm regardless of the wheel width 7,5 or 9,5

19" wheel


20" wheel

DennisMitchell

Could it be that Section Width is the width of the footprint on the road. Some manufacturers give more sidewall curvature in their design, hence the overall width appears wider. FWIW.

gk1

Not true...
Read...
http://www.tirerack.com/tires/tirete...jsp?techid=200

While that calculator is good... I use it myself...the "section width" info highlighted is only showing the 255 from the tire size description. Put the tire on a 7" wide rim vs. a 10" wide rim and the measured section width will not be the same...

In the OP's case since they are both 8.5" wheels there should be a difference of about 0.6".

MP4.2+6.0

The width (255 for example) is nominal and varies by brand. Thus, if important go by the manufacturer spec sheet or TireRack's site for both the tread width and the section width (where it bulges on the sidewalls). Fairly often you can't get those specs for any given tire, but always worth checking if possible. TireRack's numbers have been wrong in my experience at times too, but often it's pretty obvious when you look from one tire brand to another, or up and down in a range.

Three examples of non standard from my direct experiences:

1. Last gen A8's use 275/35-20 in the optional 20" fitment. But S8's use 265's. However in at least the OE Yoko's, they were both actually the same--the manufacturer just cut the sidewall down a bit. Apparently that's common for adjoining sizes--sometimes you get the "wide end" of the bargain on tread width, sometime the comparatively narrow.

2. Mini S fitment. Stock is 205/45-17 on the upsized wheels. JCW's run 215's. But, you can actually run 225's. However, the 225 tires vary by .4" in the section width (Mini's most critical clearance is the width; on Q5's its the height relative to the front strut location), and guess what--pick the "right" 225's and it clears fine, and pick the "wrong" ones and you are definitely hosed--not just a little wheelhouse rub, but right into the strut tube metal. Last set of PS2's I ran were 225's (one of the "narrower" ones), but this time I went with successor Michelin SuperSport's in 215. But guess what, tread width in the new 215's is actually WIDER than on the old 225's, and both were summers from same company.

3. My W12 A8. Factory 20's are again 275/35-20's. But for snows in 20's (I know, odd), guess what, the only vehicle it shares with basically is it's cousin underneath, the various Bentley blown W!2's. Then in turn Pirelli offers the only snow tire in the fitment, and they and their quasi sole source TireRack charge a good 25-30% more than obvious sister same model tires based on size, weight and speed rating, presumably since Bentley owners will pay whatever. But wait, the 255/40-20's used by Cayenne's basically work; just a little more diameter (not a bad thing winter wise anyway). Gives another high performance highway snow choice too, and while same rubber bulk, way fewer $ than the Bentley rip off size. And, when you put them side by side with my normal 275's, they are basically just as wide. Yo would think about an inch narrower, but they simply aren't. And stack them literally next to 255's from either the Q5 or my A6 4.2 in 255's, and like in OP's picture, they ar e clearly wider in reality, even with minor rim width difference. It nets to the Porsche OE spec 255's are way wider than the size would imply, which is what I could see in the TireRack width data when I went that route.

Last, for OP, all seasons also just plain appear a bit narrower because the tread shoulders tend to be more rounded than summers. I think you have some of that going on. But, by all accounts, the Michelin AS/3 really is a great tire and are up there with really good pure summers. When I wear my current 275 Dunlop Sport Maxx's out on the A8, the AS/3's will be my next set on based on the market today (and I will still use full snows in the core 2 1/3-3 months of Tahoe tough winter). Honestly, 255's are more than the Q5's "need" anyway if I'm objective, other than maybe the SQ. Having driven the 235's at the highest possible speeds for Q5's with whatever motor on the Autobahn, the softness of the suspension and ride height ultimately are its clear limiting factors, not the tires. Same in spirited cornering, no matter what you do with the gas. The width may help a bit w/ (non snow) braking, but w/in a 255 to start the differences are relatively small probably.