Mark Houlahan
Brand Manager, Mustang Monthly
November 1, 2006
Contributers: Wayne Cook Photos By: Wayne Cook

One of the most important improvement we do to our classic Fords is upgrade the wheels and tires. Not only do wheel and tire sizes usually increase, but we can also take advantage of technology that is ever evolving.

Replacing a steel wheel with one made of aluminum reduces unsprung weight, and that's always a good thing. Another plus is that an aluminum wheel can be a thing of beauty, while a stamped-steel rim is rarely so.

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When it comes to tires, few would argue that a bias-ply or bias-belted tire is better than a modern radial. The only exception we can think of is for concours-show usage. Modern radial tire technology just keeps getting better and better, and this is something many classic Ford enthusiasts should take advantage of.

The first issue in any wheel and tire upgrade is determining whether the desired combination will fit your car. You'll want to fill the wheelhouse completely while having no part of the tire protruding from the car and no interference during steering or suspension travel. Remember also that once you mount a tire to a wheel, you've bought both. At that point, no company will refund your money if the combination you've selected doesn't fit your car.

We'll examine some popular wheel and tire upgrades, and talk about some of the different aspects of size that you need to be aware of before you shop for a new set of rolling stock. To begin, you'll need to determine the fitment parameters of your car. First, you must measure the backspacing on the wheel you want and the wheelhouse depth on the car you have.

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'65-'66 MUSTANGS
Wheel Backspace Tire Size
15x6 4.000 P215/70R15
15x7 4.250 P225/60R15
15x8 4.500 P235/60R15
16x7 4.250 P225/60R16
16x8 4.500 P225/50R16
17x7 4.250 P205/50R17
17x8 4.500 P235/45R17
'67-'70 MUSTANGS
Wheel Backspace Tire Size
15x6 4.000 P215/70R15
15x7 4.250 P225/60R15
15x8 4.500 P225/60R15
15x9 5.500 P235/60R15('69-'70 only)
16x7 4.250 P205/55R16
16x8 4.500 P255/50R16
17x7 4.250 P205/50R17
17x8 4.500 P235/45R17
17x9 5.500 P245/40R17 (P275/40R17rear axle)
18x10 6.500 P225/40R18
20x10 5.000/custom P225/35R20 (rear axle only)

Why Nitrogen in Tires?
Craig Knarich of Pit Crew Tire Service explained to us that since nitrogen is denser than oxygen, the larger molecules escape less easily from tires, resulting in a more gradual loss of pressure over time. Research shows that a tire inflated with nitrogen loses its pressure three times slower than if it were inflated with air. As a rough rule of thumb, if your tire pressure is 20 percent below the optimum, you'll reduce tire life by up to 50 percent and the additional rolling resistance can add 10 percent or more to your fuel consumption. Across the life of a tire, that's a big financial penalty. The Department of Energy reports that 4,000,000 gallons of gasoline are unnecessarily wasted every day due to low tire pressure.

Nitrogen is also moisture-free, so pure nitrogen-inflated tires experience less steel-belt and rubber degradation, resulting in longer tire life. The use of nitrogen also reduces valve and wheel corrosion. Nitrogen-inflated tires also run cooler and require less maintenance, according to a Goodyear application bulletin. Non-flammable nitrogen technology has been used in race-car tires for over 30 years.

Decoding Tire Codes
The series of letters and numbers on a tire's sidewall tell a lot about what you're getting for your money as well as the tire's capabilities. The first series of numbers denotes tire size. After that, the two most important things to look for are the service description and the uniform tire-quality grade or UTQG.

Using the information in the service description, we know that a set of our P215/60R16-94T tires will carry a load of 5,908 pounds at up to 118 mph safely. While the load range is fine for our '67 Mustang, the 118 top speed could easily be exceeded, calling for a tire with a higher speed rating. We should note that the speed rating doesn't apply to tires that are worn out, repaired, damaged, retreaded, or not properly inflated.

LOAD INDEX CAPACITY (IN LBS)
71 761
72 783
73 805
74 827
75 853
76 882
77 908
78 937
79 963
80 992
81 1,019
82 1,047
83 1,074
84 1,102
85 1,135
86 1,168
87 1,201
88 1,235
89 1,279
90 1,323
91 1,356
92 1,389
93 1,433
94 1,477
95 1,521
96 1,565
97 1,609
98 1,653
99 1,709
100 1,764
101 1,819
102 1,874
103 1,923
104 1,984
105 2,039
106 2,094
107 2,149
108 2,205
109 2,271
110 2,337

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The second half of the service description is known as the speed rating. Devised to give the buyer an awareness of the tire capability for safe operating speed, it is the T in the 94T service description. Three of the most common speed ratings are S, H, and V. The complete speed-rating table is as follows.

SPEED RATING MAX MPH
M 81
N 87
P 93
Q 99
R 106
S 112
T 118
U 124
H 130
V (VR) 149
W (ZR) 168
Y(ZR) 186

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