I'm starting to look at a wheel change and was wondering if anyone has run a 20-19 or 19-18 combo? I’ve tried searching around the forums but didn't yield any results. I thought it might look cool but would like to see another car with a similar setup.

Thanks
Bobby

 

Why would you want to do that ??? The overall diameter needs to be very close otherwise the traction control will go nuts, so I don't understand why you would want to go different rim diameters....

 

Thanks for your reply and that’s why I asked. I didn't take into consideration what the t/c would do and I didn't know how close in overall diameter they would have to be. I thought a bigger wheel in the rear may look good on the car but I guess the front wheel sidewall would have to be too big to make up the difference and would look dumb.

 

Don't stagger the wheels. Beyond the practical considerations, this is a surefire recipe for long-term damage. Stick with 18s and nice big sidewalls.

I'll never understand why people buy bigger wheels than absolutely necessary. Doesn't help the car go any faster / turn any better. Ever seen the sidewalls on an F1 tire?

--Dan

 

Well, the rolling radius would be the same because he'd end up changing to a smaller tire on the larger wheel, right?

But you're right - it's a terrible idea and fraught with disaster.

--Dan

 

Visually, I can definitely see where you're coming from. I like that whole aggressive stance look in the rear. Have it a bit more slanted look. You could just lower the front a bit more to get that look going

 

The computers tolerances are very touchy. Your wheels have to be the same Height or your car will freak out and go into limp mode. (It's thinking your sliding, Loosing control etc, because one set of wheels is spinning faster thank the other set.)

 

You'd have to run a thicker sidewall tire on the smaller front rim to compensate for the difference in diameter. I'm sure a tuner could program for this and correct the data for the computer if you were really motivated, but honestly.. the lines of this sedan don't lend themselves well to a staggered look like a C5-C6 Corvette does, or a 2010+ E350/550 would.

Bobafett- most people put larger wheels and tires on their car because they like the way it looks plain and simple. You may not like the way it looks, but some folks do.

BTW the tire size and profile on an F1 car is completely irrelevant to the tire size on any passenger vehicle. An F1 car weighs not much more than a large motorcycle and if it were to bear the mass of any Mercedes Benz road car the tire sidewall would most certainly be shorter, ala Rolex GT-class.

The OEMs have been increasing the size of wheels for a few reasons. One being that the vehicles themselves are increasing in overall size ( a new civic is larger than an old accord) so the wheels need to be proportionally larger. Second the power levels are increasing so the need for a larger tire contact patch drives the tire size wider and taller.. And automotive fashion has made it seem awkward to have thick sidewalls that would normally accompany those increased dimensions, so now we have cars with 19 and 20 inch wheels becoming more and more common whereas 15 years ago, 20s were only for body dropped show trucks at SEMA and the rear of the Plymouth Prowler

 

I thought the whole idea of bigger wheels was mainly to allow for bigger diameter brakes .

 

You are correct, sir. Nice to find a logical response. Of course, you're right that aesthetics are a highly subjective matter. My F1 comment was made in jest, but the essence is something you've partially alluded to.

Vehicles have been growing at a ridiculous pace. The 1 series is the same as the old 3 and even older 5, etc. etc. Larger tires are absolutely necessary, but larger wheels aren't. It's unfortunate that a thick sidewall is considered awkward, as you put it, because functionally it is a far better alternative to the same rolling radius with a smaller one.

I really don't care what idiotic choices people make, except that with popularity shifting towards ever-larger wheels, tire availability for the smaller rims becomes increasingly limited. On the F40, I had to change to 18 inch wheels from the stock 17s, partially due to the need for a larger braking system (yes marc, but only to an extent) - but really because the choice of tires for 17s, especially the rears, was narrowed to essentially one option. I hate to think that in a few years I'd have to find sets of 19s that compromise the road-going of the vehicle even more, simply because of a lack of 18" options.

Another example is the 1M. I have to imagine that BMW tested all manner of wheel and tire sizes for this car, even if it was a parts-bin model. The stock 19s that it comes on makes the car good for nothing more than being a hooligan, as you spend most of your times sideways. The ride wasn't all that great either - not overly stiff, just not well done. A switch to 18s made a HUGE difference. Even on a regular road going tire as opposed to the 2nd set which is on R compounds. The car suddenly hooks up in first and second, is far more compliant, has predictable wheelspin, rides better, etc. I guess I just don't understand the obsession of sacrificing function for form.

--Dan

 

Dan - I agree with much of what you said about going ridiculously big rims & small side walls for a street car. That said there is a bit more to it.

BMW, and especially the M group, is known for their suspension design. BMW is focused on developing a great road car that can give the owner the feel of a finely tuned race car with the compliance for the street. A larger sidewall is generally better for launching the car or straight line sprints. A smaller sidewall will generally give you better feel, better turn in, and higher cornering speeds. That said it comes at a big expense - (1) k factor is much higher (which then needs to be addressed in the suspension), (2) comfort, and (3) rim destruction. Obviously another thing the engineers are always focused on is gearing....

On a street car, which lets face it all of our cars are, I don't understand why anyone would want to ride on a sub 35 profile - too harsh and rim damage is inevitable.

-- Christoph

 

Bobafett- Who knows... Perhaps the 19s on your 1M could have come down to a decision as simple as " competition x has y size wheels/tires, this car will need >y or be considered <x in car/driver shootouts"