# Questions about 20" BMW Style 361 Rims & All Season Tires



## Macadamia (Mar 30, 2009)

Short version of the post:
Can I legally have tires installed on my car that are a different load index and speed rating? Currently my car has "Y" rated tires front and back, and the ones I want to put on are "W" in the back & "Y" up front. My installer says he cannot install the rears since the current rears are "Y" rated.​
Long version of the post: :yikes:
I recently purchased a 2012 335i Sedan with the 20" BMW Style 361 Rims & Pirelli P-Zero Run Flats.

Tire & Rim Stats from the BMW website:


Genuine BMW F30/31 3 Series Dual Spoke 361 20in Wheel/Tire Set - Bi-color, ferric gray. RDC complete wheel set - includes four wheels with Pirelli P Zero Run-Flat Tires in 225/35 R20 90Y XL fronts, 255/30 R20 92Y XL rears. Front: 8"J x 20", H2 IS: 36 Rear: 8.5"J x 20", H2 IS: 47. (stats from TireRack.com)

Living in Eastern Idaho, I really need at least all-season tires. I've been looking at the Continental Extreme Contact DWS 06. They do not have an exact match in sizes, but I found this combination to be close to the original tires and very close in overall diameter.

Rear Tire: Continental Extreme Contact DWS 06 (stats from TireRack.com)

SIZE: 255/35ZR20 97W XL
UTQG: 560 AA A
MAX. LOAD: 1,609 lbs.
MAX. INFLATION PRESSURE: 51 psi
TREAD DEPTH: 10/32"
TIRE WEIGHT: 24 lbs.
RIM WIDTH RANGE: 8-10"
MEAS. RIM WIDTH: 9"
SECT. WIDTH: 10.2"
TREAD WIDTH: 9"
OVERALL DIAM.: 27"
REVS. PER MILE: 769

Front Tire: Continental Extreme Contact DWS 06 (stats from TireRack.com)

SIZE: 245/35ZR20 95Y XL
UTQG: 560 AA A
MAX. LOAD: 1,521 lbs.
MAX. INFLATION PRESSURE: 51 psi
TREAD DEPTH: 10/32"
TIRE WEIGHT: 24 lbs.
RIM WIDTH RANGE: 8-9.5"
MEAS. RIM WIDTH: 8.5"
SECT. WIDTH: 9.8"
TREAD WIDTH: 8.6"
OVERALL DIAM.: 26.8"
REVS. PER MILE: 775

So, if I understand the specs correctly (please correct my misconceptions and downright errors, thanks):

Overall Diameter % change = 0.743494423791819%
Overall Revolutions per Mile % change = 0.7772020725388601%
So, both values are within 1% for the staggered set - check.

And, comparing the Pirellis to the Continentals, specifically load ratings & max load:


Rear Pirelli: Load Index & Speed Rating - 92Y (1389 lbs. & 186 mph)
Rear Continental: Load Index & Speed Rating - 97W (1609 lbs. & 168 mph)
Front Pirelli: Load Index & Speed Rating - 90Y (1323 lbs. & 186 mph)
Front Continental: Load Index & Speed Rating - 95Y (1521 lbs. & 186 mph)

So, I guess my question is: Can I legally have these tires installed on my car which currently has "Y" rated tires front and back? The Continentals are "W" in the back & "Y" up front. My installer says he cannot install the Continental rears since the Pirelli rears are "Y" rated and the Continental rears are not. (I could not get a straight answer from 2 different BMW dealerships I phoned. (they would only talk about run-flat tires, and kept steering the conversation back to the P-Zero tires...))

Any and all help here is appreciated. For those who are just going to suggest a completely different set of winter tires, that's option 2, and I have a set of 17" rims and Blizzak tires ready to pull the string on. All of the above research is option 1, the route I prefer to go.

And of course, there is always the possibility of option 3: find someone who really loves these 20" rims and trade for a staggered set of 19". If I go with option 2, I will probably pursue this option for the future.

Thanks!


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## JayR04 (Jul 17, 2015)

AKAIK that car, or most BMWs are not even capable of reaching 168 mph. So, you should be fine with the "W" speed rating. I'd just try a different wheel shop.

Maybe there's some type of scientific formula that I don't know about with mixing different speed ratings.


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## Macadamia (Mar 30, 2009)

JayR04 said:


> AKAIK that car, or most BMWs are not even capable of reaching 168 mph. So, you should be fine with the "W" speed rating. I'd just try a different wheel shop.
> 
> Maybe there's some type of scientific formula that I don't know about with mixing different speed ratings.


So, from the installer and from the BMW parts dude: The speed rating is really a misnomer. They use a top speed as a guide, but really, it has to do with loading of the tire during normal driving, braking, cornering, as well as outright speed. As the heat builds in the tire, it can get to the point where it can fail.

And, as you say, my car probably cannot even get to the 168 mph and I will not be tracking the car. As a daily driver (albeit spirited), I should never get near the loading limit on the tires.


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## LycanNyc (Apr 11, 2012)

I'm in a similar situation actually.. My new car is coming with 245/40-20 & 275/35-20 
But my #1 choice tires (Ultra High Performance All-Season) Delinte D8 (Dessert Storm) popular in the SRT8 cars and only comes in 20+ size. 
But its 245/45-20 and 275/40-20 wondering the same as you .. I know the Y/W is not going to matter as much as is the tire going to fit correctly without rubbing or issues


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