Downhill Secret Revealed: Flat Tire Defender Foam Inserts - First Look

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.










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.




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.



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.




Pinkbike's Take:

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