One calculation and a handful of in-store checks is all it takes to ensure your next road bike takes you smiling to work, not grimacing to the osteopath.
It's easy to buy a road bike that's the wrong size, wrongly set up for you, or even the wrong type of bike entirely. That's because bike fit theories and sporty experts often start from the assumption that you want to ride like a racer. Unless you really are a racer, you don't. The requirements for commuting and recreational cycling are very different.
Racers are concerned primarily with aerodynamics and power output. Comfort is a distant third. If you're not racing, comfort is king. The time gains you can make from a racier bike might be important in a five hour race but won't add up to much in stop-start urban traffic. You can even arrive at work quicker by riding slower. So don't set your heart on a flat-out racer. Consider instead a bike that doesn't make your back, neck and hands ache, such as an endurance road bike or a cyclocross-style commuter.
Carry on the conversation and
Guesstimating your bike size
Saddle height is variable over a huge range on almost any bike: 200-300mm is possible by moving the seatpost up or down in the seat tube. So it's odd that bikes are sized by seat tube length – especially when you consider that seat tube length is not consistent between different bike types or models. A bike with a downward sloping top tube might have a seat tube length of 50cm, yet be the same functional size as a 54cm bike with a horizontal top tube.
While you can't ever be sure that one seat tube size will suit your height, you can make a reasonable guesstimation for any given model of bike. The Medium sized model in any range will be designed for Mr Average or, less often, Ms Average. Bike seat tube lengths vary half as much as cyclists' height. So take the amount you are taller or shorter than average, halve it, and add or subtract that to the seat tube length of the average size bike in the range. That's your size in this model of bike. Probably…
Bike fit is a dynamic issue that can be determined only approximately by static measurements. People have different bodily proportions and different levels of flexibility. It's not uncommon to find that you're more comfortable on a bike that's one size 'too big' or one size 'too small', whatever method you use to determine the right size.
The best way to be sure about a road bike's fit is to go the bike shop and try it for size. If the shop employs an experienced bike fitter, rejoice.
If not, you can still make some useful checks yourself.
• Stand over the bike: You need at least a couple of centimetres of clearance between your crotch and the top tube or you risk bruising your undercarriage when you get off the saddle.
• Set saddle height: Sit on the bike. (You'll need an assistant or a wall.) Adjust the saddle height until, with your heel on the pedal, your extended leg is just straight with the pedal at its furthest point. That's your approximate saddle position. The bike must let you adopt this.
• Assess handlebar height: Many road bikes have the handlebar set very low relative to the saddle. A better starting point for non-racers is to have the top of the handlebar level with the top of the saddle (whose position you've just set). Can you get the handlebar this high by moving the stem up the steerer tube and/or fitting the stem the other way up? If not, you may need a different stem – or a different bike!
• Assess handlebar reach: The saddle-to-handlebar distance determines how stretched out you'll be on the bike. You can estimate a position you'll find comfortable like this: put your elbow against the nose of the saddle and reach your fingers towards the centre of the handlebar. If it's more than two-to-four fingers' width away, the bike is probably too big or has a stem that's too long. If it's closer than just-touching distance, the bike may be too small or have a stem that's too short. Sit on the bike to check, putting your hands on the brake hoods. You want a slight bend in your elbows. If your arms are locked out, the bike is too long for you. (Don't shuffle forward on the saddle!)
• Assess weight distribution: Many road cyclists carry too much weight on their hands, enduring tingling or numb hands, a stiff neck and an aching back. Here's a simple check, which takes account of core strength. Sit on the bike with your hands on the brake hoods. Now, without changing the angle of your torso, remove your hands and hold them loosely behind your back. Can you hold this position? If not, the handlebar is too low and/or too far forward.
There's a fair amount of leeway for moving a road bike's handlebar and saddle positions until they suit you. By swapping the stem for one that's a different length or angle, and to a lesser extent by switching the seatpost for one with a different amount of 'layback', you can fine tune the fit further. But at there are limits. If the steerer tube has been cut off 6cm from where it emerges from the headset, you can't raise the stem any higher than that. (It's not a great idea to have an excessively long steerer tube in any case, unless it's made of steel, as it may crack.) So a large part of being able to get the handlebar high enough is having a frame with a long enough head tube. A genuine racing bike won't have a long head tube. That sportive bike or cyclocross bike, on the other hand…