This is the most basic measurement on a wheel.
Simply, wheel diameter is the height of the wheel.
Late Model vehicles don’t generally see smaller than 14? and can go as high as 20? from the factory.
Aftermarket wheels generally are going to be larger in diameter than their factory counterparts.
When going to a larger diameter wheel you must also go to a larger diameter tire.
The reasoning for going to a larger diameter wheel is different for different people.
Reasons for changing wheel diameter:
- Looks. Generally speaking a larger wheel looks better than a smaller wheel, of course there are exceptions to this rule. There tend to be more styles of wheels in the larger (17?+) diameters as well.
- Brake Clearance. Larger diameter wheels have more space for larger rotors and larger calipers. When changing wheel diameter be sure the new size will be compatible with your current/future brake setup.
- Tire Selection. Changing wheel diameter can open up access to a larger selection of tire sizes and compounds. When selecting wheel diameter one should also look at available tire sizes and pricing, just because a 255/35 18 is the ideal size in both width and height doesn’t mean it is readily available in all compounds.
- Offset and Width availability. This is my personal favorite reason to change wheel diameter. Some vehicles come equipped with a relatively uncommon wheel diameter. The MY03 WRX is a good example, with a factory size of 16×6.5 and an offset higher than +50mm finding a 16? wheel with the right width and offset can be difficult. Upgrading to a 17? wheel allows for more widths and offsets to choose from.
Negative Aspects of Changing Wheel Diameter:
- Weight. Looking at two wheels of the same brand/style/width and offset where the only difference is diameter the larger diameter wheel will weigh more. Weight is the enemy when it comes to performance (handling, acceleration, deceleration). The extra weight can also cause added stress to a vehicle’s braking and suspension systems. When upgrading from a factory wheel it is possible to save weight (even when increasing diameter) if the correct brand/model/size is selected.
- Cost. Changing the diameter from the current size costs money, not only does one need to purchase the new wheels, but the current tires will not work on the new wheels which means it’s time to buy new tires. When upgrading to a larger diameter wheel the tires tend to be more expensive (and they get more and more expensive the larger you go).
- Too big. When increasing wheel diameter it is possible to create rubbing problems that were not there previously. Just because some guy down the street fit 22? wheels on his monte carlo doesn’t mean they will also fit on your accord coupe*. Increasing wheel diameter without increasing the overall tire diameter is the key, this is accomplished by decreasing the sidewall height of the tire**.
- Too small. When decreasing wheel diameter it is possible to create rubbing problems on brake and suspension components. Before decreasing wheel diameter be sure the needed clearance is there.
- Availability. When changing wheel diameter the concern of being able to replace the new wheels in the event of an accident or failure one should consider the wheels availability. Is this new diameter a limited edition wheel? Is this new diameter hard to come by? Do I need to wait 10 months for them to come by boat? Are they stocked by my favorite vendor? All of these availability questions can be answered by the company you purchase the wheels from.
*Is it possible to make anything fit? Of course and we will get into model specific fitment at a later date.
**Detailed information on tires will be covered at a later date.