Most people who ride a bicycle for daily transportation understand the basic principles of bicycle tires, including the methods for changing and/or patching a flat, whether in the garage or out on the road. Like it or not, most anyone who has ridden a bicycle has encountered a flat. This being said, with a utility bicycle –especially one carrying children– the last thing you want to be tasked with under load is a flat tire. This is the exact reason I added tire liners to Keri’s box bike –aka, Goliath– quite some time ago.

Tire liners add a very small amount of weight yet perform a very beneficial service, preventing the vast majority of road debris from compromising the tender tube nested within your tire. The most common offenders for compromising bicycle tires are glass shards, thorns, nails, tacks, and the occasional jagged rock or metal bit that has rumbled off a passing truck. Whatever the issue, tire liners typically lower the potential for flats. The two most prominent brands available at most bike shops are Stop Flat and Mr. Tuffy. I use both and find each to be satisfactory –though Mr. Tuffy liners seem slightly more robust. There are other brands available and in the many I’ve inspected, they all appear very similar.

This being said, this past week I encountered a flat that a liner simply could not resolve. The issue? Overcapacity on a cheap tire. Always trying to squeeze maximum life out of my tires, I’ve been putting off swapping out Big Beef’s rear tire with a Schwalbe Marathon. From the factory, the box bikes come equipped with fantastic, massive 2.25″, harder-than-nails, industrial-strength monster tires. Yes, they’re heavy and wide, therefore adding a good deal of rolling resistance, but they’re also quite strong. Unfortunately, the rear tire is also just a wee-bit too wide for the wheel lock included with the bike. Of course, this isn’t terribly evident until you pack the bike with heavy loads (typically 90 pounds or more). Under these more extreme loads, the tire will expand outward just enough to rub on the wheel lock.

To avoid this rubbing issue altogether, Big Beef’s rear tire was simply swapped out for a spongy 1.9″ Shenzhen street tire (a commodity stock tire on most all Chinese bikes). Unfortunately, this tire was simply not up to the task. While I outfitted Keri’s box bike with super-sweet Schwalbe Marathons (HS 368) front and rear –complete with tire liners for extra protection– on Big Beef I decided to grab a few more miles from a basic tire. This was a mistake. On two separate occasions my rear tire slowly deflated under high load as the tire itself simply didn’t have the strength to handle the weight of a 70-pound bike, 170-pound rider, and more than 50 pounds of cargo.

I should’ve expected this behavior from a commodity, low-end tire designed for basic street cruisers. The Shenzhen tire features a very weak compound and high thread count, making it very flexible and spongy (and light), and therefore prone to too much side-roll on the rim. This leads to pinching (of the tube) when your air pressure is at the tire’s maximum 60 pounds (Schwalbe Marathons run at 70 pounds of pressure). I’m going to swap out the tire tonight for a Marathon.

Schwalbe Marathons are well-designed, high-quality tires built for a multitude of uses under a multitude of loads. Marathons feature a very stiff sidewall composed of a much denser compound than a commodity tire. Marathons also feature a low thread count in the body of the fabric, which translates into a much tougher overall tire. I’ve been very impressed with the ride and performance of the Marathons since installing them on Goliath, and I look forward to the same experience on Big Beef.

To learn all you could even need to know about bike tires, I highly recommend reading Sheldon Brown’s excellent article.