How plush is cush (core)?
Tires are the first and most important suspension for a gravel bike but to gain most of it you have to run a tire with the lowest possible air pressure. This comes at a cost of bottoming out the rim and compromised cornering feel. CushCore foam insert promise to solve those problems and, at least in theory, make your bike much safer, comfortable and faster. Does it deliver?
CushCore insert was first made for a hardcore downhill bikes where every bit of suspension and traction is crucial for a fast, yet safe descend. Then it found its way to MTB and now it tries to conquer a gravel bikes segment. The idea behind CushCore insert is very simple. You put a special foam ring onto your rim and by this, firstly, you protect it from hard hits that are a common thing when riding tire with low air pressure. Secondly, you improve the overall comfort compared to the same tire with the same air pressure. How? The CushCore makes the tire less bouncy because it stabilizes its sidewalls. But, in my opinion, it also improves comfort simply because in the tire is effectively about 1/3 less air (this is roughly the volume of the inserts) compared do the normal tubeless setup. And we already now that the less air in the tire, the more cushioning it will offer. Thirdly, CushCore improves the tire behavior both on a rough road and in tight corners by limiting the unwanted tire movement (aforementioned bounciness and tire roll) so you can push forward with more speed on those occasions.
The installation… is not effortless.
First, you have to realize that CushCore works only in a tubeless setup. So you have to have a tubeless-ready rim and tubeless-ready tires (and have a CushCore valves because your standard tubeless valves will not work). In general, installing tires tubeless is for me an easy thing to do after doing it so many times. So I thought that I will have no problems with additional CushCore inserts. I was wrong. My testing setup was a 650b wheel, an XC CushCore inserts (CushCore gravel dedicated setup is available only for a 700c rims with inner width between 19 to 26 mm and XC 650b variant is suitable for rims between 22 and 32 mm) and a Panaracer GravelKing SK 50 mm tires. Those tires are a tight fit with my DT Swiss m1900 spline wheels. So, as you can imagine, adding a CushCore foam insert did not make things easier.
The whole process starts with putting the inserts onto the rim. This is a rather easy task because the inserts have ridges that nicely fit the inner of the rim (but still you have to use some force to complete the task). Then things become much more challenging. Squeezing the tire beads requires a lot more force than usual and a lot of water with soap to help the tire find its place. Of course, the most challenging part is the last part when the tire is already stretched to the point you have to use two tire levers and push really hard to finish the job. I think that with time and gained experience the whole process will become more easy but it will always take more time than a standard tubeless setup installation.
Was it worth it?
Absolutely! Comparing to a standard tubeless setup run at 20 psi, CushCore really provides a more comfortable ride (both subjectively and in my measurements) and it’s doing so without any noticeable drawbacks. Honestly, I was thinking that tires with CushCore inserts will behave strangely, especially in corners but the opposite was true. Subjectively, the tire behavior improved compared to a standard tubeless setup run at the same air pressure. It cornered better and rolled better on the rough roads. When measured, tires with CushCore inserts showed 8% fewer front vibrations in the forest and 14% less on a fast gravel route (I conducted tests on a rigid bike without Lauf Grit SL fork and Redshift suspension stem).
CushCore maker suggests that when using its foam inserts you should lower air pressure between 1 and 5 psi. So I tried that and lowered the air pressure to 15 psi. Normally 15 psi is simply unusable for a 650b 50mm tire (for me it is barely usable on a 2,25 inch Schwalbe Thunder Burt tire) but, to my surprise, it worked well, at least for the front tire, which behaved very predictable and without any perceptible roll on tight corners. The rear tire sometimes exhibited first signs of too low air pressure, especially when cornering fast but it was mild sensation and to be honest, you don’t need that low air pressure at the back in the first place (that is why I run my Soma Cazadero 42 mm 25 psi at the front but 28 psi at the back without any comfort decrease while the rear tire behavior and traction is noticeably improved compared to 25 psi). Interestingly, my measurements at the front of the bike with 15 psi air pressure showed no real improvement in terms of comfort on a fast gravel route (comparted to 20 psi CushCore setup), but on a bumpy forest road, there was an improvement (5,3% fewer vibrations).
After all of my testing, I believe that a 15 psi at the front and something like 18 psi at the back is a sweet spot for a 650b 50 mm tire with CushCore. At least for a Panaracer GravelKing SK tire. I can’t help but wonder if I could achieve even better comfort when using a more supple 650b tire like Soma Cazadero. Maybe we will find out in the spring…
So this is a must-have for gravel riding?
It depends. If you are weight-obsessed it for sure is not a solution for you. I tested a 650 XC CushCore that adds a 140 g of weight to each wheel. A gravel-specific 700c CushCore is lighter (110 g per insert) but still, with a sealant (by the way, you use the same amount of it as with standard tubeless setup) you are adding something like 200 g of weight. Did I feel it? Not really. But if you want to race on your gravel bike it for sure will be a handicap. Then there is the whole debate about rolling resistance. Riding with very low air pressure on flat surfaces is not what most people will recommend you if you want to quickly achieve, and more importantly, maintain the high speed (with or without the CushCore). So if you like to run a higher air pressure then the benefits of the CushCore inserts will be hard to perceive and the added weight simply not worth the cost and effort. But if you already had experimented with very low air pressure and loved the added cushioning effect then this is a product for you. It simply makes riding with low air pressure more enjoyable and safe. But at a cost of 149 dollars (699 PLN) for the complete set of two inserts and two valves. So it is no cheap solution, yet, if you compare it to the cost of buying something like a Lauf Grit suspension fork it starts to feel like a bargain. Especially when you realize that the added cushioning effect will be felt both at the front and at the rear of the bike…