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I just got my first full suspension and I am having trouble getting the rear shock pressure set right. For starters, when i pump the spv up to the desired pressure for my weight, about 100psi, i hear a hiss when i release the air shock pump. (i am using a rock shock pump) I understand some hiss is normal, but if i hook the pump immediately back up, the pressure reads around 65 psi.

Seccondly, when i just sit on my bike, the rear shock compresses about 1/4 of the way down. Riding it around my neighborhood over a few curbs almost causes the black ring to hit the bootom.

So, my questions are: (1) What pressure should someone who is 5 foot 10, 180 pounds use? I dont do much in large drops and dont ride too hard, yet. (2) what sag pressure would you use? (3) Is the rock shox pump i got with my Reba front shock ok to use with the manitou rear shock, and if so, does anyone have any reccomednations besides tightening the inside of the schraeder valve on the rear shock, to keep the pressure in the shock at what it reads before the hiss when i relaease the pump?

I appreciate any and all comments.

justen
 

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your shock pump is the problem

it is not disengaging properly. I posted a fix for this before and a photo (do a search) . Basically you need a small spacer like an o ring in the shock pump head.

jgrech said:
I just got my first full suspension and I am having trouble getting the rear shock pressure set right. For starters, when i pump the spv up to the desired pressure for my weight, about 100psi, i hear a hiss when i release the air shock pump. (i am using a rock shock pump) I understand some hiss is normal, but if i hook the pump immediately back up, the pressure reads around 65 psi.

Seccondly, when i just sit on my bike, the rear shock compresses about 1/4 of the way down. Riding it around my neighborhood over a few curbs almost causes the black ring to hit the bootom.

So, my questions are: (1) What pressure should someone who is 5 foot 10, 180 pounds use? I dont do much in large drops and dont ride too hard, yet. (2) what sag pressure would you use? (3) Is the rock shox pump i got with my Reba front shock ok to use with the manitou rear shock, and if so, does anyone have any reccomednations besides tightening the inside of the schraeder valve on the rear shock, to keep the pressure in the shock at what it reads before the hiss when i relaease the pump?

I appreciate any and all comments.

justen
 

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ride
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jgrech said:
So, my questions are: (1) What pressure should someone who is 5 foot 10, 180 pounds use? I dont do much in large drops and dont ride too hard, yet. (2) what sag pressure would you use?
Set it up with enough pressure in the main chamber to achieve approximately 1cm of sag (25%). You'll have to check by pumping it up and riding gently across a smooth even road. Get off the bike very gently and check the o ring on the shock shaft.

jgrech said:
(3) Is the rock shox pump i got with my Reba front shock ok to use with the manitou rear shock, and if so, does anyone have any reccomednations besides tightening the inside of the schraeder valve on the rear shock, to keep the pressure in the shock at what it reads before the hiss when i relaease the pump?
The pump is fine - there is nothing wrong. The hiss you hear upon detaching the pump is the air leaving the pump. The SPV chamber holds such a small amt of air that it will read a drastic change after reattaching the pump. When you reattach the pump air flows from the SPV valve into the pump and the gauge. Because you've essentially created a larger volume then, the pressure goes down by about 35 pounds. Pump it back up to 100psi. When you detach the pump, 100lbs stays in the shock and the other 100 that was in the pump will hiss out.
 

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I agree with the previous post regarding your shock pump i.e. it's just the air volume in the pump playing tricks on you. The previous poster explained it well enough.

I also agree that you should start by setting the sag to 25% of total shock travel. Make sure you are wearing all your cycling gear and Camelbak etc when doing this to get the correct weight. Small differences in sag will make quite a difference to the ride, so you need to be precise. Rather than ride slowly along level ground, it is more accurate to maesure sag by sitting stationary on the bike in your normal riding position. Use a wall or something to prop yourself up. Be careful not to bounce on it when getting on or off though. Before you do this it's a good idea to ride the bike for a couple of minutes, bouncing up and down on it to loosen everything up. Don't be afraid to experiment with sag settings - some people prefer nearer 30% or more for a plush ride. Obviously, if it bottoms out harshly you need to reduce it.
 

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You should not lose 35 psi taking off and putting back on a shock pump on a 3way. My 3 way only loses about 10psi doing that.

I had a problem with a rockshox pump and my 3 way. it would start to hiss air after only a few turns screwing on the pumphead. Once fixed, there should only be a short hiss just as the head is removed (i.e in the last turn of the pumphead)

For 180 lbs, 100-120 psi is the range. I run 120 on my RX, and I am 185 and only have about 1/4" sag.
 

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heatstroke said:
You should not lose 35 psi taking off and putting back on a shock pump on a 3way. My 3 way only loses about 10psi doing that.
I think he was talking about the SPV pressure, not the main pressure. The SPV volume is very small and the amount of pressure you lose (when re-connecting the pump) depends on the air volume of your pump. I have 2 shock pumps. One loses about 15 psi and the other about 30 psi when re-connecting to the SPV valve. Both of them lose less than 10 psi re-connecting to the main pressure valve. This is because the relative volume of the main canister is much bigger, so the pump volume has less influence.
 

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If it feels good, it is good

Even if you don't trust the pump, you can trust your senses. If you pump up the IFP, ride, and it feels utterly devoid of platform or you have to go way over the recommended pressure in the air spring to get the proper sag, then maybe it IS the pump.

But I tend to agree with the other posters that the hissing and indicated pressure loss is totally normal.
 

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shouldn one experiment with the main air chamber..

as well? My 3 way was way harsh even with the proper sag setting, which was caused by having too much pressure in the main chamber. The way I understand this shock (please let me know if I am wrong as my understanding of it is very limited!) is that the spv pressure initially resists compression but once it is overpowered, the main chamber does the rest of the work until the shock is about to bottom out, where the spv air volume creates a progressive resistance at the end of the travel. If this understanding is correct (again, set me straight...), would it make sense to experiment with the main chamber pressure first so that dampning and rebound are good and then set the spv pressure to resist pedal induced motion?

One thing I can say for certain is to be careful threading on air pumps on those valves as they are fairly weak!
 

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Valve extenders...

jgrech said:
I just got my first full suspension and I am having trouble getting the rear shock pressure set right. For starters, when i pump the spv up to the desired pressure for my weight, about 100psi, i hear a hiss when i release the air shock pump. (i am using a rock shock pump) I understand some hiss is normal, but if i hook the pump immediately back up, the pressure reads around 65 psi.

justen
I just did two things that seemed to help get the pressure right in both chambers of my 3-way. First, I replaced the shrader valve in the main chamber with a new one bought from an automotive store (very cheap and they sell a valve removal tool as well, which is just a few bucks) as the old one was too long and I would loose to much air when I unscrewed my air pump.

Also at the automotive store, I bought some steel valve extenders (again real cheap). As my shock valves are kind of hard to get to (intense tracer) the extenders make unthreading the pump much easier and faster, which helps with not loosing as much air when taking the pump off.
 

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Te mortuo heres tibi sim?
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i was having the same problems. 3-way coil swinger, losing waaaaay too much air when undoing my shock pump. rather than mess with the vavles, i found a pump that worked far better. you thread the outer part around the air valve, and the inner part that engages the inner valve core threads in afterwards. pump up the shock, reverse the process. abit more time consuming, but fixed my problem. also ground down the end of the pump head to get a bit more clearance.

i found that the "standard type" shock pump i had would hit the shock body before it was threaded onto the vavle all the way. no problems with this pump, especially after the grind job.

http://www.performancebike.com/shop/profile.cfm?SKU=17604&subcategory_ID=5423
 
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