From classic bicycles to sloping: a look at the history
The classic geometry of bicycles was very simple: the top tube was completely horizontal to the ground — in some sizes even reversed (higher at the seat tube end than at the head tube end) — and the seat tube was much longer than what we see today.
For many years, bicycle frames were built with that straight, uniform shape, which allowed for stable but uncomfortable handling — or so it was thought back then, because today we’ve learned it had more drawbacks than benefits.
Riders had to maintain a very upright, static posture to keep their balance on the bicycle, because the centre of gravity of the bicycle-rider system sat very high off the ground, with the rider’s own centre of gravity poorly balanced relative to the bicycle. This was rather uncomfortable and tiring. On top of that, the straight, uniform frame shape limited the rider’s ability to move and manoeuvre over rough terrain.
Source: pirelli.com
Over time, however, riders and bicycle makers began to experiment with frame geometry. In the 1980s, the first sloping frames appeared on mountain bikes, where they were used to improve handling and performance on rough terrain.
You’ve probably wondered at some point: what exactly is sloping on a bicycle?
Sloping consists of tilting the frame’s top tube downwards at its junction with the seat tube, which allows greater freedom of movement for the rider and a more comfortable position. Over time, this technology was refined and adapted for use in other disciplines, such as road and city cycling.
Today, sloping is part of every type of bicycle, and has become a key element in improving comfort and performance for riders. A sloping frame geometry allows smoother, less tiring and safer riding, which has helped popularise cycling and made it useful as both transport and leisure.
In short, the history of sloping in bicycles is an example of how innovation and experimentation can improve products and the experiences of users. From its origins in mountain bikes to its adoption on the road and city bicycles, sloping has revolutionised bicycle frame geometry and made cycling more comfortable, more efficient and safer.
Classical bicycle geometry
Classical bicycle frame geometry is a concept that dates back to the earliest days of the bicycle. It’s characterised by a top tube height equal to the seat tube height, a head angle of 73 degrees and a ground clearance between the seat tube and the bottom bracket of around 27 centimetres.
Over time, classical geometry has been widely used across all kinds of bicycles, from city bikes to road bicycles. With time, however, its limitations were uncovered — as I’ve explained above.
What’s more, classical geometry didn’t adapt well to different riding styles, meaning riders had to choose between a bicycle that offered stability and one that offered handling — which limited their performance.
How sloping revolutionised frame geometry
Sloping is a relatively new concept in the history of the bicycle. It was introduced in the 1980s and has become an essential element of modern bicycles. The idea behind sloping is to create a frame that’s easier to handle and more comfortable for the rider.
With sloping, top tube height drops, allowing a more comfortable position for the rider and improving the bicycle’s handling by accommodating a wider range of head angles without penalising behaviour.
What’s more, sloping has made it possible to build more aerodynamic frames, improving rider performance — especially on the road, where “Marginal Gains” can mark the difference between winning and losing.
Over time, sloping has evolved alongside bicycle geometry and has been refined to the point of producing remarkable test data. Experimenting with different head angles, tube heights and frame shapes to create more efficient and comfortable bicycles has led to a much wider variety of bicycles on the market and a notable rise in rider performance.
Sloping has revolutionised the way riders ride. It has allowed makers to build more aerodynamic, more comfortable bicycles, and has improved rider performance. The evolution of sloping has been a milestone in the history of the bicycle.
The benefits of sloping
Fewer sizes
The sloping top tube removes the need to produce many frame sizes, because the same frame fits a wider range of people.
This quirk simplifies the production process, makes it easier to scale and reduces the risk of producing frame sizes that don’t sell.
Bike shops benefit too, since they don’t need to keep a huge inventory on hand to cover their needs.
As you can imagine, this is a benefit for large-scale mass production, but not for building custom bicycles — in that world, where everything is hand-built, the frame is adapted to the rider, so sizes don’t exist.
Lighter, stiffer frames
A sloping top tube produces better load distribution, which increases stiffness and, in turn, improves the bicycle’s handling.
At the same time, a more compact construction makes it easier to achieve lighter, more manageable frames.
The sloping top tube creates a smaller rear triangle, which gives a stiffer bicycle, and a longer seatpost, which gives a more comfortable ride.
Greater stability
It’s worth noting that sloping also contributes to improving the bicycle’s stability, because it lowers the rider’s centre of gravity relative to the bike-ground system, and the centre of gravity of the whole bike-and-rider relative to the ground — all without altering how the bicycle works.
The frame, being stiffer, is better able to withstand the lateral and transverse forces applied to it, which allows for greater safety and stability in handling.
The following diagrams show the forces applied to frames in different situations.
Source: iberg.recherche.usherbrooke.ca
Why do I see modern frames without sloping?
