I have purchased a used car, ten years old. This car went for six figures new, but never really caught on, so I got a bargain in my opinion. It has a pretty high tech suspension system, which I quite frankly know nothing about.
The wheels are 16 inchers, and look pretty dated compared to the rest of the car, so I would like to change them out. Nothing outlandish, probably 18 inches.
I do not want to mess up the “$100,000 ride feel” of the car in the slightest, since this was a major selling point for me. I don’t feel like I can trust Mr. Aftermarket rim seller, because he is obviously going to be biased. Also, it’s hard for me to separate signal from noise in the car modification boards, I mean, I don’t know if Mr. 20 inch rims on a Honda guy really know any of the physics and mechanics behind this.
Can anyone in the know help out?
The car in question is a BMW 850 Ci, if it makes any difference.
Upsizing to 18 inchers will screw with the 100k feel.
This is because if you upsize your rims by 2 inches, then you must downsize your tire sidewall by 2 inches. (you must do this because your speedometer works by tire circumferance x revolutions = speed). The less sidewall you have, the more bump you’re going to feel, simply because theres less of a cushion of air between you and the road.
Generally, keeping the overall diameter of the wheel+tire combo the same, larger wheels usually translates into slightly better performance but at the cost of ride comfort.
You can offset this when selecting a larger diameter wheel, by selecting a tire that offers comparable sidewall height to the factory 16" tire size, but at the expense of throwing your speedometer/odometer off by a certain percentage since they were designed to measure the factory tire size.
17"/18" wheels should be ok if you select a good matching tire. Some tires are designed for performance and will have a harsher ride, while others are designed for comfort. www.tirerack.com and read some reviews. Do not get 20". 19" is doable… but not as practical tire prices are better in 17/18" sizes, as well as tire selection/sizes as well.
are you also asking about performance issues, or just ride comfort/feel? more weight translates into slightly slower acceleration and decreased gas mileage, among a few other small things.
You should also note that If you run a bigger overall diameter of rim+tire or a wider tire you run the risk of the wheels rubbing against the struts/fenders(usually on turns). Every car has a different suspension geometry, so theres no way anyone here would know what kind of rim/tire sizes you can run safely.
If it is not too late, I would suggest calling a BMW dealer and having them give you some advice. It might even be worth it if you can have them do it (if they are willing to do it), because if there is a problem, it will fall on them.
That is a big ass car you have. Enjoy it!
*if you don’t mind me asking, what did you pay for it?
I know someone who moved to Maine and was forced to replace his aftermarket rims with stock. He was told that the DMV would not register a vehicle that had wheels larger than were specified by the manufacturer. . He speculated it might be for the speedometer problem, or maybe interference with steering, but didn’t know the rationale behind the rule. You probably should check to make sure the same rule doesn’t apply in your state.
Ditto on everything else that has been said. Additionally, you’ll want to pay close attention to the new wheel’s offset (the relationship between the hub mating surface and the wheel’s centerline). Messing with this can lead to really quirky handling as well as complicate tire/fender clearance.
If you decide to go with a wheel/tire package that meets your criteria (clearance, handling, ride comfort, etc.), the speedometer error that may be introduced can often be corrected by swapping out the gear that turns the speedometer cable in the transmission. Again, the folks at BMW or a BMW-specific message board are probably your best bet for reliable information.
Yet one more reason to avoid increasing the outside tire diameter is that it’ll hurt the car’s accelleration. You’d effectively be changing the car’s gear ratio.
I’ll second Bobalude’s recommendation for Tirerack. I’ve bought from them and know tons of other people who have as well. You can enter the car make, model and year and look up wheels and tires they recommend. If you order wheels and tires together they mount and balance them so when they arrive you can just stick 'em on your car yourself. If you can’t decide what tires would best fit your needs, give them a call, their sales people are very knowledgable and can help you decide. Also their prices are quite a bit lower than if you go to your local tire dealership.
That’s insane! I’d love to hear the state’s justification for that one. Are they gonna start prohibiting owners from painting their cars a different color than the one it originally came in?
If it were me I’d just borrow someone stock wheels, register the car then switch them back.
I certainly don’t want to change the overall size, so this is probably what I’m looking at. It makes sense that less sidewall would make bumps more noticeable, but how do high end cars these days get around this? If you look at, for example, a new M6, it has massive wheels and small sidewalls. Never been in one, but I would imagine it is pretty comfortable to boot.
You would be better off calling a tire shop. As I work in a new car dealership , that type of info is not available from a service or parts standpoint. The manufacturers position is that the wheels that came on the vehicle are the ones you should be using . Just as an added bit of info , the larger the wheels , the thinner the tires , the greater likelyhood of flats .
The difference is that on cars that come from the factory with lower profile tires it’s taken into account when they design the car. They select suspension components to work with the chosen wheels and tires to get the ride and handling they’re looking for.
www.tirerack.com shows 16, 17, 18, and 19 inch wheels for your car. The selection page shows the car with representation of the wheels as mounted. Details for the particular wheels indicate recommended tire sizes. As posted above, larger wheels will get a tire with a lower cross-section. Generally a stiffer ride but better lateral grip.
If you went with what is known as a ‘plus one’ upgrade, you would leave with a total tire diameter nearly identical to stock, a bigger rim (1" bigger).
Plus One conversion generally offer crisper response with a slight dent in the ride. A plus one is very standard fare.
On a very expensive car, it is unlikely that anyone could tinker with a plus one conversion and actually improve anything. I’d suggest a new 16" wheel set with the proper offset (very very mandatory) and a very high end tire.
Kelly’s Blue Book lists private party purchase price - excellent condition - 1996 model to be $28,505. Considering the risks, doesn’t sound like much of a steal to me. Everyone I’ve ever spoken to says they are an absolute nightmare to maintain.
I actually tend to doubt that a BMW M-series car would be all that comfortable anywhere but the highway. The M series by BMW is designed for performance, and as such has much stiffer shocks and upgraded tires (as well as a healthy boost of HP), so it will beat you pretty good on bumpy roads.
Well, considering I’ve been wanting one for a decade, there are only a few hundred in the United States (and much fewer in my preferred color and with low miles), and the fact that I couldn’t buy a new car for 25K that I like nearly as much (or is as nice or stylish) I think I got a hell of a deal.
And I’ll have a sweet coffee table if that V-12 gives out on me
.
Don’t overlook the relative weights of the wheel/tire combos you’re looking at. Most of the larger wheels commonly available are ridiculously heavy. The less mass in the wheel and tire, the easier it is for the springs and dampers to do their jobs. Also, acceleration will be helped by not having to spin up such a large mass.
Example: my car came with 16s in front and 17s in back. The serious autocrossers and track freaks have all gone to a 15 inch wheel all around and have noted serious improvements in their times. Apparently, the engineers wanted to go with the 15s in the first place but were overruled by marketing. I haven’t made the jump to 15s, but have ordered much lighter forged wheels for track use.
Not that I am doubting you, but what car came from the factory with 16" fronts, and 17" rears? I’ve never heard of this. Different aspect ratio tires F/R yes, different rim sizes, no.
Also better lap times with 15"? The reason for +1 and +2 was to decrease sidewall height, to improve handling. This was before the marketing guys got ahold of the idea. Now you are telling me the reverse is true?
