GEOMETRY GONE WILD – ARE LONG REACHES BECOMING A STRETCH?

Mountain bike geometry has been evolving at a rapid pace over the last decade. Every year it seems bikes get “longer, slacker, and lower,” but can this trend continue forever? And what does it mean, exactly? Our “Geometry Class” series started with head angles and then we covered seat tube angles. This month we dive deep into the subject of reach.

As we have explained before, any and every geometry dimension works in a direct relationship with the others. And you cannot judge a bike by a single number. There is a lot to learn about geometry and how it affects your ride. We know a lot about geometry, but not as much as the folks who design them, so we checked in with David Turner of Turner Bicycles and Daniel Oster, Canyon’s Global Director of mountain bike R&D  to get their take on reach since they helped to push the reach-measurement movement in one way or another.

 

INVENTION

Reach is defined as the horizontal measurement between the center of the bottom bracket and the center of the top of the head tube. The idea of reach and stack was spearheaded in around 2008 by Transition and in part, David Turner because downhill bikes were being developed without traditional seat tubes. It was common for downhill frames to have a short tube to stick a sawed-off seatpost in it that tied into nothing on the frame geometrically speaking. Bikes before then had a tube that went to the bottom bracket so things such as seat tube angle, top tube length, and overall bike sizing made sense.

“Customers had no idea how a new DH bike would fit, or how to size their old bikes and compare them to a new one,” says Turner. “Chaos!” He explains that since a seat and seat location is kinda irrelevant on a DH sled, because riding them is usually done in the attack position, the distance from your feet (bottom bracket center) to the top of the head tube in height (stack) and length (reach) is what you will feel. That’s how reach and stack were born. “Transition and Turner Bikes were on the same page and the rest is history,” says Turner.

EVOLUTION

Since the invention of the reach measurement there has been a steady march towards longer numbers. Across the board from cross country to downhill, reaches have gotten longer and stems shorter. One of the first to embrace this concept on a large scale actually did so before the term “reach” was even invented. Gary Fisher developed a concept that pushed the reach longer while the stem and chainstays got shorter. He called this Genesis geometry and the aim was to increase overall stability by positioning the rider farther behind the front wheel. Overall, this concept worked, but it was not really until around 10 years ago that reaches started getting significantly longer and, in the last five, much longer.

“With the old geometry where a short reach was the norm, the short reach numbers were  created primarily by the slacker seat tube angles,” says Turner. “Creating a bicycle geometry is not only about performance, comfort, manufacturing costs and such, but various percentages of all these factors and more. Since most companies haven’t increased their effective top tubes more than a thumbs breadth or so over the last 10 years, the longer reach numbers have been largely derived from substantially steeper seat tube angles.”

The primary driver of the long reach movement is stability. “Getting the front wheel further in front of the rider’s feet creates a lot of stability when banging through rough sections of the trail,” Turner claims. “Of course the head tube angle could be further slackened to increase wheelbase and create more front center and more stability, but at some point the head angle is too slack and the bike becomes overly stable for its intended use.  On a trail or enduro bike this would show up as the resistance to nimbly change direction at speed. The front end would also be flopping back and forth at slow speeds. By tempering the slackness of the head tube angle, and pushing the whole front of the bike forward by steepening the seat tube angle or increasing top tube length, we can pursue a geometry that is more responsive to slower speed steering and still have straight line stability.” In other words, we get to have our cake and eat it too.

Another benefit to longer reaches is an improved rider stance. Canyon’s Oster says that reaches have become longer because tracks have gotten faster, the average ride style has grown less “average” and a lot faster for many riders. “Also, on our side, we’ve learned more about optimizing the center of gravity and balancing the relationship between the front and rear center to create bikes that offer a better overall blend of stability and agility,” he says.

