Cyclocross Clinchers: Pressures, Sealants, and Tube Variations

Nov 25 2011

latex sealant bubbles through a punctured innertube

Burble, burble, burble… / by Ben Freeman cc-by-nc

Wonderful for most cycling applications, the humble clincher tire does not perform well under the rigors of cyclocross racing. While I’ve discussed this before, there are a few things I didn’t bring up in the previous piece that definitely deserve mention.

The first thing that ought to come up in this discussion—as readers have noted—is pump gauge accuracy. I get the sense that most floor pumps are built to conveniently air up the volumes needed for fat MTB tires, and the high pressures needed for road tires, with the gauge itself being more of an afterthought.

I checked my pump’s readings against an automotive gauge last fall and found them more or less identical, but many other pumps are widely reported to over-estimate pressures in the CX range. Tiny changes make a huge difference in cross, so a digital gauge, or one of those cool cordless compressors is definitely the way to go if you’re going to be picky about it.

The second thing I’d like to cover is the massive variety of innertube types available. I generally ride on standard CX-width 700c butyl tubes, but I’ve still found time to play around with a variety of different innertube types this season. Here are my experiences:

Road tubes: I don’t know why people do this. The only time I’ve had road (18-23mm) tubes inside CX tires is when I have no CX-sized tubes on hand and really, really, really need to ride. They are lighter, but flat almost on a whim. I’m all for kludges and shoe-horning, but this is one shortcut you want to avoid.

Latex tubes: most riders seem to take an interest in latex for its lighter weight and improvements in suppleness. My main interest was in alleged puncture resistance. The lighter weight is indisputable, and I guess I noticed a slightly better ride (though not better enough to be outside the range of the placebo effect). What I did not experience, however, was a reduced number of flats. The problem might be the size (I used 25-28mm, the largest I could find), but short of tearing up old tubulars, I can’t seem to find a source of latex tubes in a ‘cross appropriate size.

Sealant/removable-core butyl tube: this would seem to be a great solution, as most tubular tires are readily repaired/nearly flat-proofed by a quick shot of Stan’s or CaffeLatex. But alas, in my experience it’s proven worthless at fighting off/repairing the dreaded pinch flat in standard butyl tubes. My guess is that the way in which butyl fails—breaking in half-inch-long tears against the rim—is just not the same sort of tubeless tire puncture that sealant is able to close up.

Sealant/removable-core latex tube: there may be some hope here. Unlike butyl, latex seems to pinch flat with tiny, non-tearing holes, and I’ve successfully repaired them with a post-flat application of Stan’s. That said, I’ve still managed to pinch-flat two sealant-filled latex tubes: one by casing a marble curb post-race at Providence (which I consider forgivable), and one by riding easy, afterthought gravel at on the bell lap at Gloucester (which I do not).

Thornproof tube: I readily concede it is pretty much impossible to pinch a thorn-proof tube. However, it’s damn near impossible to race ‘cross on one as well. There’s a significant decrease in suppleness from the extra material, but that probably won’t come into play because at CX race pressures (≤40psi) the tube doesn’t inflate fully enough to press against a 32mm tire with the appropriate amount of force. Best case scenario, the tube wobbles around inside the tire, and you finish the race before the rim hole tears the valve free from the rest of the tube, flatting you out. Worst case, the tire unseats from the rim under hard cornering pressure. Either way—avoid.

Pre-sealed tube: In a commendable mea culpa for last season’s bead-breaking tubeless fiascos, Hutchinson sent me some of their pre-sealed tubes this fall. There’s a noticeable-but-not-awful weight penalty, and through a month of racing—including some not particularly well-chosen lines over the roots at Northampton, they seemed to hold up great.

Even after a pinch-flat on an unlucky rock at the Connecticut State Championships, the pre-sealed tube still held air long enough to see me over a fairly tough off-camber section before deflating. But the very next time I attempted to ride one of them, a pinhole puncture—the sort of thing sealant should have no problem fixing—flatted me out of a ride before I could even leave the parking lot. For the weight, I’d like something a little more reliable.

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