How does Electronic Suspension work?

Motorcycle electronic suspension comes in three varieties right now.
Let’s look at the systems in a little more detail.

Passive Electronic Suspension

The suspension uses the conventional setup of springs, forks, and hydraulic dampening you see on most bikes and adjusts passively depending on the road surface and riding conditions.

How does electronic suspension work?

The rider selects a pre-set suspension setting, usually done via a mode selection button, with the setting displayed on the dashboard.

Dash showing suspension setting (1)
Dash showing suspension setting (1)

Depending on the manufacturer’s setup, these presets are named “Soft”, “Hard”, “Comfort”, “Off-Road” “Sport” etc. The suspension is automatically adjusted depending on the pre-set selected by the rider. In some setups, the rider can also tweak the settings a little or create their own presets.

The suspension adjustment knobs, clickers, or screw controls for manual compression, rebound, and pre-load controls are replaced by servos or stepper motors on the rear suspension and front forks.

Depending on the preset selected by the rider, the suspension will be adjusted using the servos and stepper motors, replacing your hand or screwdriver, also the time needed to look up all the options and settings in the user manual.

Servos instead of Clickers
Servos instead of Clickers

So how does this work in practice?

If you decide to ride two-up, select the “Two-Up” preset and you are ready to go. Throw the wife off, select the “Sport” preset and the bike is back to being set up for an aspiring MotoGP rider.

Encounter some dirt or gravel, select “Off-Road”, and the suspension is optimally set up for those conditions. Think of it like the traction control modes many bikes have for power delivery but for the suspension.

The upside is you don’t need any tools and you can change settings on the fly. For most riders, it also takes away the intimidation and some of the guesswork out of setting up the suspension.

Sounds great right? It gets better…

Semi-active Electronic Suspension

Ducati and BMW in 2013 were the first manufacturers to introduce semi-active suspension.

The rider selects a pre-set suspension setting just like the passive electronic suspension setup but now the suspension adjusts reactively depending on the road surface and riding conditions.

Semi-active suspension still uses the conventional springs, forks, and hydraulic dampening setup and offers all the features of Electronic Suspension. The main difference is with the aid of a more complex ECU (computer), multiple sensors, and electronically controlled fluid control valves, the suspension reacts or adjusts hundreds of times a second to the road surfaces and changes in road surface conditions, as opposed to being preset.

How is that possible?

Sensors (linear stroke, accelerometers, or air pressure) are added to measure the up and down vertical wheel movements. This is very much manufacture-dependent, as they all have their own sensor and data capture preferences to monitor the suspension dynamics of the bike.

e.g Ducati uses accelerometers and Aprilia on some systems to measure air pressure inside the damper to determine its position.

Moving on…

The servos or stepper motors used on an electronic suspension described above are replaced with much faster-reacting electronic hydraulic fluid control valves. These valves control the oil flow in the dampers, adjusting the compression and rebound dampening, every few milliseconds.

Let me give you a couple of examples.

When you slam on the brakes hard, the compression damping on the front forks is increased to stop nosedive. Sensors detect the decrease in speed, wheel height change plus a few other sensor inputs (ABS, IMU, etc), which all feed into the ECU. The ECU algorithm based on the input data decides how much compression dampening force is required via the electronic hydraulic fluid control valves needs to be applied to reduce the amount of nosedive. All this happens in a few milliseconds and translates into increased stability for the rider.

When you hit a bump, the suspension reduces the compression damping allowing the wheel to move up vertically easier, and then the rebound damping is reduced, allowing the wheel to move down vertically easier. Sensors detect the sudden change in wheel height and the ECU tells the fluid control valves to apply less or more compression or rebound dampening. Once again this happens in a few milliseconds and translates into a lot smoother ride over the bump.

That sounds amazing, right? What could possibly be better than Semi-active suspension and what’s coming you ask?

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Active Electronic Suspension

Fully active systems are not currently available, but most manufacturers have systems in the prototype stage and under development. It’s a long way off, but I have no doubt it’s coming.

Personally, I think this will start appearing as we rapidly progress towards a future of electric motorcycles.

What’s the difference?

The more conventional springs, dampers, and forks are thrown away and “potentially” replaced with linear hydraulic or electromagnetic rams that actively lift and push the wheel up and down depending on the road surface.

Bose electromagnetic ram
Bose electromagnetic ram

Can you manually adjust electronic suspension?

In most setups, you cannot manually adjust the suspension with tools like a C-Spanner or adjusting knob, due to the servos, and sensors mounted on the suspension components. That said, on most systems you can adjust or tweak the settings electronically, via the dashboard, creating your own pre-sets and preferred suspension setups.

What happens if the electronic suspension fails?

Normally, it will stay in its current mode or default to a set mode. Often you will get a warning message or error code on the dash, helping to identify the exact fault.

Based on reports I have read online from riders who have experienced electronic suspension failures, they can still ride the bike. So, in most cases, you should be able to ride to the dealer or workshop to get it fixed, or worst-case scenario, replaced.

What are the downsides of electronic and semi-active suspension?

Complexity & Reliability: When you start adding more sensors, complex electronics, and weight, you inherently increase the unreliability factor. That said, most of the stuff I have read online by owners, appears positive with few reliability issues.

Cost: When you add a bunch of stuff, the price goes up. If it breaks, it can be expensive to fix.

Limited upgrade options: Only a few aftermarket players right now, with Öhlins appearing to be the largest player for aftermarket upgrades.

Limited control over the suspension settings: Manual setups allow for an infinite range of settings. That said, in my experience, most riders never touch their manual suspension once they have it set up how they like it or the shiny new toy syndrome has worn off. On the flip side, electronic suspension is a lot easier to adjust and play with, so riders tend to change their suspension more.
Chicken and the egg 🙂

Also… We have yet to see a Dakar winner using semi-active suspension and for good reason.

Is the electronic suspension really worth it?

Fortunately, lots of bike-specific forums online help answer that question from an owner and rider perspective. So get yourself over to Google and knock yourself out!

More Resources:

Link to BMW Dynamic ESA overview.

Video of the KTM WP SAT semi-active suspension overview.