We Tested the New Ultra-Sticky Shoe Rubber Made From F1 Racing Tires

Ratom’s new shoe rubber was destined to go viral. Rub two shoes with a swatch of the rubber together, give them a firm press, and voilà, they stick together with gravity-defying magic.

Max Fisher, a Flagstaff-area resoler with early access to the Japanese climbing company’s GP Rubber, says he was flooded with suspicious comments after posting a few Instagram videos of his resoled shoes sticking to climbing holds and windows. Commenters alleged magnets, glue, and other tricks of legerdemain; even more common were cries of “aid!”

A trick it is not. Ratom rubber really is stickier than nearly any climbing rubber out there. Whether it counts as aid, well, time will tell.

The ramifications of this climbing-shoe innovation seem clear. Scary slab could be a thing of the past, with shoes that let a climber grip like a gecko to any surface. Competitions may never be the same, as contenders hike casually up slick Dual Tex volumes. Speed climbers might forgo footholds altogether and simply run up the wall.

Technical breakthroughs to climbing shoes have remade the sport on more than one occasion, from the dawn of sticky rubber in 1979 to the aggressive downturns that unlocked high-end moves on steep terrain. Could we be entering the Ratom era of rock climbing?

How Ratom’s climbing shoe rubber works

Ratom’s GP Rubber is made from retired racing slicks, the super-sticky tires that 11,000-horsepower drag racers use to launch themselves to 300 miles per hour in seconds, and which let Formula One cars take corners at up to five Gs.

In retrospect it’s a bit of a no-brainer—or at least it seemed that way to Ratom founder Katsuhito Arai, a former motorcycle racer who I spoke with through a translator. Looking to take advantage of his father’s empty ironworks, he founded a climbing gym in Iwaharamachi, a small municipality a bit less than two hours north of Tokyo, in 2015.

“When I saw the climbing shoes, they immediately reminded me of slick tires,” he says.

But when Arai tried a pair on for himself he was disappointed: they didn’t seem to stick as well as he thought they should. “It was always in the back of my head, ‘what if we put a slick tire on a climbing shoe?’” he says.

The question inspired a years-long search for the right racing slick, of which there are many varieties. Eventually, Arai says he settled on four kinds, which made up Ratom’s initial line of products. They are divided into two groups, GP1 and GP2, with a hard and a soft version of each. GP1 is the softest rubber on the market today, Arai says, and even their harder compounds are softer than most rubbers in use for climbing. (Arai says Ratom will soon transition to a new product line featuring three rubbers: one tentatively named GP ZERO, GP1, and GP2.)

Ratom sources its rubber from Japanese racing teams, who would otherwise be discarding old racing tires. Used rubber seems to work best, Arai says, adding that Ratom tried brand new racing slicks and found they actually stuck worse than used ones. The sustainability advantages of used rubber appeal to Arai anyway, who says he’s happy he can take a material once seen as trash and give it a second life with climbers.

Once at the factory, processing is minimal, and mostly amounts to sanding off dirt and pebbles stuck to the tires and turning them into flat sheets. Then, they send the sheets off to affiliated resolers like Fisher who cut out climbing soles from them.

Fisher caught wind of Ratom last summer, when he saw a video posted online by Luke Stirling, who had got some GP Rubber from Arai and was trying to do his own resoles with it. (Stirling is now head of Ratom North America.) Fisher offered up his cobbling skills and got a few sheets of Ratom rubber in exchange, and when Ratom had a larger batch available he purchased most of it.

Fisher says that, for him, the rubber feels like a good tool to have in rotation. After swapping in his own pair of GP-enhanced shoes while trying a river-polished V4 outside Flagstaff that had been spitting him off, he says he sent the problem first try. He says his customers have similar reports.

How Ratom’s rubber performs in the field

GP Rubber is so new that no climbing shoe manufacturer is selling shoes with it yet (Arai says a few have reached out, though he declined to share specifics). The only way to get it on your boots right now is to go through a Ratom-affiliated resoler, like Fisher’s Rhythm Resole in Flagstaff. Though his supply of GP Rubber was almost gone, Fisher sent me a pair of well-loved Five Ten Moccasyms with a GP1-hard (the second-softest of their initial lineup) half-sole to test out.

I put them to the test at local bouldering gym Climb Tacoma and on medium-coarse Leavenworth granite, swapping off with a pair of Unparallel UP Moccs and La Sportiva TC Pros. My overall impression was positive, though with some reservations.

