For motorsports enthusiasts,
tires are the key
ingredient connecting our
beloved machines to the
road. For the last decade, the biggest
technology and performance advances
have come at the pointy end of that
spectrum: the extreme performance
summer tire category.
These are tires that deliver amazing
stick during aggressive maneuvers, but
also have sufficient road manners for daily
use in typical summer weather. They’re
a cost-effective compromise, delivering
almost as much grip as track-specific
R-compound tires while having none of
their harshness, short lifespans or lack of
puncture resistance.
Whether you satisfy your g-load cravings
on twisty canyon roads, the local road
course or around the cones, these tires are
your ticket to long-term enjoyment–for
the competition set, we’re talking about
tires legal for the SCCA Street and Street
Touring classes as well as LeMons and
ChumpCar endurance racing.
But which ones are the best for you? To
answer just that, we gathered examples
of all the latest offerings and put them
through their paces in a variety of venues.
First up is our autocross test.
A History of Conflict
Just like cars, tire models usually have
a life cycle of about five to six years. After
that span, they’re generally replaced by a
new model designed for the same purpose.
But because the extreme category has
become so popular, those tire designs are now getting tweaked on a one- or two-year
basis. Many times the upgrade comes
courtesy of a new compounding technology–
often a silica variant–that improves
durability and allows for more grip across
wider temperature ranges.
At the same time, tire makers are also
pushing the limits regarding what constitutes
a 200-minimum-treadwear tire–the restriction
most sanctioning bodies have in place.
We last tested this crop of tires two years
ago, and the BFGoodrich g-Force Rival rose
to the top. Since that time, Dunlop tweaked
their Direzza ZII design with a Star Spec
version. Hankook did the same with their
Ventus RS3, though the official name has
not changed–it’s unofficially known as the
RS3V2 in the enthusiast community.
Bridgestone brought out the all-new
RE-71R to supplant the RE-11 and
RE-11A. Then there’s BFG’s new sibling
for their Rival, known as the Rival-S. It
will be sold alongside the original.
Each of these tires goes about its business
in a different way. We designed our
test not just to find out which one’s fastest
on test day, but to elicit their unique
characteristics so that you can decide
which tire synergizes best with your own
car, driving style and setup.
In the past, we’ve typically tested tires
on small, light, front-drive cars sporting
fully sorted suspensions and wide wheels.
This provides an optimal environment for
the tire to show its prowess.
We feel our method has bookended
nicely with the comprehensive testing done
by our friends at Tire Rack. They use heavy
BMW 3 Series on narrow OE wheels–just
like those running in the new SCCA Street
classes. By viewing the data from both sets
of tests, you can better match the results
with your own application.
Field of Battle
We set up shop at the massive asphalt
pad at Texas’s Mineral Wells Airport in
early April. It was a mild, sunny day
with ambient temps rising from 55 to
65 during our testing period. The road
surface cleans up quickly, but it is old and
a bit abrasive.
We’ve been testing here for years and
have marked permanent skidpad and
autocross courses. The latter is a simple
loop affair, emphasizing handling over
driver skill: a medium-speed slalom
down one side, higher-speed offsets up
the other, and a pair of constant-radius
sweepers at each end.
The site is on a slope, though, so one
sweeper is on-camber and the other falls
off. As it turns out, the entries to these
two corners reveal the biggest differences
between tires tested.
Plan of Attack
Leading the charge for the test were
drivers David Whitener and Andy Hollis,
both multi-time national champion autocrossers
and veterans of GRM tire tests.
David lives near the site and has literally
thousands of laps around the Mineral
Wells permanent test course. As a result,
he knows its every nuance.
The test vehicle for the day was the
championship-winning, Street Touring
R-prepped 1999 Mazda Miata of Michael
and Kyung Wootton. The Woottons consigned
their Miata to David for suspension
development, and he’s already knocked a
full second off the car’s lap times.
Because of his familiarity with both
the car and the course, David served as
our test’s expert, someone who could
quickly extract maximum tire performance.
Andy played the role of guest
driver, examining each tire’s adaptability
and ease of use. Note that the car’s setup
was based around the Toyo Proxes R1R,
which is a tremendously forgiving tire.
For today’s test, all tires were in the
205/50R15 size and mounted on the
15x8-inch 6UL wheels made by 949
Racing. Tires were unshaved.
