Motorcycle design: getting the balance right

Designing a high-performance motorcycle is rather like riding one. You need to maintain a careful balance between emotion and practicality, between sensitivity, confidence, good judgment, and style. You also need to stay focused and composed. Above all, you need to stay the course.

When I joined the team developing Savic Motorcycles’ C-Series prototype in 2019, we had a beautiful design for a café racer that was utterly unique. But because of this, we also had a multitude of challenges: we couldn’t simply add a standard off-the-shelf chassis or suspension and expect the bike to handle perfectly. Each component had to be designed, built, modelled, and tuned from scratch.

Like many products that combine stunning aesthetics and smooth aerodynamics, the team had to go back to basics to marry the C-Series’ design with its weight, performance, and conduct on the road.

Jed Metcher expertly manoeuvres the C-Series during testing at the iconic Phillip Island Circuit

Starting with the rider

Matching the size, shape and proportions of a motorcycle can be approached in different ways. You may have decided that you’re developing a café racer or an adventure bike, a tall or squat bike, with a short or long wheelbase. You may think the bike needs to be designed in a certain way to gain the rider’s admiration. In this case, you’ll be addressing the overall package around these ‘hardpoints’.

When the engineers start working on the preliminary design, it’s often a surprise to most people that a central element of their conceptual drawings and CAD models is the manikin representing the rider.

Example of a SAE 95th Percentile Adult Male onboard the C-Series

It cannot be overemphasised how critical the rider – and if there’s capacity, the pillion passenger – are to the overall vehicle architecture. They directly or indirectly influence virtually every aspect of the motorcycle’s design. Like most car and truck companies, motorcycle designers tend to use a ‘SAE 95th percentile adult male’ manikin: an international standard equivalent to a person who’s 1.86m tall and weighs 102kg. These basic measurements are used to set up the bike’s standard handlebar positions, foot pegs, hand controls, and rider ergonomics.

There’s a good reason for maintaining this laser-sharp focus on ergonomics. If you don’t have the right rider setup from the outset, no amount of reengineering or fancy new technology will save you. A comfortable riding position must be embedded in the design at the earliest stage and continue throughout the design process – whether or not it will (and it most likely will) change some of those initial hardpoints.

There are absolutely no trade-offs here. Fatigue reduces the rider’s ability to focus, so designing with safety in mind must always be paramount.

Keys for manoeuvrability

Once the basic chassis design is locked in, the next parameters to establish include: the wheelbase, the rake angle, the trail (the horizontal distance between where the tyre and the steering axis touch the ground), along with the steering angle and suspension travel (or vertical movement). Most of these factors are strongly tied to the motorcycle’s weight and the centre of its mass – which determine the load distribution between the front and rear wheels.

Combined together, these geometric parameters will all contribute to the manoeuvrability of your motorcycle. And because of the strong correlation between them, it is impractical – if not actually impossible – to study their impacts in isolation.

Analysed diagram of the design parameters overlayed on our C-Series

In designing the C-Series, we incorporated the full gamut of design parameters into our modelling – and then, into our testing on the road. Here are some of the key parameters that had the greatest influence on our production prototype:


The wheelbase is the distance between the contact points of the tyres on the road. In general, and assuming the other parameters remain constant, an increase in the wheelbase will reduce the transfer of load between the two wheels when braking or accelerating, and increase the directional stability of the motorcycle.

However, too large a wheelbase can also increase pressure on the frame and adversely affect the bike’s manoeuvrability – increasing its turning circle and making riding at slower speeds more challenging. So again, getting the balance right is absolutely critical.

Caster angle:

The caster angle (also called rake), or the angle between the vertical and the steering axis, is not only a key parameter for a bike’s dynamics but also plays an important role in its aesthetics. Long-angled forks are for cruiser bikes, while shallower caster angles are commonly found on sports bikes.

The value of the caster angle is closely related to the values of the trail. In general, in order to have a good feeling for a motorcycle’s manoeuvrability, an increase in the caster angle must be coupled with a corresponding increase in trail.


The distance between where the tyre and the steering axis touch the ground, ‘trail’ is a vital key to the stability of the motorcycle – particularly when riding in a straight line.

Small trail values tend to generate more vibrations in the tyre contact patch, so that even if the rider has the impression that the bike is steering well, it becomes more sensitive to irregularities in the road surface. Higher trail values, obtained with greater caster angles, will increase the stability of a motorcycle riding in a straight line, but also dramatically reduce its manoeuvrability. So again, the trail is a delicate balancing act!

Testing to perfection

In order to develop and deliver the best riding experience possible, the design and engineering teams at Savic Motorcycles had to study, trial, model, and road-test all of these different parameters. On fast highways, suburban streets, mountain roads, or in stop-start city traffic, the C-Series had to deliver a ride that was not only exhilarating, but comfortable, safe, responsive, and easy to manoeuvre.

Marc Wilson gracefully manoeuvres the C-Series through Lukey Heights during testing at Phillip Island

After testing, tweaking, retesting and refining, we believe we have designed a motorcycle that is not only worthy of the title of Australia’s first high-performance electric motorbike – but a template for the whole family of pioneering e-vehicles that will come after it. Finally, after all this testing and tuning, we believe we have got the balance right.

Rafael Donadio

Rafael Donadio has been the Chassis Engineer at Savic Motorcycles since 2019. He also works at Ford Australia, where he is a Senior Project Engineer involved in architectural design and systems integration for a variety of cutting-edge vehicle design projects. Raf is a published motorcycle design researcher, with his own simulation code for angular motorcycle dynamics.

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