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      06-11-2012, 06:15 AM   #1
Trips
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Big difference between 19" and 20" wheels for winter duty?

I prefer the looks of the 20" oem wheels but have heard the 19" wheels do much better in the snow. Thoughts on this guys?

Thx!
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      06-11-2012, 08:47 AM   #2
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It is simple physics. The wider the tire, the wider the path it has to "plow" through deep snow and the greater chance of losing traction--particularly at the rear wheels in the M5. I would recommend the standard M5 19" wheels for winter duty not because of their smaller diameter, but because of their narrower widths of 265/40 R19 front and 295/35 R19 rear.

The optional M5 20" wheels are 265/35 R20 front 295/30 R20 rear.

It is possible that some other 19" wheel with an even narrower width will also fit the M5, which (assuming that it didn't radically upset the M5's delicate suspension) would be an even better choice for driving in snow, but we know for sure that the standard 19"s will fit so that's probably the way to go for now.
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      06-11-2012, 10:49 AM   #3
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Quote:
Originally Posted by SleepTight View Post
It is simple physics. The wider the tire, the wider the path it has to "plow" through deep snow and the greater chance of losing traction--particularly at the rear wheels in the M5. I would recommend the standard M5 19" wheels for winter duty not because of their smaller diameter, but because of their narrower widths of 265/40 R19 front and 295/35 R19 rear.

The optional M5 20" wheels are 265/35 R20 front 295/30 R20 rear.

It is possible that some other 19" wheel with an even narrower width will also fit the M5, which (assuming that it didn't radically upset the M5's delicate suspension) would be an even better choice for driving in snow, but we know for sure that the standard 19"s will fit so that's probably the way to go for now.
Im assuming OP is referring to the wheel size with a winter snow tire in mind as well. If so then the width of the stock tires would not matter. However, Im assuming the 19" wheel is more narrow than the 20" wheel, which would allow for a skinnier snow tire, which was your argument.

Also, I'm assuming with a tire that has a larger sidewall by an inch would provide a deeper tread, aiding in snow traction. In that case I'd say 19's are better.
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      06-11-2012, 11:10 AM   #4
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Is it true that the 19's are narrower than the 20's?
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      06-11-2012, 11:43 AM   #5
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I thought that the width would be the same and only the sidewall is different as both have widths of 265 (in mm) for the front and 295 for the rear. If expressed in inches 265/25.4 would be 10.43 inches wide front and 295/25.4 would be 11.61 inches wide rear. Now it is the sidewall aspect ratio that are different. So where is the width difference being discussed?
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      06-11-2012, 11:54 AM   #6
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Width and tread depth are the same.

The only difference is that the 19" tire is more flexible, and so will maintain contact better.
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      06-11-2012, 12:04 PM   #7
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I was mistaken, 20x10 rear and 19x10 rear, so it's the same.
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      06-11-2012, 01:11 PM   #8
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Same width front and back for both sizes, 9 front and 10 back. I'd be putting the same size tires all the way around for either size, 255s I believe.

I think the only difference then would be an extra 1/2" of sidewall height on the 19s. I know this improves ride comfort as well as handling, but is it a big deal for performance in the snow, safety wise?

Thanks again.
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      06-11-2012, 04:50 PM   #9
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I ran the Pirelli's in the OEM size (19" wheels 255/40f, 285/35r) on my E60 M5. I could not even back out of our driveway without spinning the tires in the snow. With 400+ lbs of weight in the trunk, the snow performance was tolerable. If you want to have reasonable traction in the snow, FOLLOW THE BMW RECOMENDATIONS! The recommendation was to run '4-square' 255/40-19's all around as the previous poster did. I didn't, because I really hated the way the Blizzaks felt in the dry, and then I switched to more performance oriented snow tires, and still didn't like the dry handling. I went with the OEM setup because I got much better handling in the dry. I would not do this if you want any kind of traction in the snow - the rear tires are just too wide.

Here's how 'wide tires' were explained to me in one of my driving schools at Mid-Ohio. If you look at the 'physics' of tires, all tires have a contact patch with the road. The contact patch is simply the cars weight divided by the air pressure in the tires. If you're running the same air pressure in wide and narrow tires, you have the same amount of rubber contacting the road. The difference is that a wide tire has a narrow and wide patch that is ideal for cornering. A narrow tire has a long, narrow patch that is less prone to 'hydroplaning', or riding up onto the snow/rain. This is the reason you want to use the narrowest possible tire in the rear when driving in snow. The larger, softer sidewall doesn't transmit the axle torque to the road as directly as a smaller, stiffer sidewall, and so makes the wheel less likely to spin.
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