When asked by riders about the size and style of bike they should buy next, or what’s the best riding position on the bike they’ve got, I usually try to change the subject as it’s not an area I feel at all comfortable with. I’d been riding nearly 15 years and had had several bikes before I finally found one, which I would consider ‘a perfect fit’. Even then, it wasn’t past experience that told me what I needed. It was going to a bike shop that specialised in road bikes, had a jig that I could sit on, and taking advice from the proprietor, who had been a top class rider.
Most people won’t want to go to that much bother though, so here are a few tips.
Re saddle height, put the heels of your cycling shoes on the pedals; the maximum saddle height would be one which just enables you to pedal without rocking from side to side in the saddle – your knees will be slightly bent.
There is a more ‘mathematical’ way – recommended by no less an expert than Greg Lemond. Take your inside leg measurement in centimetres – from crotch to the floor. Multiply this by 0.883 and adjust your saddle so that this figure equals the distance from the top of the saddle to the centre of the bottom bracket axle, and then you should drop your saddle 0.3cms (3mms).
Saddle forward or back? Have your cranks at the 3o’clock position – i.e. horizontal. Your forward leg should be in such a position that a plumb line dropped from the front of your kneecap bisects your pedal axle. When you’ve done this and made a change, you may need to change your saddle height, as moving your saddle back has a similar effect to raising the saddle height and vice versa.
Stem height and extension? – the stem height should be not more than 5cms below the top of the saddle (Burke – Serious Cycling). I’ve just checked this out on my bikes – my winter bike fits the pattern but for my road race and time trial bikes the figure is 8cms – and both are very comfortable (for me).
For the extension, ride on your drops, and look towards your front hub. If the handlebars largely obscure the hub, the length is about right (again from Burke – Serious Cycling)
Regarding frame size, and shape:
If you buy a dedicated time trial frame, the angle of the seat tube will be slightly nearer to vertical than a road frame. The result of this is that you’ll be thrown forward more – which is good for aerodynamics as you can get lower, but could be uncomfortable, if you have tight hamstrings. As time trial courses are becoming hillier and more winding, a steep seat tube angle is less of an asset as it is not so good for climbing and bikes based on road frames tends to handle better. Having had a dedicated time trial bike and a lo-pro based on a road frame, I far prefer the latter, but then the courses I prefer are ones that are hilly and winding. Talk to Kim Lewington or Bill Barrie – they may tell you different.
If you’re buying a bike off the peg or just buying a frame, unless you are still growing, if you are in doubt about size of frame, always go for smaller rather than larger – you can always change stem and seatpost if it’s a bit small, but if the frame proves to be too big, you’re stumped.
A woman buying a bike should at least try a bike with a women’s geometry frame. As most women, compared with most men, have relatively longer legs and shorter upper bodies, the top tube on women’s geometry frames is relatively shorter, so more comfortable for them.
The main message is to get the bike that you are comfortable on, not the bike that you’d like to be comfortable on.
Dave Birch