Want to spend an afternoon down a rabbit hole? Excellent. Just type ‘geometry road bikes’ into Google, slip into your Bugs Bunny outfit and away you go. Unfortunately, even carrots won’t sharpen the focus in this world of jargon, sizing and angles. That’s where Rouleur comes in. With the help of a bike-manufacturing behemoth and one of the world’s leading bike-fitters, we’ll do our darndest to arm you with the knowledge to ensure your next bike fits like the proverbial bike glove…
Tubing 101
Okay, let’s start with the definites. Ostensibly, you have three tubes (top tube, downtube and seat tube) that forge the central triangle. Outback you have four slimmer tubes: two chainstays and two seatstays. Upfront you have a fork. And there you go. Time to return from lunch and get back to work…
Ahh, if only things were that simple. You see, the lengths of each affect the geometry and characteristics of your bike. As mentioned, burying yourself in the minutiae of his interplay is a fast track to madness. So, to a degree, we’ll keep things broad. And that starts with the road-bike categories, which really centre around ‘race’ and ‘endurance’.
The former possesses a more aggressive geometry to steer you into an air-slicing, aerodynamic position, while the latter’s more about comfort, often with a more upright position. That’s the clear bit. What’s less clear is when you click on a manufacturer’s sizing guide and you’re suddenly confronted with a series of terms. But fear not, let’s unpick some of the jargon to maximise your money…
Importance of angles
“A race bike is characterised by a steeper headtube angle,” says the aptly named Felix Fitting, technical product manager at Canyon. The headtube, or head, angle is the angle between the fork and the ground. “This results in a sharper steering radius. Its handling is easier to initiate, helped by a smaller amount of trail based on fork offset. It’s nimbler. A race bike’s also defined by a long and low front to enjoy a more aggressive aerodynamic position.”
Brief explainer required. Trail is the amount that the tyre contact patch sits behind the steering axis and an imaginary line running to the ground. Less trail equals faster steering; more trail equals greater stability. Trail, rake and head angle work together to influence the steering properties of the bike.
“That’s fine,” I hear you ask, “but what the hell is rake?” Rake, or offset, is the difference between an imaginary line (there are a lot of imaginary lines in bike fitting) that follows the headtube angle to the ground and an imaginary line that runs parallel with this and runs through the front axle. A larger rake results in faster steering; a smaller rake adds stability.
“On the other hand, a slacker headtube angle results in a more relaxed set-up,” says Fitting. “Throw in a longer top tube and longer wheelbase and you’ll have greater stability. If you have a more endurance-focused bike, the snappy handling and aggressive low geometry of a race bike will not be your friend, especially on really long rides. Colleagues of ours did Paris-Brest-Paris [a 1,200km self-supported ride that was first run in 1891]. In situations like that you definitely want something that’s calm and predictable.”
Another explainer. We’re sure you know what the top tube is but the wheelbase is the length from rear axle to front axle. Again, longer bikes tend to be more stable; shorter ones are more nimble. It sounds simplistic, though there are design and manufacturing issues that need to be taken into account.
“If the wheelbase is too short, you’ll have toe overlap with the front wheel, which means that your foot might rub against the tyre as you pedal,” says Fitting. “That’s obviously not a good thing.”
Importance, or not, of degrees
To dig a little deeper into our rabbit hole, let’s talk numbers, especially the head tube and seat tube angles. In general, the higher the number, the racier the position. As an extreme example, Canyon’s Speedmax has a head angle of 73 degrees – not too extreme – but a seat angle of 80.5 degrees. This is Canyon’s time trial and triathlon bike, the idea of that vertiginous set-up to steer the rider further forward over the pedals, sending the upper body further forward, too, so that the arms can stretch out on the aerobar extensions. Not only does this result in a more aerodynamic position, but it also eases the strain on the thigh muscles, which pays particular dividends in triathlon when you have a run to follow.
When it comes to your bread-and-butter – aka road bikes – a racier bike historically has a steeper seat angle, and to a degree head angle, than an endurance bike. But that’s when top tubes were straight. Now sloping top tubes are so popular, that’s disturbed the equilibrium somewhat. As has the fact that a bike is clearly more than just head and seat angles.
As Fitting’s kindly given us his time, let’s use Canyon again as an example. Canyon’s Aeroad CFR Di2, as used by the likes of Mathieu van der Poel at Alpecin-Deceuninck and Enric Mas at Movistar Team, features a head angle of 73.3 degrees and seat angle of 73.5 degrees. That’s for the large. Compare that to the Endurace CFR Di2, aimed at you and me who lack the flexibility of an elite, and you have a seismic difference…? Well, actually you don’t. The head angle is just 0.3 degrees shallower at 73 degrees and the seat angle is the same at 73.5 degrees.
So, what’s going on? Back to Fitting. “Headtube angle can Influence a racy feel and how agile the steering is, but other factors also impact things. Yes, the historic difference between race and endurance bikes is more focused on a steeper headtube angle, shorter wheelbase and low stack for race, and a slacker headtube angle, longer wheelbase with higher stack and shorter reach for endurance riding…”
Explainer interlude again. Reach is the horizontal measurement from the steerer tube to an imaginary vertical line above the bottom bracket. This affects how long a bike feels. Stack is the vertical distance from the bottom bracket to an imaginary horizontal line off the steerer. This is how tall a bike feels. Back to Fitting once more…
“…But at Canyon, the seat-tube angle is the same for all road and gravel bikes,” Fitting adds. “That’s because the riding position in relation to the bottom bracket remains similar independent of how long or low the front is for proficient biomechanical power transfer.
