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When it comes to bicycle performance, there’s nothing more important than literally where the rubber meets the road. Sure, there are other factors that come into play, but when all is said and done, it’s all about the tires.
Most of us are used to the standard variables affecting tire performance: casing construction and suppleness, rubber compounds, tread design. However, regardless of what tire you’re running, the biggest variable is air pressure. It’s an especially important tuning parameter when it comes to gravel bikes, where the tire sizes are relatively small, the terrain often borders on MTB territory, and traction is never as good as you want it to be.
In those situations, dropping your pressure even just 2-3 psi can make a profound difference to things like cornering and climbing grip, rider comfort, and braking distances. But given those smaller casing volumes, there’s only so low you can go before pinch flats become more prevalent. As such, the end result is that most of us end up running higher pressures than we’d ideally like to.
Foam tire inserts have long been used in the mountain bike world, particularly in harder-hitting disciplines and rockier terrain where even 2.6″-wide tires and relatively high pressures aren’t enough to prevent pinch flats and rim damage. But they’re a much newer thing in the gravel space, and — we’d argue, at least — actually more impactful (no pun intended).
Tire pressures in gravel aren’t much higher than they are for mountain bikes, and yet the tire widths and volumes are much, much lower. As a result, gravel riders are more often forced to make bigger performance compromises to prevent flats and rim damage. But with foam inserts, you really can have your cake and eat it too, since you can now run as much as 5-10 psi less pressure without having to worry as much about pinch flats and casing squirm.
There are limits, of course.
Much of the performance gains — and drawbacks — will depend on which liner you use, and there are a lot of them on the market now, including from CushCore, Vittoria, Effetto Mariposa, Rimpact, and more. Something like CushCore with a denser foam that more firmly fills the base of the tire will provide more casing support, for example, while Effetto Mariposa’s more minimal design basically just provides rim protection, but is less expensive and easier to install.
Stay tuned for more in-depth reviews of all of the liners mentioned, but in the meantime, consider putting one of these on your wish list. Be as skeptical as you’d like, but we dare say you might be very pleasantly surprised.