I have access to the a different staggered Winter tire set than our regular 255 and 285.

This alternate tire set is 245/40/20 and 275/40/20. Is this set going to work on my XFR? The owner states that he had them on his XF. Any thoughts? In my mind the 245 and 275 will probably be better in the snow compared to 255 and 285 but I am not sure if I will have any other issues with the sidewall being a tad more on the rears.

 

That's a big difference in rolling circumference between stock and your choice. I wouldn't try it. Although taller tires do work better in winter the slightly narrower tires you are considering will be very similar in handling characteristics on snow to the stock sizes.

Try this handy tire size calculator.

http://www.powerdog.com/tiresize.cgi

 

You'll be fine. The overall diameter is only 1.15% out (smaller) and you are generally fine up to 3% variance. I bet you won't even notice it on the speedometer.

 

Using that tie size calculator I get 6.7% difference between 275/40x20 and 285/30x20 for those important rear tires. Am I missing something? Agreed that the fronts are only 2.5% out but the rears are only 30 series for the wider tire.

 

Sorry my bad, the rears are 275/35/20. Thanks for all your comments! Using the tire calculator seems like its within a reasonable limit?

 

ok. I didn't realize the factory 285 aspect ratio was 30. A 275/40 then is way too big. 35 should be ok though. if you go narrower then generally you need to add 5 points to the aspect ratio.

 

One of the issues with non factory rolling circumference is computer related problems. The ABS, traction control and TPMS all rely on assumed rolling circumference to work correctly. How far out the proposed new tire can be before the ECU's revolt can only be answered by the factory sources or actual on the road experience.