|
Bike Fit
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
November 2005
|
