Tech Talk: Suspension

Nitron

High-quality aftermarket suspension components are pricey, but can totally transform your ride.

Originally published in Slipstream magazine, July 2016.

Along with power output and brakes, a motorcycle’s suspension is the component most often discussed in any new review, yet it’s the part most often ignored by riders. Suspension doesn’t work on-demand like brakes or throttle, doesn’t make any cool noises, and is usually tucked away out of sight. Like your plumbing, you only notice or think about it if isn’t doing its job, but regardless of how well it’s performing the effects are generally poorly understood and rarely credited. If a bike ‘feels’ good or bad to ride, whether it inspires confidence during cornering and whether the tyres are able to find grip or not is all down to the suspension.

At some point, both the car and bike world convinced themselves that hard suspension was good and soft suspension was bad; that the best performance vehicles would have shocks so stiff that every tiny pebble would send their pilots flying out of their seats. In the bike world soft, absorbent shocks are believed to result in motorcycles that would wallow and dive when ridden above 10mph, and were fit only for sluggish tourers and two-wheeled Cadillacs.

Donnington Park

Stiff suspension works well on track, but can make real-world roads extremely difficult.

The reality is that suspension has just one very simple job: to keep both wheels in contact with the ground at all times. If rubber doesn’t meet the road, you can’t put down power, nor can you brake effectively. You can’t feel what the road’s doing through your two contact points if they’re not actually touching the road, and it’s very difficult to ride well without that critical feedback.

Both your forks and rear shock are different packaging methods for the same type of engineering. Both contain two parts: a spring and a damping assembly. Springs provide bump absorption by slowing sudden movement and transmitting that energy into the chassis over a longer period of time. This ‘averages out’ the road surface, isolating the ‘sprung’ components of a motorcycle from the sudden bumps and dips the wheels encounter.

Shock Absorber

Some shock absorbers feature external preload adjusters or piggyback gas reservoirs.

The problem with this approach is that springs have a momentum of their own, as does the vehicle itself. As the spring is compressed by a bump pushing upwards, it tries to extend to its original length, pushing the vehicle up into the air. If the spring was compressed hard enough, then the upward movement could cause the chassis to gain sufficient momentum to lift the wheels right off the ground before gravity takes over and presses it back down again. Then the springs compress, absorbing the new impact, and the cycle continues, bouncing you all the way down the road until things finally settle.

To solve this problem shock absorbers were added, just like those in a modern motorcycle’s forks and rear ‘shock’ assembly. Shock absorbers are also known as dampers because they dampen the effects of the spring compressing or extending by adding friction to the movement. Ideally, a suspension assembly would compress to absorb the bump, then extend only back to its original rest state, no further, thereby arresting any ‘bounciness’.

Bumpy Road

Rippled tarmac like this provides a serious challenge to any motorcycle’s suspension.

If these two elements seem to be working against each other, it’s because they are. Make the damping too extreme, and the spring won’t be able to compress quickly enough to absorb sudden impacts, transmitting them straight into the chassis of the bike. Under-damped suspension, on the other hand, will see-saw down the road, making you seasick as the dampers fail to arrest the enthusiastic movement of the springs.

Compromise is therefore necessary, with carefully chosen spring and damping rates to match both a bike’s weight and it’s expected use case. A sportsbike, ridden on glass-smooth racetracks can benefit from stiff springs and dampers to prevent pitching and rolling as power is applied using the high-performance engine and brakes. On a bumpy, pothole-ridden road this would make for a jarring, uncomfortable ride, compromising grip as the suspension fails to react in time and the wheels lose traction under power or braking.

BMW R1100RT

A heavy, softly-sprung motorcycle can become a real handful on fast, bumpy roads.

A touring bike, on the other hand, will use softer springs and dampers to isolate it’s passengers from expansion joints and rippled tarmac, but would react poorly to sudden throttle or brake inputs, to say nothing of extreme cornering forces. Turn the wick up on a twisty road and the bike will seem to wallow and become vague as the suspension fails to cope. Advanced as modern bikes are, a Honda Goldwing would be a poor substitute for a Triumph Daytona 675 on a racetrack.

So, suspension has to be designed for the purpose for which the bike is intended. But there’s another problem: you. Springs and dampers aren’t just trying to control the weight and momentum of all that metal and plastic moving around, they’ve got to manage the weight of all the jiggling bits between the seat and handlebars as well. And while every FJR1300 weighs exactly what Yamaha thinks it does, the weight of the rider could vary dramatically.

Nitron Suspension

Custom-made suspension ensures the shock and spring are correctly matched to your weight.

