Sprint Filter P08 F1-85 Air Filter for Racing – Honda ST125 Dax (2023–2026) SM288S F1-85

The Dax name is a good deal older than most of the advice attached to it. Honda first put a bike on the road under it more than fifty years ago, and around that little horizontal single grew half a century of tuning lore — jets, kits, open intakes, opinions handed down through clubs and later through forums. The ST125 arrived into all of that, inheriting an aftermarket written for a different engine and largely for carburettors. This element is one of the few parts in the whole tradition whose case is a measurement rather than a story.

Key Features

• Dry polyester in racing specification: 85 µm, 15,000 l/m²/sec
• The highest flow figure in the Sprint Filter range, roughly triple the standard P08
• Measured retention of 95.22 % on 100-micron particles, where the P08 records 93.13 %
• The series airbox takes it as it stands: nothing cut, nothing remapped
• Never oiled at any stage; an air line is the whole service kit
• Meant to outlive the motorcycle it is fitted to; two years' warranty from purchase

What the sheet says, and what it means here

Two figures, and neither behaves the way workshop lore expects. The F1-85 is rated at a wider 85 µm than the P08's 80 and still keeps more of the test dust out, while passing roughly triple the air. Read closely, though, and only one of those halves is doing anything on this motorcycle. The flow rating describes a ceiling that a standard, road-registered 125 has no mechanism for approaching — not on any road, not in any gear. The retention figure applies to every minute the engine turns. Bought at all, this element is bought for the second number and never for the first.

A reason that is not a performance claim

Said plainly: this is the dearest element made for the housing, several times the standard P08 for an identical fit, and it leaves a standard Dax exactly as quick as it was. No series airbox gives anything back for what goes into it, and the registration class settles the matter above that in any event. Most owners should fit the P08 and give it no further thought. The honest reason to choose the SM288S F1-85 instead is that you want the best part built for this airbox on a machine you happen to love. That is taste rather than engineering, and taste is a perfectly good reason as long as nobody dresses it up as the other thing.

Care and cleaning

Hold an air line to the clean face and blow outward — that covers the routine. Anything oily the road has left behind comes away with warm water and a little mild washing-up liquid, rinsed off until the water is clear, then dried right through in open air. Heat destroys polyester, so keep it away from radiators, hot air and flame, and put nothing on the weave afterwards. It is refitted dry. The maintenance sheet for the SM288S F1-85 is in the Downloads tab.

Fitment & Compatibility

Fitted to the Honda ST125 Dax of model years 2023 through 2026, which is the entire fitment list. Two other media, the standard P08 and the fine P14, are catalogued for the identical housing. See the Fitment tab.