Is adjustable geometry the next tech thing to get your head around? Until now geometry adjustment has been the reserve of mountain bikers, but a few new gravel bikes launched recently are utilising adjustable geometry to tune the handling for different requirements. Let’s take a closer look at what this means for you.
Geometry is determined by the bike designer and is the result of wanting to offer a certain ride characteristic, whether it’s relaxed and stable like endurance or touring bikes, or quick and nimble like road racer or cyclocross bikes. Unless you go custom, you don’t really get much say in it, it’s decided for you. There have been some examples of geometry adjustment on road bikes though, Argon 18 has a novel head tube extension system for adjusting stack height, and some bikes have flippable seat posts for altering the effective seat angle.
Otherwise, road bike geometry is a fairly settled thing, having been honed over many decades of development. The numbers between different models usually only vary by a small amount. In comparison, gravel and adventure bikes are a lot more varied but generally, you can expect a gravel bike to be slacker, lower and longer for more stability on rough terrain.
Not all gravel is the same, and neither are the bikes. We’re seeing gravel largely being used as a catch-all term for everything from people going bikepacking or doing ultra-distance events like the Transcontinental Race, to people interested in the versatility for mixed road and off-road riding along with commuting applications, to cyclists who just want to escape congested roads and get lost in the woods. Then there are many gravel race events cropping up around the world.
Most manufacturers are trying to design bikes that either accommodate all these varied demands, or pick one particular stlye of gravel riding and focus on that. As a result of this huge variety, some manufacturers are looking into adjustable geometry as a way to ensure to allow the rider to tune the handling to suit their needs. Adaptability is certainly becoming a focus for some gravel bike designers and adjustable geometry is one way of offering this.
Trek’s Checkpoint gravel bike features sliding dropouts to provide adjustable wheelbase. The wheelbase can be changed from long and stable to short and lively, the former is better for long rides and bikepacking, the latter for gravel racing, according to Trek. It also offers the opportunity to ditch all the gears and go singlespeed.
“The new dimensions are comfortable over the long haul and on rough roads but remain aggressive enough to provide the speed and responsive ride-feel most gravel riders are looking for,” explained Trek at the launch of the Checkpoint.
Sliding dropouts is a neat idea, but what appears to be a growing trend is adjustable fork dropouts, and we have a few examples to talk about here. With adjustable fork dropouts, the idea is to alter the trail, which can have a noticeable impact on the handling.
As a reminder, trail is the distance between the centre of the wheel contact patch and an imaginary line drawn through the centre of the head tube to the ground. The distance between these two points is the trail, the wheel ‘trailing’ behind the steering axis.
Shorter trail results in more nimble and faster steering, longer produces more stable and relaxed handling. It helps to think of the differences between a road race bike and a touring bike. The former has a shorter trail for quick handling, the latter has a longer trail for less twitchy handling.
The trail can be adjusted by altering the fork offset, often called rake. Offset is the distance of the front axle to the steering axis, using that imaginary line drawn through the centre of the head tube again.
GT revamped its popular Grade adventure bike with a flippable chip in the carbon fork dropout. The two positions change the offset from a regular 55mm to a longer 70mm. The 55mm offset produces a 57mm trail, the longer 70mm offset shortens the trail to 39mm.
The idea is that the shorter trail results in more nimble and faster steering and can be used to counteract the effect of heavy bikepacking bags, while the longer trail is used for general gravel riding and racing without luggage.
GT hopes the Flip Chip will allow the new Grade to cater for the different demands of fast gravel riding and fully loaded bikepacking. “Run the 55 mm offset for gravel races or flip to the “low- trail” 70 mm offset when you’re loaded up with cargo on a bikepacking adventure,” it says.
Polish company Rondo offers variable geometry on several of its bikes with adjustable fork dropouts. Called Twintip, an adjustable fork dropout lets you choose a lower and steeper set up for racing and fast riding or a higher and more relaxed stance for adventure, exploring and bikepacking. It lets you adjust not only the handling but also the ride position.
