BOS Kirk shock review£599.00

Super tuneable shock for experienced fettlers

BikeRadar score4/5

The BOS Kirk is one hell of an expensive shock – but for very suspension savvy racers looking for the ultimate in flat out control and a firmly supportive feel, it might just be worth it.

If you’re looking for an easy shock to set up and pillow smoothly off down the trail on then save your money. If you’re not prepared to sacrifice a fair amount of riding time just re running the same sections over and over again to refine your shock settings then the Kirk isn’t for you either.

Related: Six of the best MTB air shocks

Let's not mince words here: this is the most frustrating and patience stretching of all the six shocks we tested for our recent 'best-of', and several times during our two month setup saga we were wishing we could just stick a Monarch or Fox back on and just go and enjoy the rest of the day.

As with most shocks it comes with no volume spacers installed (they’re supplied in the box) which creates a very linear spring rate. Even with the spacers in it still needs more pressure than average and a good dose of high speed compression damping to hold it up.

However, while most dampers tread a very fine line between noticeable compression control and sudden spiking, the BOS adjustments are super subtle. That makes them almost impossible to notice if you’re just bouncing round in the car park but gives awesome fine tuning accuracy if you’re prepared to spend time firing through the same sections repeatedly to get each aspect of the stroke dialled.

Once you start clicking the high and low speed compression adjustment into place, the full potential of the shock opens up like a cracked safe and its ability to stay composed, on target and in control through the most hectic sections is outstanding. Done right, the feeling is very similar to a really good tyre – plenty of micro grip and controlled compliance, but no bounce at the contact point of the trail, pushing through to stable and solid support that lets you search for the most aggressive exit lines with total confidence.

The flipside is that because it’s so tuneable, we were never totally happy with our overall setup on different trails or even different sections of the same trail – so you’ll have to learn to live with a permanent fettling itch. It’s worth noting that as a race optimised damper it always retains a firm ‘skim over’ rather than ‘suck up’ response to bigger hits, even with the compression backed a long way off too.

That’s because racers want maximum feedback to pump and drive the bike along the trail, not floppy forgiveness to soak up mistakes. In other words, don’t BOS your bike if you like your trail more latte than double espresso.

This article was originally published in Mountain Biking UK magazine, available on Apple Newsstand and Zinio.

Guy Kesteven

Freelance Writer, UK
Guy started filling his brain with cycle stats and steaming up bike shop windows back in 1980. He worked the other side of those windows from '89 while getting a degree in “describing broken things covered in mud" (archaeology). Dug historical holes in the ground through the early '90s, then became a pro bike tester in '97. Guy has ridden thousands of bikes and even more components the world over since then and can remember them all in vivid, haunting detail. Can't remember where the car keys are, though.
  • Age: 45
  • Height: 180cm / 5' 11"
  • Weight: 68kg / 150lb
  • Waist: 76cm / 30in
  • Chest: 91cm / 36in
  • Discipline: Strict sadomasochist
  • Preferred Terrain: Technical off-piste singletrack and twisted back roads. Up, down, along — so long as it's faster than the last time he did it he's happy.
  • Current Bikes: An ever changing herd of test machines from Tri bikes to fat bikes and everything in between.
  • Dream Bike: His Nicolai Helius AM custom tandem
  • Beer of Choice: Theakston's Old Peculier (not Peculiar)
  • Location: Yorkshire, UK

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