Straightening a bent alloy wheel is more complicated than just taking a hammer and pounding out the bend. What once may have worked for a steel wheel will most likely damage an alloy wheel beyond repair so it is very important to bring your bent alloy wheel to a shop that really knows how to straighten wheels. The straightening equipment that is used to straighten out large bends or small bends in wheels has become very sophisticated.
First, the tire must be removed from the wheel because there is no way to accurately fix a bent alloy wheel with the tire on. Also, because it is necessary to use heat while repairing a bent wheel, leaving the tire on while the wheel is being straightened could cause damage to the tire.
Next, the wheel must be attached to and spun on equipment with a gauge that will show exactly where the alloy wheel is bent. It is true that just spinning a wheel on a balancing machine, for example, can help you see the wheel is bent but when it comes time to repair a bend in an alloy wheel properly then a gauge is a necessary tool to see where every bend is located (most bent wheels have more that one bend in them).
After the wheel has been spun with a gauge and marked where all the bends are located then the bent wheel can be straightened out. The first wheel-straightening machine that the bent wheel is attached to is used for taking out larger bends. With the wheel secured to the machine, heat can then be applied to the bent area of the wheel. Depending on the make of wheel and type of alloy used we usually heat the wheel to somewhere between 250 – 350 degrees. When the wheel is hot enough the bend is literally massaged out. In some cases this may take a few attempts since the aluminum wheel has “memory” and sometimes wants to return to its starting point. The use of a measuring gauge is critical here because when the bent wheel is being straightened out there must be an indicator as to what is “back in round” – you cant just press the bend in wheel until it looks round (because it probably isn’t).
After all the major bends have been taken out then the wheel is running true with just VERY slight bends around the rim. This is when the wheel is connected to the second straightening-machine where a high-powered torque motor rolls the wheel over a “shaper” that re-shapes the wheel. This process varies it time but will eventually get out the slightest bends in the wheel so the wheel will be running true within hundredths of an inch. All wheels are allowed a certain amount of variance (usually hundredths of an inch) but the necessary last step when straightening a bent alloy wheel is to have a good balancer. With the use of a balancing machine (after the tire has been re-mounted) then the last bit of variance can be trued out using weights.
One final straightening-machine (that is only used when necessary) helps us with lateral bends in the wheel – or when the very edge of the wheel is bent inwards or outwards. By using this combination of straightening-machines we have a mix of what we call half science, half art form, which allows us to straighten most of the bent alloy wheels that come into our shop.