“The best frame material really depends on what you’re going to use the bike for, and what you want to prioritise” says Jake Voelcker, designer of Bristol Bicycles’ frames and forks. “Is it low weight? Or is it strength and durability? Or is it the appearance of the bike?”
Is steel real?
“A lot of people talk about steel frames being comfortable. They say there’s an inherent springiness or suspension in a steel frame, and that aluminium frames are too harsh or too rigid.”
Perhaps controversially, Jake disagrees: “That’s completely not true” he says. “It’s a bit of a myth that’s built up around the whole ‘steel is real’ and ‘steel is better’ and ‘steel bikes are much more comfortable’ thing, but it’s not true and I’ll show you exactly why.”
For a frame to be comfortable or to have any degree of suspension, it has to be able to flex in a vertical direction, and the only way that a frame can actually do this is if it’s broken.
“That sounds surprising, but because the front and the rear triangles of the bike frame are completely triangulated, there’s no way that they can flex. There’s no way that they can absorb a vertical bump from the road unless the frame is actually broken.”
Jake goes on to explain that the supposed comfort of a steel frame is actually entirely in the fork. Because the fork is only attached at the top, it’s effectively a long lever and so there’s a lot of flex possible (in both the fork and the steerer tube).
“That gives a high degree of vertical flex exactly where you want it for suspension” says Jake.
“So a steel frame isn’t any more comfortable. What you want from the frame is stiffness and strength to be able to carry luggage and to resist pedalling forces particularly when you’re accelerating or going uphill.”
Why do Bristol Bicycles use aluminium frames?
The advantages of an aluminium frame are twofold. The first is that aluminium is a much lighter material. The second advantage of an aluminium frame is that when it’s correctly designed it’s a lot stiffer than a steel frame.
Are there any disadvantages?
“I’ve heard people say that for a expedition bike or for a touring bike there’s going to be used for a round-the-world trip they would always choose steel because at least if the worst comes to the worst, steel can be repaired” says Jake.
“Aluminium, because it needs expensive industrial heat-treating after it’s been welded, basically can’t be repaired if it ever breaks.”
The problem is that a steel bike frame of any quality is going to be very thin walled tubing and a pretty specialised alloy of steel which is very difficult to weld.
“Anybody who’s used to working on farmyard equipment (or welding car chassis, or that sort of place where you would take the bike to be repaired if you were stuck in the middle of nowhere) isn’t going to have any more luck welding steel than they are welding aluminium because the type of steel that quality bike frames are made from needs very skilled, pretty low temperature brazing rather than agricultural welding technologies.”
For Bristol Bicycles we’ve gone for the best of both worlds. On the one hand we use an aluminium frame which is both lighter and stiffer, but on the other hand we use a steel fork which gives a nice degree of built-in suspension through its inherent flexibility.