“The new Awesome-O 5000 is longer and slacker for this season, and....” How many times have you read a similar line when a new bike is first introduced? Mountain bike geometry is constantly evolving, but the pace seems to have picked up over the last five years. Longer and slacker has become the prevailing theme for any new bike model, and the concept of running shorter stems on frames with longer reach numbers has gained widespread acceptance, for good reason.
But there's a limit to just how long you can make a bike before the handling and fit are compromised, especially on a trail bike, where a comfortable climbing position is just as important as its downhill handling. With that in mind, imagine for a moment that the limits of just how long and slack a bike can be (for its intended purpose) had been reached – could anything else be done to improve its handling?
Transition Bikes thinks so, which is why they've unveiled their Speed Balanced Geometry, or SBG. It's a multi-faceted concept, but the main idea revolves around fork offset, or, more specifically, running forks with less offset than what is currently considered “normal,” along with slackening the bike's head angle and increasing the reach. The goal is to create a bike that remains even more stable and composed at high speeds and on steep terrain, but can still easily be navigated around tight turns while climbing up the trail. Transition aren't the first company to experiment with this idea — Mondraker, Pole, and Nicolai are a few of the companies that come to mind with regards to pushing the boundaries — but Transition's widespread use of SBG for their upcoming line of bikes puts them at the forefront of what could be the next big shift for modern mountain bike geometry.
Before diving in too deep, it's worth taking a few minutes to go over some of the basics regarding trail and offset. If you've heard it all before, feel free to skip ahead, but otherwise, here's a quick rundown.
The basics of offset and trail
Offset: Imagine you were to take off your stem top cap and shine a laser pointer straight through the exact center of that star-fangled nut. This is your steering axis. Now, measure how far away the front axle is from that line. That's your fork offset. Fork offset varies between wheelsize, and most suspension forks for 29” wheels currently have either a 46 or 51mm offset. For 27.5” wheels that number is typically either 42 or 44mm and for 26” wheels (remember those?) it's 37 or 40mm.
Trail: Trail is the distance from the center of the tire's contact patch to the point where the steering axis (that laser you aimed through the star nut) hits the ground. Trail is only one part of the equation that determines how a bike will handle, but the general rule of thumb is that a higher trail number can lead to more stability as speeds increase but at the cost of increased wheel 'flop' at slower speeds. Less trail can create quicker steering, which is why most 29ers ended up with forks with more offset — the idea was to reduce the trail number so that it was closer to what you'd find on a 26" or 27.5" bike with the same head angle, thus creating a similar steering feel.
It's worth noting that as the trail number decreases, the wheelbase increases, and vice versa. In other words, if you use a fork with a reduced offset, the front wheel will actually move back, increasing the trail, while shortening the overall wheelbase.
Confused yet? Hopefully not, but there's no denying that these concepts can seem overwhelming at times. As easy as it is to ride a bike, figuring out and explaining why they behave in a certain way is much more difficult. There's also the fact that there's no absolute set of figures that will create the perfect bike. Take chainstay length, for example, a number that's led to countless heated arguments online and in the real world. Should they be as short as possible? Is longer better? Or is the Goldilocks number somewhere in the middle? The truth is, there's no right answer. Chainstay length, head angle, reach, trail; the list of variables goes on, and it's impossible to say that one school of thought is absolutely better than the other (unless that school of thought states that really long stems and steep head angles are a good thing... I like to think that we've moved past that by now).
What made Transition decide to adopt a new geometry philosophy?
Nerd alert. Lars Sternberg and Sam Burkhardt are serious about creating better bikes, but they also know when to lose the pocket protectors and have a good time.
The initial push for the geometry change came from Lars Sternberg, Transition's resident tinkerer. With a little bit of downtime on his hands as the 2015 season came to an end, he stumbled upon an article describing Chris Porter's
experiments with running reduced fork offset. Inspired, he raided his parts stash and began experimenting. He started by taking the upper crown assembly from a 26” Fox 36 which had 37mm of offset and reinstalling it on a 27.5” fork. He then put an angleset into his Patrol in order to steepen the head angle by one degree.
