Tire Testing – Behind the Scenes

What do you, the racer, track day driver or time attack competitor want from a tire? Maximum traction seems to be a good starting point. What about wear? Feel and feedback are desirable. And if you are on a budget, cost plays a big role. Tire companies invest heavily in tire testing, mostly for the high profile, big dollar series, but almost all pro racing series and most club-level racing series use a spec tire from a single manufacturer.

Firestone in IndyCar, Goodyear in NASCAR and Pirelli in F1 actually have it pretty easy. The cars are similar, if not identical. The specs are the same. In these series, the focus of testing relates to traction and wear for a specific circuit. Once parameters like sidewall stiffness, tread design (even on slicks) cord angles and specific design parameters are determined, it comes down to rubber compounds to establish the balance between wear and maximum traction. Once the tire company nails down the best compound (or compounds) for a given track, it’s up to the teams to fine tune the chassis settings and tire pressures in an effort to extract maximum performance for the tire for a given track.

What actually goes into tire compounds is a closely held secret. Not that tire engineers would ever share what goes into tire compounds, but even if they did, the information is so far over most of our heads — unless you happen to be a Ph.D. in chemistry — that the information is virtually useless. But minor changes to the rubber compounds can have major implications for the teams in the quest to find the optimum setup for the car. And that relates to professional, top-tier teams. The small club racer run in a spec tire class with a multitude of different cars has a greater challenge.

My first experience with a spec tire was the IMSA BFG Radial Challenge in the 1970s. The racing sedans covered the spectrum of small sedans available at the time. The tight rules for modifications made setup a bigger challenge. While the BFG T/A radials were a great tire at the time, their designs suited some cars better than others. The IMSA Firestone Firehawk series also presented significant setup challenges. The Firehawk tire was difficult to tune for optimum performance. NASA offers several spec tire classes like Honda Challenge and American Iron where a variety of different cars compete. This situation creates challenges for the club racer. While a spec tire in classes like these may come in different compounds and structures for different sizes, the task of tuning the suspension and tire pressures for optimum performance is left to the team and driver.

Over the span of my 50-year racing career, I was extremely fortunate to be involved in many tire tests, mostly as a driver but also as an engineer and an observer. I still do considerable tire testing in the off-road tire market. The design challenges and compromises in an off-road tire make testing far more daunting than for an asphalt track competition or ultra-high performance tire.

We typically conduct about 22 different tests, often comparing different designs from a manufacturer or comparing different brands of tires. We use one vehicle, so many tire changes are required. And if we miss the chosen line by more than an inch or two, we must rerun the test. Driver input becomes the primary form of data collection. I wish I had tested off-road tires when I was competing. You develop a finely-honed feel for what a tire does in dirt, sand, snow, mud and rocks.

When a tire company tests a race tire, it is usually for a specific class or even a specific car. The NASCAR Cup series is a good example. With the exception of the body style, a Cup car is virtually a spec car. And since there is only a single tire company providing tires, performance is not an issue. Tire tread compound for a given track is the focus of testing in most cases. While performance is a factor, creating a tire compound that will offer good performance for at least the duration of a fuel load is important. Even at that, tire performance will fall off considerably within a few laps. The team that does the best job at finding a setup that minimized tire degradation has an advantage. And so does the driver that can best manage tire wear.

Spec tires for a club level race series like the NASA Honda Challenge creates a different task for the tire manufacturer, especially considering that the spec tire is likely used in other spec classes and even some non-spec tire classes. Tires are usually optimized for an “average” car, meaning a weight that is middle of the road with a moderate level of power. It is up to the racer to figure out the optimum suspension setup for a given car.

Over the years, I have been fortunate enough to participate in several tire comparison tests for magazines, suspension companies and tire manufacturers. The typical scenario is to use one vehicle, set up several tests and swap tires for each test. Tests may include a straight line 600-foot slalom, 100-foot-radius skid pad and a test track or other road course. The test vehicle receives a baseline setup for caster, camber, toe and ride heights if applicable. The test engineer or editor will determine a tire pressures used on all tires.

I have always had an issue with this procedure. Every tire is a little different. The car setup may be ideal for one tire, but it will not be ideal for all tires. Tire compounds and sidewall stiffness all play a role. One tire may need more camber because it has a more flexible sidewall. A stickier tire should be faster, but since the tire makes more traction, it will cause more weight transfer and chassis roll, and may need more camber. Also, the stiffer-sidewall tire may need less pressure to achieve maximum performance. The point is that the test platform really should be tuned for each tire. In most cases, this is completely impractical, but it does give you a clue that chassis setup needs to be customized for a specific tire. Not doing so likely assures that some time will be left on the table.

So what does this mean for the club-level racer in any class or series? If you want peak performance, you must conduct your own tire testing, even if it’s on a limited basis on an event weekend. Professional race teams have a host of engineers with highly sophisticated data acquisition, but a couple of modernized old-school tools can provide you with a lot of data. And this data is more than enough to optimize your car setup for maximum traction.

A stop watch and a tire pyrometer can give you important data. Modern versions make data recording, storage and analysis much simpler. But even a stop watch feature on a smartphone or a $100 probe style pyrometer can make a big difference. The most interesting pyrometer currently available not only has a big memory, but calculates average tire temperatures. The Longacre 52-50650 Tablet Memory Tire Pyrometer uses a tablet to record and analyze temperatures taken with a probe, which is inserted into the surface of the tread and is much preferred to the laser or infrared style pyrometers. But any device to monitor tire temperatures will help point you in the right direction to in the quest to go faster.

Average tire temperatures provide important clues about what direction to go in when tuning the tires and chassis. The average temperatures of each tire can be compared and offer clues about tire pressure and camber settings. Left side versus right side average temperatures offer clues about weight bias and chassis balance. Front versus rear temperatures tell you about handling balance and comparing diagonal average tire temperatures may indicated ride height adjustments are needed to balance diagonal cross weights.

For more details about tire and chassis tuning using tire temperatures refer to the 2013 article by this author in NASA Speed News: Tuning Tires – Tracking tire temperatures and tuning your setup accordingly can pay dividends on the racetrack.

Understanding tire temperatures leads the team to improving performance. While tuning the chassis to a specific tire is important, even crucial, tuning tires and chassis to the track and to weather conditions requires even more attention. Even tuning the tires and chassis to optimize performance based on heat cycles can pay dividends. This also can help the team monitor tire degradation.

Here are some points to consider:

• When a tire goes through heat cycles, traction is reduced, causing less weight transfer and chassis roll.
• Track surface temperatures change throughout the course of an event requiring adjustments to tire pressures and possibly camber.
• Different track surfaces will generate different levels of grip requiring possible setup changes.
• Skid-pad testing provides an excellent opportunity to fine-tune mechanical grip.
• Tire temperatures offer the most concise information about the dynamics of handling.
• Monitoring and recording tire temperatures gives a team cost-effective and consistent data to optimize setup for peak performance.

While not quite rocket science, monitoring tire temperatures takes commitment and hard work. But then winning at anything takes maximum effort. Taking tire temperatures and utilizing average tire temperatures and provide your team with a distinct advantage.