Dale Amy
March 3, 2010

Few modifications can have as profound an impact on a classic Mustang or Ford as the right set of rims and tires-a declaration that holds true for both looks and performance. In fact, we can think of no other single investment so effective at personalizing a ride. Back in the 1960s, names like Cragar, Ansen, E-T, and American Racing were common buzzwords when talking about "mags" for one's muscular Ford. Like most other aspects of life, things were simpler then-rim diameters beyond 15 inches were practically unheard of, hardly anybody upsized their brakes, and wheel manufacturers could be counted without even taking your socks off.

Today, the wheel market abounds with brand names, and the range of available diameters, styles, offsets, prices, and even materials and construction is positively staggering. For the truly custom-minded, some companies will now build rims to customer specs. But while it's easy to get all wrapped up in the appearance equation, your first and foremost task in all this is to be sure that whatever hoops and rubber you decide upon will actually fit. Few things are more disheartening than to hear or feel that pricey new rolling stock rubbing or scraping on something even before their large Visa bill arrives. This fit thing may be relatively straightforward if you haven't, or don't plan to, modify your ride's brakes or other major suspension components, and are sticking with near-standard-size wheels that are specifically engineered for whatever classic Ford you're working on (like maybe going from 14x6s to 15x7s). Naturally, such off-the-shelf simplicity goes out the window when shopping for a truly custom look, when sizing after track width-altering suspension mods, or when trying to work around manhole-sized brake rotors or giant mono-block six-piston calipers.

So, where to begin? As with any project, the best place to start is with an overall plan, especially in relation to chassis and braking upgrades. For example, if your ride is to remain otherwise nearly stock, odds are you may not want to go too radical with its new footwear, especially if you're not thinking of lowering ride height. The tall tire sidewall that comes with a stock 14-inch rim is visually forgiving of any gap between it and a wheel lip, whereas the ultra-low profile rubber necessary for something like 18-inch rims can make stock ride height look both geekish and agricultural. On the other hand, a slammed and radical ride will in all likelihood demand more than 15-inch footwear.

Practically speaking, we can't foresee a lot of application for rim diameter greater than 18 inches on a classic Mustang. Beyond that, the required tire sidewall height becomes so short as to start looking out of place on something that was designed more than four decades ago. Remember also that such short sidewalls exact a stiff (pun intended) ride penalty. But, hey, if you're bound and bent on a set of 20-inch blings, maybe the following info will help you determine if it's even possible.

Tired yet?
We can't talk about rims without some mention of tires, and that brings us to a quick discussion of "plus sizing"-the concept of going to a larger wheel diameter while staying as close as possible to original overall tire diameter and circumference. Proper plus sizing retains both speedometer accuracy and good visual proportions, while also avoiding any change in effective final drive ratio, and hopefully taking height-related clearance issues out of the equation.

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