Large vs small stack & reach

Question

I'm looking at getting a new bike, but struggling with the most suitable one given the different geometries.

Given a particular torso angle, is there an optimal stack & reach? A large S&R would see the arms stretched out further in front, while a smaller S&R would see the arms pointing more down toward the ground. If too small, the knees would hit the elbows and if too large, one would struggle to take weight on the hands, but is there a parameter that would dictate the "correct" sizing?

I'll try to add an image soon to help clarify if needed.

Cheers!

Answer 1

I think what you are getting at in your question is: is there and optimum bike geometry for any given rider and riding position or style? Yes, there is, but stack and reach are not the measurements used to specify bike fit per se and they are not the only frame geometry parameters that affect bike fit. Seat tube angle is also important as it affects where the seat is located.

The basic measurements used in bike fit deal with the three contact points on the bike: feet, butt and hands:

• Saddle height above bottom bracket
• Saddle horizontal set back aft of bottom bracket
• Horizontal saddle to bars distance
• Saddle to bars vertical drop

If you know what those are for a rider you can pick a frame with stack, reach and seat tube angle that will allow seat, seatpost, stem and handlebars to be positioned and adjusted to get that fit.

Of course, that is not the whole story. The steering geometry that is influenced by wheelbase, chain-stay length, head-tube angle and fork trail are big factors in bike selection as well as cockpit geometry.

I think because stack and reach, along with other frame geometry parameters are published by bike manufacturers people thing they need to find 'their' preferred or optimum stack and reach. I would not pick a bike that way. The best advice is to test ride an array of bikes at a number of different stores and let bike store staff give you some advice on sizing and fit. See what feels best for you.

Answer 2

Stack and reach are the ways of measuring a bicycle's fit - and yes, there are optimal measures of stack and reach for each cyclist.

Test ride a few bikes, find one that fits you well/best. Measure stack and reach of that particular bicycle. Those are your prefered stack and reach measurements. Then, when choosing a new bike, measure the stack and reach of that bike.

P.S. Common mistake people make is setting saddle to bar distance by altering saddle position. Saddle position should be set relative to the bottom bracket (pedals). Bars position is set after that. Fit basics explained in more detail.

Frame geometry (in terms of fork trail, seat tube angle, chainstay length etc. - the things apart from the stack and reach) is not something that a customer need worry about too much (as long as they get the stack and reach that fits them), especially if going for a "known brand" bicycle frame. It's usually designed to suit the frame's intended use - whether it's touring, gravel, road, MTB... As long as you pick the frame marketed for your intended use, you're fine. Or as good as it gets, considering modern frame design trends.