Underbiking and Sloppy Steering - The Mystery of Tire Squirm and Rim Width

We’ve reached the top of the climb - a nasty rutted “road” locally referred to in a tone of reverence and caution simply as “143.” As we look down the descent before us I long for a mountain bike. “Gravel” riding in Southern Arizona is rowdy and hard. I’ve grown accustomed to ending rides with my hands and triceps as tired as my legs. This one takes the cake.

We begin the descent, bouncing and skidding down baby-head strewn two-track punctuated by unexpected 20% climbs and sandy washes, dropping towards the desert two thousand feet below. As we lose elevation the road carves into the hill in countless tight, sweeping turns. My riding partner Nick falls out of sight behind me. Normally the faster descender, I fearing fear he’s fallen and wait.

He stops when he sees me, frustratingly shaking his head. “How the hell are you dealing with these tires!?” He asks. “They’re squirming so bad I can’t hold a line!”

In anticipation of today’s long, rough adventure we’d mounted up the same 48mm gravel tires the night before. My tires are handling marvelously and I’m grateful for the extra volume.

We continue down the descent, sighing with relief when we hit a short stretch of pavement, shaking out our hands. We proceed into cactus strewn desert, sand replaces rubble, and we ride on. Periodically Nick swears at his tires and when the terrain is mellow enough to speak, we ponder the mystery of his poor-performing tires.

That evening, after cold showers and plenty of calories Nick digs into his bike. With tires off and time to inspect, the riddle is quickly solved. “Rims.” I say, pulling off a tire, “They’re too narrow.”

With the rise of gravel riding came a whole slew of new component choices and bike variables. Rim width, once a detail we didn’t give a thought to became fodder for daily discussion. Our long ride and Nick’s bad experience illustrates its importance.  

With rims at just 22mm wide and a 48mm tire with relatively supple (and thus flexible) side-walls, his tires lacked support. The difference between rim and tire widths created a balloon-like profile that encouraged the sidewalls of his tires to unpredictably lean over on fast corners. Handling a bike drifting in loose dirt is one thing, add tire flex to the situation and you’ve got a recipe for disaster.

Meanwhile, I was riding 25mm rims which provided a better profile and base for that wide tire. Even weighing considerably more I could run nearly the same pressure and have no issues in the corners because I had a better tire-rim match. The result was a more comfortable ride all day (similar pressure while weighing more means a more compliant ride) and still being able to rely on the integrity of the tire’s sidewalls through corners. Lastly, since the wider rim I was on reduced the balloon effect that characterized Nick’s wheel/tire profile, I was less likely to pinch flat.

With the mystery solved, what’s to be done? Should Nick ditch his expensive carbon wheels because they’re too narrow? It depends.

When it comes to wheel selection you should consider what range of tires you will most often ride and go from there. If, for example, you live somewhere like Steamboat Springs, CO where the gravel is smoother than Tucson’s pavement, or most of your rides include big doses of pavement you’ll normally be using narrower tires. In this situation you’re better off with a narrower rim or a hooked all-road wheelset designed for that purpose. This allows you to run higher pressure as needed, your tires will retain their intended profile and likely be a bit lighter. The Hyalite models and the Ares4 AR are good examples of wheels for this application. They can take road or ‘cross tires if you want, but can also handle wider rubber. As Nick showed us, you can even run big chucky chunky 48-50mm tires when needed. It’s just not ideal. But if that’s a rare occasion, you’re still in a good spot.

If like me, you’re surrounded by rutted, wash-boarded, rock-covered roads wide tires are your friend. In this case a tire with a wider 25mm rim width is the right choice. The Hyalite 25 or Hyalite Carbon Wide models are good examples. (deeper all-road wheelsets like the Ares4 AR are designed with a focus on speed and acceleration over comfort on rough stuff, so they aren’t the best choice for this application). In this situation you can run some narrower tires, but within reason. Proper road tires and ‘cross aren’t ideal or necessarily approved, so your speedy options hit some limitations. Again, no biggie – if you only rarely ride pavement, simply enjoy the cush and accept the speed penalty of the narrowest approved tire you can mount.

Part of the draw of the gravel bike is versatility, and rightly so. Never before have we had so many bikes capable and fun to ride on so many surfaces. But for one bike to do many things, there will be compromises. Get realistic about the range of riding you’ll really be doing and choose your wheels from there.

Since Nick was traveling from out of town and headed to San Diego shortly after our ride, he knew he’d once again be running 32mm file-treads on smoother roads and his rims would be perfect. He rides rough stuff occasionally and on those days if he wants to run a wide tire he’ll accept the compromise, slow down in the corners and enjoy the cushion the rest of the ride.

As for me, I’ll be sticking to my wide rims and the biggest tires my bike can fit. We only get one set of teeth, after all, I need all the squish I can get.  

Written by Loren Mason-Gere

Photos by Nick Belkowski & Loren Mason-Gere