Fox RP23 Rear Shock with Boost Valve

2011 Fox RP23 with Boost Valve

This shock is off a 2011 Giant Anthem X frame. It has a "L" rebound tune, "F" compression tune and 300psi in the boost valve.

It weighs 211g including bushing and mounting hardware (only on top eyelet).

How does the 2011 Fox RP23 with Boost Valve go on the Anthem X?

The short answer: it works really well. It does seem like Fox have finally arrived at a rear shock that has all the pedalling efficiencies of the propedal platform but none of the "platform" drawbacks. Shock feels plush even on the firmest propedal (3) setting, which is really saying something.


  • propedal works - setting 3 on the Anthem X makes it feel like a hardtail, but small bump compliance is still there;
  • lever to turn propedal off is a great thing - the Anthem X's maestro suspension doesn't really need a platform shock - with propedal off this shock is plush;
  • bottom out resistance is great - gives the Anthem X rear suspension a "bottomless" feel to it;
  • propedal setting 1 - if you're a set-and-forget type of guy then this your setting. Small bump compliance feels almost as good as propedal off, but propedal's there for cranking out the watts.

After playing around a little with air pressures which resulted in sag from between 10mm and 7mm I settled on 9mm of sag which provided the plushest feeling without wallowing in the mid-stroke. For me this was about 140psi in the air spring.

My favourite shock on the Anthem X to date has been the Magura Hugin - with this shock on the bike you simply forget its on there as it soaks up everything the terrain throws at it without fuss. The proper high and low speed adjusters on this shock (and lack of a platform) allow you to really dial this shock in. Its features are pretty unique in 165mm eye-to-eye shocks.

I was really surprised that the 2011 Fox RP23 with Boost Valve compares really favourably with the Hugin. This is definetly the best Fox shock that I've had on the Anthem X. The stock Float R had too much platform and the RP3 had too much platform and too little rebound damping, even with the adjuster at full slow. I revalved the RP3 a few times to try to get a good setup but the complex relationships between the rebound, pro-pedal and compression circuits made the thing a nightmare to tune and I can't say that I ever got it to the stage where I though it was great. Good yes, but not great.

Anything on the 2011 Fox RP23 with Boost Valve not to like?

Every fox shock I've had seems to suffer from the same crappy rebound adjuster. What's crappy about it? Most of the adjustment range doesn't seem to make any realy difference until you get to a certain point and one click more is too much rebound damping and one click back is too little. This is probably something to do with the shape or design of the rebound needle and the orifice in which it works.

I was really hoping that on the 2011 shocks they would have fixed this.

RP23 testing grounds:

Steep climbs with rocks and roots have been the achilles heel of fox propedal shocks. The platform from the shock makes the rear end skip and loose traction over such things, particularly if you're out of the saddle and have transfered alot of your weight forward. The Boost Valve really seems to cure this problem.

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