Photography by Andy Hollis
[Editor's Note: This article originally appeared in the April 2020 issue of Grassroots Motorsports.]
Our amateur motorsports scene got a bit of a reboot right around the turn of the century: Street-rubber autocross classes had just made their debut, and in 2002 Falken introduced the Azenis RT-215, a tire that packed a punch without a premium. The stars aligned for Falken, upgrading the brand to major player status in the U.S. motorsports scene.
Fueled by a new generation of gearheads weaned on “Fast & Furious” as well as those looking for a less complicated autocross experience, Street Touring quickly blossomed into a whole category of classes. The driving factor behind ST’s explosive growth was simple: no more swapping to race tires the morning of an event.
Compared to the R-comp tires that had dominated autocross for decades, these new street tires lasted longer and cost less. At the time, a 205/50R15 Falken could be had for around $60. Plus, they could truly be driven on the street. They also became favorites among track day enthusiasts as a way to drastically reduce consumable costs without lowering the fun factor.
Other manufacturers took notice, and in 2006 Bridgestone came to play with its Potenza RE-01R, supplanting Falken as top dog. Falken responded with the Azenis RT-615, but it wasn’t enough. Later, Kumho, Toyo, Dunlop, Yokohama and BFGoodrich all took turns at the top of this category.
Meanwhile, Falken turned its focus to drifting as a source of performance image marketing. The RT-615 was revised several times, becoming the RT-615K and finally the RT-615K+, but no version could make it to the top of the heap in autocross and lapping.
Today, this 200-treadwear Extreme Performance Summer category has exploded. It’s now the standard for several autocross categories and is rules-mandated for amateur endurance road race series such as ChampCar and Lemons. It’s also a requirement for the One Lap of America and Optima Ultimate Street Car events.
With such a huge potential sales channel, Falken is once again serious about fielding a top-level contender with the Azenis RT-660. Will it measure up? Let’s get out the timers, cones and tools to find out.
We set out to answer two questions: First, how much of an improvement is the new RT-660 over the RT-615K+? Second, how does it compare to one of the category benchmarks?
At the time of our test, production of the new tire was just starting to ramp up for a Q1 rollout, so available sizes were limited. One of those was the 225/45R17 that’s typically used by ND Miata drivers in SCCA’s C Street autocrossing. It’s also the required tire size for the Solo Spec Coupe class, which has mandated the RT-615K+ for the past two years.
The test mule was a 2019 Mazda Miata–an SCCA Time Trials Nats winner–and for this test we used OE-sized, 17×7-inch wheels. This pinched setup better replicates that found in C Street and Solo Spec Coupe competition. We then chose the Bridgestone Potenza RE-71R as a benchmark since it works well when pinched and served as the target for the new Falken.
Our drivers for the autocross portion were a pair of multi-time national Solo champs, David Whitener and Andy Hollis. Hollis also handled the track driving at Harris Hill Raceway, where he has thousands of laps. The grippy asphalt at the Mineral Wells airport hosted our autocross testing.
First Impressions
As always, we used a skidpad to establish optimal tire pressures. After a couple of circles in each direction to get a little heat in the tires, laps were made at a variety of pressures. Notes were also taken as to the feel of the tire, since driver confidence can be a key factor in ultimate performance in competition. We sprayed the tires at one point in the progression to see if heat management affected times. We then zeroed-in on final pressures by using small pressure increments in the reverse direction.
First up was the RT-615K+. At higher pressures, it was very manageable with easy turn-in and progressive breakaway. As pressures were lowered, it became less precise, but grip increased and lap times improved. This trend continued until lap times finally stabilized in the 24–28 psi range. Spraying the tires had an immediate positive effect, but only for a single 10-second lap. Reversing direction indicated an optimal pressure of 28 psi hot.
Staying with the Falken brand, we bolted up the RT-660. This tire delivered a similar overall feel to its predecessor, but with way more grip. Likewise, lowering pressures increased slip angles as the car leaned more, producing more lateral g-loads and quicker times. Spraying this tire had no discernable effect, though, even as optimal pressures were once again confirmed at 28 psi. The big story was the solid three-tenths improvement in lap times on a 10-second lap.