“The Ruut range was born from the need to have a REALLY versatile bike. One that would be comfortable enough for backpacking and long-distance riding, but at the same time would retain a clearly sporty character. At Rondo we are all competitive guys - we ride fast, we race - but we don't need a bike for the CX World's. What we want from a drop-bar bike is to be able to go long, and go fast, especially on rough roads. So, after over two years of development, we came up with a tool that we believe is the ultimate solution for real-world riders,” explains Rondo of its variable geometry design.
Providing adjustable geometry via a fork dropout change requires investment from the bike manufacturer. Step forward fork supplier Columbus. It has developed the Futura Cross Fork with a flip chip to adjust the fork offset between 47 and 52mm. Nearly all carbon gravel forks come with the same 47mm offset.
“The innovative multi-rake system provides frame designers with more freedom when it comes to geometry and trail, and an adjustable set-up based on use and choice of tyres ensures riders will find the perfect fit,” says Columbus.
The impact this has on the trail will depend on the head angle of the frame it’s fitted to. So far the only brand we’ve seen to spec the fork is UK company Kinesis Bikes. It has fitted the new fork to it latest Tripster AT adventure bike. The adjustable fork is intended to allow you to increase the stability for bikepacking and touring or liven it up for gravel riding exploits.
That will depend on your style of riding, the terrain you’re riding over, and the size of your wheels and the volume of your tyres. It’s this difference in the wheel and tyre size that has prompted Cervelo to introduce its TrailMixer solution on its brand new Aspero gravel bike.
The TrailMixer is an adjustable fork dropout that changes the offset by 5mm and is intended to maintain a 62mm trail regardless of wheelsize.
In the forward position, the trail is shorter and designed for 650b wheels. The rearward position increases the trail for 700c wheels. Cervelo has even developed three forks to ensure the right fork offset across the size range.
It’s intended to maintain the desired handling with any wheelsize on any size frame. What Cervelo has done is try to minimise the impact on handling and steering that changing between different wheel sizes and tyre widths have. Cervelo has a target handling trait and the adjustable flip-chip lets you ensure that no matter what wheels and tyres you’re riding, you’re getting the handling that Cervelo intended for the bike.
“Now athletes can choose the fastest wheel/tire combination for the day’s conditions and never sacrifice essential high-speed control, allowing them to push for their personal best,” explains Cervelo.
Do we need adjustable geometry?
Is user-adjustable geometry a good or bad thing? Is it a fad during the formative and uncertain early years of gravel bike development, or a tech feature we’re set to see more off? Is this just the start of a wider push towards greater geometry adjustment, or will it be confined to relatively small fork offset changes?
They are all good questions and ones that can only really be answered with extensive testing of the bikes mentioned above, which is something we’ll be looking at in the coming months.
With gravel bikes now having to accommodate such a breadth of wheel size and tyre volume sizes, and the impact such a change can have on the handling of a bike, being able to adjust the geometry as a way to mitigate the changes introduced when swapping from fat 650b tyres to skinny 700c wheels does appear to make some sense.
So a shorter trail for smaller wheels and big-volume tyres, longer trail for narrow 700c gravel tyres. Or, as GT hopes, to counteract the impact lots of heavy bikepacking luggage has on the handling. Adjustable geometry could also be used by a rider to fine-tune the handling to suit the terrain or their riding style, so if you prefer quick or slow steering, you have the choice.
These geometry adjustments aren’t trailside tasks, more a job to be done at home before you head out into the wilderness. We can certainly see some brands challenging that though and maybe producing adjustable geometry that can be done almost on the fly.
There’s a lot of talk about gravel bikes being able to take the place of two or three regular bikes with a change of tyres, but could adjustable geometry go a step further in really seeing a modern gravel bike become the only bike you need and able to switch to a different style of riding at the flick of a fork dropout insert?
What do you think of adjustable geometry? We’d love yo hear your thoughts on the subject in the comments section below.
David has worked on the road.cc tech team since July 2012. Previously he was editor of Bikemagic.com and before that staff writer at RCUK. He's a seasoned cyclist of all disciplines, from road to mountain biking, touring to cyclo-cross, he only wishes he had time to ride them all. He's mildly competitive, though he'll never admit it, and is a frequent road racer but is too lazy to do really well. He currently resides in the Cotswolds.