If you believe a lot of bike manufacturers you might think that it doesn’t. You just look at their chart, pick the ‘right’ size according to your height and adjust the saddle height according to the length of your legs.
But this is patently ridiculous!
Let’s consider a number of people of exactly the same height but with different body shapes. They’ve all bought the same bike, based on their height, with a cool integrated front end and a swanky profiled seat post. The saddle is adjustable for height, but moving the handlebars is a day’s work for a mechanic as it involves, at a minimum, disconnecting and re-cabling the hydraulic brakes. It’s highly likely that they spent several thousand pounds on the bike, but unlikely that any of them anticipated spending several hundred more to feel comfortable and safe on it.
Adam is the lucky one who is just the shape the manufacturer thinks everyone is.
He just rides and doesn’t really have any problems at all. Lucky him. Except that when he buys another bike, with a slightly different geometry, he might start to understand what some of the guys and girls below are going though.
Beth has shorter legs than Adam, but a longer back and longer arms. (Leonardo didn’t do Beth many favours, but at least her hair looks OK).
Beth has to adjust the saddle downwards for her short legs which means that the handlebars are now closer and higher relative to the saddle. Oh dear, that can’t be right. Surely with her longer back and arms she’ll want the bars further from the saddle.
Charles has longer legs than Adam, but a shorter back and shorter arms.
He adjusts the saddle upward to accommodate those long legs, which means that the handlebars are now further away and further below the saddle. Oh dear, oh dear.
For Beth and Charles it’s clearly illogical select a size based on their height. It’s a crazy idea that simply changing the saddle height will be enough. What’s more, that integrated front end now seems like a ridiculous concept.
The integrated front end isn’t the only ridiculous concept. Let’s look at Daisy and Eric. They’re also the same height as Adam, and they both have the same length legs so they want their saddles to be at the same height.
Daisy has the same length legs as Adam, but she has longer femurs (thighs).
This means that even though she wants the saddle height and the distance between the saddle and the handlebars to be the same as Adam, her knees are in front of the pedals when she rides. As a result she always ends up sliding to the front of the saddle.
Eric has a long back, like Charles, but short arms, so he too wants the same saddle to handlebar distance.
He doesn’t slide forwards like Daisy, but his long back means that his centre of gravity is over the handlebars and as a result he gets hand, arm, neck and shoulder problems.
No amount of shifting the saddle up and down will help Daisy and Eric. They both need the saddle further back.
That’s tricky with the profiled seatpost. They might be able to solve the problem with different saddle, but that could could be a long, painful, expensive and ultimately futile process. If the bike had a round seatpost they could simply swap the seatpost for one with more setback.
Adam and co might not look that different at first sight, or even lined up next to each other. Indeed I deliberately didn’t make them too different as you don’t have to be extreme to be sufficiently different from Adam to be uncomfortable on ‘his’ bike after and hour or so …and in agony after five.
And this is all without getting on to Fiona who has a long neck, Graeme who is carrying a little extra weight around the middle, Hilda who has childbearing hips, Isaac who has a chest and shoulders like a barn door, and all those from Joanna through to Zak with their various real-world inflexibilities, injuries, immobilities and asymmetries.
And it’s not just discomfort that spoils your cycling if your bike isn’t set up to fit you well. Your control and safety are compromised too and that’s stressful.
Unless you’re Adam there may be more to setting up your bike than adjusting the height of the saddle.