If you ride a 10-plus-year-old bike, one of the first things you’ll notice is how cramped you feel with your hands not far in front of the knees. When standing and riding hard this creates a sense of instability. “I think this is noticeable when you’re standing up and hitting the trail hard, as you are ripping down the trail the impacts want to throw the rider forward, and having the hands too close to their center of mass doesn’t give one much of a mechanical advantage to resist the G-forces,” says Turner. “The weak stance doesn’t create enough of a ‘stability triangle’ between the feet, hands and the front wheel, so in addition to being cramped, the short Reach feels unstable when driving the bike hard into the trail.”

 

MORE IS BETTER

As reach has gotten longer with each model iteration, one has to wonder, how much is too much and how much farther can it go. “At the moment, it feels like we are having hitting a bit of a sweet spot, with geometries that work for different ride applications,” says Oster. “The geometry on a Spectral, more of an all-rounder bike for aggressive trail riders is, very intentionally, different than the geometry on a Torque park bike or a Strive enduro race rig. There is no single magic reach number, seat or headtube angle…it really is a matter of working with racers and riders to find the right geometry for each ride style.”

Bikes and even geometry continue to get better, but there are signs that we are at or past the reach limit now. Not long ago some of MBA’s wrecking crew had to size up to get the reach and stability they prefer, but now after a few years of not needing to, they are having to go the other way and moving a size down because the bikes are too stable and difficult to corner.

“If the last 10 years of increasing reach and slackening head tube angle are great, how much more awesome will bikes be if we progress linearly for another 10 years?” asks Turner. “Well, we have hit the wall, and now that we are here, I think it will be all about incremental changes. A half degree here, a couple millimeters there, it’s time to start tuning what the longer lower slacker revolution wrought in the last decade.”

Another sign things have gone too far are pro racers sizing down, as much as two sizes in some cases. For example, last season, 6-foot-2 enduro pro Jack Moir was racing a size-small Strive. When you plug his stats into Canyon’s size calculator it says he should be on a large. Canyon says that Jack did, in fact, compete on a small Strive during the first race in 2022 and had his worst result of the season. After that he swapped to the size medium and his results improved. They say that given Jack’s overall height he could certainly have fit a size large, but Jack also has a mix of short upper body and arms paired with a long lower body. That mix of proportions led Jack to choose the 475mm reach on a medium Strive instead of the 500mm reach on the large.

Turner suggests that pro racers are trying to make as much time cornering as possible. “Like almost everything except drag racing, races are won in the turns, and pros corner better than we do,” he says. “Just as they can weight and unweight the bike in a split second to maintain straight line control at eye watering speeds, the pro level rider can also rip the side knobs off both tires in the tightest turns. So the pros that are downsizing are playing to their strengths—cornering.” So no, the average rider should probably not take such drastic measures and likely benefit from the stability more than maneuverability.

 

SIZE CONFUSION

With reaches nearing or breaching the limits, the old days of thinking you’re a certain frame size have pretty gone out the window. Nothing can be assumed any longer. Some brands have even given up the standard sizing convention altogether. Specialized had adopted S-sizing for some of its models that dictates frame size based on reach and Guerilla Gravity has taken a similar approach with simple numbers assigned to its sizes. With stack being lower across the board, riders can size up or down depending on their preference for agility or stability. Another solution for sizing is based on MBA contributor and coach, Lee McCormack’s RAD fit theory. Check out this story where he explains how to choose a bike with the correct length reach and his thoughts on new reach trends.

A curveball comes in sizing for different disciplines. Generally speaking, riders can size gravity-focused bikes based on reach since it dictates the feel of the front end when you’re standing. Ironically, one of reach’s founding fathers claims cross-country riders should think differently. “I get e-mails all the time with riders shopping for cross-country and gravel bikes by reach,” says Turner. “But, in my opinion, they should still be shopping by effective top tube length, because unless one can stand up most of the ride, effective top tube, plus saddle setback, plus stem length, minus bar sweep is really what the rider will feel hour in and hour out. Not reach! They will only feel reach when standing. And yes, modern geometry has created a lot more reach and roomy feel largely due to steeper seat tube angles. But, as soon as any rider sits, it’s all about effective top tube and the other cockpit variables. What they really should be using is stack and effective top tube length.”