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Old 08-06-09, 05:57 PM   #1
stevage
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Do I need a shock pump?

So I bought a Giant Yukon FX3 with "GIANT air shock" rear and "RockShox Dart 2 100mm travel, TurnKey lock out" fork. Obviously the fork doesn't need to be pumped

Question is, do I *need* a shock pump? I haven't assembled it yet, so I'm not sure whether I need to get one asap before even riding it. How often do you have to keep putting air in the rear shock?

Steve
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Old 08-06-09, 06:05 PM   #2
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It's a matter of adjusting the shock, you'll need a pump to do that, unlikely it's been setup ideally for you out of the box. The shock/fork once setup shouldn't lose air, though (although if it has a seal problem it will).
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Old 08-06-09, 06:27 PM   #3
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Yes
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Old 08-06-09, 07:49 PM   #4
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You at least need a pressure guage to check to see if the pressure is correct. Then you need a pump to adjust it if it needs to be changed. The pumps usually come with a guage. They're inexpensive so just get one then you will be prepared.
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Old 08-06-09, 07:56 PM   #5
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Scratch that, I finished rummaging through all the packaging that came with the bike, and they included a shock pump! Sweet! There's no brand on it, but it looks identical to this.

Next question: In the manual for the shocks, it has lots of tables and methods for calculating the "correct" pressure. Do I need to follow those, or can I just play around until I find a pressure that works for me? Surely there are tradeoffs between harder and softer, so "correct" is kind of subjective anyway...

(Sorry to be a noob - never had suspension before )

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Old 08-07-09, 12:32 PM   #6
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Quote:
Originally Posted by stevage View Post
Scratch that, I finished rummaging through all the packaging that came with the bike, and they included a shock pump! Sweet! There's no brand on it, but it looks identical to this.

Next question: In the manual for the shocks, it has lots of tables and methods for calculating the "correct" pressure. Do I need to follow those, or can I just play around until I find a pressure that works for me? Surely there are tradeoffs between harder and softer, so "correct" is kind of subjective anyway...

(Sorry to be a noob - never had suspension before )

Steve
I'd use their recommendation as a starting point for sag and and adjust in small increments from there until you find the setting that works best for you. Glad you found the pump in the box, thought it was a bit odd the bike didn't come with one but never bought a Giant. Most of the shock pumps are just rebranded anyways, no worries.

As to using just a pressure gauge, not a great idea unless you know how much pressure you lost using the gauge alone and compensate on the fill accordingly with another pump...too complicated, shock pump much better. On that note, when you reattach your shock pump you will see a lower value than when you last used it...that's the air being used to "power" the gauge...
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Old 08-07-09, 02:40 PM   #7
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Another advantage to having the pump is you can adjust the rear shock pressure as needed during your ride. The rear shock on my Jeckyl has no lockout, so I pump it up to 150lbs. to keep it stiff for long climbs such as forest service roads, then let the pressure down to get travel back for the fun stuff. Mine does gradually lose air pressure, but then it's 8 years old.
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Old 08-16-09, 07:23 AM   #8
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Ok, now I've had a few play runs, and I still can't figure out why I need to set up the suspension properly for my weight. I've done a few little jumps, and I don't think I've bottomed out either end. So what's the benefit of carefully calculating the sag and setting it up "correctly"?

Sorry if I'm being dense. It's like with tyres, you can increase the pressure for faster rolling, or decrease it for grip and comfort. There's no "correct" value. You can run high gearing for faster top speeds downhill, or lower gearing for climbing. There's no "correct" value. So why is there a "correct" value for suspension - or if there isn't, what's the tradeoff?

Steve
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Old 08-16-09, 07:49 AM   #9
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I use sag only as a beginning point for experimenting. When I set up my Gary Fisher Hifi,I began by finding the air-pressures that yielded the recommended sag points in the fork and the shock. Then I adjusted until I got the "feel" of the bike where I like it. I actually run less air in my rear shock and quite a bit more (10-15 psi more, depending upon my mood) in my front shock than sag would suggest. I do those things because I prefer a stiff front-end and a forgiving rear.

A few rides confirmed that my settings work out for the way that I ride. So I wrote them down for future reference.

I do want to add that some shocks change their behavior as you move through the travel. The new FOX shocks used on the 2010 Gary Fisher Rumblefish, for example, are designed with a secondary air chamber that opens at the 40%-of-travel mark. If you allow sag to take you to that 40% mark, then the chamber will be open all of the time. That may or may not matter, but it's something to think about.

In the main though, it is reasonable, IMHO, to begin with the recommended pressure, and then adjust up and down until you are happy with the resulting ride.

Once I took a fork and ran it through 5-psi increments, testing it each time in my neighborhood. It was illuminating to do that many back-to-back tests and note how the decreasing psi -- I began with a high value -- affected the ride. I quit my tests when I almost flew over the bars in my driveway after the psi got low enough to allow brake-dive to totally compress the fork when I tapped the brakes.
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