Suspension

Suspension for your motorcycle

The suspension keeps the tyres in contact with the road and determines how the bike behaves under braking, through corners and over bumps. If it is worn or set up wrong, you feel it through the bars long before you can see it.

A complete system consists of the fork, rear shock, springs, steering head and swingarm bearings, plus the seals that keep the oil in. A worn joint can easily feel like a bad damper.

The choice matters, because the factory setup is built for an average rider. If you weigh significantly more or less, or ride two-up, the standard springs are working outside their range.

This guide covers dimensions and markings, the difference between progressive and linear springs, choosing by riding style, signs of wear and setup after fitting.

We stock parts from Ohlins, Hyperpro, HyperPro, Progressive Suspension, Yss, Kyb, Moose Offroad, Pivot Works, All Balls, Epi, Legend Air Suspension, Zodiac, Drag Specialties, MCS and Custom Cycle Engineering. Use Find your bike on Partsdenmark.com — and there is free shipping on orders over €200.

The technical basics of suspension

The spring carries the weight, the damping controls the speed of the movement, and the geometry distributes the forces. Once you know the dimensions of your fork and shock, you can choose without guessing.

Dimensions and markings you need to know

Almost all suspension parts are ordered on the basis of a few key figures.

• Fork tube diameter — typically 39, 41, 43, 48 or 49 mm measured on the inner tube.
• Oil seal dimensions — inner diameter x outer diameter x height, e.g. 43 x 54 x 11 mm.
• Shock eye-to-eye length measured centre to centre, unloaded.
• Spring rate in N/mm or kg/mm, matched to total riding weight.
• Travel — road bikes typically 110-130 mm, offroad around 300 mm.

How the system is built up, front and rear

Knowing the order of the parts makes it easier to find the fault.

• Fork with inner tube, outer tube, spring, damper rod or cartridge and oil.
• Seal kit with oil seal, dust seal, bottom bolt and guide bushings.
• Rear shock with spring, piston rod, oil chamber and gas chamber.
• Swingarm and linkage with bearings, bushings and spindles.
• Steering head with tapered bearings carrying the entire front-end load.

A stiff swingarm or a tight steering head bearing gives the same symptoms as a worn shock. Always check the bearings before you replace more expensive parts.

Choose suspension to suit your riding

Your riding style decides whether you need a progressive setup, a linear rate with adjustable damping or a lowered solution.

Riding style	Type	Advantages	Disadvantages	Brands in the range
Road and touring	Progressive Fork Springs and Shocks	Comfort, does not bottom out with luggage	Less precise on track	Progressive Suspension, Hyperpro, Yss
Sport and track	Linear Springs, adjustable damping	Predictable response, full control	Requires setup, considerably more expensive	Ohlins, HyperPro, Yss
Offroad and enduro	Springs by weight, Forks revalve	Long travel, takes hard landings	Short service interval	Moose Offroad, Kyb, Pivot Works, Epi
Custom and cruiser	Lowering kit, air and Revo	Low seat height, adjustable ride height	Less travel, risk of bottoming out	Legend Air Suspension, Zodiac, Drag Specialties
Commuting, worn original	Replacement, Seal and Bearing	Cheapest place to start	Does not fix a wrong spring rate	All Balls, Pivot Works, MCS, Custom Cycle Engineering

If you mostly ride solo on the road, progressive springs up front and new Shocks at the rear often give the biggest improvement on an older machine. It is the upgrade that pays off fastest.

For track and rough terrain, adjustable units make sense, where compression and rebound damping can be changed independently. The spring rate has to be right first — adjuster screws cannot save a wrong spring.

Materials and variants explained

The difference between two springs or two fork tubes lies in the material, the surface and the winding. That determines both the feel and the service life.

Progressive and linear springs

A progressive spring has varying coil spacing and is soft at the start of the travel but stiffens up towards the bottom. That gives comfort and resistance to bottoming out with a passenger on the back.

A linear spring has the same rate all the way through and is easier to read at speed. We stock both types as Fork Springs and Springs from Progressive Suspension, Hyperpro and Ohlins, among others.