Next was our benchmark, the Bridgestone RE-71R. In past tests, we’ve found this tire to be fairly pressure-agnostic, centering around 28 psi as optimal and delivering crisp response at small slip angles throughout. Given that, we only did three rounds of laps in one direction to get relative steady-state lap times to compare to the RT-660. That result? The newcomer from Falken was a touch quicker.
Skidpad Results
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Do We Have a New Contender?
Our permanent test course loop consists of a five-cone slalom opposite a three-gate offset sequence, along with a pair of steady-state sweepers at each end–one on-camber and the other off-camber. Laps are done in pairs to see how a tire performs in the typical 50–60-second autocross. Driver swaps occur after doing two sets of two laps, and then tires are changed. The baseline tire is run at each end of the test to measure changes in surface, weather and driver skill.
After putting down a string of 24.7-second baseline laps, David said the RT-615K+ felt “easy to drive but lacked mid-corner grip.” Andy’s times varied, with a best of 25.2.
Changing to the RT-660, Andy lauded the high level of grip and slalom response as he ran about a half-second quicker than the baselines. David also averaged a half-second improvement but noted vagueness at the limit: “These tires will reward getting to know them.”
With the benchmark Bridgestone RE-71R in place, Andy continued to find time. “Love these tires. Very intuitive. Incredible slalom response.” David matched his RT-660 times, noting a decrease in sweeper grip balanced by quicker transitional performance: “Very confidence-inspiring.”
Bracketing our test on the RT-615K+ again showed each driver averaging within a tenth of his earlier baseline times, giving confidence in our results.
Autocross Results
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Can the New Tire Survive the Heat?
Traits that make a tire quick around the cones don’t always translate to the track. Long, sustained turns can overheat a tire’s compound, as can heavy braking from high speeds. Further, quick transitional response is not very important at most tracks, while predictable breakaway is.
Test day dawned clear, cool and partly cloudy. We ran each tire for a series of seven laps to allow the driver to grow more comfortable, as it’s a challenge to extract maximum performance in a single lap from an unfamiliar tire. Our bracketing session at the end was cut short due to fuel starvation, though we easily confirmed the test’s veracity with the three laps we did complete.
Our baseline RT-615K+ showed why it’s so popular among grassroots enduro teams, as it was easy to drive, needed little warmup time, and delivered consistent lap times: high 1:28’s, with a single flyer at 1:28.3.
Heading out on the RE-71R felt like home. It easily drove down to the apex, was very intuitive to keep at the limit in long sweepers with minor throttle changes, and put down power really well. That resulted in more than a second improvement in lap times versus the baseline.
The RT-660’s lap times fell about halfway between the other two tires. Its prodigious grip gave up some in long turns and was difficult to modulate–especially on a bumpy surface. It was also a challenge to trail-brake, causing it to lose time on corner entries after long straights.
Track Results
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Falken is Back
One thing is clear: Falken is back in the 200-treadwear game. The RT-660 is a player, at least for autocross use. It will most likely take some car setup changes and driver familiarization to extract all that it has to give, but it delivers enough to be considered alongside other category front-runners.
While not its primary strength, the new Falken is a solid performer on track. The soft compound does have to be managed well for best results, especially when ambient temps are high, but it’s sticky and predictable. Welcome back, Falken.
The new Falken RT-660 wore the quickest, forming a pronounced wedge shape as its soft compound bent under lateral loading. The Bridgestone RE-71R developed a similar shape, though not nearly as pronounced. The outgoing Falken RT-615K+ was the most durable, showing minimal wedging.
Wow. They stole the Bridgestone's tread pattern. I'm mean STOLE IT.
_ said:Wow. They stole the Bridgestone's tread pattern. I'm mean STOLE IT.
The Dunlop z2 says hi 
aw614 said:_ said:Wow. They stole the Bridgestone's tread pattern. I'm mean STOLE IT.
