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[CanAutM3]

I am at the point I need to replace the PSS on my car. I really like the PSS and want to stick with it. I am presently debating keeping my current size of 255/35R19 and 275/35R19 or going back to the OEM size.

I was pondering going back to the OEM size because of not much more thread width (+5mm at the rear) for significant extra weight (+2.9 lbs) as debated in this thread: http://www.m3post.com/forums/showthread.php?t=831495

Now another element that is making me ponder more is the size of the thread blocks (the width of the longitudinal grooves). As you can see from the pictures below, the longitudinal grooves on the 255/35R19 fronts on my ///M and on the 235/35R19 on my wife's S4 are significantly wider than the ones on my 275/35R19 rears. This results in significantly more rubber on the road for the 275. I am wondering if the 265/35R19 have wide grooves like the 235 and 255 or narrow grooves like the 275. If the grooves are wider on the 265 than the 275, it could make the extra weight of the 275 worthwhile...

Please post pics of your 265/35R18 here


275/35 255/35

235/35

[Denk]

Here you go. Wide I'd say, threw a quarter on for reference. I think I'm the only guy on here that prefer's stock sizes.

[CanAutM3]

Originally Posted by Denk

Here you go. Wide I'd say, threw a quarter on for reference. I think I'm the only guy on here that prefer's stock sizes.

Thanks buddy, exactly what I needed

[CanAutM3]

OK, so I have done a little extrapolation based on the picture provided by Denk and some math to figure the difference between the 265 and 275.

Here are the results for thread block width in mm

265/35R19 (Total thread width 254mm)
47+32+32+32+47 = 191mm (75%)
275/35R19 (Total thread width 259mm)
58+38+38+38+58 = 230mm (89%)

So even if the 275 total contact patch width is only 5mm wider than the 265 contact patch, it offers 39mm more rubber contacting the road because of the narrower grooves. This is 20% more. This could justify the 2.9lb of extra weight (+12%).

Decisions, decisions...

[GIdriver]

Yep, the 265's (which I have) have the wide groove. Definitely more contact with the 275's.

[dmppdx]

Anyone have any idea why for a 10 mm change in width, they change the grooves so much? It seems like they would follow some ratio that that was calculated to be optimal for tread width to grooves. Having increased traction is great, but for people who live someplace where it rains, it seems like a 275 would hydroplane way more than a 265. It also seems like a 275 might make it understear more with a 255 in the front with wide channels.

[CanAutM3]

Originally Posted by dmppdx

Anyone have any idea why for a 10 mm change in width, they change the grooves so much? It seems like they would follow some ratio that that was calculated to be optimal for tread width to grooves. Having increased traction is great, but for people who live someplace where it rains, it seems like a 275 would hydroplane way more than a 265. It also seems like a 275 might make it understear more with a 255 in the front with wide channels.

My guess is that the 275 is specifically designed as a rear tire. It can tolerate less water drainage as a "path" in the water is opened by the front tires.

You are correct, the increased lateral grip provided by the 275 would shift the handling balance more toward understeer.

[tha_good_life]

Originally Posted by CanAutM3

My guess is that the 275 is specifically designed as a rear tire. It can tolerate less water drainage as a "path" in the water is opened by the front tires.

You are correct, the increased lateral grip provided by the 275 would shift the handling balance more toward understeer.

THis is an interesting post because I'm in the same dilema with my wheels. I'm currently on 265/35/19 and 295/30/19 on BBS FIs. Because of the larger tires, I'm gaining additional weight. I was thinking of changing my rears to 275/35/19 and see if there is any difference. The additional weight defeats the purpose of the lighter wheels.