Road bike sizing & fit for beginners - Part 2

This is a continuation of my previous article on bike fit - Road bike sizing & fit for beginners - Part 1.  We are going to go deeper into the rabbit hole here.


BIKE GEOMETRY AND TYPES - UNDERSTANDING STACK AND REACH

Krish from The Bike Affair (Hyderabad) provided some useful feedback on this article.    He pointed out that many beginner riders are not very flexible.   In such cases, when a rider is between 2 sizes, he may find one size to be more comfortable than another, even allowing for the fact that both sizes can be set up for the same fit coordinate.    They do enough bike fits and sales that this is a useful data point.

To understand why this is so, we need to understand bike geometry.    Take this:

 This is a list of all the dimension and angles that make up a bicycle.      The bike sizing is typically and traditionally based on the seat tube length, but because of differences in all the various other dimensions, the size itself is only a very approximate guide to the bike's fit range.   Luckily, for the purposes of figuring out fit, you can safely ignore most of these other measurements and just focus on 2 elements, stack and reach.

If you remember, we talked about the 2 aspects of fit:  where to put your saddle and where to put your bars.    The position of your saddle relative to the crank is what it is, and can be set up identically across bicycles of the same genre (eg road bikes).      If your bike's seat tube tube is steeper, you will slide the saddle a little further back.   If your bike's seat tube is shallower, you can slide the saddle forwards.   So you can achieve the same saddle position regardless of bike size or geometry (within reason), in terms of how high above and how far behind the cranks it sits.    So for the purposes of this article, that setting can be ignored when comparing across bikes.

That leaves us with where to position the handlebars - how far forwards and how high.   That, in turn, will depend upon the geometry of the bike, more specifically, the stack and reach, as shown in the photo below.
  .

Pic credit:   Slowtwich (see link at the bottom)

Different bikes, even of the same size, can also vary in geometry and size.    Some bikes, designed for racing, tend to be "long and low", and put the rider in an aggressive position - these have a low stack and high reach.      Other bikes, designed for more endurance riding, tend to "short and tall", and put the rider in a more upright position - these have a high stack and shorter reach.

People who ride in a more upright position typically need a higher stack for a given reach.    However, if you try to fit them on a race oriented bike, getting both dimensions to match may be a challenge.   Eg, if you get the reach correct, you might find the handlebars to be too low and need a lot of spacers to get them in the correct position.    On the other hand, if you get a bike size which puts the handlebars at the correct height, they end up being very far away.

 As an example:
- A size 56 race-oriented Specialized Venge has a stack of 555mm and a reach of 398mm
- A size 56 endurance-oriented Trek Domane has a stack of 591 and a reach of 377.

So even though the 2 bikes are the same, when you go from a size 56 Domane to a size 56 Venge, the starting point of the handlebars is going to be massive 36mm lower and 22mm further.    That's an enormous difference, considering that most fit changes typically tend to be in the range of 10-20mm in each axis.    So can you get these 2 bikes to have the same fit coordinates?

In order to get a Venge that has the same reach as size 56 Domane, you will need to go down 3 sizes to a size 49!!   And in that case, the stack drops all the way down to 504mm - which is much, much lower than a Domane and there is no way you can make that up with spacers. 

Alternatively, if you want to get the Venge to have the same stack as the Domane, you will need to go 2 sizes bigger, to a size 61.   And in this case, your reach extends to a massive 411mm - almost 34mm longer than that of the Domane.  Correcting this will require a very short stem, which will adversely affect the handling of your bike and make it very twitchy.

So even though the 2 bikes are the same size, it can be very difficult to get the same fit coordinates on both of them - if one fits very well, you are going to be at the extreme range of fit on the other.   


IMPLICATION FOR BIKE BUYERS

As we saw above, not all bikes will provide the ideal range along both stack and reach.     In some cases, if you get the stack correct, the reach may be too short or (more likely for beginners), too long.    Alternatively, if you get the reach to the correct length, the stack will end up being too high.    You may be able to fudge together something for a particular size, but you definitely will be on the extreme end of a bike's fit range and will have limited possibilities for adjusting fit later.

So it is useful to take a step back and consider what TYPE of bike you are looking at.   A beginner rider who is not very flexible and who is struggling with bikes that are putting him in an aggressive position should consider an endurance geometry, as opposed to a race geometry.   These bikes are designed for a slightly more upright, comfortable position that normal people - as opposed to racing snakes - can hold for several hours with ease.

And don't think that endurance bikes don't go fast - for an identical body positioning and with identical components, the endurance bike will give you pretty much the same sort of speeds as a race bike.    The term just refers to the bike's geometry and design, and not to its performance.

So when going to try out bikes, try out both a race-specific geometry and an endurance-specific geometry (sometimes called sportive geometry).      You might find the latter works better for you.   And if so, instead of a Specialized Venge, consider a Roubaix.   Instead of a Cannondale SuperSix, consider a Synapse.    Instead of a Giant TCR, consider a Defy.   Instead of a Trek Madone, consider a Domane.    And so on.   Virtually every bike brand has a racer-style geometry and an endurance-style geometry. 

Getting the more aggressive bike because it looks cool or because your favorite pro rider rides in the Tour is a recipe for a miserable cycling experience.   Remember - if you are uncomfortable on the bike, you will not be able to go fast, nor will you want to ride the bike.    A good fitting bike is the first step towards having a great cycling experience.


ADDITIONAL READING

Here is the first of a very comprehensive set of articles on understanding stack and reach, as it pertains to bike sizing and as a way of comparing different bikes:
Stack and Reach Primer 

It pertains to triathlon bikes, but the same principles apply to road bikes as well (instead of pad height and reach, just think handlebar height and stem length)

Questions?   Feel free to ask on BikesZone Reborn.