Archive for September 14th, 2019

Schwalbe Marathon Plus and Michelin Protek vs. Glass Chip

The rear tire of my bike was flat before our morning ride and pumping it up produced a hissing sound with a spray of tube sealant:

Marathon tire puncture - tread gash
Marathon tire puncture – tread gash

We run Schwalbe Marathon Plus tires on the rear of our Tour Easy ‘bents, because otherwise I’d be spending far too many hours repairing flats by the side of the road. Searching the blog for the obvious keywords will produce many examples of what it’s like to ride a bike in Dutchess County NY.

Schwalbe says the tires have 5 mm of “highly elastic special rubber” and claims “Even thumbtacks can’t puncture it.” They use the term “Flat-Less” in the sense of “flat less often”, rather than “not flatting”, which seems disingenuous at best.

Flatting less often may be true, but they obviously haven’t tested against Dutchess County road debris:

Marathon tire puncture - glass chip
Marathon tire puncture – glass chip

It’s not quite 5 mm in the longest dimension, but it was embedded deep enough in the tire tread to cut through the armor belt and nick the Michelin Protek tube:

Marathon tire puncture - tube damage
Marathon tire puncture – tube damage

Of course, the hole is dead-center between the two bumps that are supposed to compress around the puncture while the goo fills and seals the void.

Before taking everything apart, I tried gently inflating the tire and putting the puncture at the bottom to let the sealant fill the hole overnight. In the morning, the tire was once again flat, although the floor wasn’t covered in goo. Pumping the tire up produced another spray of sealant.

It’s likely the Protek tube got me home with a slow leak on the previous day’s ride, but it definitely didn’t solve the problem and, frankly, I’ve had ordinary tubes do the same thing. Given the trivial size of the puncture and the complete lack of permanent self-repair, I don’t know what kind of damage it’s supposed to cure.

I’ve already discarded two Protek tubes with slow leaks through the valve stem and no punctures, so they’re definitely not worth the hassle. Michelin no longer lists the tubes on their bike tire site, so it seems they agree.

I made up a boot by punching a 5 mm polypropylene disk, sticking it to a small tire patch, then sticking the patch over the puncture on the tire. With a bit of luck, nothing will line up with the gash and punch through the boot.

I recently replaced all four tires on the Forester, slightly ahead of schedule for reasons not relevant here, and it’s worth noting that a Marathon Plus tire costs about a third of what I paid for a car tire; they’re not to be discarded lightly.

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