You can’t efficiently do a test like this
without a small army. Kim Whitener
worked the timers and recorded driver
impressions, while Forrest Windecker
at Texas Track Works handled the onsite
mounting and balancing. After each set of
runs, there was always a fresh set expertly
mounted and waiting for us on the alternate
wheels.
Gerry Terranova then stepped in to get
tires installed quickly during post-run
driver interviews. The crew ran like a
well-drilled military unit.
Early Skirmishes
Our first hint of each tire’s performance
came on the skidpad. When testing tires,
we first run three laps in each direction
to scrub off the mold release and awaken
the cold rubber for duty.
To determine optimal tire-pressure
ranges, we then run each tire around the
circle under maximum load for three laps at
time. We start at 40 psi and then drop pressures
by 4 psi until performance drops off.
We then go back to the indicated optimal
pressure and retest to confirm the data point.
We measure performance strictly with
a timer–no pyrometer–since we’ve found
it provides more reliable results. We glean
additional data from relative lap times
between tires, a leading indicator of
steady-state grip. Information about each
tire’s heat tolerance also emerges as they
endure heavy loads for a solid 30 seconds
at a time–no respite. We cool them as
needed with a water sprayer.
Once we have our ideal pressures, we
move to the test course. For this day, we
chose to do two-lap runs in sets of three for
each driver. That put the total time in the
typical 50-second autocross range, while
allowing for split times to examine heat
characteristics and mine for a flyer performance.
The test course is fairly busy, so
putting two blazing laps together is a challenge
when drivers are running for hours.
In addition to retesting a control tire
at the end of the day, we also inserted
it into the middle. This verifies that
the course or driver isn’t getting better
throughout the long session, as can
often be the case. We used the winner
of our last test, the BFG g-Force Rival,
as our control.
Fire at will!
BFGoodrich g-Force Rival
Despite handily winning our previous test across several sessions–
autocross on asphalt, autocross on concrete, and laps on
the road course–later reports from the field did not always agree
with our results. Some Rival drivers had difficulty adjusting to the
feel of the tire or matching it to their car’s setup. Others found it
worked great, but only at certain sites and tracks.
It has found a loving home, though, among low-buck endurance
racers and track day aficionados. They appreciate this tire’s
long tread life and ability to easily deliver lap after lap of consistently
fast performance. In the cone-dodging world, it has been
quite polarizing: Some drivers love it, others curse it.
The last time we tested it, we loved this tire. However, upon
mounting it on the tightly wound, well-balanced Miata, we started
to appreciate the naysayers’ perspective. And because it served as
our control tire, we got plenty of time to examine it.
On the skidpad, we could quickly find the Rival’s limit and
keep it there. The Rival delivered the same times between 28 and
36 psi–the largest spread of any tire tested this time. The Rival
was also unaffected by the heat buildup of continual lapping.
Unfortunately, progress has left this guy behind: It was the slowest
of all in sustained steady-state grip.
On the test course, both drivers struggled to make peace with
this tire. They found it especially challenging to brake deep into
the uphill sweeper after the fast run through the offsets. The Rival
simply wanted to lock up.
Similarly, our drivers felt uncertain on the downhill run out of
the slalom and into the bottom sweeper thanks to the required
multitasking. They also had difficulty putting down the power
in the offsets, as the rear wanted to over-rotate and the slalom
rebound after each turn-in was hard to predict.
This unpredictability showed up in the results: Each driver
struggled to put together two fast laps in a row. The single best
lap times were consistent but also the slowest of the field.
Yokohama Advan AD08R
The Advan AD08R is the latest in a long succession of
products that began with the AD07. This is the tire that
proved Yokohama was back in the game.
On the skidpad, the AD08R appeared to be very pressureagnostic,
turning similar lap times with inflations varying from 28 to 40 psi. After a few iterations, the Yokohama did start to exhibit
some temperature sensitivity: Succeeding laps fell off a touch from the first. It was very predictable and easy to drive at the limit close
to the cones. Final skidpad results landed it in the middle of the pack on average, but it delivered a few flyer laps that were among
the best of the bunch.
That ease of use showed up again on the test course, where both drivers adapted quickly. Compared to the Rival, the Yokohama was
better at putting down power and was much more intuitive in transitions, requiring way fewer mid-course corrections.
