Jans expert Mike Caldwell riding the Bow Hunter trail.

Shifting Trends: The Evolution of Mountain Bike Geometry

Reading Time: 4 minutes

Mountain bikes have changed drastically in the last 10 years; it seems there’s basically no aspect of the contemporary bike that hasn’t undergone a radical design revolution. Seatposts have become height-adjustable at the flick of a switch, wheel size experimentation has produced an almost absurd amount of variations, standard issue cassettes have almost doubled in size and range, and building materials have pushed the limits of mechanical integrity.

But aside from all these things, bikes have changed in one major way: their shape. As riders and designers have pushed forward in search of the fabled one-bike quiver, we’ve seen more bikes that have slack headtube angles, more reach, lower bottom brackets, and longer wheelbases. And for the most part, these changes have been met with critical acclaim. In the last few years, many bikes have been released that are exceedingly capable compared to their predecessors. They can handle steep, technical climbs as well as rocky, aggressive descents. You don’t need to watch more than one or two Enduro World Series transfer stages to see proof of this.

What started this push for progressive geometry?

Since mountain biking’s inception, there has been a dichotomy: those who go uphill, and those who go down. Climbing bikes had steep angles, short wheelbases, and little to no travel, while downhill bikes had superfluous amounts of travel (Marzocchi’s famous Monster T fork clocked in at over a foot of travel at one point), as well as heavy, bulletproof frames, but they lacked any semblance of playful maneuverability.

Looking back now, one could easily see that it was only an amount of time before someone sought to design the “happy medium” of mountain bikes. Unlike skiing, the vast majority of mountain biking isn’t lift-serviced. And for the many riders who lack the resources to lap shuttle runs or ride lift-access bike parks, lugging a 40+ lb downhill bike to the top of a hill seems like more of a chore than a reason to smile. The image of Sisyphus pushing his boulder up the mountain for eternity comes to mind…

But it all changed with a bit of ingenuity

When bike manufacturers figured out a way to make carbon fiber full suspension bikes, and component makers nailed down hydraulic disc brakes and reliable drivetrains, riders started having a much easier time getting up hills.

After building medium-travel trail bikes that could climb with traction and stability, the bike industry set its sights on integrating those features into a bike that could descend like a World Cup downhill bike.

How does new geometry affect the way a bike rides?

One of the major aspects of this change was headtube angles, which slackened almost universally. In 2015, the Specialized Stumpjumper EVO had a headtube angle of 68 degrees. The 2019 version comes in much slacker at only 63.5 degrees. This puts the front wheel further out in front of the rider, and makes the rider feel more like they are between the wheels, than on top of them. It also makes turning slower, especially at low speeds. However, with the headtube angle slackened, the wheelbase also lengthens dramatically, which makes the bike more stable at higher speeds and on steep, unpredictable terrain.

In short, a slack headtube angle (65 degrees and below) is great if you like to ride rough terrain at speed. If your rides are gravity-focused, you may enjoy this geometry. It makes the bike feel longer and more stableand as a result, it’s easier to stay rubber-side-down when things get hairy.

The steeper headtube (66 degrees and over) appeals to those who spend more time climbing technical trails, or like to ride trails that can’t be reached by fire roads. It also makes the bike more maneuverable at low speeds. So if you like weaving through the trees at a slightly lower-speed, or playful trails with frequent chicanes, you may like a more moderate headtube.

Another product of modern geometry is the extra-low bottom bracket. In 2002, Santa Cruz’s famous World Cup-winning V10 had a bottom bracket height of 399 millimeters, while this year’s has dropped all the way down to 351 millimeters. When you really think about it, 48 millimeters, or five centimeters, isn’t that much. But when you take into consideration that the ‘02 V10 had 26-inch wheels, while the new ones sit on 29er’s, you realize what a feat it was to let the pedals drop that low.

The lower bottom bracket was almost unanimously favored by gravity-focused riders. This new stance brought the center of gravity lower to the ground, making the bike much easier to handle in low-traction or off-camber terrain. However, it does put the cranks and pedals well within striking distance of jutting rocks and roots.

Here again, the rider is at a crossroads. Do you want an exceedingly nimble bike that is a bit more vulnerable to impacts from rocks? Then you may consider a range of 325 to 350 millimeters in bottom bracket height. Or if you prefer higher ground clearance and the slightly decreased agility that comes with it, a 350+ millimeter bottom bracket height may fit you well.

You still have options

At this point, you may be wondering if the mythical one-quiver bike even exists after all. If there’s still so much variability in the features and capabilities of trail bikes, how could any one bike be good at everything? And you’re right to be skeptical, but the manufacturers have seen that coming too. That’s why many new bikes come with adjustable geometry.

By introducing technology like flip chips and multiple linkage settings, manufacturers have let riders take geometry into their own hands. While the adjustability on most bikes is limited to a centimeter or less of bottom bracket height, and a few degrees of headtube and seat tube angle, it still gives you the option to set your bike up in a way that appeals to your personal style of riding.

If you’re curious about different types of geometry or frame sizing, we recommend demoing a few models and sizes before you think about making a purchase. Whether it’s long and slack or steep and tall, the only real metric is whether or not you enjoy it. After all, if you’re not having fun on your mountain bike, you’re doing it wrong.

Jeff Walker, content writer, jans.com

Shifting Trends is our latest blog series covering recent changes and developments in the bicycle industry. This is the first in the five-part series. Check back next month for our second installment