On paper, that steepening of the head angle created a bike with the same trail number as before the fork swap, but once his tires hit the dirt, Lars realized that the ride characteristics felt completely different. The reduced offset put the weight balance in a different spot, and the bike felt as if it was cornering better than ever.
Intrigued, Lars continued to experiment and soon realized that going with a slacker head angle (rather than the steeper setting he initially tried) and a reduced offset seemed to be the ticket, creating a bike that was even more stable at high speeds, but still maneuverable for slower sections of trail. “If you just shorten the offset and don't do anything else you get the steering change, but what you incur is tuck. You're basically just pulling your front wheel back, so when you're coming into a section that has a sharp turn, your front wheel wants to knife under you. If you're going to shorten the offset you need to slacken the head tube angle so you achieve better handling in those scenarios,” says Lars.
The Super Smuggler, one of the bikes that Lars used for his offset and head angle experimentation.
Sam Burkhardt, Transition's product manager, started to join in on the experiments as well, but according to Sam, “I was initially a little bit of a naysayer – I told him [Lars], 'It's cool, I think it's great if you keep doing this, but this isn't something that's going to work for us [Transition] – we need to be working with things we can buy.” Without the ability to easily obtain reduced offset 27.5” or 29” forks the project didn't seem like it would go much further than the experimental stage. However, after talking with Fox and RockShox, it turned out that they would be able to get the forks necessary to bring this new geometry idea to the mass market, and the project began to gain momentum.
Transition's current geometry numbers fall well within the realm of what is considered modern, but the next generation of bikes, including a longer travel 29er that's yet to be officially announced, will be based around the SBG concept, and take things a step further.
“Just based on the numbers some people could be excited or other people could be freaked out,” says Sam. But despite the boundary-pushing numbers, he's quick to offer the reminder that, “Nothing we've done with the head angle is so extreme that you can't run a normal offset – you're just not getting the full benefit of it.”
Transition are working on a bike geometry fixture that will allow them to easily measure things like wheelbase, stack, reach, etc...
The components of SBG
There are five main components that differentiate Transition's new Speed Balanced Geometry from what they have used in the past. Moving forward, new bikes will have an even longer reach, a slacker head angle, a reduced fork offset, a steeper seat tube angle, and shorter stems. Even though on paper the longer reach numbers may seem daunting (a size large will now be 475mm), the new bikes will be spec'd with 10mm shorter stems, and the steeper seat angle will also help to maintain a similar bar to saddle distance to Transition's previous models. The reduced offset fork will also partially counteract the wheelbase length increase that comes with a slacker head angle.
Transition have also worked hard to ensure that the traits that made their bikes so popular aren't erased by the switch to the new geometry principles. Sure, some of the increased high-speed stability that SBG achieves could have been accomplished by increasing the bikes' chainstay length, but Lars says, “If we lengthened the rear ends significantly you're going to change how they manual, how playful they are. We're effectively bringing the stability back and bringing the rider into a better center of balance as much as you would have by lengthening the chainstays.”
That doesn't mean that things will feel exactly the same; according to Lars, “You can't change anything like this without some sort of tradeoff, but I feel what you're trading off is worth it. And in the end I've found we're not losing any positive attributes, we're actually gaining some. It's providing a more comfortable experience at higher speeds – you're allowing people to ride better.”
Is this the future?
Are we going to see a wholesale switch to reduced offset numbers throughout the industry? Are Transition simply an early adopter of what will soon become a common geometry trend? It's too early to tell for sure, but I have a strong feeling that it won't be long before we see more and more companies going down this route. Mountain biking is still continuing to evolve, and geometry ideas that worked in the past, back in the days when bikes were short and stems were long, may no longer be relevant. If it's possible to produce bikes that are more stable at higher speeds while still retaining their maneuverability when the pace slows, it only makes sense to give it a try.