“Some brands, of course, might have slacker seat-tube angles, but it’s a fine line. If it’s too slack, taller riders especially will sit too far behind the bottom bracket. Naturally, the seat post will have to be extended, which can cause lower back pain and inefficient power transfer.
‘And upfront, while the Endurace has an ever-so-slightly slacker headtube angle compared to the Aeroad, it is noticeable in combination with a different fork offset. If that fork offset’s longer, it increases the wheelbase and results in more composed handling.” (There’s that ‘fork offset’ term again. We told you geometry is jargon central. See above for description.)
Image by SWpix.com
Importance of stack and reach
In short, arguably choosing a bike based on head and seat angles isn’t the be-all and end-all. And for Canyon, that’s down to ‘effective stack’ and ‘effective reach’. This builds upon the traditional stack and reach mentioned above and, says Canyon, translates more accurately into real-world feel as these effective stack and reach numbers are calculated based on the hand position when gripping the hoods rather than the steerer tube.
“The effective stack and reach are quite different between, say, the Aeroad and the Endurace,” says Fitting. “This significantly impacts the riding position and ride.”
To that end, the Aeroad’s stack is 580mm and the reach is 401mm for a more stretched-out lower position, while the Endurance’s stack is 611mm and the reach is 387mm for a more upright, less stretched-out position.
So, from a frame geometry perspective, the stack and reach effectively determine the position you’ll be able to achieve on that bike. There’s only so much adjustment you can make with components like stem length and headset spacers. If you’re trying to shoe-horn a position onto a frame that’s not suitable for that you’re frame, you’ll compromise handling and have wasted your hard-earned cash.
Image by SWpix.com
Which bike should you go for?
So, should you go race or endurance? Don’t fall for standing on the shoulders of giants, says Stephen Roche. Roche is an expert in bike fitting, aerodynamic testing and custom builds. His business, The Bike Tailor, sits at the foot of the South Downs National Park, just outside Brighton. He’s had his hands and sensors on cyclists of all abilities and experience for 15 years now. And he warns of the dangers of following in the slipstream of the pros.
“My big problem with the whole industry is that companies will encourage recreational riders to go for a bike used by the WorldTour riders and then they’ll be smashed to pieces, aching and in pain for days on end,” he says. “That’s because they’re designed for professional racers that are racing every day or every weekend. Really, it should be about comfort for most recreational riders.”
To that end, Roche says that arguably the most important factor is saddle height. “That’s a permanency measurement. It’s central, and up from the bottom bracket to the top of the middle of the saddle by following the seat-tube line. I get that saddle height from a measurement tool we use. We then work towards reach. We usually find that the reach for most people who come in for a bike fit is too short or too long.
“This is compounded by many mainstream bikes featuring bloody laid-back seat posts. They’re my pet hate. It’s one of the first things we change, replacing with an inline seatpost. When you have a rider laid back, you’re pushing the rider back, which completely changes the pedalling position. It extends the reach, which can result in neck and shoulder pain. Again, it’s using what the elites do, but amateur cyclists are different beasts.”
Roche would be happy with Canyon, then, as on many of their road bikes they include their VCLS seat post, which is an inline seat post that features a flip-head mechanism to setback your saddle further if your flexibility allows.
A bike fit is a worthwhile outlay
This seatpost shenanigans highlights that the ideal is to undergo a bike fit and, importantly, before not after you’ve just splashed out. “The number of times I speak to customers and they say they’re thinking of buying a bike, and I say well come in and we’ll put you on the rig,” says Roche. “Then they’ll say, oh no, I’ll get the bike first.
“You’re then trying to compensate as they’ve been sold the wrong bike for them. They’ll then be, why do I need to change my seatpost? Why do I need different bars and stem? Spend a couple of hundred pounds on a bike fit before and you can then take these dimensions to ensure you buy the right bike for you.”
Fitting agrees that this is the ideal, though highlights that their Perfect Positioning System (PPS) results in 98% of customers securing their correct frame. Simply input your height and inner-leg length. An algorithm then compares the ratio of your height to inner-leg length from the 15,000 data points in their system to recommend frame sizing.
And this accuracy is needed as Canyon is a direct-to-consumer model, so it’s very hard to try before you buy. Hence, the pre-purchase bike fit is the ideal, not only for Canyon, of course, but for all bike manufacturers.
“We’re all different,” says Fitting. “If you have really long legs and a short torso, you might want a taller stack and shorter reach so sizing down might work best for you. For people like me who are built with sausage-dog legs, gorilla arms and a long torso, it’s arguably better to size up.
“And every manufacturer is different. At Canyon, a size medium bike is often a large elsewhere. Sizing isn’t universal, so we definitely recommend checking these measurements and looking at the PPS, as that’s a good starting point. If you’re on the fence, it’ll give you two recommendations. If that’s the case, feel free to reach out to us.”
As you can see, the world of road-bike geometry and finding the right size for you is a complex business, especially as each bike manufacturer will have its own processes and nuances. It’s why a bike fit is the ideal. You’re given granular details about you and your set-up that you can then apply to your next purchase, whether it’s a Canyon, Specialized, Trek, Pinarello or Raleigh Chopper. Nail your dimensions and faster, injury-free riding might not be guaranteed, but it’ll be given its best chance.
*Cover image by Signature Cycles