In the gym, I tried both smeary comp-style boulders involving volumes and slab problems with small, sloping feet, as well as a few more overhanging problems. I noticed a definite increase in sticking power on small, sloping footholds, though, interestingly, the GP Rubber seemed to hold a little bit worse on volumes than my Moccs. It felt to me like I needed to press somewhat hard to activate a better grip with the GP Rubber—when the force was spread out over a larger surface area on a volume, it didn’t latch as well. In contrast, Fisher noted that his clients did seem to like how the GP Rubber performed on volumes, so perhaps this was specific to me.

I tried out the shoe-sticking trick too, and did get them to stick together after a few seconds of vigorous rubbing. The shoes impressively stayed together even if I tossed them in the air, though I noticed I needed the rubber to be perfectly clean for it to work. Even a light coating of chalk or dirt robbed their sticking power.

I got some of the best performance on granite slabs outside, where the GP Rubber stuck more readily than my TC Pros in most cases. I was able to bounce my feet on steep smears with confidence, and ventured higher up a tall friction-slab boulder problem than I’d dared in the past. The TC Pros did have an advantage while toeing into shallow scoops or precisely weighting micro edges; the softer GP Rubber deformed and slid too much to make precise use of very small features. The shoes I was using were around a half size bigger than my normal shoes, so downsizing by a half or full size may have improved their performance on small holds.

Moving to a gently overhanging problem around the corner, the rubber’s softness was evident on a burly move that involved kicking a left foot high to a small nub, opposed by a right-hand gaston. As I pressed into place, I could feel the rubber bending around the nub, making it harder to engage my foot on the hold and altering the angle between rubber and rock, making a slip feel more likely. It felt like the extra stickiness helped to make up for this effect, though.

I didn’t notice the GP Rubber marking up holds any more than a regular climbing shoe would. I gave the wall a few good scuffs at the gym with both the GP shoes and my regular ones and noticed no difference—though testing from others shows differently.

Although the GP Rubber was undoubtedly stickier in most situations, when it did fail, it tended to do so catastrophically and without warning. My usual rubber telegraphs an impending foot pop with a few micro slips; the GP Rubber seemed to fail all at once.  As a result, I had less warning to adjust a poor foot placement before it failed completely, which felt potentially consequential for bouldering.

One significant variable in my testing was the temperature. While GP Rubber is supposed to be stickier than other rubbers even when cold, Arai told me GP Rubber’s sticking power increases significantly as it warms up—that’s why you need to rub them together vigorously to do the magic-shoes trick.

The gym I tested them in hovered between 60-65°F, and I tested my GP shoes outdoors in both cooler and warmer temps: on shady problems at around 50°F and on sun-toasted slabs on a warmer day. I noticed a boost in stickiness on warm rock (though this does mean they get even softer, making them even worse for edging). While the grip was improved, I didn’t notice a huge difference in my climbing between the warm and cold days, though on hard, friction-critical moves I could see it making a difference.

Ratom’s distinct temperature range and responsiveness to heat could open up a new realm of temperature-beta for climbers, Fisher says. Finding the exact pairing of rubber and temperature could unlock the ideal stickiness for climbing. With their enhanced responsiveness to temperatures, GP Rubber shoes might allow for more meaningful temperature-rubber matches. Shoe quivers of the future could be augmented with an array of rubbers tuned for different temperatures, letting climbers optimize friction throughout the day and year, or when switching aspects.

Does Ratom rubber really make a difference?

Climbing with GP Rubber didn’t make me a significantly better climber. I certainly felt, and moved, better on slabs. (Granted, friction climbing is so psychological my “improved performance” could just be a placebo effect from believing my foot would stick better.) I also noticed an uptick in performance on insecure, sloping footholds—as long as the edge wasn’t too small. Conversely, the rubber’s softness is a real downside in some situations, like small edges in vertical terrain, and its performance on overhangs was mixed. In steep terrain GP Rubber performed reasonably well on larger holds where its stickiness meant I could relax a little more while still keeping my feet on. Conversely, on smaller holds where I needed to actively press into a position, the rubber would deform and make it more likely for my foot to skate off.

A caveat is that GP Rubber does seem to perform differently enough that it could take small adjustments to style or technique to get the most out of it. Soft, very sticky rubber demands a different kind of footwork in some situations, such as a bias toward dropping your heels to maximize surface contact versus toeing into an edge as you might with a stiff shoe. It’s possible I might have noticed more of an improvement over time as I got used to it.

