The facts.
| Brand | Öhlins |
|---|---|
| Part Number | 21040-29 |
| Spring Rate | 90 N/mm |
| Free Length | 160 mm |
| Inner Diameter | 51 mm |
| Stroke | 78 mm |
| Construction | Straight |
| Finish | Powder-coated yellow |
| Country of Origin | Sweden |
DescriptionThe whole story▼
Öhlins part number 21040-29 is a shock absorber spring rated at 90 N/mm, 160 mm long with a 51 mm inner diameter. Adding a pillion or luggage changes the load enough that the standard rate stops working.
Key Features
- Measured spring rate 90 N/mm
- Free length 160 mm
- Öhlins part number 21040-29
- Straight-wound, constant rate
- 78 mm of usable stroke
- Powder-coated yellow
- Inner diameter 51 mm
Manufacture and Tolerance
Two units carrying the same part number behave the same way out of the box, which is the whole point of testing each one. Every Öhlins dealer can re-valve the unit, because the shim stack is a documented, serviceable assembly. Rates are offered in defined steps, so a change can be made in one direction at a time.
The Numbers That Matter
At 160 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 90 N/mm
If the suspension bottoms out or the geometry collapses under load, this is the direction to go. Support under braking improves; small-bump comfort gives a little back. Firm rates trade some small-bump comfort for support — the right trade on a good surface at speed. Road surfaces are the hardest test of a spring rate, because the fork has to cope with both a smooth stretch and a broken one.
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. A spring that has settled in service sits shorter than new, which quietly lowers the bike and steepens the steering. Two riders 20 kg apart on the same motorcycle genuinely need different rates, not different clicks.
Applications
Where Öhlins lists this size against a particular unit, the listing is a starting point rather than a boundary. Selection is by measurement. If the diameter and free length match your fork, the remaining question is the rate. There is no model list for this size because the spring is a dimensional part: it fits whatever fork it physically fits.
Fitting
Fork oil should be replaced at the same time — it is already out of the leg. Fitting is a fork-oil job: the legs come apart, the springs go in, the oil level is set to specification. Set static sag after fitting; the rate is only right if the sag figure lands where Öhlins specifies.
Road Approval
Road approval: none is issued for springs as such — they replace an existing component of the same function. Any model-specific approval is listed under Applications.
Fitting and Setup Service
This is not a part to rush. Öhlins recommends installation by an authorised service centre, and we are an authorised Öhlins service centre — fitting, servicing and setup all happen here. Get in touch if you would like the work done with the order.
Specifications
- Brand: Öhlins
- Part Number: 21040-29
- Spring Rate: 90 N/mm
- Free Length: 160 mm
- Inner Diameter: 51 mm
- Stroke: 78 mm
- Construction: Straight
- Finish: Powder-coated yellow
- Country of Origin: Sweden
FitmentWhich bikes this fits▼
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