I have an '11 SC with staggered 20 inch tires, 8.5 front, 9.5 rear. I like the look of the 20 inch staggered, but want to get a decent winter set of wheels and tires. I understand that downsizing to 19 inch will benefit the pothole crossings due to higher sidewall, but if the tire/wheel set up does not get narrower, say down to 8 inches (versus 8.5 inches), is the benefit for traction that significant? Most of the available aftermarket rims for XF's are 8.5 inches wide. Doesn't seem like a huge improvement.

Thoughts and experiences welcome.

 

Go with the smallest (shortest) factory rim size and use the recommended size tire size and load rating on it. That will allow for more sidewall flex to assist traction, but it's the winter tire's compound and tread pattern that's going to make the huge difference. Trying to arbitrarily get a skinnier tire on it is a bad idea, IMO. The improvement in traction from switching to a good winter tire from a summer performance tire is going to blow your mind!

Bruce

 

I concur from experience. The main advantage to downsizing a winter tire to a smaller rim is added sidewall flexibility which significantly aids traction and braking.

Retaining similar tread width hardly affects the grip levels at all, except in that important area: bare roads. Going one or even two inches down in rim size ( assuming the smaller rim fits over the brake calipers) and retaining as much of the original tread width as supply of tires will allow gives the best compromise between added grip on the slippery stuff and retention of performance on bare roads.

Wider tires have a minor disadvantage in deep snow. On ice or packed snow there is no advantage to going narrower in section width. Rallying is a totally different process and narrow " ice tires" are used there for different technical reasons, no good for street driving.

 

Bruce and Jagular, thank you for the replies. Based on your feedback it would seem a 19 x 8.5 (original OEM size for XF's) and that will fit over S/C brakes with a 245/40/19 winter tire is the way to go. I was thinking of trying to go 19 x 8. Sounds like the .5 inch difference is not a huge improvement. There are more choices in 8.5.

 

Width of the wheel has a minor effect on sidewall flex. I am fitting 18x8 wheels with my winters but only because 18x8.5 are hard to find. Width of the wheel need not affect width of the tread, within fairly wide parameters.

Sidewall height makes the most difference. Wheel width stiffens up the tire in lateral loading, a small amount. This only affects cornering loads.

 

Good advice from Jagular and Bruce who are both experienced snow country drivers.