[MRV99]

I have had 4 X5's(E53,(3)E70) and I have had winter sets on all of them. I have had many different wheel sizes so I feel I have a pretty good idea of the differences between the group.

Where to begin......

I am a strong believer in dedicated Winter/Summers (on all of my BMW's) and have had many personal experiences why winters are so much better than All Seasons. I would rather have best performance in winter/summer than pretty good over the entire time.I am not going to debate this, it is just my belief.

I have no issue swapping wheels twice a year and storing the off season set(for both cars). Plus the nice summers don't get abused with less cleaning and salt.

The cost of two sets over the life of the car is almost the same as single all season set so that is not a factor to me(have many different cars to prove this case over the years)

Now for sizes.

19' vs. 20' To me, there is very little difference in ride quality between the two. When I switch from the 20's to the 19's, I can detect the taller sidewall and skinnier tire but that sensation goes away very quickly. I would say 2-3 days and I have forgotten the switch(other than the nasty skinny look compared to the 275/315 look). Since the X5 is the wife's car, I do have RFT's winters/summers so there will always be a bit of harshness compared to the non-RFT's. I do have/had Adaptive Drive on all my E70's I have owned. I can say that it rides better with AD compared to just sport(had a sport loaner w/ 20's for 30 days during 63 day in the shop lemon). My definition of harsh ride may be different than yours. I really like a firm ride and feeling the road when driving is not that bad to me.

Side note: On a past X5, I did have 18' winters and had 20' summers. The transition from 20's to 18's was very noticeable. The X5 felt very floaty on the 18's, so much that I sold the 18' winter setup(after 1 month) and bought 19' wheels if that says anything.

Winters:
The 19' or 18' does not have an effect in snow performance. What really affects the performance is the tire width. When looking at the 19' vs 18' the sizes are 255/50/19 vs 255/55/18 These have the same tire width so there is not a advantage/disadvantage in the tire width. People do say smaller rims are better in the winter mainly due to the more forgiving sidewall of the 18' compared to the 19' which in winter can help prevent damage from potholes. The main point is, wider tires, the worse they perform in the snow. The rim size is a personal preference.