Choosing the New Bike using Stack and Reach
As a professional bike fitter, I frequently come across two different scenarios with clients. One is an athlete coming in to be fit on a bike where we make it through the extensive background interview and about 10 minutes into the fit and I end up telling the athlete the bike is not the right bike for the athlete. Either the size within the brand is not correct or the geometry of the bike is not correct. The other scenario is where I have an athlete that wants a certain bike, for whatever reason, and they want to know what size bike to get. These are both very serious situations and one in which proper planning and knowledge is necessary. All too often someone wants to ride the bike of the latest champion or they fall into the trap that just because a certain advertisement says model X of brand Y is the fastest bike on the market (by that logic there are about a half dozen bikes on the market that are the fastest based on the latest issue of Triathlete magazine).
So how does one go about picking the correct bike? I have experienced some athletes attempt to use some of the online calculators out there and the problem I have with these calculators is they assume every athlete with the same body dimensions are the same in terms of physical fitness and flexibility. Not every athlete that is the same body dimension in terms of leg and torso length can fit into the same bike due to hamstring flexibility issues (not to mention lower back issues). For example, two athletes with the same general body dimensions may find one fits better on a 50 cm Felt DA while another fits more comfortably on a 51 cm Orbea Ordu.
This brings up another important point regarding picking a bike. You cannot choose a new bike when switching brands based on your current bike size regardless if you are comparing a road bike or even a time trial/triathlon bike. This is due to difference in geometry between bikes. So how do you compare bikes? The easiest way is to compare the stack and reach across bikes. To put it very simply, stack is the height of the front end of the bike and reach is the length of the bike. An example will help clarify this.
One of the bikes in my stable was a 54 cm Felt B2 with a 90 mm stem. This bike has a stack of 51.0 cm and a reach of 41.5 cm. Let’s pretend I am neither a professional triathlon coach nor a professional bike fitter and decide I want to change bikes and go to a Blue Triad. The closest fit with the Triad model is a ML, which has a 55.8 stack and a 41.4 reach. The reach is dead on. However, I did not have any spacers left on top of my head tube with the Felt, which means I will not be able to get as low on the Triad. Would I be comfortable on the Triad? Likely. However, I would not be able to get as low in the front end as my body would allow. A better option would be a 52 cm Trek Equinox sizing up in the stem to a 100 mm stem.
The take home message is you should never buy a bike solely based on marketing or assuming sizes carry over. To determine the proper bike, you need to determine how you fit on the current bike, take the proper measurements and then compare the stack and reach among the various bikes out there to make any necessary adjustments for the new bike. In the above example, you can see that by crossing brands, I would have to size down one model. Furthermore, one must take into account the number of spacers above the head tube and the stem length of the existing bike, If you are riding a bike with 4 spacers, you can go up in the stack of the new bike (or vice versa), if you are riding a tri bike with a 75 stem, you may want to get a bike with less reach.
The alternative is to go to a shop with trained, knowledgeable staff that have a size cycle or the equivalent and be and then determine the proper bike based on stack and reach for your new bike based on the fit on the size cycle.
Where do you go to compare bikes? Dan Empfield has developed a nice chart at slow twitch where you can compare the various brands and models
Petersen Performance Lab 