Texas Toasted Tires: Part 1


Story By Per Schroeder

A new autocrossing season is upon us, and you know what that means: Time to determine who makes the best tire.
The industry labels our subjects as extreme performance summer tires, but we have a more specific application in mind for this test: the Sports Car Club of America’s hottest autocross group, Street Touring. The SCCA mandates a minimum tread wear rating of 140—weeding out the true race-ready R-compound tires—and several companies have thrown their hats into the ring.
We started gathering intelligence on newly released tires during last fall’s SEMA Show. While cruising the aisles, we asked questions and took notes regarding available sizes, wear ratings and introduction dates. That last bit of info is especially important, as a tire model must be available by April 30 into order to be eligible for SCCA competition.
While street manners might matter to some consumers, for this exercise we were purely concerned with autocross performance. We simply wanted to find the best tire for carving cones. Tread wear, noise and wet-weather performance were all off the table—manners, shmanners.

We tested these wares using a powerhouse pairing of man and machine: Multi-time Solo champ Andy Hollis was our driver, and his 1989 Honda Civic Si served as our test car. The Civic has been prepped to the category’s limits and was fastest on course at the 2008 Solo National Championships.
The 205/50R15 size is the usual tire choice for a Street Touring Civic, as it works well on either 15x7- or 15x7.5-inch wheels. We tested all of our tires on a wheel combination that has worked well for Andy: The front wheels are 15x7.5-inch SSR Type-C alloys, while the rears are 15x7-inch Enkei RPF1 alloys. The class rules allow up to a 7.5-inch-wide wheel, but Andy has found that the wider wheels don’t fit inside the Civic’s rear fenders—plus, there seemed to be no performance benefit.
Several companies currently offer Street Touring-suitable rubber, and we chose to use a past winner, the Falken Azenis RT-615, as our benchmark. We then added the Dunlop Direzza Sport Z1 Star Spec, Kumho ECSTA XS, Toyo Proxes R1R and Bridgestone Potenza RE-11.
There are four notable companies missing from this test. We wanted to try out the Federal 595RS-R, Hankook Ventus RS3, Nitto NT05 and the Yokohama Advan Neova AD08, but they aren’t available in our chosen size. We expect that they could be top players in this market segment, and if they twist our arms, we’ll go back for a second day of testing.

Tire testing is rarely glamorous work, but knowing the results can help make you a front-runner.

In one of the great ironies of racing on true street tires, most top contenders shave their tires for that last little bit of competitive edge. Shaving a tire to 3/32 or 4/32 inch reduces the movement in the tread blocks and the resulting heat buildup. It also increases the amount of surface area that hits the pavement, as the process eliminates some of the extra grooves designed to move water through the tread.
We shaved down all of our tires to 3/32 inch. The Tire Rack and Vilven Tire shared the shaving duties, and we verified the work with a tread depth gauge.
The morning before our timed test runs, each tire was scrubbed in and given a heat cycle. Tire pressures for each brand were also sorted during this scrubbing-in process.
Our tire test took place in Andy’s hometown of Austin, Texas, just as the area was starting to see spring. The temperatures were in the low- to mid-60s with low humidity. In short, it was nearly perfect weather to test tires without breaking a sweat.
Driveway Austin, a new test facility and driver training course, served as our venue. Our course started out with a series of tight left- and right-hand corners that exited onto a short straight and seven-cone slalom. After the slalom, the course bent off to the left for a high-speed sweeping segment and finally a long left-hand sweeper. Driveway Austin’s high-grip surface has proved to be relatively consistent throughout a range of temperatures and conditions.
Vitek Boruvka of AXWare collected the times. He used his company’s wireless start and finish lights plus proprietary software to quickly gather the results and segment times. Vitek’s wares are seen in regional and national timing booths around the country.
Our test procedure had each driver take four runs for each tire—GRM Tech Editor Per Schroeder, another longtime, nationally ranked autocrosser, joined Andy on course. The tires were then allowed to rest for four to five minutes after each run, and their temperatures were monitored for overheating.
We ran the tires in the following order: Falken, Dunlop, Toyo, Bridgestone, Kumho. We then retested the Falken to make sure the surface conditions or drivers hadn’t changed significantly during the day.

