Comment on Wheels Tyre Test – April 2007
The Wheels tyre test in the April 07 issue is a credible effort to objectively test tyre performance, and the test has turned up some interesting and useful results.
This is a difficult thing to do, and car and tyre manufacturers go to exhaustive lengths to assess tyre performance and match it to a vehicle, usually on a test track or racing circuit hired for the day. The stakes are high for both car and tyre manufacturers, and usually they spend lots of research and development dollars to ensure they get the best result possible.
Both car and tyre manufacturers have well-developed test protocols established from many years experience of this type of testing. These test protocols must “square up to” the same issues that faced the Wheels crew in planning and executing the 2007 Tyre Test. Some of these issues are:
1. Controlling the test conditions
Variation in test conditions means the difference in results from successive test runs on different tyres isn’t solely due to the different performance of the two sets of tyres, and effectively renders the results useless. Significant variations in ambient temperature, track surface (surface roughness/texture, level of “contaminants” such as rubber dust, etc.), water depth for wet testing, degree of wear on test tyre treads, even wind speed – the list goes on and on, and all factors must be controlled or their effect minimised. The Wheels tyre test crew did a pretty reasonable job in this department.
For example, it isn’t possible to eliminate the effect of wear on a tyre tread, as some wear will occur during the course of the test. Rather the amount of wear must be minimised by limiting the number of test runs each individual tyre does, so that the wear is minimised and does not become a significant factor. The Wheels crew did this by using “objective” assessment methods for all the tests conducted. Using objective assessment methods means the number of test runs can be minimised, the amount of tread wear is minimised, and the length of time taken to complete any set of tests is minimised, meaning there is less chance of variation in weather conditions – which would cause variation in the tyre performance, and therefore unreliable test results.
2. Objective versus subjective assessment
Objective assessment simply means that some mechanical or electronic means are used to measure tyre performance – for example, measuring stopping distance, lap time, deceleration/acceleration – are all objective assessments. Objective assessment is regarded by development engineers as being more reliable and repeatable, but in the final analysis, does not provide test data on driver feel criteria, such as linearity and predictability in a tyre’s performance. Some tyre performance parameters, such as steering response or skid recovery, can only be tested subjectively – that is – rated by a test driver.
Subjective testing, means the test driver rates the tyre’s performance compared to the previous set of tyres, during multiple test runs on different sets of tyre types/brands. Subjective assessment is much more difficult to do well, and requires a much greater investment in time and money. With any realistic number of test tyre types, subjective assessment means a greater number of test runs must be done, as each set of tyres must ideally be compared with each other set of tyres, to enable the driver to make a direct comparison between each pair of tyre types (or brands).
For example to test 4 tyre types/brands A, B, C and D ideally requires a total of 8 test runs, and 2 runs on each tyre. The tyres would be tested in the following order:
A, B, C, D, A, C, B, D
With more sets of tyre types/brands to be tested, the number of test runs that must be done increases significantly. This often means that additional sets of each tyre type/brand must be used in the test, to limit the effect of tread wear on the test results.
As subjective testing relies on a driver’s assessment of a tyre’s performance, issues of driver preference, or bias, can also creep into the results. For this reason, more than one test driver is used, and the results pooled.
Tyre and car manufacturers rely on a combination of objective and subjective test methods, depending on what tyre performance parameter is being tested.
3. How can the test results be used?
Accurate and repeatable results are what we want from any test – otherwise we haven’t succeeded in sufficiently controlling the test conditions or there is some other basic problem with our test procedure.
The Wheels tyre test covered a number of very important tyre performance characteristics. The Wheels test crew went to considerable lengths to control or mitigate test variables, and obtained credible and useful results. But can these results be applied to my or your car?
Unfortunately, the answer to this question is not simple, although some indication of an answer can be seen in the different rankings obtained for the two different tyre sizes used in the test. There were relative differences in the performance of the different brands in the two tyre sizes, when tested on two quite different vehicles. This is not at all surprising, when it is considered that most aspects of tyre performance on a vehicle are affected by interactions with the vehicle and it’s suspension, wheels and brakes. These interactions are complex, and often unpredictable without specialist engineering knowledge, which of course, is not readily available to the average tyre consumer. A further complication arises from the influence of the multitude of electronic vehicle performance aids that are becoming increasingly available on modern vehicles – such as ABS, EBD, EBA, ESP, etc, etc. These technologies can tend to mask or compensate for the differences between tyres.
4. How do you use this information for your own tyre purchase decision?
Which is the best tyre for you and your car? This is really two questions – the first being what tyre performance parameters are important to you – only you can answer – but Wheels’ comments are worth considering. The difference between “cheap” and quality high performance rubber as tested by Wheels in this test, can often be significant, and can be the difference between injury, or walking away from an accident or potential accident. The difference in cost between the “cheap” tyre might be recovered many times over, by the absence or reduction in damage to your car, or even worse, in injury to yourself.
The second question – what tyre works best on your car? By all means use the Wheels test as a guide. Another way is to check the CarbonBlack website for comments made by other drivers, who just may have commented on your vehicle and the tyres you may consider buying. While most consumers won’t have had the opportunity and the skills to really put their car and its tyres to the sort of test run by Wheels, they will have experience in the everyday conditions that may be just as relevant to your decision. The more comments you can aggregate and factor into your personal assessment and decision, the better informed you will be!