Frank Stacy has been designing tires longer than most Pinkbike members have been riding mountain bikes, and before that, he was doing the same for off-road motorcycles. Stacy keeps a low profile, and he's worked for a number of elite brands, so while you've may have never heard his name, there is a good chance that you have ridden his work. Stacy's latest brainstorm is called "Flat Tire Defender" and it's a cylindrical, closed-cell-foam tubeless tire insert that prevents pinch flatting and protects the rim from sharp-edged impacts.
Flat Tire Defender Details:
• Long-wearing high-density closed-cell foam insert does not absorb sealant • Requires no special tools to install or remove • Intended to work in conjunction with tubeless tires • Stabilizes tire bead interface to prevent burping and side-wall flex • Eliminates pinch flatting and reduces rim damage • Kit includes liner, tubeless valve and Zip ties to assist installation • Sizes: Six options to fit 26", 27.5", 275+, 29", or 29+ tires • Weight: 275 to 350 grams • MSRP: $69.50 USD (single), $121.50 (double) • Contact: Flat Tire Defender Foam Inserts
Before you start chuckling, you should know that since 2014, when Stacy began developing it, prototype Flat Tire Defenders have been raced at the highest level by Tracey Moseley and Justin Leov on the EWS circuit, and on the World Cup DH, by Laurie Greenland, Brook Macdonald and Neko Mulally. Aaron Gwin used the inserts throughout his victorious 2016 World Cup season and also assisted in its development.
Stacy's Defender insert may have been the best kept secret in gravity competition - one that was revealed after Gwin broke a wheel 20 seconds into his World Championship run and would ride the next few minutes of the course on a slowly deflating tire - until the half way point, when he landed on a large, loose rock that had rolled into the course, ripping the low tire off and exposing the FTD insert to the world. Miraculously, nobody noticed.
Gwin landed on a large, loose rock that had rolled into the course, ripping the low tire off and exposing the FTD insert to the world. Miraculously, nobody noticed. - 2016 World Championships
Flat Tire Defender Major Accomplishments:
• 2015 Enduro World Series pro woman series champion, Tracy Moseley • 2015 UCI Junior Men Downhill Worlds, 1st Laurie Greenland • 2016 UCI Elite Men World Cup Downhill series champion, Aaron Gwin 1st Lourdes 2nd Fort William 2nd Lenzerheide 2nd Mont Sainte Anne
• 2016 UCI Elite Men Downhill Worlds, 14th place Charlie Harrison
Flat Tire Defender athletes for 2017:
• Team YT downhill riders: Aaron Gwin, Angel Suarez and Neko Mulally • Team Canyon enduro rider: Justin Leov • Team Trek enduro rider: Tracy Moseley • Pro athletes (enduro and/or downhill): Christian Gonzalez, Cole Picchiottino • Weekend test riders: Ely Woody, John Hall, Ben Arnott, James Richards
Designer Frank Stacy (left) and mechanic John Hall demonstrate the Flat Tire Defender insert in the makeshift pits. Carol Stacy photo
Stacy says the Bib Mousse foam insert concept has been around for years and has successfully solved the three issues that continue to plague mountain bike riders: pinch-flats, punctures and damaged rims. The Bib Mousse, however, is monstrously difficult to install, it's heavy, and it occupies all of the space inside the tire, so it eliminates the option to fine-tune traction and tire stability by varying air pressure.
Stacy's solution (after a dozen or so dead ends) was finding a tough, closed-cell material that had a quick rebound rate, and then molding that into an oval-shaped insert that takes up roughly, a third of the air-space inside the tire. When the tire is overwhelmed by an impact, the tread crown butts against the liner, which cushions the blow and spreads out to prevent the tire carcass from pinching against the rim flanges. The air space makes room for liquid sealant and allows the tire to perform in all other respects, like a conventional one - except for one remarkable detail.
The 27.5+ sized liner illustrates that the tubeless tire is free to react normally until the crown tread makes contact with the Flat Tire Defender.
Gwin began the 2016 season with a victory for the YT Mob - and for the pre-production Flat Tire Defenders.
Aaron Gwin Talks Tech
It seems that the insert has a positive effect upon the suspension. At the Flat Tire Defender launch in Laguna Beach, California, Aaron Gwin spoke at length about how the insert performs. He acknowledged the insert's pinch-flat protection and stated that, since he began using them, the only time he suffered a puncture was when he ripped a sidewall open and that, unless he broke a wheel, he could finish a race run with zero air without losing a tire. But, the main reason he runs them is that they enhance his suspension. The liner eliminates sharp impacts, and his bike rolls over momentum-robbing square-edged hits.
