Tire inserts are steadily gaining followers in mountain biking, and as they become more widespread, brands are starting to offer insoles specifically for gravel and cyclocross. What are tire inserts and why are they needed for thin tires? What can you do that more tire volume cannot? Well there are a couple of advantages.
What are tire inserts?
Let’s start with the first question. What are tire inserts? There are several very different designs, but they all share the same basic idea. Something solid that will fit in a tire, usually tubeless tires instead of just air. Inserts can help protect the rim and protect the tire casing itself.
Where did the idea come from? Mountain bikers have adopted and adapted the idea of off-road motorcycles. With the Moto, a solid rubber foam insert – known as a “mousse” or “bib mousse” – fills the entire inside of the tire instead of air.
With bicycles, there are a few factors that make airless options impractical. First, riders have to propel their own motion, making the weight of a solid insert an obvious disadvantage. Bicycles also use a wide range of tire pressures that must change based on conditions. Instead of a solid liner, most bike options use some type of partial liner combined with air and usually tubeless tire sealant. Inserts vary widely in design, and this is where things get interesting. Each design has its own advantages and disadvantages.
The idea first found its feet in mountain biking, where tubeless tires are widespread and weight is less important. New designs are becoming lighter and tubeless is becoming increasingly popular on gravel, making the switch to 700c wheels inevitable. Early adopters include Canadian veteran racing driver and self-proclaimed gearhead Geoff Kabush, who has used it successfully at several gravel events.
What’s the benefit for gravel?
The most obvious – but not limited – benefit of the insert is protection against flat tires. Relatively small volume tires are still used in gravel riding, and a failed root or invisible loose rock can quickly deflate a fun ride.
How do deposits protect against flats? By providing a cushion of soft material between the tire or the ground and the rim. Hit something too hard and the tire will compress into the foam instead of directly touching the rim. This protects the rim from damage. It also protects the tire from entrapment and, to a lesser extent, from being punctured by more pointed stones. Glass, nails, and any other object that cuts into the tire instead of stabbing the tire are, of course, still a problem. As well as side wall panels from sharp rocks. So the benefit of stakes depends in part on where you drive regularly.
The second benefit is an offshoot of the first. Because you have less to worry about about flat tires, you can safely drive with lower tire pressures. This ensures better grip and rolling resistance on often loose and rough surfaces. It also means there is less surface rattle coming through the bars, which increases comfort and reduces fatigue.
Depending on the design, tire inserts can offer more sidewall support even at lower pressures. Some inserts, like CushCore, physically press against the side of the tire. This provides support for the sidewalls so you can still corner hard at low pressure while the tire tread better conforms to and grips the surface.
Most designs also help to some extent to keep tubeless tires in place as they physically press the tire bead against the rim. Burp less tires, burp more!
What about cyclocross?
Tire inserts are arguably even more useful for cyclocross. There are certainly fewer stones waiting to dent a rim than there are on gravel bikes. But the extremely low tire pressure for cyclocross and the almost no traction in the mud are ideal for the world of cross racing. Especially when the traditional alternative is a tubular, which can cost well over $ 150.00 per tire.
Tubular tires are popular in cross-country sports because they let you ride low pressures with less risk of flattening. A low tire pressure in turn ensures that the treads adapt to the ground and grip it in slippery conditions. Some professional racers drive tire pressures below 20 psi, even into the mid-teens. This is as good as impossible with a tube and tire. It’s more practical with tubeless tires, but, and especially for those of us who are heavier or less sensitive on the bike than a pro, tubeless on its own can start burping or slipping off at extremely low pressures. As with gravel, inserts provide sidewall support to keep the tire on the seat when the pressure drops. Some designs even let you drive them on a flat tire, although they usually recommend driving slower or more carefully. It should be enough, however, to pit you in a racing situation and ride better than on the rim.
While the added weight of tire inserts might put off top pros (who also won’t have to pay to replace the tubes that have flattened them), for the rest of us an option is to get the performance benefits versus barrel tubes at a lower price Price offers than tubes.
A clear marking that shows where the inserts cushioned the tire from direct contact with the rim
Cush Core has found ways to reduce the weight of its cx / gravel insert
Further signs of success
What are the weaknesses?
Of course, tire inserts have some disadvantages. Whether they outweigh the benefits depends on how you drive and, to some extent, where you drive.
The first and most obvious disadvantage is weight. Adding inserts means adding more weight to your rim. Mountain bikers can often compensate for this with lighter tire casings, but the difference in weight between the casings on gravel and cyclocross tires is less than that of mountain bikes.
There is an additional step to install and remove. The lighter weight of material for narrower tires usually means this process is easier than some mountain bike insert designs, but it may require a bit of engineering.
Lastly, most insert designs don’t protect much from cuts on the sidewall. As with the tubeless run, a sizeable sidewall cut can force you to put in a tube. The difference is that depending on where you are, you’ll have to take the insert out and carry it around before you can insert a hose. This happened to me at a cross race this fall, where a sidewall cut left me flat about 15 minutes before the start. It was a scramble, but I was still able to remove the inserts, drop in a tube and rush to the start with a single tire lever.