Every time a P.A. system or microphone is turned on anywhere in the free world, the person in control of the mike says, ``Testing, 1-2-3...Testing.'' Why is that an automatic response from anyone in this situation? Don't you find it annoying?
The truck tire industry isn't any different. Any time a dealer approaches a potential fleet account with new tires or retreads, after the sales pitch comes the perfunctory, ``How about testing a few tires and see what they'll do?'' (Testing, 1,2,3...Testing!) Let me tell you, fleets find this annoying.
Tire testing for fleets is a royal pain in their maintenance systems. For many fleets, simply finding enough vehicles to test tires requires a great deal of concerted effort.
Then it demands considerable labor to take tire tread depth measurements and record the findings. (This is pretty tedious work for the average mechanic, who would rather be doing the more glamorous transmission overhaul and is being paid the big bucks to do mechanical work.)
Then someone has to analyze the data and compute the results-probably the same person who fielded the sales pitch.
Is it any wonder he or she may be annoyed by the presumptuousness of this query, especially since this was not the first tire dealer that day to pose that question?
Tests cost time and money and are not easy to do correctly. Since fleets usually bear the burden of running tire tests, I suggest you differentiate yourself from the ``crowd'' by offering to run the tire test yourself on the fleet's equipment. Any fleet will take you up on that proposition.
However, it's important to know how to run the test correctly in order to reduce the large number of variables that can influence the quality of the results.
Let's look at running a simple treadwear test. The first thing to do is determine what you are testing for. It is important to test only one variable at a time: one brand of tire vs. another brand of the same type/vocation; one retread brand vs. another; mold cure vs. precure; a conventional size tire vs. a low-profile tire etc.
Notice, in all cases you are running two samples of tires: the test vs. a control group or another test group. A real test is not just throwing a few tires on a vehicle and seeing ``what they'll do.''
Next, determine the number of tires required to ensure that the test results will be statistically significant. (Statistically significant means the odds are good that the fleet will obtain similar results after buying your tires on a regular basis.) To get repeatable results, you should have at least 30 tires of each test group at the end of the test.
Was that a cry of shock I just heard? I know that's a lot of tires. You can get by with smaller samples that may provide useful data that indicate differences in the groups of tires in the test, but the results may not be repeatable.
My advice is to use as many tires as possible in each test group if an ending number of 30 is out of the question.
Now select the vehicles on which the tires will be installed. Tire wear rates can be affected by vehicle type, make, year and variations in engines and transmissions. Use identical vehicles in all test groups. If this is not possible, use the same number of differently spec'ed vehicles in each group.
Of course the vehicles should be representative of the fleet's equipment, and if they are new, that is better yet. All vehicles should be aligned at the start of the test.
The vehicles should be hauling approximately the same weight, traveling in the same geographic area(s) and the drivers should be representative of the fleet's personnel. Drivers with unusual driving habits should be screened out.
All test tires should be installed within a 30-day time frame to ensure they all are exposed to the same variations in weather.
All new and retreaded tires in a treadwear test must be made within a one-year period as designated by the DOT code to eliminate changes in casing design.
If testing retreaded tires, use the same brand casing for all tires in both the test groups. Inflate all tires to the pressure the fleet normally uses, ensuring that it is adequate to carry the load, and use positive-seal valve caps. It's wise to visually identify all test tires or their wheels in some manner so you can pick them out easily.
Once the tires are running, tread depths should be measured at specific intervals. Tires on vehicles in over-the-road operations should be measured at least every 30,000 miles or at scheduled intervals. Mileage projections can be made when at least 50 percent of the tread has been worn, but should only be used as indicators of tire performance.
For tires in pickup and delivery service or other high-wear conditions, use measuring intervals that equate to 25, 50 and 75 percent of wear and at removal. These percentages may be based on anticipated mileage or time, depending upon the operation's means for determining tire life.
Wheel position affects tire wear. Typically, a tire on the left front position of a truck wears faster than the one on the right front. On tandem drive axles and tandem trailer axles, the tires on the rearward axle wear faster than the tires on the forward axle.
For this reason, treadwear evaluations should be analyzed by each position. Left steers should be compared with left steers on the control or other test vehicles and rights with rights etc.
Usually, half the test vehicles are equipped with tires from one test group while the other half has tires from the comparison group.
If desired, tire test groups can be mixed on the same vehicle to equalize exposure to random variables. The positions of the test and control tires placed on one vehicle should be mirror images of the tires placed on the second vehicle.
When inspecting tires, make sure the same person takes the tread-depth measurements. Take such measurements in each ``major groove'' in two ``representative'' locations on the tire about 180 degrees apart. Make sure not to take the measurement on the treadwear indicators.
Check inflation pressure and look for irregular wear, cuts and snags in the sidewall, remove nails in the tread if they don't penetrate the casing, and note driver comments on tire performance.
If tires have to be removed for repair, try to have them reinstalled in the same position. If this is not possible, the tire is ``lost'' from the test as are tires that are damaged beyond repair.
When the test is complete, analyze the data. Exclude tires removed for road hazards and accidents, but include those removed due to manufacturing defects.
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.
And voila! Tire treadwear tests made easy! All you have to do is do the work. But at least you know how. The fleet will be really impressed and grateful you took this burden off its shoulders.
You'll be a prince among tire dealers and will undoubtedly earn the fleet's business, since you were a professional with help and expertise rather than an annoyance.
Ms. Fisher, former president of Roadway Tire Co., is a consultant based in Columbus, Ohio.
For single axles with dual tire assemblies, a left-side, right-side installation method can be used for test groups.
The X-pattern installation method for tandem axle vehicles is seen above. Mixing sample groups on vehicles is less important as sample size increases.