Tresca define bike sizing using Stack and Reach and here’s why.
Whilst researching the ideal geometry for our TCA-1 frame we found something interesting. Defining a bike frame size by a single variable (such as top tube length or seat tube length) is simply not good enough.
It is not uncommon for different makes or models of bikes to both state the same size (54cm for example), but in reality they have a large variation in actual geometry. In extreme cases this can mean that a 52cm frame from one manufacturer has a larger fit than a 54cm frame from another. This can be compared to clothes or shoes, where sizes differ slighly between brands. This causes confusion, and we don’t want that with our bikes.
‘Stack and Reach’ is a methodology of bike fitting. These two measurements are simply two dimensions on a bike frame that define what matters most when fitting a frame. This system is used by many other bike manufacturers, and it works well.
Stack is the vertical height between the bottom bracket centre and the top centre of the head tube.
Reach is the horizontal distance between the bottom bracket centre and the top centre of the head tube (the same two points as Stack).
So what do these numbers mean for you, the rider?
Starting simply, if the Stack and Reach numbers increase or decrease proportionally then the fit of the bike (and thus the riding position) remains the same, but the fit can cater for a larger or smaller rider.
If the Stack measurement increases (and Reach stays the same), the riding position becomes more relaxed and upright. This is common with bikes designed for comfort rather than speed.
If the Reach measurement increases (and Stack stays the same), the riding position becomes more horizontal and aggressive. This improves the aerodynamic efficiency of the rider and lets you really put the power down.
Stack and Reach measurements compare only the fixed parts of your bike (ie, the frame). The fine tuning of the riding position is done through careful setup by adjusting the seat post length, saddle setback, and stem length.
Using Stack and Reach during the early design stages allowed Tresca to ensure that each size is proportionally larger or smaller. Giving us a linear size range and allowing you to always find the correct bike fit.