[BD550]

So I would like to swap out the summer tires for all season. First to eliminate the hassle to switch between summer/winter but also to add comfort/wheel protection versus the stock tires that come with the 668M. Considering two options:

- Michelin Pilot Sport All Season 4 front 265/40/20 and rear 295/35/20. This configuration results in a front total diameter of 28.3" and rear 28.1" a 0.7% difference. Front and rear width 10.4" and 11.6" and side wall 4.1". Will the 265's fit on the front rims and would the rears fit the wheel well with the 11.6" width and 28.1" diameter? The new Michelin's have few size choices thus the configuration with 265 / 295 setup. I have had P/S 3's on prior car and liked them a lot.

Alternatively, I could use Continental Extreme Contact DWS+ with the front 245/45 and rear 275/40/20. This configuration has a diameter of 28.7" and a 0% difference between front and rear. Width front is 9.6" and rear 10.8" with sidewall of 4.3". The only question here is whether the 28.7% diameters would fit. Conti's have many size choices and could drop to 245/40, 275/35 if needed.

Either way this should significantly improve comfort and wheel pothole protection without the hassle of tire swap for the season.

Any thoughts would be helpful if either or both would work.

[Zereldo]

I am of the opinion that neither set up will work. First one because of the width and second one because of the diameter.


Why I think they won't work:

668M wheels measure 8 inches front and 9 inches rear. The maximum tire width these wheels can accommodate is 245 front and 265 rear - on paper atleast. I know these wheels come with 245 35 R20 front and 275 30 R20 rear. You may be able to get away with 255 in the front but I wouldn't go any wider in the rear as the tire will be compressed.

You will run into rubbing issues given the aspect ratio is above 40. I currently have 245 40 R20 front and 275 35 R20 rear on a set of 649i wheels that measure 8.5 inches front and 10 inches rear.

[Zereldo]

Depending on where you live, but if you experience snow then it is worth having a dedicated set of winter tires and a dedicated set of all weather/summer tires. All season tires do not perform well in the snow. You can drive carefully, put your car in "snow" mode and so on but that will not change the fact that the tires simply aren't designed to tackle ice and snow nearly as well as snow tires.

The cost of two dedicated wheel set up vs a year round wheel set is about the same given the fact that you will be using each set for a portion of the year hence they will last longer individually. It's also worth keeping in mind that salt takes a toll on wheel finish and so it's a good idea to have a less fancy set of wheels for winter abuse. On another note, wide tires like 265, 275, 295 mm do not do well in snow at all. Instead of digging through it, the wheels will slide over it - picture hydroplaning.

[BD550]

This is very helpful Zereldo. I was worried about the rim width. So if I want to go with all-seasons best case we are talking about 245/40 and 275/35, but may need to do 265/35 on rear. I live in Chicago area which has long cold winters, and gets a decent amount of snow but it gets plowed quickly so rarely am I driving in more than 2". I currently have Pilot Sport A/S 3+ on my Audi s6 and they have performed very well. The thing about this area is that you can experience winter conditions November thru March and often April. But there are many warm days in between which is why the A/S have historically been a good choice.

But your point about the salt damage to the wheels is an important thing to weigh. And you are right, over time the cost of carrying two sets evens out as the tires wear. I dont have the room for storage so I need to look around for winter tire storage service that can also swap them out, as our dealers dont do that. My new 550 is on order so I have some time to figure it out. Thanks for the help.

[Zereldo]

265 on the rear will work given the front tire width is reduced to 235 (235 40 R20). I hear you about storage space. I store them in my garage so its of no concern. Based in what I've seen, tire/wheel storage costs up to $100 to $200 annually. I cant say if I'd be willing to pay that.

In my opinion, go for 245 40 R20 front and 275 35 R 20 rear. You will have extra sidewall and so the car should have similar ride quality as OEM G30 19 inch wheels. As far as winter season and winter road elements are concerned, you can take the necessary measures to protect you wheels by coating them in ceramic coatings or paint sealants. It's a good practice to wash the car atleast once a week (be it just hosing it) to prevent salt from staying on surface for extended periods. I was referring more to the fact that roads degrade in winter time so there will be more potholes to contribute to damaging wheels.

Whatever tire size you go for, make sure the rolling diameter is within 1% of each other (front vs rear). 245 40 r20 and 275 35 r20 is "proven" so I was confident in buying the tires knowing I will not have any rubbing issues. It may be possible to go 245 45 r20 and 275 40 r 20 - though I'm more or less certain that there will be rubbing. This is X3M and X4M tire size.