The Dunlop z2 says hi
Yeah, they all look very similar. I wonder if it's like how car styling will get more and more similar in the pursuit of aerodynamics, is there a certain tread pattern for performance tires that is inherently better and all tires will migrate towards that design.
To see that these perform on par with RE71Rs and come in my 245/40R15 size is very exciting. Maybe I'll make the jump to these after I chew my BFGs up. I know the BFG is a solid performer but I just do not like how they feel.
this makes me happy. Not to get some in the right sizes
In reply to _ :
If you're gonna go there... Dunlop has been using basically the same thing since the Direzza Z1. Bridgestone "stole" that pattern from the ZII. So if you're gonna rag on someone for copying it...
How'd they wear compared to the re71r?
So, the more top-tier options (RE-71r, Rival S 1.5, Yokohama A052), the better. The wear question is a good one after seeing how quickly the A052 wears. Price makes a difference for some of us.
225 45 17 are all I see available through TireRack at the moment. Hoping to get some 245 40 18 VERY soon. Like in a week. Anyone got a line on who may be holding?
In reply to Andy Hollis :
Hey are the drivers in this blind as far as information? Do you guys get to know which tire you are testing Beforehand? Do you think results would change if the study was "blind" so to speak?
I think a wild card placebo would be interesting. Especially if they pranked the drivers with some 400 tread wear turd.
Wonder if they'll come in 996 turbo sizes? I'm running the 615K+ right now...
captainawesome said:225 45 17 are all I see available through TireRack at the moment. Hoping to get some 245 40 18 VERY soon. Like in a week. Anyone got a line on who may be holding?
That size is on the list of sizes supposedly expected to arrive at the end of this month, theoretically at the same time as the 225/17s. What that means for when you can actually order and receive them is a different story, probably not any sooner than those 17s.
I am stoked that the rt-660 will continue carrying the torch for 275/17 users. If Falken can keep pricing in line, there will be many jubilant voices ready to break the shackles of the 255/17 ranks
They have a listing of sizes on their website.
https://www.falkentire.com/tires/passenger-car-tires/azenis-rt660-tire
docwyte said:Wonder if they'll come in 996 turbo sizes? I'm running the 615K+ right now...
Looks like a yes!
They have 315 and 295/18s and 235 and 245/18s so the gt3 may have to try a set as well.....
The A052 has my eye as well for HPDE work versus running dedicated NT01 wheelset.
225/45R15 for the ES crowd.
I can't wait a month for these unfortunately so I'm just going to stick with the tried and true rt615k+ for one more set. Hopefully these 660s hold up as well as the 615s for longevity, or at least somewhere close to it. Looking forward to some more reviews soon.
The 615k was the longest lasting 200TW tire we've used on the racetruck. I wonder how these will hold up to endurance racing.
In reply to buzzboy :
Try the Hankook RS4. Last longer than the 615k+ and have a little more grip.
Based on Andy's testing these wear faster than the re71s do.
In reply to Sonic :
I had the rs2s and loved them but I haven't used any Hankooks since those were released. I'll have to check into those
In reply to Olemiss540 :
Nice! I've decided not to buy a dedicated set of race tires for the turbo, I don't hit the track often enough to use them up in time. So I'll just run the 615k+'s, that way I don't have to swap wheels/tires. I don't care about how long they last, I don't drive the car that many miles since it's not my daily.
I was going to try the Yoko 052's next but maybe I'll try these new 660's instead. I run 245/40/18 front and 315/30/18 rears...
615k is easily one of my favorite 200tw for what I do..... I really hope they wear and have the rain capability that the 615k has.
So if it's on par with the RE-71, is it cheaper to justify switching from the gold standard? The 052s appear pretty awesome but have priced themselves up near Hoosier territory last time I looked.
How is the wear rate on the new RT-660? From the single picture of the 3 tires, it seems like the old RT-615K+ has the least wear, and the RT-660 had the most wear. But it is a single picture, and it is always difficult to see how much wear there is unless I'm looking at the tire in person.
