We had a chat with Luis Arraiz about his involvement in the design of the all-new Cannondale Habit trail bike and the ins and outs of suspension design.
You’ll no doubt know the name, as Luis Arraiz was the man behind K9 Industries at the end of the Naughties. He’s the man behind the new GT Force and Sensor suspension designs, and now, the Cannondale Habit too.
The Cannondale Habit is a 130mm travel trail bike that will take 27.5+ or 29″ wheels. Here’s the story behind its development.
Who is Luis Arraiz?
I am just an engineer who is passionate about bikes and how the rider/bike interaction works.
What’s your background in suspension design?
I have a background in automotive engineering, with a Masters in motorsports. My main interest is in chassis and vehicle dynamics.
How did you get involved in the Habit project?
Once I got to CSG, we analysed where Cannondale and GT stood in overall suspension performance, and how they fared against the competition. This lead to a two-year R&D project that culminated in the Habit which is Cannondale’s first production 4-bar suspension design.
Had you designed a suspension platform for a major brand before?
Almost simultaneously, we developed the new GT LTS platform now found on the new Sensor, Force and Fury. My previous design experience was at K9 Industries, a very small project in the UK over 10 years ago.
How much free rein were you given on the Habit?
Most of the decisions that impact the Habit’s performance were made by data driven results; this refers to the bike’s pedalling, braking and overall suspension feel and behaviour. Geometry-wise the product management team did an excellent job determining the needs of the Habit rider on the trail.
With the Habit, my main job was packaging and laying out the bike’s suspension to achieve our performance goals as well as meeting the industrial design requirements. We wanted to keep a certain look and layout while keeping the stand-over low, adding a full-size water bottle and meeting all our engineering clearances.
What are your priorities when designing suspension for a mountain bike?
Each bike is different. A trail bike has to be a great all-round bike. There is a balance between efficiency, comfort and fun which defines a bike like the Habit. Those requirements change depending on the bike’s application.
How did the short chainstays on the Habit affect how the rest of the frame and suspension design developed?
The chainstays play a factor into the overall balance of the geometry. For the Habit, they enhance the bike’s playful characteristic and its direct power delivery.
Cannondale say that loads of work went in to getting the sizing right for the frames.
They claim that the size of bikes has a big impact on suspension performance. Can you talk about that for a bit?
More than the size of the bikes, research went into the different positions of the riders in braking, attacking, pedalling as well as the different centre of gravities of the system, both rider and bike, and how that determines the overall dynamic behaviour and performance of the bike.
Did having two frame materials affect how you approached the design of the Habit’s suspension?
Not when it comes to kinematics and geometry. The material and construction methods were taken into consideration by other members of the engineering team who did an amazing job with the Habit.
Do you design the platform first, then tune the shock to suit, or do you design them in tandem?
There are certain parameters that we follow to ensure the bikes work well with shocks from our main suppliers. These are taken into consideration when initially designing the kinematics. However extensive testing is performed afterwards to determine, select and confirm the right tunes and air volumes for each bike.
How do modern shocks make it easier or harder to create the “perfect” system?
The new shocks and technology currently available make it a lot easier to get an ideal balance between the bike and shock. And, let’s not forget the fork, the balance has to be expanded to the fork so that the whole bike works as a single system rather than have mismatched suspension performance and feel between the front and back of the bike.
What limitations does a traditional drivetrain place on a suspension platform?
On a standard chain driven bike, the suspension is affected by the chain line, chain ring and cassette spread as the chain line forces alters the suspension behaviour when pedalling. The design and functionality of a motorcycle is simpler as you only have one chain line combination.
On a mountain bike we must make sure the bike works well in all gear combinations. However, we can use the different chain lines to tune for different suspension behaviour at different parts of the cassette. For example, the Habit has an increased pedal efficiency on the climbing gears and reduced pedal feedback in the middle and lower end of the cassette.
How do you go about mitigating those limitations on the Habit?
This is done by the exact arrangement of the linkage, the position of the instant centre at sag and the different chain lines throughout the cassette.
Does a frame’s ability to accept 27.5+ and 29” wheels change your approach to designing suspension?
Yes. It not only effects the BB height with the different tyre diameter, but it also has a different feel on suspension as the tyres behave differently under load. When dealing with different wheel sizes, we have to make sure that all clearances are met, which adds extra complexity in the 3D modelling phase.
In layman’s terms, what does the ‘Proportional Response’ design offer the rider?
We make sure the bike works exactly the same for all different riders on different size bikes. The key, is the consistent chassis behaviour under braking, pedalling and overall balance.
Would it be fair to say that the Proportional Response is a Horst Link with an extra rocker between the shock and the other link, and how do they differ mechanically?
We used the Horst Link and swing link to achieve the braking, pedalling and packaging requirements. The Proportional Response is a design philosophy in which we re-configure the linkages per size, so that it provides the same ride characteristics in each and every size.
What are the benefits of designing a bespoke platform rather than adapting an existing design?
It gives the designer the freedom to create a different and unique solution. However, there are different ways to achieve similar performance, each unique design has its pros and cons and that has to be balanced. I believe that right now we are in a stage of refinement in evolution rather than revolution.
At what point in the design did you weigh up the options between bearings and bushes, and what made you go for one over the other?
At no point did we consider bushings. Cannondale has a long history of using bearings in suspension applications, and we are not going to change that. Bearings on paper may not look as attractive as bushings, but in terms of reliability in real world mountain bike applications they are still the best option.
How difficult is it to design a pivot locking system, like the LOCKR, that doesn’t overload the bearing/bush but is easy to install and remove?
Again, this hardware system has been part of Cannondale and has been used successfully for several years in different platforms and works very well. We are only using proven designs that offer legitimate benefits.
How did you test each design going forward?
During the initial development process, there was a lot of testing with data acquisition, simulations, and video analysis. Then the data had to be analysed, interpreted and finally confirmed with more testing. It was a lot of work but also a lot of fun.
What were you looking to achieve with the Habit, and how did you know you were where you wanted to be?
We wanted a very fun bike; neutral, playful and intuitive. A bike that was easy ride and easy to own. It is more than efficiency and number. At the end of the day you can have the best bike on paper, but if it does not translate to fun and easy to ride then it is not a good trail bike.
How much real-world testing did you do once you had narrowed down the final design?
During the development process, we tested several different mules for over two years as well as numerous competitors’ bikes in different sizes. Once we knew how we wanted the bike to work, it was easy to achieve. The arrival of the initial pre-production bikes further cemented that we had a really good bike. It was hard to get enough time on the few samples we had as they were always out on the trails and it was hard to pry them off the test riders.