Making Sense Of Suspension: ELECTRONIC SUSPENSION

PART 3 of 4: Understanding electronic motorcycle suspension systems.

In the last two installments of "Making Sense of Suspension" (click HERE to see parts one and two) we covered the mechanics and basic theory behind springs and damping, the two component parts that constitute today's suspension systems. Now we're going to press fast-forward and take a look at the latest breakthrough in suspension technology—electronic suspension.

Electronic suspension currently comes in two varieties. There’s basic electronically adjustable suspension with presets for spring preload and damping settings, and then there are semi-active, self-adjusting systems that automatically tune damping to better suit the road surface and riding maneuvers.

A dead giveaway for electronic suspension is wires or servos attached to the fork or shock, like this Aprilia Dynamic Damping setup.

Let’s explore the simpler setup first. Electronically adjustable suspension has been around for more than a decade and in essence just replaces the bike’s manual adjusters with servos, allowing for push-button adjustment of spring preload and damping. The user chooses one of several spring-preload levels, as well as the damping arrangement. Common damping schemes include Comfort or Soft, Normal or Standard, and Sport or Hard, with compression and rebound settings bundled together. Some systems pair spring preload settings with damping settings, while others separate the two. Obviously, electronically adjustable suspension is a huge convenience. There’s no need for tools and no need to get off the bike or even come to a stop—just hit the button and the changes take effect in seconds. For riders who aren’t in the habit of adjusting their suspension or are intimidated by the process, electronic suspension takes the guesswork out of suspension setup and can even be educational since feedback is immediate.

Electronically adjustable suspension certainly allows you to more readily adapt your suspension to a given riding scenario, but it’s no silver bullet. You might not have to break out the screwdriver and spanner, but these are still static systems, which means the settings are a compromise. Call it a bronze bullet.

Semi-active suspension is a lot closer to perfect. It takes electronic control of the fork and shock a step further by automatically altering damping (and sometimes spring preload, to set sag) to suit the given riding scenario. The rider still selects the basic damping scheme and often spring preload as well, and then the bike’s brain fine-tunes compression and rebound damping as you ride, based on information gathered from a variety of sensors. Adjustments are made in about 10 milliseconds. That’s nearly instantly. That kind of speed requires different mechanical components than the basic electronic-suspension setup—servos are too slow, so semi-active systems use fast-moving solenoids to quickly alter oil flow through the dampers.

Many companies—including Aprilia, BMW, Ducati, and Yamaha—offer dynamic suspension systems. Some systems are more comprehensive than others, and there are many variations and strategies used, but the objective is always the same: to maintain chassis attitude under all riding scenarios for maximum comfort, control, and traction. Apply the brakes and the system increases compression damping in the fork to reduce dive; twist the throttle and it firms up the shock to reduce squat. Hit a bump and the ECU pulls out compression damping to allow the wheels to move up more easily; ride into a dip and rebound damping is reduced to permit the wheels to extend quicker. It’s good stuff, and it benefits every aspect of riding, from rider and passenger comfort to traction to braking stability.

So how does the bike’s computer know when and how much to adjust the damping? The suspension system’s ECU is fully integrated with the rest of the bike’s electronics and polls the same sensors used to inform the traction control and ABS. There’s often some form of suspension-travel monitoring system to determine how fast and in which direction the wheels are moving vertically. It could be several sets of accelerometers (mounted to the sprung and unsprung portions of the machine, as on Ducati’s Multistrada), a potentiometer that physically measures travel (as on the swingarm of BMW’s R1200R), or even a sensor that calculates suspension position based on internal air pressure (as on the fork on Aprilia’s Caponord). Many systems only actively monitor the movement of one wheel and then extrapolate the position of the other wheel. By crunching all this data, the ECU is able to get a surprisingly accurate picture of the bike’s dynamic situation, and adjusts the suspension to suit.

This incredible ability doesn’t mean that semi-active suspension is perfect, but it gets a lot closer to perfection than conventional systems, which can only really be perfect for one specific scenario. Dynamic suspension has its drawbacks of course, including increased expense, increased weight, and increased complexity. And just because it’s the highest-tech stuff available doesn’t mean the spring rates are going to be right for your weight or that the damping is going to give as much adjustment as you’d like. And no, semi-active systems don’t completely eliminate fork dive and rear-end squat—that would entail locking out the fork or shock, thereby eliminating suspension action entirely, which would compromise traction.

Okay, so electronic suspension is impressive, but what if you just want to know more about tuning the old-fashioned, manually adjustable stuff? We'll press rewind and cover that in the next and final installment of "Making Sense of Suspension."

THE SERVICE SCENARIO

So What's This Going to Cost Me?
Complex systems seem more vulnerable to failure and often prove quite expensive to fix, so it would stand to reason that electronic suspension components could pose a major threat to your bank account down the road. BMW has had its ESA (Electronic Suspension Adjustment) on the market the longest (since 2004), so we polled a high-volume suspension shop and a bike-rental company to get their take on the reliability and service scenario for these high-tech parts.

In terms of durability, bike-rental company MotoQuest has put BMW’s ESA to the test. “We have 10 R1200GSs, with 30,000 to 50,000 hard rental miles on each of them,” MotoQuest’s Kevin Hagerty says. “We did have one malfunction right out of the gate, but it was fixed under warranty, and we haven’t had any problems since.”

“Once you take off the electronics, they’re just regular shocks,” says Pierre Vaillancourt of Works Performance Shocks. That means they’re susceptible to the same seal and shaft wear as conventional components, but they can also be rebuilt like standard components. Vaillancourt says he’s seen the preload motors and sensors on early ESA system fail, but that’s it.

“We’ve adapted our shocks to accept the ESA components,” continues Vaillancourt, “so we can build a custom shock for about half the price of a replacement OEM unit.”

That’s a good deal, assuming your ESA components are all in working order. If an ESA component does fail and your bike is out of warranty, you’re in a tight spot. BMW doesn’t sell individual components, which means you’re stuck buying a complete shock for $1,800 to $2,500.

TWO LEGS, SEPARATE FUNCTIONS

Many of today’s forks task the legs with separate functions: One leg will contain the spring and the other the damping circuitry. What’s up with that?

By eliminating a spring, manufacturers are able to build lighter, more affordable forks. Removing the spring from one fork leg also allows for bigger damping pistons, which can offer a performance advantage. Fork springs rub on the inside of the leg as the suspension compresses and extends, and with only one spring there’s less internal friction, and the damping oil stays cleaner.

You might be thinking there needs to be a spring in each leg. The days of skinny, flexy forks are mostly behind us, and today’s large-diameter fork tubes, massive hollow axles, and beefy triple clamps are stiff enough that lateral flex isn’t an issue.

WHY ONLY "SEMI-ACTIVE"?

Why are these electronically enhanced forks and shocks called semi-active instead of active? There’s certainly a lot of activity going on, after all. Since these systems still rely on springs and hydraulic damping to control wheel movement, they can only react to the road. Active suspension, on the other hand, would literally lift the wheels up over bumps and push them down into dips. Active systems are under development in the automotive industry, but the components’ size and weight mean we’re unlikely to ever see them on motorcycles.

A dead giveaway for electronic suspension is wires or servos attached to the fork or shock, like this Aprilia Dynamic Damping setup.