Are you a tiny 40-kg weakling or a 200kg professional bodybuilder? If you’re settling into the driver’s seat of a 2-tonne SUV, it makes very little difference to the total weight of the vehicle, and so car manufacturer’s don’t really have to worry about the variance. But when I sit on my 180kg Triumph Street Triple I’m increasing the total vehicle weight by almost 40%. Despite this, and as evidenced by its too-stiff springs and damping when new, Triumph was, in fact, expecting a slightly heavier average rider, leaving me to foot the bill for any necessary corrections.

Many larger riders complain of the opposite problem of course. If you yourself weigh 180kg, then the springs on that same motorcycle will be too soft to properly support you, and the dampers will be insufficient to manage all the momentum of that unexpected mass. This means that unless you happen to weigh exactly what the manufacturer had in mind when they specified the suspension, it’s always going to be wrong.

Triumph Suspension

All factory-fit suspension is necessarily a compromise, designed for the ‘average’ weight rider.

So what’s the solution? Well, the heavier the bike, the less accurate the rider weight needs to be. Today’s big, heavy ADV bikes are frequently 250kg or more, so your extra doughnuts aren’t going to matter as much as they would with a featherweight learner motorcycle. Some motorcycles also have mechanical or even electronic suspension adjustments, allowing you to increase or reduce the damping at both ends of the bike to suit heavier or lighter loads.

Don’t be fooled into thinking you can increase or decrease the stiffness of your springs by adjusting the preload on the forks or shock, however; this is a common misconception. All that does is pre-tension or ‘pre-load’ the spring by compressing it mechanically; further compression, caused by a rider sitting on the bike or by a bump pushing a wheel up will now require more force to gain a result. In practice, this means that you’ll just increase the ride-height at whichever end you increase the setting, which is useful for ensuring your bike stays level as you add passengers or luggage.

Preload Adjuster

Changing the preload allows you to level the bike for when you carry luggage or a passenger.

Setting preload to extremes could mean a bike with no travel left at either end of its range, resulting in suspension that tops out over the smallest of dips, or bottoms out over the slightest of bumps. It also messes with the suspension’s operating range, which can adversely affect damping performance.

Ideally, you want the suspension to be sat right in the middle of its usable range, with you sat on the bike in full gear. This means that it has room to drop and fill dips, and space to compress to absorb bumps. It also means that the damping is working in its most effective range, where it can behave as designed.

In summary, if your spring rate is wrong, no amount of preload adjustment will fix it, and the only solution will be to replace the springs themselves with stiffer or softer versions. This needn’t be expensive – you don’t need to swap in a £2,000 aftermarket shock; just ask your local suspension shop to change the spring. Forks are the same – and while they’re at it, your suspension expert can change the fork oil and maybe even re-valve the existing shock to better match your weight and preferred riding style. Some people like to ride more slowly, so soft and comfortable suits them just fine!

Electronic Suspension

Some motorcycles feature on-demand electronic adjustment of the damping or spring preload.

A lot of modern bikes now feature electronically-adjustable suspension, but contrary to misleading marketing this is not really a complete solution to the problem. These systems often make tweaking damping settings a push-button affair, which is nice if you want to dial back damping for long, cushy motorways and firm it up for sporty riding once you reach some nice, twisty roads. Many offer preload adjustment, either automatically based on load (Triumph Explorer 1200, Aprillia Caponord) or by using a button to tell the on-board computer if you’ve got luggage or a pillion on-board.

Just remember that these pre-programmed damping settings are just presets, and only work within a set range dictated by the manufacturer. If you’re particularly light or heavy you may find that even the extreme soft or hard settings don’t help much. Getting these systems re-valved is also a much trickier, more expensive process than on a fully analogue suspension, and may not even be possible on all models.

I’m impressed by Triumph and Aprillia’s auto-levelling systems, as these appreciate that pre-programming preload options is silly; BMW can’t possibly know how much your pillion or luggage weighs, so it’s yet more compromise. But until someone invents a system that can magically adjust the density of the metal springs in your suspension, electronic adjustment will remain a fancy hi-tech bandaid that can’t really fix the problem.

Used Fork Oil

Dirty, contaminated suspension oil loses its ability to arrest the movement of the forks or shock.

And even if your suspension is set up perfectly for your weight, it’s not set-and-forget. The oil inside your forks and shock gets literally shredded by the forces exerted on it, and over time becomes thinner and less effective. Just 12,000 miles after I first replaced the fork oil in my Suzuki V-Strom, my aggressive riding had transformed it from golden-syrop to snotty goop. Nitron recommends servicing their shocks every 10-12,000 miles for this reason, and you can really feel the results afterwards.

So; service your suspension. Damping adjustments can help, but the correct springs and oil will make a far larger difference. And while electronically-adjusted suspension is getting better, it still can’t adjust spring rates, nor do manufacturers know how much you weigh. Overhauling your suspension can cost less than any amount of engine tuning, and make you a far faster, smoother, and more comfortable rider!

Thruxton Race Circuit

It’s amazing what good quality, confidence-inspiring suspension can do!