On 4 Apr, 21:13, blackhead <
[email protected]> wrote:
> Firstly, are there places which can work out my frame size without me
> buying a bike from them, but paying for the measurement?
>
> Which system would you recommend for determining frame size?
>
> Thanks for your interest
Due to variously sloping top-tubes and the many differnt ways of
deciding where the top of a seat-tube is, there is no longer any
predictable relationship between "frame size" and the size of person a
bike will fit.
I offer the following method, which assumes that the manufactuer is no
fool and offers bikes in a range of sizes to fit the majority of adult
males. The middle sized frame should accordingly fit a man of median
stature, i.e. 176cm tall. As for other sizes: they'll vary by inseam
height and that's near enough half of stature - remember this is NOT
an exact science! So for every 2cm your height differs from Mr Average
176cm, you want a bike that's 1cm different from the middle-of-the-
size-range.
Simply choosing bikes by stature goes against the classic inseam
measurement monopoly. That's a GOOD thing, since it also allows trunk
length to influence the choice. Top-tube length matters just as much
as frame height - arguably more. The time to bother about leg length
is when your ideal size falls between two of the available sizes.
Then, like Rob Morley says above, leggy people should go for the
smaller one and those with short legs, who will hence have a
proportionally longer back, should choose the bigger i.e. longer
frame.
Average leg length is actualy a bit less than half, i.e. 47.5% of
stature. And a better, more consistent way to measure it (than the
classic book-between-the-legs-and-shove-till-it-hurts method) is to
take the difference between sitting height and stature. Just get
someone to measure your height as normal, standing in socks, and also
sitting on the floor. The differnce is legs, obviously. Most people
are between 45% and 50% leg, by this method. But I have measured one
person who was 53.5% leg - a man by the way.
All of this works only for blokes and tall women. Even when
manufacturers offer a women specific range, they never offer bikes
small enough for the truly petite, so the middling size cannot be
assumed to fit Mrs Average (who is only 162cm tall, by the way). For
women-specific ranges you've got to refer to the manufacturer's sizing
recommendations. Failing that: cross-refer to a similar specification
"mens" model.
It's a complete myth that women, on average, have longer legs and
shorter bodies for their height. But women do tend to sit more upright
on a bike, due to differences in the shape of the pelvis. This is the
reason that women generally need their handlebars a bit higher and
closer relative to the saddle. Women-specific bikes accordingly have
shorter top-tubes and stems and taller head tubes than similar-sized
"mens" bikes.
