Cush Core Inner Tire Suspension System Reduces Squirm, Damps Bounce

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In between appointments at Sea Otter last week, I noticed the Cush Core booth and had to learn more about the company’s “Inner-Tire Suspension System.” On the surface, the solution seems pretty straightforward: add a piece of moderately stiff, lightweight foam to the rim and reduce tire squirm due to under-inflation or flimsy sidewalls.

But the company’s claims go much deeper than just offering a sidewall stiffener for mountain bike tires. According to the Cush Core website, the product adds damper-like performance to a traditional pneumatic tire, which by itself works as an un-damped air spring. If you’ve ever ridden a large volume fat bike or even plus tire over bumpy terrain, you’ve no doubt experienced the negative effects of tire bounce, which is clearly not the same as suspension (despite of what some manufacturers may claim).

As tire volumes have grown over time, many riders have come to appreciate the ability to run lower tire pressures. But this introduces a new problem: tire squirm, where the tire’s sidewall actually folds over or collapses during aggressive cornering maneuvers. Some tire manufacturers are addressing this by offering reinforced sidewall features, though there is a cost in terms of added weight.

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Cush Core adds weight to the tire as well; the company says the insert weighs about as much as a standard inner tube. However, the company notes that with a Cush Core system, riders can get away with lighter tires AND lighter wheels that don’t need to be reinforced, for overall weight savings.

Beyond the claimed performance benefits, Cush Core also notes that the insert reduces the chance for pinch flats, sidewall tears, and tire burps. The product is also said to reduce rim dings from square-edged hits.

I took a bike fitted with Cush Core inserts on a quick spin around the expo area at Sea Otter, leaning the bike over at extreme angles, and it felt very comfortable. I also hopped over a few rocks to see if I could ding the rims at all, and I came up ding-free. This was all the more impressive since the bike was running just 17psi front, 19psi rear on standard 29er tires. Before the test I squeezed the tires and estimated they were running around 30psi, which shows just how much of a difference the inserts make.

Cush Core is designed to be used with tubeless tires only. I asked one of the company reps if it was possible to run a tube with Cush Core (you know, in case you have to throw one in an emergency) and he said it should be possible. In fact, he said a road bike tube might work best due to the reduced headspace inside the tire.

Note the side holes on the special valve stem.
Note the side holes on the special valve stem.

The company offers Cush Core inserts for 27.5″ and 29″ diameter wheels and prices the complete, two wheel system for $149 online. Note: special valve stems are required to ensure the airflow is not blocked by the foam insert.

How does this work in the real world? I have no idea, but it’s certainly an interesting concept and one that seems to solve some of the problems with running high volume, low pressure mountain bike tires. See the video below for more info.

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