Tire tests involve a lot more than buying a set of tires and installing them on a tractor to “see what they’ll do.” To do it right-to collect meaningful data you can use to make a better investment in your tires-you need a plan. Here are six ideas for making the results of your tire tests more reliable:

1. Decide what you want to measure and compare. Common tests pit one brand of tire versus another, one retread brand versus another, mold-cure versus precure, a conventional-sized tire versus a low-profile tire, etc. Test only one variable at a time, but in each case run two samples: the test product versus a control group or another test group.

2. Determine how many tires you’ll need. What you want from your test, remember, are repeatable results. Ideally, you’ll need at least 30 tires of each group at the conclusion of testing. That’s a lot of tires; you can get by with fewer and still get useful data, but such results may not be repeatable. If 30 is too many, use as many tires as possible in each test group.

3. Choose which vehicles, drivers, and routes to use. Vehicle type, make, model year, and variations in engines and transmissions all can influence tire wear-rates. That’s why you should use identical vehicles in all test groups.

If this isn’t possible, use the same number of differently spec’d vehicles in each test group.

Of course, the vehicles should be representative of your fleet’s equipment. Test vehicles should haul approximately the same weight and travel the same geographic area, and the drivers should be representative of your fleet’s personnel.

All vehicles should be aligned at the start of the test. All test tires should be installed in a 30-day time frame to ensure they are exposed to the same weather variations.

4. Compare apples to apples. All new tires and retreaded casings in a tread-wear test must have been manufactured within a one-year period (as designated by the DOT code) to make sure you won’t be affected by changes in casing design. If you’re testing retreads, use the same casing brand for all tires in both groups.

Inflate all the tires to the pressure your fleet normally uses, ensuring it is adequate to carry the load, and use positive-seal valve caps. It is wise to mark all test tires or their wheels so you can easily pick them out visually.

5. Measure carefully. Once your tires are running, measure the tread depths at specific intervals. Tires on vehicles in over-the-road operations should be measured at least every 30,000 miles or at scheduled PMs. You can start to make reliable mileage projections when at least 50% of the tread has been worn.

For tires in pickup and delivery service or other high-wear conditions, use measuring intervals that equate to 25%, 50%, 75% of wear and at removal. These percentages may be based on anticipated mileage or time, depending on your operation’s means for determining tire life.

6. Scrutinize the data. Because wheel position affects tire wear, it’s imperative to analyze each position separately.

For one wheel position, compute the average mileage for each test group by adding the total removal mileage of all the tires in that position and dividing by the number of tires that completed the test from that group.

In cases where dual tire/wheel assemblies are used, average the inside and outside tire for that position by tire test group.

To determine cost per mile, simply divide the original cost of the tire or retread by the average removal mileage.

When your test is complete, exclude tires that were removed for road hazards and accidents, but include tires removed due to manufacturing defects. Accidents happen, after all, but a defect-related failure is a something you shouldn’t ignore.