Falken Azenis RT-615

Mean Time: 35.302 sec. Quick Time: 35.125 sec.

The Falken Azenis RT-615 and its older brother, the RT-215, were consistently at the top of the charts during past GRM tire tests. These two tires offered good grip and response, but they fell behind this time. We suspected they’d now been eclipsed by the latest maximum-performance tires. Despite the lack of development, Andy noted that the RT-615 is still a great all-around performance tire: “It’s consistent and manageable at the limit, both in transition and steady state.” He added that good feedback and smooth breakaway characteristics at the limit allow this older design to remain within shouting distance of the new top dogs. The Falken trailed the field during its initial sets and improved slightly during the retest, but it still wound up well short of the new leaders. We’re hoping this manufacturer soon introduces another maximum-performance tire. The Falken’s traditional selling point has been its low price, and the current RT-615 is no different. The 205/50R15 runs just $83. For less than the price of two true R-compound tires, you can buy a full set of Azenis. That’s a bargain. Conclusion: Still strong, but showing its age.

Dunlop Direzza Sport Z1 Star Spec

Mean Time: 35.209 sec. Quick Time: 35.061 sec.

We first sampled the Dunlop Direzza about 18 months ago. We felt that Dunlop had a ringer on their hands—provided the limited available sizes worked for a particular driver’s application. The sizes have tended to favor the larger end of the spectrum, and those running 15-inch wheels had just one choice, the awkward 195/55R15.
Fast-forward a few months, and there’s a new Star Spec compound that’s even softer and more responsive. Alas, this tantalizing tire still favors the larger rim diameters.
We tested the available 195/55R15 and, as predicted, this wonderful tire was crippled by less than optimal diameter and width. We noted that the tall 55-series sidewalls resulted in slow transitional response in the slalom, while the narrow 195 section width—just 7.2 inches of tread—put less rubber on the ground during sweepers. “The sticky Star Spec compound makes up for much of that, though, with high grip and smooth breakaway characteristics,” Andy noted.
At just $89 apiece for our 15-inch size, the Dunlop is one of the least expensive tires that we tested. That’s a compelling price point for a tire of this caliber. After all, it performs well both on track and on the street. Conclusion: Size does matter.

Toyo Proxes R1R

Mean Time: 34.522 sec. Quick Time: 34.452 sec.

The Toyo Proxes R1R really blurs the line between street and race tire. Despite its sticky rubber compound, the Toyo R1R is actually quite streetable, much like the company’s true R-compound tires.
That engineering really shines when you ask an R1R-equipped car to corner. “Awesome grip is the Toyo’s strong point,” Andy explained. “You feel like you are literally glued to the ground.” Impressive for a tire that can be found online for just $124 apiece.
Unfortunately, the Toyo was a bit hard to control at the limit due to its abrupt breakaway manners. Andy noted that pushing the tire over the edge resulted in “a heavy staccato chatter that is hard to modulate due to a lack of feel.”
The Toyo also exhibited the slowest turn-in response, requiring a total reset of driving technique and timing to make use of all that grip. It helped to give the car more lead time in the slalom, but the tire still took too long to react. That hurt the Toyo’s times, which were solidly in third place.
Toyo does offer something that the others don’t, however: a wide variety of 15-inch sizes. In addition to the 205/50R15 size that we tested, the Proxes R1R is also available in 195/50R15, 195/55R15 and 225/45R15.
That 225/45R15 is a great, fat tire that works well on a 15x7.5-inch wheel. Another option is the 205/45R16; it’s about two tenths of an inch taller than the 205/50R15 and 225/45R15, but offers more precise transitional response thanks to its short sidewalls. (By the way, we’ll be testing these various options in an upcoming issue of GRM.)
Conclusion: Leech-like grip, but also just as squirmy at the limit.

