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10025 All About Tires - Vintage & RWD Volvos

Created on 2011-03-03 by IPD Staff

One of the most often asked questions by Volvo enthusiasts is, “What size tire does ipd recommend for my Volvo?” No wonder, the vast selection in the tire market makes the choice seem overwhelming!

What do all the numbers mean?

Let’s start by defining some tire terms. The U.S. Dept. of Transportation requires that tires be marked with some specific information: tire size, speed rating, load range, tread type, pressure range, construction type, Universal Tire Quality Grading and the Dept. of Transportation’s approval code. Tire size is the most misunderstood and gives rise to most of the questions we receive. For example, in the 195-60 HR 15, found on most Volvo Turbo models, 195 is the section width, or the width of the tread in millimeters. 60 is the aspect ratio, a percentage used to determine the height of the sidewall. For example, the 195-60 HRI5 has a sidewall height of 195 x .60, or 117mm. When you hear talk of “50 series,” “60 series,” etc. tires, they’re referring to the height of the sidewall. Some sizes, such as the 185 SR 14 (most 240s), don’t list the aspect ratio. These are generally “80 series” tires with an aspect ratio of 80. The 15 in our example is the diameter in inches of the wheel which the tire will fit.

Reading The Letters

The first letter designation is the speed rating. H designates speeds up to 130 mph; S is for speeds up to 112mph and V is for speeds over 130mph. The letter following the speed rating designates the type of construction: R for radial, B for belted. Our 195-60 HRI5 example is a radial tire for speeds up to 130 mph. Load range, tread type and pressure range depend on the tire and use. They are important when the tire will be used in extreme conditions such as heavy towing or overloading. The Uniform Tire Quality Grading (UTQG) covers tread wear, traction and temperature. These are usually found on the sticker on new tires, although some manufacturers do print it on the tire. These ratings are not federally regulated, but are used by the manufacturer as a subjective means of comparing to other tires in its own line. This rating is of little use in comparing different manufacturers’ tires.

Trade Offs In Performance Tires

When considering performance tire sizes, keep in mind that there are generally drawbacks in any deviation from the original tire size specified by the manufacturer. Wide tires tend to hydroplane more than skinny ones and slide easier in ice and snow. They tend to follow grooves and cracks in the road surface, but boy are they fun in the dry!

Lower profile tires, like 50 and 60 series may feel harsher on bumps since they have less sidewall rubber to absorb impact. The advantage is that the stiff, short sidewall flexes much less in cornering, so more of your tread stays on the road providing increased traction. These generalizations don’t describe all tires but are useful in helping you make a decision. Here are the sizes we’ve used on Volvos:

  • 122, 1800 165-15 up to 215-60-15
  • 140, 160 165-15 up to 215-60-15
  • 240, 260 185-14 up to 225~50~l6*
  • 700, 900 185-14 up to 225-50-16

*May require fender lip bending depending on the wheel you use. If you’re considering oversized tires, stay within the tire manufacturer’s recommended rim width.

PLUS CONCEPT

When purchasing a new set of wheels you may want to consider going to a plus size. Here’s how the system works:
1. Maintains overall diameter
2. Decrease the aspect ratio (sidewall height)
3. Increase the section width of tire
4. Increase wheel diameter
 

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