I am the proud owner of four bicycles – the acceptable minimum for any civilised human being. All but one of those bikes has round tubes for the main triangle on the frame, and that’s no accident. That’s the way I like it. That’s the way it should be because the round tube is the best tube.
Nature has proved it. Take a look at bamboo – Nature’s scaffolding pole – which is round in cross-section. Millions of years of evolution haven’t seen fit to square off the corners or ovalise it to enhance its compliance. And have you seen a pine tree recently?
Those things stand solid against the worst that Nature can throw at them, and what shape of tree trunk seems to work best for them? The good old circle.
Photo: Adam Gasson
It stands to reason. As any schoolkid who does physics will tell you, the circle is the most structurally sound shape you can get – equally strong in every direction while offering the largest volume for the least amount of material.
However, I’m aware that most schoolkids are idiots, and I’m equally aware that I’m no engineer, so I decided to talk to someone who knows all about bicycle tubes: Keith Noronha, managing director of great British tube manufacturer Reynolds.
I put it to him that, considering the many and complex stresses placed on a bicycle frame, the most efficient profile shape for the tubes of the main triangle (stays are a different matter) is a circle.
‘Well, no, not always,’ he replied. Dammit, I was certain he was simply going to confirm my suspicion and I could put the phone down.
‘With some shaping, especially with carbon fibre, the stiffness of a frame tube can be optimised in a particular plane,’ he continued, making me nervous about the direction the conversation was heading. ‘So shaping can improve how a frame reacts, but that doesn’t mean the round tube has lost its allure.’ Aha!
Photo: Adam Gasson
‘Round tubes, although they look simple, can actually be quite complex. By changing the diameter or the wall thickness or the butting, you can effectively change the stiffness in certain areas. For example, an increase of just 3mm in the diameter of a typical round down tube, from say 35mm to 38mm, can increase the stiffness of that tube by over 19%, although only increasing the weight by 9%.
‘There’s no doubt that a round tube can serve very well for a number of frame designs. They don’t necessarily have to have more elaborate shapes. And I think that the danger is that fashion – the need to get a new look for the bike – can sometimes take over from the underlying mechanical properties.’
OK, so not the unequivocal validation I was hoping for, but I’d still call that a true endorsement for round tubes from a man who knows what he’s talking about.
But what about aerodynamics?
Yes, yes, I’m getting to that. It’s true that round tubes are poor aerodynamically, clinging to the air like a needy child to its mother, but the shape of your tubes all depends on what you want from your ride.
Teardrop-profiled tubes may carve through the air, but those deep blades will almost certainly have to compromise in areas such as weight and compliance. Ride feel is sacrificed at the altar of speed, which makes perfect sense if you’re a pro, but for the average punter (and they don’t come more average than me), shaving a few seconds off my ride time isn’t worth a backside battering.
What I want is a bike that still feels comfortable to ride after 80km, doesn’t waste my efforts and flatters me on the hills. A good case in point is Specialized. Having made its Tarmac more and more aero for its pro racers, it then decided to produce a non-UCI-compliant bike for everyday riders where the focus was purely on lightness and stiffness.
And what did it come up with? The Aethos, which has near-enough round tubes. The bicycle manufacturer with all the finite element analysis and computer modelling power in the world concluded that the best tube shape was a circle.
Image: Reynolds
Style never goes out of fashion
If I’m honest, all this talk of ride feel and mechanical efficiency is beside the point. The main reason I love round tubes is that they look great. A round-tubed bike will be forever stylish, endlessly elegant. It simply won’t date in the way that an aggressively shaped frame will.
To use Specialized as an example again, the original Venge was space-aged and exciting when it launched in 2011, but a decade later it looks frumpy and lumpy next to modern aero bikes.
So take my advice. Whether you choose your bike for its performance or its aesthetics, always go for one that is well-rounded.
As the man who dreamed up the idea of Cyclist and launched the magazine as editor ten years ago, Pete has long been at the forefront of cycling style. Cycling is, in fact, the only thing on Earth in which Pete is at the forefront of style
Main image: Adam Gasson