Proportional Response is size-specific suspension that goes further than the usual geometry adjusting or spec fettling for different bike sizes in a range.

>>> Well, they finally did it: the single crown Lefty fork

Innovation and Cannondale go together like mountain and bike, it’s the brand that brought us the Lefty fork, the Dyad pull shock and BB30 bottom bracket, and now it has something new for us. Cannondale has created size-specific suspension, available on the new Cannondale Habit.

This new concept actually tunes the suspension for different sized riders. Not just specific damping for heavier/lighter riders, but completely different suspension layouts and pivot placements throughout frame sizes. It’s pretty much a world-first, and, assuming engineers got it right, means the newly launched Cannondale Habit it just debuted on should ride exactly the same, whether you’re 200cm tall and 100kg in weight or half that size.

Luiz Arraiz spearheaded the new concept

Luiz Arriaz is head of frame engineering and delved deep into the complexities of centre of gravity analysis while developing this project. We asked him about Cannondale’s pioneering new project.

MBR: Talk us through Proportional Response. Why did you decide different frame sizes needed different pivot locations?

Luiz: “After a lot of testing and feedback, something we wanted to do to was ensure each rider’s experience was the same, whatever their size and shape. We measured and surveyed lots of riders on different bikes and on all kinds of tracks – our bikes, competitor’s bikes, and the more we dug into it, we spotted real trends. Looking at what was actually happening in various scenarios through the use of telemetry, video, photography as well as the feedback from riders, there was a surprising amount of consensus.”

What was happening?

“We concluded very quickly that riders were having totally different experiences on the same bike, dependent on what size they were, and the frame size they were riding. The main trend was that smaller riders were experiencing worse suspension performance under braking, and larger riders were experiencing worse pedalling performance. The lighter riders were most affected by anti-rise and the effects of braking and the bigger ones were squatting the suspension more under power and weigh shifts.”

What did you find?

“Well we knew that rider mass is a huge proportion of the total system weight of the bike and rider, so we worked to engineer the kinematic on each bike so the suspension reacts the same on each size for the kind of riders likely to use that bike. We also switched to a four-bar design as we found additional benefits in terms of holding speed and tracking terrain doing that. Based on the modelling we did from mapping different rider sizes and centre of gravity heights for various pedalling and braking scenarios, each frame now has our desired anti-rise and anti-squat characteristics. At sag levels, this means we keep the anti-rise levels the same on all sizes, while the anti-squat stays at a high enough level for efficient pedalling as you go up the sizes.”

Anyone else doing this?

“Well it’s just way easier to use the same layout, so to move the pivot locations around on each size like this is something unique to Cannondale. Our main goal on the Habit was to make a fun bike that’s easy to ride and one where you don’t have to think about how it’s working while you’re on it, and to do that we needed to be sure it’s going to perform the same for every single rider, and that’s exactly what Proportional Response is all about.”