Climbing Youtuber Magnus Midtbø has also tested some GP Rubber (though it’s unclear which variant he used), and he seems to be reasonably impressed by its performance on indoor boulder problems. Putting a pair of resoled Dragos to the test on a variety of hold styles in the gym, he says he might end up using the GP shoes about half of the time—probably more than I would end up using them. (Though Midtbø does climb almost exclusively in super-soft Dragos, meaning he might be more comfortable with soft rubber than most people, and nevertheless might have received a softer GP Rubber than me.)

Overall, the improvements felt marginal, but potentially impactful in specific environments, like friction slabs, or small, sloping footholds. Ratom’s product seems likely to find a role as one element of a larger shoe arsenal for climbers who want to truly optimize their shoe game. High-level climbers may find specific uses for different GP compounds on difficult projects. Climbers in colder places might like GP Rubber during the wintertime, helping them maintain grip at lower temps.

Still, I don’t think GP Rubber is going to revolutionize climbing, or negate the need for good footwork. Arai seems to agree.

“Do I think the rubber is good? Yes, 100%,” he says. “However, is it going to drastically change the climbing industry or the climbing world? I don’t know.”

He thinks beginner climbers are most likely to benefit from GP Rubber, as the grippier rubber could make up for poor foot technique. At the more advanced end of the spectrum, “the climbers’ technique and the skill sets [are what] really matter the most when it comes to climbing the most difficult routes or climbing their most difficult projects,” he says.

Arai says a few pro climbers are currently using GP Rubber on their shoes, though he declined to say who.

The future of climbing shoe rubber

Ratom’s rubber raises an interesting question: how soft can climbing rubber go? Climbing rubber is rated on the Shore A hardness scale, which goes from 0 to 100, with higher numbers being harder.

According to Ratom’s website, their rubber ranges from 55A to 65A on the scale, which is significantly softer than other popular climbing rubbers. While exact data is hard to find, a 2024 paper in the journal Sports Engineering from researchers in the United Kingdom tested various kinds of Vibram rubber, used on most Scarpa and La Sportiva shoes, and offered by many resolers, and found a range of 70A to 74A. Some sources online put Five Ten Mi6 rubber, rumored to be the stickiest ever made, at 60A, right in the middle of the GP range.

Softness might not be the only factor when it comes to stickiness, though. That same 2024 paper put a number of different climbing rubbers through a controlled test using lab-grade tribological equipment made for studying friction. Five Ten’s Stealth C4 rubber performed second best in one test of sticking power, despite being one of the hardest rubbers tested, while Vibram’s XS Flash rubber was consistently less sticky than others, even though it was one of the softest.

The paper’s authors say much of that difference could come down to adhesion at the molecular level, where factors like “Van der Waals forces” can cause molecules to stick together. Different rubber compounds may yield better or worse molecular adhesion, affecting how well they stick. Surface roughness was another differentiator: Harder rubbers stuck better to smooth surfaces, while softer rubbers performed relatively better on rough surfaces, where they could deform to bite into microscopic irregularities.

I reached out to a few climbing shoe companies for their take on GP Rubber. While most didn’t get back or declined to respond, a representative for Scarpa noted that softness is just one factor the company considers when picking rubber compounds for their shoes.

“Super-sticky rubber is amazing for certain uses, but you have to be thoughtful about using it in other places where you need to balance stickiness with other factors,” says Matt Ginley, the North American sales manager at Scarpa North America. “Ultimately it’s a case of putting the right material in a particular place for specific kinds of climbing shoes rather than simply using the stickiest rubber available in every application.”

Ratom’s list of affiliated resolers is expanding rapidly, and Arai says the company has partners in North America, Europe, and Southeast Asia. The biggest roadblock to getting GP Rubber for yourself might be supply: Arai says he’s had trouble keeping up with demand, though the onset of racing season in Japan should help. Importing the rubber into the U.S. has also brought headaches, which Arai says he hopes to have sorted out soon.

Right now, on the strength of viral videos and word of mouth, Ratom rubber is quickly finding new markets and new customers. Future developments, whether new compounds or partnerships with shoe manufacturers, could increase its usefulness and capabilities. Putting the rubber on a pair of board-lasted shoes could increase their stiffness, for example, and shoe manufacturers may find novel ways of designing shoes around racing slick rubber that boost performance.

GP Rubber seems worth experimenting with for most climbers, though you’ll likely need to put in some work to feel out exactly where and when the rubber helps you best. For the dedicated shoe nerd, GP Rubber is worth having in your rotation.

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