What causes alloy wheels to bend?



I have owned three cars. The one with 14" steel rims never experienced any rim problems ever. The two cars with 16" alloy wheels ended up needing new rims after bad potholes or slowly became unbalanced with every extra pothole.

I want to purchase a new Subaru Legacy Outback, but the package comes with 17" x 7" alloy wheels. The base package comes with 16" x 6.5" steel rims.

I live in the city of Philadelphia where potholes, rails and other road issues are commonplace. I don’t want to continue replacing alloy wheels if I can just avoid the problem by purchasing steel.

My question, what really causes alloy wheel damage (besides the actual pothole)? Is it a poor quality wheel? Is it a suspension issue? Is it due to the tire aspect ratio?

Is there any way for me to predict the quality of an alloy wheel?


You may find this url interesting: http://en.wikipedia.org/wiki/Aluminium_alloy

In your case you have pointed to two issues.  First most consumer alloy wheels are not as strong as steel wheels.  The real race car wheels are stronger but you would pay more for one than you are paying for all four of what you have.  The second part are those 16" wheels.  They likely have "thin" tyres.  that is they sidewalls are not as tall as the tyres on your 14" wheels so they can't absorb the same size bumps.  

Those 17" wheels are likely to be even worse.


This has been one of my suspicions, that lower aspect ratio (50 series) tires allow more damage to the rim than do higher aspect ratio (65 series) tires. When a car with low aspect ratio tires hits a pothole, does the tire sidewall collapse and the rim hit the road surface? Is that what causes the damage? Are there tires with stronger sidewalls that would be less prone to this? would higher inflation pressure reduce this damage?


Interesting. So basically the aluminum alloys are lighter than steel but are also equally less stiff (strong) than steel. I continued researching the internet after reading this article and found that alloy wheels are of higher consistency than steel because they are cast from liquid alloy vs. the steel rims that are stamped from steel plate. Other articles I read mentioned that aluminum alloys used in rims are stronger than their steel counterparts.


Lower aspect ration tires subject rims to higher likelihood of damage. If your brake calipers iwll accomodate 1" smaller wheels, go to those (in steel) with appropriate tires (see www.carbibles.com for a good calculator) and you should have fewer problems.

But I gotta tell ya, I drive 215/45s, even in Boston, as does my son who lived in Boston, and neither of us has damaged our alloy rims. The number of problems you’re having suggests that more care might be in order also. Sorry, but I gotta be honest.


Of course the after market wheels are not strong. Of course there are some, like BBS, ENKEY, RAY and a few others but they cost. Another thing, low profile tires do not help them either. Not sure if a lot of people notice, but most sports cars do not really have really low profile tires. Most of them they have high 245 or higher width with 35 series, that is almost as a 45 or 50 series tires. Also, you can have aspect ratio higher and still handle great if you get a tire with a more weigh loading options.


Don’t confuse stiffness and strength, they are completely different. Aluminum is 1/3 as stiff as steel; doesn’t matter what alloy it is. However, there are many aluminum alloys that are stronger than many carbon steels and alloy steels, so even though the aluminum alloy in the wheel may be less stiff, it’s still possible for it to be stronger.

In the end though, it’s the design of the wheel, including the geometry that determines the maximum load capacity, not just the material that wheel is made from.