Behold the Terra CLX EVO. A versatile superstar of a gravel wheel featuring a massive 30mm inner rim width that would have been considered ludicrous on a mountain bike less than a decade ago, the Terra CLX EVO is not something that traditional sentimentalists can easily wrap their heads around. It’s twice as wide as most road rims used to be, if we use the same decade-ago measure of time. Yet it is ridiculously light, incredibly strong, and it exists for a very good reason: It will help you go and your gravel steed go faster. And you’ll go faster with more control, and more comfort, than ever before.
But still, 30mm... damn, that’s wide. How did we get here? In order to make sense of this, we need to recap the evolution of both road AND mountain bike wheels, and the tires that people mount on those wheels. With road bikes, this is easy. 700c road rims (for the sake of this discussion we will sidestep Dunlop’s attempt to push 27” rims as the way to go, and focus on the old tried and true 622mm bead seat diameter known both in tubular and clincher as 700c) have been around since the early 20th century, first with glued-on tubular tires, then with hook-bead clincher rims becoming prominent by the 1980s. Tires, by the time high-pressure, hook bead clinchers became commonplace, were uniformly narrow. If you wanted to be seen as in the know, you’d be running 23mm or narrower tires. 25mm tires were a sign of weakness, and 28mm tires implied not just weakness but also advanced decrepitude. Those tires would invariably be inflated to upward of 120psi. Wider tires were thought to be slower, and lower pressures were thought to induce drag.
Meanwhile, right as the high pressure pinner road tire was enjoying its 15 minutes (or three decades, more likely) of fame, something was stirring in dirt. Mountain bikes were crawling out of their primordial sludge (or, more appropriately, a hazy shimmer of dust and smoke somewhere in Marin County), and being derived initially from the fabled Schwinn Excelsior cruiser, they featured 26” wheels. There were scads of alloy BMX rims available in that diameter, with nice 25mm inner widths, and they played perfectly with the roughly two-inch wide tires that the burgeoning mountain bike scene was using.
Two things then happened that caused radical, and regressive, change in mountain biking: Cross-pollination of road technology, and racing. Cross-country racing took off, and everyone started making products to suit that endeavor. To pursue that end, Keith Bontrager cut down some Mavic MA2 rims from 622mm to 559mm, glued them back together, and set the narrow mountain bike rim craze in motion. Lighter is faster, right? Thing is, 13mm inner rim widths paired with superlight 2.2” tires made for a terrible ride experience. In order to avoid pinch flats as well as to stop the flimsy sidewalls of the tires collapsing mid-corner, these things had to be inflated super hard. Any traction benefits that might have been available due to the wide tire footprint were nullified as racers and recreational riders alike had their teeth rattled out of their skulls while pinballing down rocky trails with no real semblance of control. It was a dark time in terms of ride comfort.
(image c Jeff Frane)
Thankfully, the evolution of mountain biking, both in terms of terrain ridden and equipment to handle said terrain, didn’t just grind to a halt in 1994. The progression of riding that continues to this day pushed equipment manufacturers to meet the demands that riders were placing on their equipment. And as such, tires, then rims began slowly growing wider. 29” (which are the same 622mm rim diameter as road) wheels asserted their prominence during the past five years, and we are now commonly seeing mtb rims around 30mm or so wide, running tires anywhere from 50 to 65mm wide mounted on them. A rough 2:1 tire to rim ratio these days is a happy relationship; it allows tires to be run at relatively low pressures (thanks to sealant absolving most pinch flat gremlins of years past) while still having decent sidewall support. This, in turn, means that traction, comfort and control are all optimized.
Along the way, as mountain biking evolved to this point, it became overwhelmingly evident both in mtb racing as well as cyclocross, that lower tire pressures resulted in faster lap times. There was less tire bounce, so traction and control was better. Comfort was enhanced, so fatigue was reduced. Braking confidence, cornering performance and stability were all improved at lower pressure. People on the road cycling side of the fence began to take notice of this, and as a result, we are now seeing former adherents of the old 21mm, 125psi, “harder is always better” philosophy change their ways. Pro racers are beginning to toe the line with 25mm clinchers. It is whispered that 28mm clinchers may be the new secret speed weapon.
Okay, fine. Road rims are ever so slightly growing wider, and mountain bike rims are wide for a reason. But still, 30mm inner width, for a gravel wheel? That’s gotta be a bit over the top, right?
Nope. Hear us out. We offer the Terra CLX with a 25mm inner width to satisfy the needs of a broad population. It works great with tires ranging from 28mm all the way up to 47mm. High pressure, low pressure, run them how you like; the tires that will work on Terra CLX wheels showcases a huge range of intent and versatility. And realistically, not a whole lot of gravel bikes are being made to handle tires wider than about 45mm at the moment. However, gravel is a lot like where mountain biking was back around the time that Mr. Bontrager cut down his first set of MA2s. Gravel riding for some people might mean rough pavement and occasional dirt roads. For some other people it might mean loaded touring off-road for months. Others still see gravel as a blank canvas that only begins to be worth contemplating once the pavement well and truly ends. And for many of these riders, there’s no current limit to how wide they might want their tires.