Traction equals performance and for traction you need rubber. The wider the better, but how wide is too wide? Since we don't all own tire and wheel shops, we can't randomly test-fit tire and wheel packages all day just to mount wide rubber. So we need a way to test-fit tires without mounting them on wheels. Lucky for us there's already a company making a tool that allows just that.
The tool is called the Tire Mount Mate from Wheel Works, and it allows test-fitting tires on just about any size wheel and on any car or truck. The tool can simulate wheels from 7 to 16.5 inches wide and can create up to about 12 inches of backspacing. The tool is cast from 1/2-inch-thick aluminum, so it's strong enough to bolt the tire on the car with the suspension, creating just enough down force to simulate the bulge in the sidewall when it's inflated and sitting on the ground. The Mount Mate IS NOT designed to support the weight of the vehicle, so don't lower your car down on it.
Where the Mount Mate really comes in handy is for test-fitting large tires on a car to figure out what backspacing (also referred to as offset) will be needed when you order your wheels. If you want to go drag racing and have a traction problem, this tool allows you to mount the biggest tire you can fit and check clearance even under full suspension compression with the help of a few friends' pushing down on your bumper while the axle is supported on jack stands. The only thing the Mount Mate cannot simulate is how wide the inflation pressure will make the sidewalls grow.
The best way we've found to determine this is to measure a mounted tire's inflated width on the same size wheel you plan to run and compare that to the uninflated tire size as it hangs on the Mount Mate so you'll have a good idea of how much it'll grow. That's important because drag tires have very soft sidewalls that will grow quite a bit when inflated. You'll need to know if the sidewalls will clear your car's wheelwells, frame, and leaf springs or lower control arms. The Mount Mate will let you hang the tire you want under your car and play with wheel backspacing until you get it right.
Up front, the Mount Mate can really help out if you're building a g-Machine and want the widest rubber for grip. Turning the wheels introduces a whole new area of problems with wide front rubber, and braking can compress the suspension enough to make wide tires rub. Again, the Mount Mate can help out here, along with a few friends' pushing down on the front end. With jack stands under both control arms, mounted as close to the tires as possible for leverage, hang a tire on the Mount Mate and bolt it to your car.
Then have your buddies push down on the bumper or frame (don't push on the fenders because they may dent) while you turn the steering wheel lock to lock. You'll need one more sharp-eyed friend to look underneath and see if the tire is hitting anything. Be especially careful to check interference at the tie rod ends and control arms: Remember a wheel will go in there, so leave extra room, because deep wheels with lots of backspacing will hit these spots.
In addition to trying out a few tires with the Mount Mate we've included a bunch of tire and wheel tips for you to check out. If you want to learn more about fitting big tires and wheels on your car and what proper sizing can mean for you, check out the Tire and Wheel Tech Sections on The Tire Rack's Web site at www.tirerack.com. The Mount Mate isn't inexpensive (roughly $300), but get a few friends to go in on it with you (or charge them to use it) and it won't be long before it's paid for. Anyway you slice it, the need for big rubber will always be there, and this is one of the best ways to satisfy it.
Tire Sizing ExplainedTires used to be sized in inches and were pretty easy to figure out. Drag racing tires and most large truck tires are still referred to by height and width, like 28x10.5, or 35x12.5, etc. Most passenger car tires use the metric sizing system, which lists the overall tire width from sidewall to sidewall, aspect ratio, and wheel diameter, in that order. It may also have the letter "R" for "radial" or "ZR" for "high-speed radial" in there (see sidebar "Sidewall Definitions" for more info).
Comparing tire sizes today is difficult due mostly to the aspect ratio, which is simply the ratio of sidewall height to width. The aspect ratio is actually a percentage of the tire's overall width and determines the sidewall height. For example: a 225/60R16 tire has a 225mm width and its sidewall is 60 percent of that (225 x 0.6 = 135mm). To determine the tire's overall height there is a little more math involved. The folks at Falken Tire were kind enough to give us some formulas to help out. Remember: To find inches you must first convert from millimeters. The conversion factor is 25.4 mm per inch.
225/60R16 Tire Example1. Calculating Width Width / 25.4 = Actual width in inchesEx. 225 / 25.4 = 8.86 inches wide
2. Calculating Overall HeightCalculate sidewall height by multiplying the aspect ratio times the width.Ex. 0.6 x 8.86 = 5.32 inches
3. Calculate total sidewall height; there is sidewall both above and below the rim.Ex. 5.32 x 2 = 10.64 inches
4. Calculate total overall height by adding the rim diameter in inches to the total sidewall height. Ex. 10.64 + 16 = 26.64 inches