I'm still messing around with the idea of using 15" wheels on my 07 MCS to put snow tires on. I've posted before on this and now I'm narrowing down my options. I understand the Motegi wheels at Tirerack will fit over both front and back but I like the look of the Rota Slipstream a lot better. Iautox sent me a lot of information on his experience with this wheel. However, he ended up going with a 16". I guess the problem is with the back wheel not clearing the support arm. It appears that either the 15x6.5 (40 offset) or 15x7 (35 offset) would come close but would require a spacer. I just want to know if anybody out there has done this one on an 07 MCS so I can learn from their experience.

 

Are you getting some new springs too? The wheel wells on the R56 seem big even with 17s...

 

Nope. I have 16s on it now and I'm ok with them. Frankly, the reason for the 15" wheels is to be able to put some narrower (more effective in snow) tires on it for the winter. It's my daily driver and we get A LOT of snow where I live at 8000' in the Rockies. I want to put 185/65/15 snow tires on it. Finally, I'm not concerned with the wheelwell space. Around here in the winter nobody's paying attention to that.

 

If your goal is to get to 6.5" wide, why not just do 16x6.5s? same deal. It would be like me trying to go to a 14" wheel at 5.5" wide, when I could just use 15x5.5. . . That way you can avoid all the potential problems with the fittiment. Slightly more expensive on the tires. Maybe $10 each.

 

For 15" wheels (assuming they can fit over the MCS calipers)
195/60-15 is recommended with (tread width 6.1")
185/65-15 as alternate size (tread width 6.1")

For 16" wheels
195/55-16 with (tread width 6.7")
205/50-16 as alternate size (tread width 7")

Both 15" tires would do better in snow.

 

Why do 15'' tires perform better in the snow?

 

In my experience it's not that it's 15" or 16" or whatever. It's the width that matters. Wide tires tend to float on the surface of the snow while a narrower tire will not. Additionally (and this is a factor for me), 15" tires are considerabley cheaper than the larger diameter ones.

 

I could see how that logic might work. However wouldn't you think that a heavier, 16'' wheel penetrate through the snow on a narrower width be better?

 

Narrow tires will offer less resistance when used in heavy snow.

Narrow tire will often offer less rolling resistance for higher mpg as well.

To fit the MINI wheel often 15" rims use fairly narrow tires- more so than any other rim size. 16" comes close.

I'm not sure how much difference a light vs heavy wheel (tire and rim combo) makes in the snow. Given slower speeds I would guess that it is very small.