I’m sorry to tell you you’re mistaken — “every modern bicycle has sloping”. I put it in quotes because there may be some city models like fixies, track bikes or retro replicas that still keep an almost horizontal top tube line — though not completely horizontal.
Sloping varies depending on size, discipline and even the tyres.
I’ll give you the visual explanation I wrote a few days ago to a client who asked me why I couldn’t build his bicycle without sloping. I’ll also give you two details: 1.65 m tall and a 29×2.6” tyre — I tell you this so you understand there are physical and geometric limits, and if we step outside them, either the rider goes uncomfortable, or the bicycle becomes unrideable, or both at once.
Your inside leg is 785mm barefoot — if I put the tube where you’re telling me, do you know what will happen? You’ll feel the hardness of the steel right against your inside leg.
This is approximately where it should sit, without having fully refined the geometry yet.
So, since you’re showing me an endless list of road and gravel bicycles without sloping (according to you) — because they all have it, but they’re not your size and so it’s less obvious — I’ll start by working your bike fit into a road bicycle. You have an X/Y distance from the centre of the handlebars to the centre of the bottom bracket of X (417) / Y (612) so that your torso angle suits this bike. That would give you a standover of 673 (rear) – 739 (medium) – 806 (front) and a Stack and Reach of 557 and 372 respectively.
We’ll work mainly with the standover.
You can see in the image a road bike with 700×28 tyres.
If I fit this bike with 29×2.6” tyres (I’m only changing the tyres so you can see the difference), this is what you get: 708 – 774 – 841.
But I’d still need to change the fork because, as you can imagine, the wheel doesn’t fit in a road fork, so it would end up like this.
But those two tubes — top tube and down tube — shouldn’t end up like that, along with other details we’ll come back to later. So we arrive at the first sketch I drew based on what you were asking for and your bike fit.
Do you see anything odd in the previous image? Do you see your foot and the wheel? So I did this: lengthen the X to 444 and raise the Y to 645 to try to keep the bike-fit position.
Here comes the next problem: we’re going to fit a rack and mudguards. I adjust the Q-factor and the position of your cleats/shoe. Do you see your foot again?
What can I do? Increase the X to 455 and slacken the head angle by 1°, from 71 to 70°. And now it looks like we have room for everything. But the steering is more twitchy — though that doesn’t worry me because we’ll work with the fork to get what we want.
And this is where we settled before moving to production.
But if this same bicycle were for someone 1.90 m tall, look at the difference. I think it’s quite striking. (These are examples adjusting stack, reach and saddle height — the geometry isn’t worked out to perfection)
And if we turn it into a road bike, even more so. (Remember these are always examples adjusting stack, reach and saddle height, and the geometry isn’t worked out to perfection)
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And as a final note, 99% of what you’ve seen is worked out around the bike-fitting position; at the same time, the bicycle’s handling also has to be shaped to what the client is asking for and to the type of bicycle, together with the components it’s going to carry right now — and the components this particular bicycle will eventually have fitted.
I want a bicycle without sloping
I’ll build whatever you want, but I don’t want you to make the wrong choice and I’ll advise you as best I can within my knowledge, never dogmatically.
Let me give you an example: you’re a sales rep and you spend the week travelling all over Spain by car — a comfortable car for motorway driving that lets you do your job with plenty of headroom. One day, through unfortunate circumstances, it breaks down and you have to buy a new one.
You love the Seat 600 to death, it’s your favourite and you don’t want anything other than a 600. You’ve got your eye on a second-hand one at a great price — but you already know it’ll never be like a modern car with all its mechanical and technical advances, the comfort or the journey times.
Would you be the brave sales rep travelling all over Spain in a 600 in 2023?
And what about the head tube?
The head tube is one element often affected by this feature. With a steeper angle and a more aggressive shape, the head tube on a sloping frame tends to require more careful design and construction to ensure its integrity and strength.
Sloping lets us fine-tune the bicycle’s behaviour far more precisely, giving us more agile, responsive handling thanks to head tube adjustments.
At the same time, the rider’s position is better dialled in while keeping the aesthetics — without needing an excessively long head tube above the top tube to gain more height in the rider’s position.
So what’s the conclusion?
We can say that sloping geometry represents 40 years of evolution in bicycle geometry, offering a series of advantages and improvements over classical geometry.
Sloping allows weight savings, improved stability and greater frame stiffness, which translates into better speed and efficiency. It also enables better ergonomics for riders, improving comfort and safety on the bicycle.
That said, it’s worth stressing that every bicycle is unique and that each rider needs a geometry that may not suit others or every cycling situation. So it’s important to evaluate your individual needs and preferences before choosing a particular geometry. But if you opt for a custom frame, you already know it’ll all be easier, because you won’t have to adapt to a fixed set of measurements.
Overall, we can say that the adoption of sloping geometry is a significant step forward in bicycle design, making bikes faster, more efficient and more comfortable.