Fork tubes and surface treatment

Standard tubes are hard chrome plated, while Coated Fork tubes have a hard coating with lower friction. It is most noticeable on small movements, where the fork would otherwise bind.

The coating takes stone chips better, but a deep nick ruins the oil seal just as fast as on chrome. Replace or polish the tube before a new Seal is fitted.

Air, oil and gas pressure

Air suspension uses air as the spring medium and lets you change ride height without changing the spring — the principle behind Revo from Legend Air Suspension. In return, the system depends on leak-free lines and valves.

Gas-pressurised shocks separate the oil and the nitrogen, so the oil does not foam under sustained load. The gas chamber typically sits at around 10-12 bar and requires special tools.

Wear, service life and maintenance

Suspension wears gradually, so the deterioration creeps up on you. The three areas below cover most faults.

Leaking oil seals

Oil on the inner tube and dirt sticking to the outer tube is the classic sign. If oil gets onto the brake disc, it is a safety fault.

On the road an oil seal typically lasts 20,000-40,000 km, offroad often only 15-30 riding hours. Change the dust seal and the oil at the same time — it comes in the same kit from All Balls and Pivot Works.

Shock service life

A worn-out shock gives a wallowing rear end and poor contact through long corners. Push down hard on the seat and let go: if it moves up and down more than once, the damping is gone.

Fork oil should be changed every two years or every 20,000 km on road bikes. Non-serviceable Shocks are replaced when they are pumped out or leaking at the piston rod.

Steering head and swingarm bearings

Lift the front wheel clear and turn the bars slowly — a notch in the middle means worn Steering bearings and instability in a straight line.

Play in the Swingarm bearings can be felt by pushing the rear wheel sideways. Check the bearings roughly every 10,000 km and grease them at major services.

How to set up the suspension after fitting

New parts only work once the sag and the damping are set for you. The order is preload, then rebound damping and finally compression damping.

Measure sag from the rear axle to a fixed point on the tail — first with the wheel off the ground, then with the bike on its wheels and finally with the rider in riding gear. Aim for 25-33 % of the travel, i.e. around 30-35 mm on a road bike.

If you cannot hit the sag figure within the adjustment range, the spring rate is wrong for your weight. Here a set of Fork Springs or Springs solves the problem in a way preload never can.

When assembling the Forks, the oil level must be the same in both legs, measured with the spring out and the fork fully compressed. A few millimetres of difference is clearly noticeable under braking.

Torque the axle clamps and shock bolts to the manufacturer's specification, and re-torque after the first few kilometres. You will find bolts, bushings and tools under suspension accessories and hardware.

Frequently asked questions about suspension

Below are the questions customers ask most often before buying springs, shocks and seals.

Which spring rate should I choose?

The rate is chosen by total riding weight including gear, passenger and luggage — not by the weight of the motorcycle alone.

If you are in the middle of the manufacturer's weight range, the standard choice is right. If you regularly ride two-up, go one step stiffer.

Can I change the oil seals without stripping the fork?

No, the oil seal sits inside the outer tube, so the leg has to be stripped and the oil drained. You need a seal driver and usually a holding tool for the bottom bolt.

On the other hand, the parts are the cheapest place to start, and a kit from All Balls or Pivot Works contains the Seal, dust seal and bushings.

How often should the fork oil be changed?

On the road, every two years or every 20,000 km is sensible. Offroad and on track the oil should be changed after 15-20 riding hours.

Does lowering ruin the handling?

Lowering removes travel, so the suspension bottoms out more easily with the original spring. If you only lower the rear, the steering becomes slower.

Lower front and rear by the same proportion, and choose a Lowering kit developed for your model. Check the clearance to the tyre and the exhaust.

How do I make sure the part fits?

Use Find your bike on Partsdenmark.com, and only parts listed for your model and year will be shown. If the bike has been modified, measure the tube diameter and the eye-to-eye length yourself.

Fork tubes, springs and seals are found under front suspension, while shocks and swingarm bearings are under rear suspension.

We offer a European price match and give 2-year right of complaint on all items. There is free shipping on orders over €200 at Partsdenmark.com.