The facts.
| Brand | Öhlins |
|---|---|
| Part Number | 21042-18 |
| Spring Rate | 68 N/mm |
| Free Length | 170 mm |
| Inner Diameter | 51 mm |
| Stroke | 89 mm |
| Construction | Straight |
| Finish | Powder-coated yellow |
| Country of Origin | Sweden |
DescriptionThe whole story▼
Öhlins part number 21042-18 is a shock absorber spring rated at 68 N/mm, 170 mm long with a 51 mm inner diameter. The damper can only control the spring it is given; the wrong rate makes every click a compromise.
Key Features
- Straight-wound, constant rate
- 89 mm of usable stroke
- Inner diameter 51 mm
- Öhlins part number 21042-18
- Powder-coated yellow
- Free length 170 mm
- Measured spring rate 68 N/mm
Manufacture and Tolerance
Öhlins sets a baseline for each part number on the machine it was developed on, so it works before anything is adjusted. Öhlins machines its own critical components instead of buying them in, and the tolerances are where the money goes. Seals are specified for temperature stability rather than for the lowest unit cost.
Dimensions
At 170 mm free length and 51 mm inner diameter, this spring is dimensionally interchangeable with anything of the same size — the rate is what makes it a different part.
Choosing 68 N/mm
A firm rate keeps the fork high in its stroke under braking, which preserves the geometry when the front is loaded hard. Heavier riders, two-up use and track days all push the choice towards this end. Support under braking improves; small-bump comfort gives a little back. A road machine spends most of its life in the first third of the fork's travel — that is the part the rate governs.
What the Rear Spring Decides
Two riders 20 kg apart on the same motorcycle genuinely need different rates, not different clicks. Öhlins supplies most of its shocks without a spring precisely so the rate can be matched to the rider rather than averaged. Öhlins sells rear springs separately precisely because rider weight varies more than machine weight does.
Applications
Rate is the variable that depends on the rider, not on the machine. Two people on the same bike may well want two different numbers. Sag figures, not feel, decide whether a rate is right. Öhlins publishes the targets for its own units. Any workshop with the fork or shock in front of it can answer whether this spring fits — the three figures above are all it needs.
What Fitting Involves
Work on both legs in one session so the fork stays symmetrical. The job needs no special tools beyond a fork spring compressor and a measuring rod for the oil level. The fork legs come off, the springs are swapped and the oil level is reset — half a day in most workshops.
Road Approval
Road approval: a spring is a like-for-like replacement of a wear part and carries no separate type approval. Where Öhlins states an approval for a particular motorcycle, it is named under Applications.
Fitting and Setup Service
Öhlins recommends that its suspension is fitted by an authorised service centre. We are one, and we do the work here: installation, servicing and a proper setup. Ask us and we will include it with the order.
Specifications
- Brand: Öhlins
- Part Number: 21042-18
- Spring Rate: 68 N/mm
- Free Length: 170 mm
- Inner Diameter: 51 mm
- Stroke: 89 mm
- Construction: Straight
- Finish: Powder-coated yellow
- Country of Origin: Sweden
FitmentWhich bikes this fits▼
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