The aftermarket BMW parts business has been steadily growing over the past 10 years with more and more products available to the public, at cheaper and cheaper prices.  In California especially, many people love to do things to their BMW that sets them apart from the rest.  From wheels to stereos to cold air intakes, I’ve seen just about everything imaginable on a BMW — some of it good, some bad, and some indifferent.  Unfortunately, the aftermarket parts industry is not based on what is good for your car, it’s based on what will sell, and the margins said product will produce.  Here are some things to consider before you take the plunge on those 20″ wheels and a new set of tires.

Don't do this!

Wheels are probably the most common custom part that people will put on their BMW.  If you see a wheel that you just can’t do without, you need to know a few things.  Wheels are expensive, at least they should be, so if you are looking at a new set of wheels at an unbelievable price, I’d stay away.  My number one complaint about aftermarket wheels is that they are made of low quality materials and bend and crack easily.   When they are really bad, the wheels will almost be impossible to balance due to a poor casting job.  I have also seen brand new wheels out of the box that aren’t straight!  So buy good quality wheels from a trusted vendor, you’ll sometimes pay twice as much, but it’s worth it in the long run.  Most importantly, make sure that they fit!  If the wheel you are looking at says that it’ll fit BMW, Acura and Mercedes-Benz, it most likely won’t fit any of them very well.  Universal wheels are typically cheap and dangerous when fitted to your BMW.

Chrome wheels on BMWs are also extremely popular, and also a huge pain in the ass.  The biggest problem with chrome wheels is that aluminum just does not like to be chrome plated.  Over time the chrome plate will begin to flake off, or bubble from underneath, causing all sorts of problems.  Not only will your wheels look like crap, but that flaking will also cause the tire to slowly leak air as it is unable to create a good seal.  I would stay away from chrome wheels unless you really have to have them.  A good aluminum wheel, painted or polished, looks great.

When deciding on what size wheel to purchase there are many things to consider before you buy into a wheel and tire package.  When changing wheels, you MUST stay within 5% of the factory’s original overall wheel and tire circumference on all BMWs produced after about 1986.  The Anti-lock Braking system depends on the wheels being of a certain size and is constantly calculating a rotational rate of each wheel to insure that the car is traveling as it should.  Later BMW’s are even more sensitive to this.  If you go too big, the ABS/DSC system will shut down and your instrument cluster will light up like a christmas tree.

Aftermarket BMW Wheels

In order to maintain this overall circumference, you’ll find that the bigger the wheel, the lower the side profile will be for the tire.  Low profile = thin tires = possible issues.  In the BMW suspension system, tires are the first line of defense throughout your every day driving.  As you lower and lower your tire’s profile, the ride of the car will get less and less comfortable.  Think of tires as women’s shoes — As her heels get taller and taller, it looks hotter and hotter, but the comfort level drops with every inch she adds.  So if you are currently running a 45 profile tire and switch to a 35, or even a 25, you are going to feel every single pepple on the road as the tire loses its ability to absorb some of the everyday shock it was doing before.  Decide how comfortable a ride you want before going too large on the wheel and small on the side profile of the tire.

When BMW decides on a particular wheel to fit to a particular car, they calculate the effect it will have on the suspension of the car and those suspension components are built accordingly.  In basic terms, they figure out how much cusion a 45 profile tire will produce and how much wear and tear the bushings, ball joints, and shocks will need to endure to work with that amount of cushion.  So, if you decrease the sidewall amount by switching from a 17″ wheel to a 19″ wheel, those components will wear faster, so be prepared to spend money sooner on worn out parts, as you’ll be stressing them beyond what they were designed to tolerate.

So happy shopping, and keep these things in mind before you spend your hard-earned money on a set of wheels that you’ll regret later.  More importantly, before spending any money on extras and add-ons, make sure that your BMW is in great running order and is not in need of any repairs as the money would be better spent on maintaining your car so it’ll continue to serve you well.

Chris Keefer

Independent Motorcars

5836 Autoport Mall

San Diego CA 92121