Bridgestone Potenza RE-11

Mean Time: 34.266 sec. Quick Time: 34.238 sec.

Bridgestone has taken aim at the maximum performance tire segment as well as the autocross classes that require them. In addition to healthy contingency payouts, Bridgestone really did their homework on the new Potenza RE-11, making improvements to the old RE-01R while it was still the reigning champion.
The RE-11’s improved overall grip becomes evident at first encounter, as we could throw it into that first corner without any drama—it just stuck. Andy found that it “inspires great confidence and is easily driven right to the limit, beyond, and back again.”
Andy did note that there was some loss of transitional response compared to the RE-01R. “Some early adopters have been adding air pressure to help compensate for this effect,” he noted. The new Bridgestone will set you back $124 for this size, about the same approximate price point as the previous-generation tire. Conclusion: Great size, great grip, great response, great tire.

Bridgestone Potenza RE-01R

On the national Solo circuit, the Bridgestone Potenza RE-01R is the reigning champ, with title wins in STS2, STS2L and STU. The tire has been discontinued in the wake of the RE-11’s release, but it’s still out there winning events—even though it was only available in a 195/50R15, not the favored 205/50R15 size.
So, how does it compare to the new Potenza RE-11? Fortunately, Andy had a brand-new set stored in sealed plastic bags.
“It feels like home,” Andy predictably said of the RE-01R. There’s no doubt that it has been the standard-bearer in Street Touring for most of the last two years. Credit the razor-sharp response in slaloms for Andy’s enthusiasm: “You can easily place the car right next to a cone with confidence, which shows up as very consistent run-to-run times.” The downside is a lack of ultimate grip in the sweepers when compared to the newer-generation tires.

Kumho ECSTA XS

Mean Time: 34.170 sec. Quick Time: 34.030 sec.

For the last five years, the Kumho ECSTA MX was an unlikely contender in the street tire wars. Its compound was rather hard and only really responded well to merciless flogging: The tire fared best at events held on punishing high-grip concrete, but it fell short on slicker surfaces.
Rumors of a successor have been circulating for the last three years. We’re happy to report that the Kumho ECSTA XS is finally here, and it’s a winner.
While not the widest or softest of the bunch, the ECSTA XS delivered everywhere. “It is the complete package of inspiring turn-in, very high grip, easy modulation, and good feedback,” Andy noted. The result in our test was quick segment times, fast overall tallies, and the lowest means for both drivers.
The Kumho is quite reasonably priced, as the 205/50R15 XS goes for $96 through The Tire Rack. Considering that it can run right there with the Bridgestone but fetches less of a premium, we expect to see a lot of local and national competitors on the Kumho.
Conclusion: Kumho has a winner on their hands.

Hitting the Streets

Before calling it a day, we retested our benchmark Falken. We wanted to ensure that the course conditions had remained consistent.
Our times dropped a few tenths—the mean went from 35.302 seconds to 34.822 seconds, while the quickest time fell from 35.125 to 34.739. However, we noted a good bit of improvement during our first stint on the Falkens. If we removed the first few runs from that initial outing, then the gains seen during the retest shrank. We’re confident that the slight improvements we saw in surface condition on this bright and sunny Texas day were not a factor in our times on the other tires.
We love SCCA’s Street Touring competition, and thanks to the current crop of tires, there’s no wondering why it’s the fastest-growing segment of autocross. The tight competition and long-wearing tires make it a great way to race on a budget.
The 2009 season is shaping up to be a good one, and we have a feeling that several brands will help drivers bring home the gold. The finishing order and the final results will largely depend on finding that perfect match between driver, car and tire.

Join Free Join our community to easily find more articles.
Comments
View comments on the GRM forums
Our Preferred Partners
g27mGQzKdsVOUCKr6dtd0p41BeCruynMiReOSIVA86NW22R7Kb3ahvB0Gj9FaKtK