When designing the new №7 and №9 we wanted to achieve two things; to give people choice and to make all the sizes of frame ride the same.
We started with the seat tube. Since dropper posts have been virtually universally accepted, we no longer need a long seat tube to achieve a high saddle height for a tall rider. Instead, we can use a longer seatpost with a larger amount of drop, meaning the seat tube doesn’t have to get longer as the frame gets bigger. So we’ve only used two seat tube sizes across the size range, allowing riders to choose the size of frame based on how the frame will fit them for the type of riding they do rather than being limited by the length of dropper post they’d like to use.
This means the traditional way of sizing a frame from the seat tube length is pretty useless as we’d have multiple sizes called the same thing. So why not just do what everyone else does and call them small, medium, large, extra large? We’re back to choice again; because we want to give you the option to build the bike you need, not what we tell you you need. We realise that some people want to use a really short stem, but also that a lot of people don’t. Our sizing gives you the choice of two frames that fit the same, but with different length stems, whilst still giving you options on what length of seatpost to use. Let’s look at an example:
Our framebuilder, Matt, is 185cm tall with a saddle height of 700mm. He’d usually ride a ‘large’ frame, but in some brands it might be an ‘extra-large’. Let’s say Matt wants a new frame, and he’d like to use a 50mm stem as he thinks these new short stems and really long bike are a bit of a fad. So which of our frames should he buy? The sizing chart suggest that in this situation Matt could use a 500mm frame, with a 170mm drop seatpost and everything will work out fine.
Now let’s say Matt wants to go long and run a really short stem (such as the new Pacenti P-Dent). Now the chart recommends a 525mm frame, and because the seat tube is the same length, he’s still fine with a 170mm drop seatpost.
If Matt was shorter with an inside leg measurement around 780mm we’d get a slightly different result. The 475mm frame uses a slightly shorter seat tube so that gives the choice of 150 or 170mm drop while using a 50mm stem. But going up to the 500mm frame (and a 25mm stem) means sticking to a 150mm drop seatpost. Having said all of that, if you want to go somewhere in between there are lots more options with 35, 40 or 45mm stems but hopefully this gives you an idea of where to start
So how do make all the sizes ride the same? Proportional chainstay length. Most manufacturers pick a chainstay length for the entire size range, then they build a few prototypes in the middle sizes and give them a whirl and bingo, everything is great. Except that the small sizes have proportionally longer stays and the large sizes proportionally shorter stays. We’ve used our experience to pick a front:rear centre ratio that will give us the weight distribution we want and we’ve applied it to all sizes. This means that the small frames have shorter stays and the really big frames get longer stays.
This also helps with our example above; if Matt wants a long bike with a short stem, by going up to the 525mm frame he also gains a little bit of chainstay length and therefor wheelbase. Extra stability at speed at a slight sacrifice to the low speed maneuverability; you decide what you want the frame to do, not us
Hopefully this has made it clearer, but if it hasn’t just get in touch and we can discuss what will work for you