What You Need to Know Before Buying R-Compound Tires

The Nature of Grip.

Grip is a funny thing with your track car. The more of it you have, the more unexpected gremlins can pop up. Swapping out tire compounds isn’t as a simple as slapping on a set of new rubber and hitting your local driving club if you want to maximize your lap times. Setups that might have worked in the past or been the hot ticket on 200 tread wear tires can suddenly become obsolete when it comes to knocking off those precious tenths. While we all know the obstacles of big power—spinning your wheels on corner exit, stressing your transmission and suspension components—the obstacles of big grip aren’t always obvious. Here are 5 things you need to know before buying R compound tires.

image courtesy of Monstery 

Tread Wear is Not Created Equal

Addressed by its full name, the Uniform Tire Quality Grade (UTQG) Tread Wear rating helps consumers decide on which choice of tires will last longer on their vehicle. The idea is that a rating of 200 will last two times longer than a rating of 100 with a rating of 100 lasting two times longer than a rating of 50. The problem is not only that each manufacturer of tires conducts their own independent testing to acquire these numbers, but that they are allowed—by law—to sandbag on the performance of their tires. The only thing they aren’t allowed to do is lie about a bad tire performing well. Comparisons are generally only valid between tires made by the same manufacturer, i.e. comparing Michelins to Michelins or Pirellis to Pirellis.

PRO TIP: If you want the highest performing R compound money can buy, it’s best to watch what high-level racers are running in the SCCA Solo Nationals, NASA PT classes, or any other national-level competition where tires are not restricted by class. Avoid time attack as a reference—they use tires that are mandated by a series sponsor.

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Compound Determines Ideal Setup

The stickier the tire compound you run on your vehicle, the more everything in your setup will need to be upgraded to cope with the increased stress. Stiffer springs, high-performance shocks, and bushings all play crucial roles in taking full advantage of these race-ready rubbers. You will potentially see parts flexing that didn’t flex before. Specialized tools like a probe-type pyrometer will help you see exactly where heat is being generated across the tire in order to get the correct numbers for your camber and toe settings. Don’t be surprised if you end up needing to upgrade your vehicle’s suspension setup in order to get more camber. Ultra sticky tires like Hoosiers can require numbers as high as -4.0 degrees to get the tire to sit flat once you fly into a corner. And you will be flying through corners on these tires.

PRO TIP: Be prepared to abandon ideas you had about your previous setup. Super sticky tires often rewrite the book on what you thought you previously knew. Launching a car with grip levels this high can exceed what many factory parts were ever designed to cope with, which means oddball failures you might not see coming.

image courtesy of walkinshawgroup.com 

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Baseline Ability

As a pro coach, one thing you need to be aware of is the lack of sensory input that a racing tire has compared to a “high-performance” street tire. Street tires talk to you in abundance when you’re approaching the limit which makes them great for the beginner to intermediate-level drivers. Not the case with R-comps and Hoosiers. Their softer rubber doesn’t squeal when it’s getting its neck wrung, which makes them better suited towards drivers who have ample seat time under their belt. This is due to the fact you will need to be better at anticipating what the car is about to do as opposed to reacting to what it is currently doing. Many people can afford to buy these tires and many people now use them, which makes them a tempting proposition.

PRO TIP: In my own driving career, I spent over 6 years before ever driving on a set. Take your time in learning street tires before jumping up to these lap time decimators. By learning to be consistent first, you will maximize grip and understand where the car needs improvements as opposed to your driving technique. This will save you tons of time and even more money.

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Tire Pressures are Important!!!

Racing tires tend to operate with lower pressures than street tires, but there is a limit to how low you can take it. Thankfully, Hoosier has a handy formula that every racing driver should have memorized. It’s not complicated and goes like this: take your vehicle's weight and divide it by 100. This is the lowest COLD RATED PRESSURE you should ever run on one of their racing slicks. Other manufacturers are likely to have different rates, so find out what yours is and lock that number into your head. Safety can’t be stressed enough when you get onto the track and start going for real lap times.

PRO TIP: Always include yourself and the weight of the fuel on board when you calculate this equation. You are looking for total vehicle weight here to ensure accuracy.

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Wheel Width is a Big Variable

I have seen the same width and compound racing tire improve almost 1 full second in lap time on a short, technical autocross course from increasing wheel width by only 1/2 an inch. Wheel size is incredibly important when it comes to R-comps, with wheel width being chief among your decisions. Generally speaking, the trend I have noticed among top tuners is a wheel that is almost the same width as the tire, but your mileage may vary. Always consult with the manufacturer before mounting and balancing. Properly sized wheels aren’t just a safety feature, they’re a modification to help you annihilate the stopwatch.

PRO TIP: You want a small amount of stretch in the tire, but not a lot. By stretching a tire you are keeping the sidewalls taught, allowing for less of a chance of deformation or deflection under lateral loading. It keeps the tire “in place” and stops it from squirming around. A more consistent contact patch means…you guessed it…decreased lap times.

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Questions?

That sums up the general sense of what you need to know about buying and using R-compound tires. These addicting little patches of rubber will drop your times faster than almost anything else you can buy. A critical component to any fast car, the racing tire is the foundation from which everything on a vehicle is determined. Once dialed in, they will transform an average car into a monster, and a monster into a mythical track day destroying legend. Everyone should try a set at some point in their life, even if their vehicle isn’t fully optimized, just to get a sense of what a car is actually capable of on great tires. Be careful, however, the grip is habit-forming and might be your next big track day fix. 

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And, for information on maintenance and repairs for your Mustang, head on over to our How-Tos at MustangForums.com!