Differences in changing wheels from 18" to 20"

[M3ZCP6MT]

Just wanted to see if any of you have the experience of changing your XDrive 35i stock 18" wheels (255/55/18) to 20" staggered set up (275/40/20 & 315/35/20). Besides the great 20" looks,

Ride quality - smoothness and quietness are better or worse?
Tread wear - uneven wears?
Handling - noticeable difference?
Gas mileage - better or worse?

Also, do you need to install a set of OEM fender flare kits?

[sparky-eg]

i have got the 20 inch on my 4.8i as stock , i have driven the 3.0i before and i can tell you that ride quality is not that good in the 20 inch wheels. but this what you get with low profile tires, you sacrifice something in return of other things, better handling with the 20in.

[X5ist]

Yes for sure 20" are much harsher and you feel all the nook and cranny on the road. I just switch to my 18 winters, of course the rubber are softer but still its feel much comfy

[jadnashuanh]

Wider tires are much more sensitive to both alignment and air pressure, and since you can't rotate the staggered sizes F-R, and, they are often a higher performance rubber compound, your mileage and initial costs will take a hit(obviously, more expensive wheels as well). There's a reason why hyper mileage vehicles use narrow tires...less rolling resistance and drag.

But, sized properly, the odometer and speedometer should not be affected nor should the acceleration. Ride quality, though WILL suffer. Whether the look, and potential increased g-force is worth it to you, is entirely a subjective evaluation. To keep the load on the bearings the same, you must use a wheel with the proper offset, and if you do, it will not change where the outer edge of the tire sits enough to cause it to stick outside the existing wheelwell. If you stick with the factory wheels, or pick one that is equivalent, everything should fit normally.

Winter tires with their softer compound and squishier tread blocks will never be as tight handling as an all-season or summer performance tire.

[smyles]

It really depends on what tires and wheels you choose. Contrary to the above, in my case the ride quality and especially mileage didn't suffer at all since I went with lighter aftermarket forged wheels and non-run flat tires, resulting in softer side walls and ~10 lb in weight savings per corner, and I don't expect lesser mileage. Steering response is different, more sensitive to road imperfections.

If you stick with BMW (or replica) wheels and run-flats, those parameters will suffer. But you'll have factory looks and security (for what it's worth) of run-flats.

[M3ZCP6MT]

Thank you all for your feedbacks

Primary reason is for the looks

[sparky-eg]

then go for the 20 inch. the rear wheels look great . if you have a spare tire kit get non RFT tires , they will give you a better ride quality and longer life, I always wanted the michelin latitude but i decided to stick to RFT since i got no space for a spare tire (got the 7seats). I am on bridgestone dueler hp and they are fine for me. price wasnt very high as well.

[M3ZCP6MT]

Will the 315 rear tires stick out and require a flare fender kit?

[jadnashuanh]

Originally Posted by M3ZCP6MT

Will the 315 rear tires stick out and require a flare fender kit?

It all depends on the wheel's offset you pick. If you stick with the factory offset (doesn't have to be a factory wheel, just the same offset), it will fit fine. The offset is where the hub section of the wheel is relative to the inside and outside edges where the tire is mounted - IOW, the vertical face where the wheel bolts are relative to the rim.

In my comparison, I was talking RFT-RFT. Swapping to a normal tire is a different story, since the sidewalls can be much more flexible - it doesn't have to be stiff enough to hold the vehicle up with no air pressure. But, a 20" tire verses a smaller diameter one WILL be stiffer, when comparing apples-to-apples, regardless of the type.

As you go higher up in the tire diameter, those tires tend to be only available in higher performance tread - often, the actual depth when new is shallower. While not a perfect reference, the tread wear guide number is fairly consistent, at least within a single manufacturer's line (not necessarily between different brands), and a good idea of how long the tire will last you.

[M3ZCP6MT]

Thanks for your great, extensive input.