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

We’ve reached the top of the climb - a rutted, rocky “road” locally referred to in a tone of reverence and caution simply as “143.” We look down on the descent to come I can’t help but long for a mountain bike. “Gravel” riding in Southern Arizona is rowdy. I’ve grown accustomed to ending rides with my hands and triceps as tired as my legs, but this one may take the cake.

We bounce and skid down the loose baby-head strewn path punctuated by unexpected 18% climbs and sandy washes, dropping to the desert two thousand feet below. As we lose elevation the road carves into the hill in countless tight, sweeping turns and as it does my riding partner falls behind. Normally a faster descender than me, I stop multiple times fearing he’s fallen.

The third or fourth time, Nick 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.”

He’s referring to the 48mm gravel tires we both installed on our bikes the day before, anticipating a long, rough day and looking for some extra cush. I’m running ever so slightly more pressure than him, but I easily weigh 30 more pounds so our set up should be the same but my tires feel great. Love as I would to attribute my cornering to better skills, we both know from experience it’s not the case. Nick didn’t come into this world with a whole lot in the fear department and he goes downhill like a madman. Normally.

We continue down the descent, sighing with relief when we finally hit a short stretch of pavement, sitting up no-hands as we pedal to stretch and shake 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 squirmy tires. He decides his are cursed, but I know the mystery can be cracked. What’s making his bike behave so differently when all the other variables seem to be the same?

That evening, back at the house after cold showers and plenty of calories Nick digs into his bike. With tires off, and time to inspect I quickly solve the riddle. “Rims.” I say, looking up. “They’re just too narrow.”

With the rise of gravel riding has come a whole slew of new component choices and bike variables. The quickly changing nature of the discipline has left many riders wondering “what the heck tire, wheel, and pressure set up do I need?”

Rim width, once a detail that only bike mechanics thought about has become fodder for daily discussion, and for good reason.

So, how’s this figure into Nick’s poor descending?

With rims at just 23mm wide, and a 48mm tire with relatively supple (and thus flexible) side-walls, his tires simply lacked support. The width disparity between rim and tire created a balloon-like profile that encouraged the sidewalls of his tires to lean over, flex and “squirm” around as he leaned his bike on those hard, 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 – or at least slow cornering.

Meanwhile, I was riding 25mm rims which provided a better profile and base for that wide rim. 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 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, 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 some town’s pavement, or in a more developed area where “gravel rides” are largely mixed affairs including smooth dirt roads and plenty of pavement, you’ll probably be running more narrow tires much of the time, and as such, you’ll be better off with a narrower rim. That way you can run higher pressure as needed, it’ll retain the intended profile of the tires and likely be a bit lighter. The Hyalite models for example, with an internal width of 23mm is the perfect “Goldilocks” rim. It can take all-road or ‘cross tires if you want, but it can also handle wider rubber. As Nick showed us, you can even run big chunky rubber on there, it’ll just need more pressure and you might not corner like a bobsled.

If, like me, you live surrounded by rutted, wash boarded, rock-covered roads you’ll be running wide tires. In this case, the Hyalite 25 or Hyalite Carbon Wide models are the right choice. You can run a smaller gravel tire without issue should you head to smoother zones or mixed-surface races, but they’ll handle the bigger rubber you ride daily much better.

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, he knew he’d once again be running 32mm file-treads on smoother roads and his rims would again 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 smoothness I can get.  

Written by Loren Mason-Gere

Photos by Nick Belkowski & Loren Mason-Gere