Sprint Filter P08 F1-85 Air Filter for Racing – BMW R 1250 RS (2019–2023) K142S F1-85

There is a number on this element that runs the wrong way and it is worth putting first. Eighty-five microns is a larger aperture than the eighty of the standard cloth for the same airbox, not a smaller one. This is the coarsest medium Sprint Filter weaves, and this part number puts twice as much of it in front of the engine as the standard-size racing element does. The result is the least restrictive combination in the catalogue for this housing — and, at the same time, the one that closes on the least.

Key Features

• Woven dry polyester with an 85 µm aperture, wider than the 80 µm of the standard cloth
• A hundred per cent more filtering surface than the standard-size racing element
• 15,000 l/m²/sec rated flow against 5,050 for the standard weave
• Retention measured at 95.22 per cent of 100-micron test particles
• No oil at any stage, so nothing can be carried forward into the intake tract
• Direct fit in the series airbox, cleaned and reused, two years of guarantee

Both directions at once

Finer means more retention and less flow; coarser means the reverse. That trade is the spine of the range and it does not bend for the racing weave, which sits at the open end of it by design. Adding area moves only one of the two: it raises what the element can pass and hold, and leaves the aperture where it was. So this is not a filter that is good at everything. It is the freest-breathing arrangement available for the airbox, bought at the cost of the finest fraction the standard cloth would have kept.

Reading the retention figure properly

Sprint Filter quotes 95.22 per cent for this weave against 100-micron test particles, a higher figure than the standard cloth's 93.13 per cent — which surprises people who have just read the aperture. The two are not in conflict: the test runs at a hundred microns, comfortably above both apertures, so it measures how each weave handles particles neither is trying to pass. It says nothing about the fine end, where the difference between eighty and eighty-five actually lives. Nor is it a power claim: an element inside an unmodified airbox does not make a standard R 1250 RS noticeably faster.

Care and cleaning

The most open weave in the range is also the easiest to clear. Compressed air from the inner face outwards will normally do the whole job in a minute or two, and the doubled area simply lengthens that a little. A wash is reserved for what air stops moving: hand-warm water, the smallest useful amount of mild detergent, and rinsing until the water leaves the cloth clean. The element must then dry right through in circulating air, with nothing warm and nothing burning near it, before the K142S F1-85 goes back into the housing. The servicing sheet is in the Downloads tab.

Fitment & Compatibility

For the BMW R 1250 RS of 2019 to 2023, replacing the standard panel in an unmodified airbox. Six entries in the catalogue cover five machines under this part number — the RS and RT of the 1200 generation and the R, RS and RT of the 1250 — each with its years in the Fitment tab.