The facts.
| Brand | Öhlins |
|---|---|
| Part Number | 66391-02 |
| Spring Rate | 75 N/mm |
| Free Length | 120 mm |
| Inner Diameter | 55 mm |
| Stroke | 75 mm |
| Construction | Tapered |
| Finish | Powder-coated black |
| Country of Origin | Sweden |
DescriptionThe whole story▼
Öhlins part number 66391-02 is a shock absorber spring rated at 75 N/mm, 120 mm long with a 55 mm inner diameter. The damper can only control the spring it is given; the wrong rate makes every click a compromise.
Key Features
- 75 mm of usable stroke
- Free length 120 mm
- Tapered-wound, constant rate
- Measured spring rate 75 N/mm
- Powder-coated black
- Inner diameter 55 mm
- Öhlins part number 66391-02
Manufacture and Tolerance
Every Öhlins dealer can re-valve the unit, because the shim stack is a documented, serviceable assembly. Two units carrying the same part number behave the same way out of the box, which is the whole point of testing each one. The finish is applied after setting, which means the coating does not affect the rate.
Dimensions
At 120 mm free length and 55 mm inner diameter, this spring is dimensionally interchangeable with anything of the same size — the rate is what makes it a different part.
Choosing 75 N/mm
A firm rate holds the chassis attitude when the front or rear is loaded hard. Firm rates also suit machines carrying luggage as a matter of course. 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.
How a Rear Spring Works
Rear spring rates run in the tens or hundreds of N/mm because the spring sits at the short end of that lever, not at the wheel. Adding a pillion or luggage changes the rear load enough that the standard rate stops working properly. On a linkage-equipped machine the wheel moves several millimetres for every millimetre the damper moves, and the spring rate has to account for that ratio.
Applications
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. If you are replacing a sagged original, measure its free length first — a tired spring often measures several millimetres short. Sag figures, not feel, decide whether a rate is right. Öhlins publishes the targets for its own units.
What Fitting Involves
Preload spacers usually need shortening or lengthening so the installed length stays correct. Any suspension workshop can fit these; the fork does not need to leave the bike for long. If the fork has not been serviced recently, bushes and seals are worth replacing while it is apart.
Road Approval
Road approval: springs are not separately type-approved in Germany because they substitute a part that is already homologated with the fork. Model-specific documents, where they exist, are named above.
Fitting and Setup Service
Öhlins suspension rewards careful fitting. We recommend having the work done by an authorised Öhlins service centre — and we are one ourselves: we fit, service and set up Öhlins components in house. If you would like us to handle the installation, just ask and we will quote it with the order.
Specifications
- Brand: Öhlins
- Part Number: 66391-02
- Spring Rate: 75 N/mm
- Free Length: 120 mm
- Inner Diameter: 55 mm
- Stroke: 75 mm
- Construction: Tapered
- Finish: Powder-coated black
- Country of Origin: Sweden
FitmentWhich bikes this fits▼
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