Still, our expert driver posted inconsistent lap times–although they were still fast. Our guest driver, who had significant prior experience
with this tire, logged tightly grouped times. Ultimately, for each driver the tire was a little slower than the Rival on average, but
it came out ahead on best run and best lap.
The biggest news regarding this tire may be its official treadwear rating: It only carries a 180 UTQG number. The AD08R can be
used for events that still only require a treadwear of 140, but the trend lately has been upward for most rule makers. Although the
AD08R feels like a 200-treadwear tire, its maker–unlike Hankook and Toyo–seems uninterested in rerating the rubber.
Based on our experience–we ran this tire in the 2014 Tire Rack One Lap of America to great effect–the Yokohama’s longevity falls
near the Hankook RS3V2 and Dunlop ZII Star Spec range.
Dunlop Direzza ZII Star Spec
Here’s a tire with an interesting history. The brand is
owned by Sumitomo in Asia, but the American
distribution rights land in Goodyear’s portfolio.
As such, new models and versions typically
debut in the home market first, then hit
shelves in the U.S. in a tweaked form and
select sizes one year later.
Gearheads armed with Google Translate
can usually know what to expect based on
the info posted overseas, and Dunlop seems
keen on frequent tweaks to stay near the top:
The Z1, Z1 Star Spec, ZII and now ZII
Star Spec have all arrived a year or so apart.
The line is known for super-responsive
handling, small slip angles and somewhat
abrupt breakaway characteristics. These
properties reward the finesse driver who
likes a willing dance partner, but punish
those who like to throw a car around.
The Star Spec version of
the ZII seems to have
softened the blow a
little on overdriving,
allowing for more
room to maneuver.
It’s especially good at
what industry experts
call compound loading.
This has nothing to do with tread compound and everything
to do with multitasking at the in-between edges of the friction
circle–where the tire is supporting large lateral and
longitudinal loads. The Toyo R1R is another tire that does
this extremely well, and the ZII is moving in that direction.
Along the way, however, the ZII Star Spec has also picked
up some heat intolerance. We first saw it on the skidpad,
where times increased along with the lap count.
Judicious use of the water sprayer was required to
get times back in line. Still, we could never replicate
those three fast skidpad laps we nailed
in the very first 30 seconds of use. Instead,
after spraying, we’d get one quick lap and
two a touch slower. And even those first
three flyers were only good enough to rank
second to last in steady-state grip. Responsive
on-course action is this tire’s forte.
Once they took to the test course, both
drivers fell in love with the dynamics of this
tire. It was a great partner in crime, seemingly
directly connected to their inputs with
no delay.
Its slalom control was the best of the
bunch–not just with turn-in response, but
predictable turn-back, meaning speed could
easily be carried past the last cones in the
slalom. Predictability and
stability in the sweeper
entries were also key to
quick lap times. By the
end, the Star Spec was
the darling of the pre-
2015-generation tires,
well beyond the Rival
and AD08R in times.
Bridgestone RE-71R
Bridgestone is a large tire maker that has always
had an interest in motorsports and highperformance
tires–and at all levels, too.
Throughout their history, they’ve veered
in and out of the autocrossing world
as their products and marketing plans
synched up with our community.
Not long ago, they were top dog in
this category with their RE-01R and
RE-11 follow-up. Two years ago they
released the updated RE-11A, but it
didn’t quite get them back on top. As
a result, for 2015 we have the all-new
RE-71R.
In addition, they’re back with 18-wheeler
event support crews and contract driver
programs. Is this tire one that deserves all
the hype? Oh yes. While it
may or may not be the
best tire for a given
situation, it is certainly
a player to be
strongly considered.
The first signs
came on the skidpad,
where we suddenly
dropped into the 9.6- and low-9.7-second range. However,
like the Dunlop, this tire was very pressure-agnostic, producing
similar results over a wide range. It also had some temperature
sensitivity, but not nearly as much as the Dunlop.
After their runs on the practice course, both drivers
came back smiling. David again praised the compound
loading, and on a couple of flyer laps he found lots of time
in the challenging sweeper entries. He also
found more confidence in the slalom than
he had on any other tire tested. Andy proclaimed
the longitudinal grip–braking and
acceleration–the best of the bunch, and
this trait should suit high-horsepower
cars nicely.
