Ever Wonder How Tires Are Tested?

Tire Testing From A to Z

There are three principal reasons tire manufacturers test their products:

  • Competitive Benchmarking – From material formulations to overall tire performance and on-vehicle testing, engineers want to get a firm grasp on what the competition offers prior to the development of their next new tire.
  • Research and Development – To develop a new tire, manufacturers test materials, compounds, reinforcements and completed tire designs. With large databases of material and performance information, computer modeling is used to accelerate the development process.
    Computers help develop constructions and mold shapes to produce optimal tread curvature. However, there are so many variables in tire design and construction that testing is required to verify the computer projections. It is especially important to ensure that the tread arc radius and footprint are correct. If the tire is too square, the tire will be harsh riding. If it’s too round, the handling may suffer. Irregular contours of the leading or trailing edges of the tread create noise.
  • Regulatory or Vehicle Manufacturer Performance Requirements – While the Department of Transportation has developed tire standards for the minimum requirements for tire performance, vehicle OEMs typically demand specific performance criteria significantly over and above the government standards.

Initial Development

Despite what most consumers probably believe, tires are very complex. Each tire has six major parts: the tread, belts, sidewall, body plies, beads and inner liner. There are as many as 200 different materials used on passenger tire production lines with a variety of processing techniques. Small changes to the materials or construction can significantly alter the final tire performance. There are many factors that can influence the quality and performance of a tire, increasing the need for testing during the development process.

The initial development of a new tire starts with setting basic targets. The manufacturer will pick specific reference tires. These may include some of the manufacturer’s own tires in addition to competitors’ offerings. Competitors’ tires will be reverse engineered and tested to establish benchmarks.

Computer modeling helps det-ermine a mold shape and overall tire profile. These digital models aren’t perfect, but they allow the engineers to begin roughing in the design of the tire’s carcass.

During this stage the designer will lay out the tread pattern. Key elements of the pattern design include determining the void ratio and the number of edges needed to meet wet and dry traction targets. Computer analysis is useful here to model linear snow traction, hydroplaning resistance and noise levels. Most manufacturers will still hand cut tread designs to confirm computer models because it’s still a more reliable technique.

Compound development starts out on a dynamic tester. Small blocks of rubber are cycled through different temperatures. These tests generate a curve of the “stiffness” of various compounds. Test results are evaluated to select a compound in line with the design targets.

A new tire’s construction, the number of plies, belt packages, sidewall stiffeners, etc., is generally a result of the engineers’ experience. Different manufacturers and their technical departments have more familiarity with certain constructions and will tend to work from there, unless they see a need to go into a different direction.

Once the tire construction dev-elopment work has been completed, tire testing begins to allow manu-facturers to evaluate the overall quality and performance.

While there are many ways to approach the testing process, the following is a common method:

Round 1 Testing

The goal at this stage is to verify the profile of the new tire and to get close on the compound. The tire’s construction may still be somewhat generic at this point, often based on an existing tire.

Most indoor dynamometer testing is done in this round. It will include endurance testing to determine the loads and speeds a tire can tolerate before it fails. Federal Motor Vehicle Safety Standards, enforced through the DOT have established minimum performance expectations for road-legal tires. Today, the DOT standards are too low to be meaningful except as a foundation for tire manufacturers’ own benchmarks.

Accelerated aging has been used extensively for the last six to seven years and the exact techniques are very closely guarded by tire makers. Accelerated aging elevates the temperature of a tire before it’s mounted on the dynamometer. It is combined with an increase in the tire’s inflated oxygen level while conducting load or speed tests. This promotes oxygen degradation of the tire and gives a more accurate picture of how a tire’s life is affected by extreme conditions.

Rolling resistance measures the force required to maintain forward movement at a constant speed. The lower the rolling resistance, the less energy required and the better the fuel mileage. OEMs put much emphasis on rolling resistance and there are pending federal requirements that will add extra to the importance of this test.

Force and moment tests measure the forces exerted on the tires at various angles, speeds and loads to determine how the tire will react and perform under different conditions. The data generated from these tests are commonly used in modeling programs used to “tune” tires to specific vehicles.

Other carcass durability tests include bruise resistance, bead un-seating and expanding a segmented rim inside the tire.

Round 1 outdoor testing focuses on trying to get the tire’s profile right and tuning the tread pattern. The list of performance characteristics the manufacturer will look at include: noise, snow traction, tread wear, wet and dry traction, and stopping distance. Some tests are done on test vehicles; others use trailers with test and control tires.

Handling tests during this phase spend a lot of time dealing with the tire’s on-center feel. The goal is to make the tire pick up steering inputs smoothly without making the tire twitchy. This can be a huge problem.

Round 2 Testing

This middle phase largely cont-inues Round 1 testing. Handling development continues and carcass durability testing should be complete by the end of Round 2. The goal of Round 2 is to end up with a tire that is 90%-95% developed.

Round 3 Testing

The focus of Round 3 testing is on consumer “feel” – trying to replicate what the end user will experience. Handling tests emphasize response, precision (tracking a straight line), mild and maximum cornering and progression, measuring how the tire reacts to steering inputs and its breakaway characteristics at the limits of traction.

Treadwear testing is part of Round 3. Tiremakers look for more accuracy than the wear projections used for UTQG. Indoor tests are not enough and the initial wear rates observed early in testing aren’t stable. There are many variables to consider, so that it remains somewhat of an art.

Additional snow testing during Round 3 confirms earlier tests.

Finally, validation of production tires is done, including more indoor testing and handling evaluations, but snow testing and treadwear are generally not repeated. Section analysis is done to assure that production tires are consistent with the design and that the plant has built the tire to the design specs. Compound properties are measured; tire footprint shape and the section appearance is verified. If it all checks out, the new tire is ready.

Some Final Notes

The development and testing process can take up to three years to do properly for a completely new tire. “Facelifts” take six to nine months. Manufacturers try to be thorough, but, except for OE tires, they can’t possibly test every size and every possible fitment. They have to pick representative sizes and vehicles within the target market.

Smaller tiremakers typically try to follow the same process major manufacturers use, but limited resources create difficulties.

Tests published by Consumer Reports and Tire Rack are important influences on manufacturers today. Like enthusiast magazine tests, the tiremakers may not agree with their methodology or conclusions, but they must anticipate that their products will be part of such tests.

In addition, independent test labs play a large part in helping the tire companies qualify designs and get to market quicker. These labs are expert at performing many of the tests required, making them a logical resource.

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