Became interested in trying an inexpensive home made insert just for ‘proof of concept’ purposes, before possibly laying out the cash for a commercial option. After a couple of rides, I think it’s worth trying.
Wheels: oldies but goodies, roval control sl carbon off my old xc race bike. Love them. Run them on my gravel bike. Narrow internal width by todays standards, don’t even know exactly—20mm? They generally keep tires at labeled size.
Tires: Gravel King sk + 37c. Wanted to try something kind of skinny for a light, climbing oriented build.
Problem: rim strikes. Comfortable, high traction climbing = low pressures at 20-25 psi @70kg rider. But descending at those pressures with any sharp edge rocks or roots = spoke pinging rim strikes that make me wince. Too much line choice and extreme caution needed in anything rough.
Solution: Bigger tires, sure. I can fit them. Buy cushcore or similar, OK, except $. So after some online rabbit hole diving I picked up some 1” closed cell foam backer rod from amazon at $13. Size around rim, cut off an extra 1-2”, remove from rim and join with gorilla tape, scissor out a small gap or scallop to position over the valve so air/sealant can enter. Mount one bead of tire. Position foam with gap over valve and stretch around rim, pretty much like doing a tube. Pop other bead on. Proceed as normal with your tubeless strategy setup—a bit easier to get beads to seat if anything. Set pressure at ‘soft’, like yeah, I can totally do a lumpy fireroad climb and this will feel great. Coming down, I might break my wheel. Then go ride and check it out.
Still getting some rim strikes, but far fewer, and they are muted, like the tire just doesn’t collapse as abruptly. Like it ramps up resistance. But bump absorption and traction are great. If you like to screw around, it’s a quick, cheap experiment to see if a commercial tire insert might be for you. I’m going to keep running these and see how they hold up, and also realize that they are not as dense and supportive as a commercial insert. However, they are light, and they do have an effect. Just did a ride at approximately 20psi and intentionally included some singletrack that has loose, sharp edged rocks capable of destroying an xc tire. It was impressive. Not as carefree as a 2.3 mtb tire, but given this is a 37c at 20ish psi...OK I’ll take it.
I used about half of the 25’ roll. Weighed the other half and my postal scale registered it at 30 grams. Accurate—probably not, but even doubling it, that’s 30 grams per tire.
Love to see other folks try this and see if they see similar results. Or violently disagree.
I like the DIY solution and creativity. I tend to pick my tire size based off what kind of pressure I need (based off of what kind of terrain I'm riding). The inserts seem like a decent solution for mountain biking where every once and a while I take a big hit from a half buried rock or something.
The density of the insert will make a big difference. being a racer at heart, I use roll bar padding for applications where I need to be able to take a big hit (like banging my helmet against a rollbar, lol). Its very effective, but not cheap.
So far I like them. Easy to do, cheap, light. The tire pressure difference is definitely more in the 5psi range, which for a low profile tire like the GK 37 completely changes the ride feel. Seems like a cheap way to get to something more like tubular tire performance. And the effect it seems to have (no data other than what I feel) of ramping the tire resistance up, making it more progressive, would be a very desirable characteristic. Tire conforms better to small rocks and bumps, gives a more comfortable ride and better traction, but then offers more resistance to collapsing with bigger hits. It’s interesting. I’ll keep using them see if they throw up any headaches.
