Sunday, March 3, 2013

Stack and Reach

Stack and reach is (are) a valuable resource when fitting a bicycle.  It seems simple enough but has been a revelation as I begin to understand it more.

The easiest way for me to understand stack and reach is to think of a framing square.  Hold the short end of the square level bisecting the center of the top of the head tube while the long side bisects the bottom bracket.  The vertical measurement from the center of the bb to the top of the square is your stack.  The horizontal from the headtube back is your reach.

Fortunately I'm short enough to get a rough measurement using that method, but more and more manufacturers are providing stack and reach numbers with their bikes (so grownup sized people can use it too).

Yesterday at the shop a dad and son were looking for a new mountain bike for the boy.  Dad was willing on spending a pretty nice sum on the bike too.   But dad was also worried about the boy having a growth spurt and be out looking to spend a pretty nice sum again pretty soon.  Pete was able to show that although the stand over on a medium Rockhopper 29 was an inch and a half higher the reach was only a centimeter more than a small.   The small would fit and have room to grow (it's spec'd with only a 60mm stem).

Personally (by dumb luck) the Fun Machine fits me pretty well.  Going by the stack and reach of that bike I was able to see I had too long a stem on the Sunday Princess, which explains the slipping forward I sometimes experience.

La Folle is a bird of a different color.  A prototype cyclocross frame with a slightly sloping top tube.  The top and head tubes measure really long.  Going by those dimensions I had put a really short stem on the bike.  It always felt off.  Between the Euro-high bb and quick angles the bike seemed too tall and rode just weird.  When I measured the stack and reach, yes the stack was greater than my other bikes, but the reach was actually a good bit shorter.  I needed a longer, not shorter stem.  I stole the Princess's stem and now I can't get enough of the Crazy Bitch.

Next time you're looking for a new bike or frame, add stack and reach to your arsenal of tools in choosing a size or brand.  Or if you have a bike that just doesn't seem right check the stack and reach.  Still can't seem to dial it in, and hate math, call Jan for a professional fitting.

2 comments:

Rigidnsingle said...

I could go all day on this subject.

The BB drop, seat tube angle and axle to crown on the fork play into this also. Many bikes that dont climb well have too short of a reach, also what goes up really well doesn't often go down worth a lick. It's all trade offs and you have to find a ballance.

I actually had to re-assemble a bike that I thought fit me very well just to take measurements. That bike climbed very well but took lots of "massaging" to ride the tech and downhill. I ended up with a compromise of the two fits. Probably the fit is right where I was intended in the first place. Funny how 2 bikes with the same geometry can be totally different.

Jacqueline Willis said...

I'm never sure about my reach and sizes. At 5' I'm sure I'm not the smallest person ever to road ride,- the only pre-requisite on choosing my current road bike was that it matched the size of my other road bike what I broke... I do wonder if the bikes I have - and the changes in size would makd a difference in handling as I do feel cumbersome going round dodgy corners.

Mx