Weight vs Performance
Weight and complexity are two factors that Stacy worked hard to minimize, but in the end, he says that there was a critical point, where if he used a lighter foam, the riders complained that the suppleness that the liner added to the ride evaporated, as did some of its ability to protect the rim and tire. Liners that fit 27.5 x 2.4-inch downhill tires are said to weigh around 275 grams each - enough to make a noticeable lag in acceleration, but not enough to dissuade competitors from using them. Gwin says that he will remove the front liner for smoother, courses that have a lot of pedaling, but that the speed he gains from the enhanced ride offsets any losses he might suffer from the heavier wheels. The fact that Trek's top enduro riders choose to run the Flat Tire Defender echoes Gwin's sentiments.
Mechanic John Hall Shows How It's Done
To address the complexity side of the Flat Tire Defender equation, Stacy has produced a video that shows how to install and remove the liner without tears, and he includes some simple installation aids in the accessory kit. At the launch, Gwin's mechanic John Hall demonstrated his installation technique, and later, using Hall's method, I installed a liner inside a Maxxis Minion DHF without tools, in about four minutes. The takeaway was that the liner creates some additional difficulty, but it isn't that tough to get it inside a tire and mounted up. The up-side of the liner is that, like an inner-tube, it naturally presses the tire's bead to the rim flanges, so reportedly, tubeless tires air up with a simple hand pump and don't burp air or sealant, no matter how hard you push them in the turns.
Frank Stacy advises first-time installers to use a zip tie to hold the insert and tire in place.
The tie frees up both hands to work the insert onto the rim while installing the bead.
Mechanically, the Flat Tire Defender functions much like Schwalbe's Pro Core system. Pro Core, however, uses a high-pressure treadless tire, inflated inside of a conventional tubeless tire and it comes with its own installation issues, including a tiny vulnerable tube inside the core, and a fussy two-stage valve. The Defender's closed-cell construction can't be deflated, and its compression and damping ability provide a superior feel (so say the athletes who have tried both systems). By contrast, Tracy's solution uses a conventional tubeless valve stem, modified with deep cross-slots on its inner face to allow air to pass freely beneath the insert, so the Flat Tire Defender is a simpler system that can be maintained with off-the-shelf parts in a pinch.
John Hall watches while I install an insert into a Maxxis DHF tire using his method. I managed it without tools. Carol Stacy photo
Flat Tire Defenders are available to fit 26 and 27.5-inch tires from 2.3 to 2.5 inches, mounted to rims with inner widths from 24 through 34 millimeters; 27.5-inch Plus tires from 2.6 to 3.0 inches on rims from 36 through 44 millimeters; and 29-inch tires and rims in similarly sized combinations. Weights range from 275 grams, to 350 grams for the largest, 29+ model.
The key player in the Flat Tire Defender accessory kit is this modified tubeless valve stem. Without its deeply grooved face, the liner would prevent air from being released.
Who Will Benefit Most Using the Flat Tire Defender?
Beginning with Frank Stacy, all those who have ridden the Flat Tire Defender inserts agree that they are best suited for gravity riders. The extra weight would be a burden for most trail riders, who would be slogging around 700-grams of rotating mass 80-percent of the time, only to reap the benefits on the fastest and steepest technical descents. Enduro racers can justify the weight, because the inserts give them a huge insurance policy against mistakes that could cost them a stage, as well as another level of bump control. For downhillers, Flat Tire Defender offers the greatest benefits. Defender inserts are a pop-in solution for racers battling for series points or searching for a way to shave off the two precious seconds that lay between the podium and a tenth-place result. And, in spite of their MSRP, the inserts should be popular among park shredders who pay full pop for travel and lift passes, and don't want to be sidelined for an hour wrestling with a flat tire.
Tracy Mosely on her way to winning round four of the 2015 EWS at Samoens, France. Downhill speeds, minimal practice, and ever-changing terrain is a recipe for wheel disasters.
Sadly, trail closures due to heavy rain prevented us from downhill testing at the Flat Tire Defender launch, but we got our bikes mounted up with inserts and Frank Stacy gave us an extra set of 27.5 and 29-inch Defenders to review later. The concept is well engineered and executed. It has posted victories at the highest level in EWS and World Cup DH, and the athletes who have participated in its development are committed to it. All indicators point to a successful product, We will be testing the Flat Tire Defenders at home, so hang tight for a full review in a month or so. - RC