Sprint Filter P08 F1-85 Air Filter for Racing – Triumph Bonneville Speedmaster (2018–2021) SM225S F1-85

Load a Bonneville Speedmaster with a passenger, luggage and a long climb, and the engine is unmistakably working. It is tempting to read that as the moment when an intake restriction begins to cost something. It is not. How much air an engine draws per second follows its capacity and the speed it is turning, not how hard the ride feels — a laden twin hauling up a pass at low revs moves far less air than the same engine spun out on an empty road. That single distinction decides what the SM225S F1-85 is for here. Its 85 µm weave and 15,000 l/m²/sec are dimensioned for engines held near their ceiling, and a 1200 cruiser does not go there, laden or not.

Key Features

• Dry polyester weave, aperture 85 µm, the most open medium Sprint Filter builds for this airbox
• Rated 15,000 l/m²/sec, a figure specified for sustained running at high engine speed
• Never oiled and never re-oiled, so the intake downstream stays clean and dry
• Approximately double the filtering surface of other performance filters, airbox unchanged
• Drops into the series airbox in place of the paper panel; no modification and no remap
• Washable, reusable, intended to last the motorcycle's life; two-year warranty from purchase

Working hard and breathing hard are not the same

The confusion is understandable, because effort is what a rider feels and airflow is not. But a filter never meets effort. It meets a volume of air per second, and on this engine that volume is capped by displacement and by a rev ceiling set deliberately low in the interest of torque. Two-up on a mountain road the Speedmaster is working near its limit and still breathing well inside the standard element's rate — which is why the extra capacity offered here has no road journey to be spent on.

What is left once flow is set aside

Quite a lot, but none of it is power: a drop-in element does not make a series Speedmaster noticeably stronger. This weave is dry, washable and built to stay in the machine for good, so the intake resistance is reset at each clean rather than climbing until a panel is bought. The medium ladder is a trade in both directions — finer retains more and flows less, coarser flows more and retains less of the fine fraction — and this element sits firmly at the open end of it.

Care and cleaning

Service the SM225S F1-85 with compressed air directed at the clean side and out through the weave. Wash it, when a season has earned it, in lukewarm water with a mild detergent and rinse until the water runs clear. Air-drying only — no heat gun and no flame — and it must be dry before it is refitted. The maintenance sheet is under the Downloads tab.

Fitment & Compatibility

Catalogued for the Triumph Bonneville Speedmaster built from 2018 to 2021. The Triumph Bonneville Bobber of 2017 to 2021 uses the same airbox and the same part number. Confirm your model year in the Fitment tab.