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Tested: How do tires perform on track as they wear? | Articles

What happens to tires after our tests? We keep running them–and we keep learning.

Our latest findings: Some tires get better the more you run them. Specifically, longterm testing of the Falken Azenis RT660 and the Bridgestone Potenza RE71RS showed that tread depth, heat cycling and rotation can impact performance over the tire’s lifetime.

Meet Our Tires

Over the next several months, we made regular visits in our Triple Threat ND-chassis Miata to Harris Hill Raceway, site of that initial test, to run two or three sessions of about six laps each. We swapped back and forth between the Bridgestones and Falkens while logging all the data.

After a while, we saw some interesting trends. First off, lap times on both tires were getting quicker–to the tune of 2 full seconds. Those times were becoming more consistent, too, with the quickest typically showing up later in the session.

Long-term Track Results

Wanting to know more about the source of these anecdotal trends, we devised another scientific test. This time we’d pit our faithful soldiers against fresh recruits, a new, full-tread set of Bridgestone’s Potenza RE-71RS. 

[Ultimate track tire guide | 200tw, 100tw, street-legal track and R-comps]

The big question we’d answer: Did reduced tread depth and additional heat cycling make the tires that much faster?

While performing this test, we’d also have to mind other possible factors: How much had the cooler fall weather helped? Was the dirt kicked up by nearby construction still impacting grip? 

Time to head back to the track. 

Shaving Off Time

Recent rains delivered a clean track the morning of our test, so we went right to work. We completed a single warmup session on our seasoned Falkens, allowed them to cool for 30 minutes, and then went back out on them to record times. 

Showing its battle-hardened consistency, the Falken delivered five laps that were all within 0.4 second, firing off a best-ever run on the final pass at 1:26.7.

Next up was the worn Bridgestone, now sporting a tread depth of just 3/32 to 4/32 inch. Not to be outdone by the Falken, the Bridgestone cracked off five laps all within a single tenth, twice matching its previous best of 1:25.6. 

And then came the moment of truth: a performance retreat back to the new Bridgestone. As in our original test, the opening salvo was its best, with subsequent laps falling off. The best time on the new tire was 1:26.3, a full 0.7 second slower than the veteran set, and the session wasn’t nearly as consistent.

Before we left, we again mounted up the Falken and did some laps to verify that track conditions and our driving hadn’t changed for the day. Indeed, they had not; we matched our earlier times. 

Once back home, the data revealed five lessons. 

Lesson 1: Less tread depth enhances both pace and consistency, at least for these two tire models. 

In back-to-back testing, the Bridgestone RE-71RS was 0.7 second quicker at 3/32 to 4/32 inch of tread than at full depth. And although we didn’t compare worn to new directly, the worn Falken RT660 was within 0.4 second of the full-tread RE-71RS, where it was 0.7 second off when we compared new to new in our first test. This suggests that the worn Falken was 0.3 second faster than new. 

This result should come as no huge surprise, as shaving street tires is a time-tested strategy. That said, there was a period when the top dogs didn’t benefit from it–we’re looking at you, BFG RivalS and Bridgestone RE-71R–and many competitors eschewed the practice. 

Shaving also costs money, both for the operation itself–typically about $15 a tire–and in reduced service life. Fortunately, a similar effect can be achieved simply by carefully wearing down the tires to their optimal depth as we did here. It does take some planning, or multiple sets of tires, to have them perfected when important competitions come along.

Lesson 2: The Bridgestone RE-71RS wears down much more quickly than the Falken RT660. 

With equal use, the Bridgestone lost about half its tread while the Falken lost less than a third. Plus, the Falken is molded with 12% more rubber. It may be a little slower, but the RT660 will deliver significantly more laps than the Bridgestone. 

Lesson 3: More heat cycles can be beneficial. 

Our Falken’s lap times dropped faster than the tread disappeared, suggesting that this tire model needed more than the initial pre-test heat cycle to develop maximum grip. We’ve also seen this trait in the Yokohama Advan A052.

Lesson 4: Diligent rotation between positions will even out the wear, prolonging service life. 

Since we always run at the same track in the same counterclockwise direction, most of our wear comes on the right side of the car, so we often trade our rights with our lefts. Further, the fronts wear in a slightly different pattern than the rears, so we also swap tires end to end periodically.

But what about the directional nature of the Falken RT660? That’s only applicable in the wet for evacuation. In the dry, you can run them in either direction. They’ll be a little noisier on the street when run backward, though.

Lesson 5: Different tires can desire different pressures. 

Thanks to our lightweight Miata’s abundant camber and wheel width, we found that hot pressures around 30 psi result in even wear and optimal performance with the RE-71RS. The Falken delivered better wear around 32 to 34 psi hot, with no change in performance from lower pressures.

One Last Lesson

Tires remain one of the most significant performance variables. And, as this test shows, a single tire model’s performance can change depending on its age and pressure. 

The trick, as usual, is to leverage those changes to your advantage. One easy way to do that: Take notes.

Full Tread vs. Worn Track Results

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