I'm close to taking delivery on my new 2020 X3 m40i. I ordered it with the 19 inch wheels, as I intended to use those, going forward, for my winter tires. My plan was to buy 20 inch wheels in the late spring/early summer to use with some top notch summer performance tires. There are almost no good summer performance tires available for the 19 inch wheels, and I can get the superb Michelin P4S tires for the 20 inch wheels. Also, I've read a number of comments both here, and in other BMW X3 forums, that the 20's ride better.
I've just recently been told that given the fact that southeastern Michigan roads are pothole ridden and otherwise not great, in many cases, that it would be crazy to even attempt to go with 20 inch wheels, as they would be destroyed by potholes within months.
Has anyone found this to be accurate? I would really hate to be so limited in tire choice if I have to stick with the 19's.
I doubt that 0.5 inch of rubber on the radius will make that much difference. Years ago I was in Michigan and saw pot holes that would trouble a medium or heavy truck.
I down-spec'ed my M40i to 20's because I preferred the wheel style and didn't want RFTs. In the UK we have quite a bad pothole problem too. You've just got to be vigilant, maybe religious too.
To compensate for the lower profile tires on my 328i I always inflate tires about 5 psi above the BMW recommendation. I've gone through two sets of tires (one set Continental and one set Bridgestone) and reached about 40k miles with each, so the extra 5 psi does not seem to have affected the wear.
If the roads in Michigan are anything like the ones in NY, I would not do 20" wheels without wheel and tire insurance - or an understanding that you will be assuming some wheel/tire repair costs (i.e. self insurance) My experience here goes only to 19's and I would not do 19's without the same understanding. I had 3 19" wheels repaired in 3 years under insurance on my '17 G12. And one tire replaced. Of course nobody can tell you with confidence that you are going to -- or not going to -- hit a pothole that dents a wheel or bubbles a tire. You can, as noted, prevent some damage by upping tire pressure but that will harshen the ride even more than the normal harshness. If that doesn't bother you, go with 20's, be extremely vigilant about tire pressure, especially as temperatures drop, and be prepared to pay for repairs - or insurance. They get you one way or the other.
Have a look at Firestone Firehawk Indy 500 tires. I recently put them on the wife's 19" X4 2.8i w/staggered setup and will soon put them on my 20" X4 M40. Very smooth tire at a great price price.
As long as you ditch the runflats and use plain old tires, 20" will be fine. I have 20's for summer (6 months) and stock 19's for winter (the 6 months it snows here). Both summer and winter tires are non-runflat.
Of course, if you're special ordering the car, order it with the space saver spare. Then it won't matter if you have run flats or not.
100% agreed, if you go to conventional tires, you'll have 1/10th of the problems. Even more so, if you get winter tires in a taller aspect ratio, you'll never have to worry about potholes. December to April, I run winter tires to avoid this worry altogether.
Of course, if you're special ordering the car, order it with the space saver spare. Then it won't matter if you have run flats or not.
100% agreed, if you go to conventional tires, you'll have 1/10th of the problems. Even more so, if you get winter tires in a taller aspect ratio, you'll never have to worry about potholes. December to April, I run winter tires to avoid this worry altogether.
Car is already ordered so no space saver spare. But then it only applies to the rear tires and cant be used with the fronts anyway, so, 50/50 at best. But absolutely agree with conventional tires.
And I do have the winter tire issue dealt with, and waiting in my garage for the arrival of the X3 m40i.
What do you mean it only applies to the rear tires and can't be used on the fronts? Of course you can put the space saver spare on the front, or have I misunderstood you?
Did anyone check with the manufacturer about this? It's all well and good to ask TireRack and Discount Tire Direct, but what does BMW have to say about it? I'm out of the country now, or I would ask my own dealer.
Am I the only one who thinks it would be odd to engineer a spare tire for just two wheels on a 4 wheel car? I wouldn't drive more miles than absolutely necessary on a spare anyway. It's for emergencies. Perhaps the tire sellers are saying you shouldn't drive on them for months at a time?
So, if you get a front wheel flat, you have to loosen the back tire lugs, jack it up, put the space saver there, lower it, loosen the front tire lugs, jack it up, and put the rear tire there? What if you took the 20" wheel option, and your rears are bigger than your fronts? You can't put the rear up there, but if you're on the side of the road, and help is nowhere in sight, can't you put the spare on the front to get yourself somewhere where you could change the tire?
How could BMW get something like this past regulators - European or American? There's got to be information here that's missing. I'm out of the country right now, or I would ask my own dealer. This is disconcerting to be sure.
I honestly don't know all the details to explain this. And, to be clear, it's associated with ANY brand, and not in any way exclusive to to BMW. I "believe" this issue has to do with the fact that the front wheels steer, but am not entirely certain.
I can tell you that, after not previously being aware, I ran this question past the three most knowledgeable "technical" automobile people that I know, two of whom are automotive engineers (one of them even helps design and develop suspensions). They were almost horrified that I was not aware of the fact that it is not safe, or intended to ever use a space saving donut spare on either front wheel position. They felt that literally everyone with a brain knew it. That was embarrassing.
Same situation when I ran the question past my designated service person at my BMW dealership. He looked at me like I was an idiot not knowing about this.
Lastly, I was admonished by the rental car manager for driving the rental car the five miles back to his location with the space saver spare on the front. His words were "Don't you realize that you can cause serious damage to the car by driving with that spare on a front wheel?"
Hi there, I just bought a 2018 M40i and have the same dilemma. It came on existing 19” all seasons that I want to mount winter tires on (maybe sell the all seasons?). Then buy 20” tire/rim set for summer. Just wondering how you made out with this? Thanks.
I would believe Wikipedia before salesmen Discount Tire Rack. They are not in business to be engineers (at minimum wage no less) but to sell you what they have to sell.
The amount of misinformation from tire stores is sometimes amazing. Somehow the relationship between tire diameter, section width and aspect ratio is a mystery to many of them.
if you search on Tire Rack for a new set of staggered 20” tires for a 2021 M40i you will find that for the Bridgestone brand I checked, the front and rear tires are exactly the same diameter (although different widths). This amazing fact is because when they switched to a wider rear tire they lowered the aspect ratio, and the diameter remained the same at 28.7”. Also, if you check the diameter of the standard 19” tires, lo and behold, it’s again 28.7”. That is why they can all use the same diameter compact spare tire, even I’d they are AWD.
The variable related to the probability of tire or wheel damage from potholes is sidewall height. Going from 19" wheels to 20" wheels, you're giving up 1/2" of sidewall height, going from 4.8" to 4.3".
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