The article mentions the wear rate looks to be more aggressive than the RE71, so I imagine the rt615k+ will still be the clear winner for reduced wear rate. Does anyone know if the 615s will be axed or is the 660 supplemental? Personally I'd like a set of 660s for autocross if price is similar to current 615 price, and a set of the 615s for track days.
In reply to captainawesome :
Same.
Comparing their price to same size RE-71s they look to be about $40/tire less; significant difference.
Nice test guys! I love how GRM gets the info out there. And how SCCA is promoting it, and you!
OTOH, your test of the Yoko 052 last year, I took it as, "eh, it's maybe a tiny bit faster", bought the RE71R's, then at Nationals /everyone/ in the trophies was wearing a set of 052's. On the real side, probably not a great idea for me to chase a couple of tenths/minute when I'm seconds behind.... 
The wear issue: Since these were pinched a little, the shoulder wear is probably exaggerated. It wasn't clear if the car used has additional camber control ("This pinched setup better replicates that found in C Street and Solo Spec Coupe competition" doesn't state whether it does, as SSC does have some suspension mods). Could you guys clarify?
If the tire burns off noticeably faster than an RE71R and costs $40 less, not so much of a good deal. The only size TR lists right now is the 225/45-17 which is indeed $43 less.
I had to chuckle at the beginning of the article were it refers to the asphalt at Mineral Wells as "grippy." I've driven quite a few events there and it is a fun venue due to its size (big, fast courses). However, grippy would not be my adjective of choice to describe the asphalt. The surface is kinda crumbly and it shreds your tires as they slip over it.
RadBarchetta said:In reply to _ :
If you're gonna go there... Dunlop has been using basically the same thing since the Direzza Z1. Bridgestone "stole" that pattern from the ZII. So if you're gonna rag on someone for copying it...
More importantly, Dunlop and Falken are both owned by Sumitomo. So free sharing of tech across the companies is a thing.
Story time...
I once did some private consulting work for Falken...they wanted to replicate a tire test I had done and see how a couple of new variants of their tire would stack up. Problem was, given the timing, one of the comparables was the then-previous-gen Direzza, so retail versions were long gone. But when tires showed up for testing, there was a brand-new set of the older Direzza with current build codes. They had them made.
PT_SHO said:The wear issue: Since these were pinched a little, the shoulder wear is probably exaggerated. It wasn't clear if the car used has additional camber control ("This pinched setup better replicates that found in C Street and Solo Spec Coupe competition" doesn't state whether it does, as SSC does have some suspension mods). Could you guys clarify?
The test vehicle this time has 3 degrees of camber all around. SCCA TT Sport 5 build. STR-lite, in autocross terms. Lowering springs, Konis, bars. The previous tire test story you mention (A052) has a sidebar on that car in the enduro tire test portion (RS4 vs VR1).
bigben said:I had to chuckle at the beginning of the article were it refers to the asphalt at Mineral Wells as "grippy." I've driven quite a few events there and it is a fun venue due to its size (big, fast courses). However, grippy would not be my adjective of choice to describe the asphalt. The surface is kinda crumbly and it shreds your tires as they slip over it.
The area we use for testing (far SW corner, top of the hill) is the best asphalt on the site, and has stayed that way for all the decades I've run there. We also blow it off clean before testing.
The rest of the site varies between knife-edge rocks that cut tires ( a band down the east-middle), smooth and clean (far eastern band), and pebbly (rest of the site). For national events, the site prep includes blowing off of the loose stuff, which then leaves a nice clean surface. Local events typically only blow off the worst bits so "crumbly" is really just pulling the loose stuff out from the relief in the surface.
So I'm good with "grippy".
captainawesome said:The article mentions the wear rate looks to be more aggressive than the RE71, so I imagine the rt615k+ will still be the clear winner for reduced wear rate. Does anyone know if the 615s will be axed or is the 660 supplemental? Personally I'd like a set of 660s for autocross if price is similar to current 615 price, and a set of the 615s for track days.