Another key point to note is the difference
in our drivers’ times. On the
other tires, David’s familiarity with the
car and course constantly had him ahead
by a sizable margin. This time, though,
the gap shrank. This data point might
mean that the Bridgestone is the most
intuitive tire and covers up any handling
quirks. Here’s how Andy summarized
it: “All the goodness of the Dunlop,
wrapped in a grippier
compound.” And if
you compare the two
closely, they sure
look the same from
the outside: similar
crowned profile
and tread design.
Coincidence?
BFGoodrich g-Force Rival-S
That original BFGoodrich Rival found some huge fans on track,
but its reception among the autocross community was spotty. In
particular, the Rival seemed to have issues with the rubber
laid down by stickier R-compound tires and slicks.
At a road race event, where different classes
share a track over the course of a weekend,
drivers have a few laps to lay down their own
rubber. In autocross, this can’t happen as the
classes are intermingled.
BFG responded by developing several alternate
versions of its Rival and then inviting key
SCCA national championship competitors to
a test day held just after the Tire Rack SCCA
National Championships–on the same courses,
even. It was a stroke of brilliance from both a
development and marketing standpoint: BFG
came back with data where they needed it most,
while those competitors left knowing how much
time they’d gained.
What the drivers did not
know was which tire would
be put into production–and
any further tweaks it might
receive. We were part of
that test in Lincoln, and
we can now confirm that
the new Rival-S was indeed
the best of that bunch.
This tire’s forte is big grip–no, check that, massive grip–for a
street tire. This became immediately apparent on the skidpad as
it set a record, dipping slightly into the 9.4s. And while it never
repeated that one cold-tire flyer, it did outpace the field with
consistent 9.5s and low 9.6s. Like some of the others, it cared
little about how much air was inside: Pressures ranging from 24
to 32 psi worked fairly similarly.
Feel at the limit is best described as rubbery. Those who
have run on the Toyo R1R will find familiarity here, though
the BFG’s breakaway is easier to predict, thus minimizing tire
wear from overdriving.
Riding the circle was super easy, though the
tire ran at larger slip angles than the Bridgestone.
How big was the grip? Andy began to complain
that the seat padding had bottomed out and the
frame was now hurting his ribs.
On the test course, anticipation was high and
the Rival-S delivered in spades for David. With
the Miata set up for Toyos, he was able to extract
gobs of hidden performance from the Rival-S,
consistently lapping in the mid-to-high 23s. His
full-course average was a solid second faster than
on the Bridgestone, although his single-lap delta
was only two-tenths.
Andy’s results were also consistent, but
slower: low 24s across the board, but only a
few tenths quicker than the RE-71R on average.
The single-lap nod went to the
Bridgestone.
Both drivers described the
tire as extremely forgiving,
very linear, and capable of
doing everything well. If
the RE-71R is a better ZII,
then the Rival-S is a better
Toyo R1R.
Who Won the War?
In many ways, the test was a stalemate.
For sure the class of 2015 dominated,
but each member did so in different
ways. And those differences are
what will eventually determine which
one is right for you. The tires will also
require different setups to extract maximum
performance, some of which may
be restricted by the rules in your area
of the sport.
As we often say, testing on your own
car is the only way to know for sure. But
you should now be armed with enough
info to make an educated guess on where
to start.
People who are used to Dunlop ZII
tires–and have cars set up for those tires–
will likely prefer the Bridgestone RE-71R.
Those who come from the looser Toyo
Proxes R1R and Hankook RS3 camps
will likely gravitate toward the Rival-S.
The Rival-S undoubtedly showed the
most potential, topping the time sheets for
both of our drivers. We’ll continue to reevaluate
both front-runners throughout the year.
Next up is track testing. Can the Rival-
S stand up to time trials? How about the
RE-71R? What about longer enduro competitions?
Wet weather? Rim size and camber
dependencies? All this and more as the testing
season continues here at GRM.
Stay tuned.
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Sources
949 Racing
wheels
949racing.com
(949) 716-3111
Auto-Spec
mounting
automotive-specialist.com
(512) 472-4977
BFGoodrich Tires
tires
bfgoodrichtires.com
(877) 788-8899
Bridgestone Americas Tire Operations
tires
bridgestonetire.com
(866) 775-6480
Dunlop Tires
tires
dunloptires.com
(800) 321-2136
Texas Track Works
texastrackworks.com
(817) 926-8863
Yokohama Tire Corporation
yokohamatire.com
(800) 722-9888
