⟲ 360° — drag meThe facts.
DescriptionThe whole story▼
Ask what a filter has collected and the answer is a quantity. Ask what the engine has to pull its air through and the answer is a thickness. Those are different questions, and only the second one decides how hard the airbox has to work. Dirt held on a small face lies deep; the same amount on a large face lies thin, and thin is what the air notices. The Sprint Filter CM231S carries roughly twice the filtering surface of other performance elements while keeping to the series airbox of the Classic 350: the extra cloth is folded into the space the paper panel occupied, and it works on the second question.
Key Features
- Dry woven polyester in one layer, filtering at 80 µm with a rated 5,050 l/m²/sec
- Roughly double the filtering surface of other performance elements, in the unmodified housing
- The ø 22 micron figure is the thread of the weave, not the gap between the threads
- Never oiled, so nothing can be over-applied and nothing can migrate onto a sensor
- Direct replacement for the factory panel — airbox, ducting and fuelling are left alone
- Washable and reusable, built to outlast the service schedule; two years of warranty
Where the extra cloth goes
Surface area does not make an engine breathe harder: a 350 single asks for a modest volume of air, and any of these media supply it on the day they are fitted. Area does something less obvious: it decides how slowly a collected load turns into resistance, because the load has to spread across whatever cloth is there before it begins to close it up. Across the model years from 2022 to 2026 the argument does not change: an element is worth choosing for how it behaves in the middle of an interval, not for how it measures at the start of one.
What it changes, and what it cannot
It cannot add power. A drop-in element does not make a standard Classic 350 noticeably stronger, and any text claiming so has left the subject. It also cannot make dirty air clean: where roads are consistently dusty the honest answer is a finer medium, and Sprint Filter builds them. Sprint Filter lists a P14 non-woven for this airbox: it holds down to 14 µm and flows 1,800 l/m²/sec. More retention, less flow: a trade rather than a ranking, worth making only where the air really is bad. On sealed roads the 80 µm P08 is where this motorcycle belongs.
Care and cleaning
The CM231S is serviced dry. Lay an air line on the clean side and work outwards, so the load is driven back off the face it settled on. Water is for the greasy occasions rather than the dusty ones: lukewarm, a drop of mild detergent, rinsed clear. Then open air until it is completely dry, never a heater and never a flame, and back into the box untreated. The maintenance sheet sits in the Downloads tab.
Fitment & Compatibility
For the Royal Enfield Classic 350 of 2022 to 2026. The same part number covers four further machines — the Bullet 350 from 2023, the Goan Classic 350 from 2025, the Hunter 350 from 2022 and the Meteor 350 from 2021 — five motorcycles on one element. Confirm your own year in the Fitment tab.
DownloadsOwner's manual · brochure▼
FitmentWhich bikes this fits▼
- Royal Enfield Bullet (2023–2026)
- Royal Enfield Classic (2022–2026)
- Royal Enfield Goan Classic (2025–2026)
- Royal Enfield Hunter / Hntr (2022–2026)
- Royal Enfield Meteor (2021–2026)
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Take out the washable lining and hand-wash it in lukewarm water. Clean the shell and visor with a soft cloth and water only — never solvents.
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