We've been told that the 615K+ will continue, for now.
_ said:In reply to Andy Hollis :
Hey are the drivers in this blind as far as information? Do you guys get to know which tire you are testing Beforehand? Do you think results would change if the study was "blind" so to speak?
The drivers are not blind. Too many cones would be hit that way, though I'm certain that we'd have no DNFs since we have thousands of laps on that test course and could drive it blindfolded :)
On a serious note, i've done blind testing before and it does enhance your "spidey senses" when you have zero idea what to expect. But it also means more "mulligan runs" and can also be more dangerous for track testing. We chose the order carefully to use this as an advantage for testing purposes, not to give advantage to a particular tire. And the bracketing results show this to typically be the case.
Its also why we use two drivers, so personal bias does not creep in. David prefers "sloppy" tires, like the Rival S or A052. I prefer "crisp" tires like the RE71R.
Why does my Google Fu fail at finding anyone who has experience with the new 7/32" A052 in a dual duty (HPDE) environment. Wondering how many weekends would they remain streetable for to/from the track in rain.....
Is the new A052 a 2 weekend tire or a 5 weekend tire?
From what I've seen in Lemons they are a 2 weekend tire. Even lightweight cars are not finishing one day with them
Re: the AO52, I would like to try a set for autocross, but not until I get a trailer....
In reply to Floating Doc :
My car is trailered and I love them.
Andy Hollis said:More importantly, Dunlop and Falken are both owned by Sumitomo. So free sharing of tech across the companies is a thing.
SOME Dunlop tires are Sumitomo tires. The rest are Goodyear. Several years ago, there was a joint venture between Goodyear and Sumitomo that when dissolved, left a few Dunlop tires as Sumitomo entities. Basically, if it comes from Japan, it's a Sumitomo tire.
I believe the whole "Direzza" line is Sumitomo.
245/40/17's now listed in stock. Someone try them, see how they wear, drive them in rain and tell me whether I want them or not.
collinskl1 said:Andy Hollis said:More importantly, Dunlop and Falken are both owned by Sumitomo. So free sharing of tech across the companies is a thing.
SOME Dunlop tires are Sumitomo tires. The rest are Goodyear. Several years ago, there was a joint venture between Goodyear and Sumitomo that when dissolved, left a few Dunlop tires as Sumitomo entities. Basically, if it comes from Japan, it's a Sumitomo tire.
I believe the whole "Direzza" line is Sumitomo.
It's a weird thing. Goodyear owns the US market rights to Dunlop. But the US tires, despite Goodyear's involvement, are still made overseas in a Sumitomo-owned factory...just with Goodyear's spec. This is why we get Direzza's a year after the rest of the world. Goodyear has Dunlop tweak them for the US market. That's my understanding.
I am unaware of any Goodyear-manufactured Dunlops. Got a source for that?
FYI a handful of sizes have popped up on Tire Rack in 17s plus 245 40 18s. I imagine they will be rolling more out any day now.
Bringing this article back up to the top. The prices of the RT660 are below everything else in the class by a solid margin. They're offering 18" sizes up to 255 now.
I just bought a set of the 205 15's for my Fit to run at Road America this weekend.
in my 205 size.. RT660 are $121 each, RE71R are $137, Yokes and BFG's are $148-ish
On another forum I frequent there is a guy who works for Falken and he said the big sizes (315, etc) will be available in November.
I'm going through the math on these right now as well. However, if you factor in rebates on the Stones, the margin gets considerably slimmer if not less depending on size.
I kinda want to try these out for TT next year instead of hoping for a rebate though.
Bought a set of RT660 in 215/40/R17 for my 2017 MX-5 due to the price difference to the A052s which I am currently running. Ran both back to back over two days at Sonoma and found them to be both within 100th of a second of each other. I am impressed based on the price delta compared to the A052s. Interested to now see how long they last in comparison.
I assume the article has tyre pressures hot? I think I might have been running mine a little warm at 32PSI.
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