Rear shock losing pressure

plife

Set up my rear shock (Rockshox Monarch 3.3) on my Boardman FS Pro according to the instructions (1 psi for 1lb body weight) so put 220 psi in. I have been on 2 rides at Bedgebury Forest and after both the pressure had dropped quite a lot and was 150 psi after the last ride. This being the first FS bike I have had am not sure if this is normal! Front shocks don't have the same problem.

.blitz

Rear shocks only contain a small volume of air and are sensitive to changes in temperature, but even so 70psi is a lot to lose in one ride. Time to put Halford's after sales to the test.

ride_whenever

how are you measuring the pressure? Shock pump?

Does the seen sag change?


I'd imagine it is leaking when you put the pump on.

Bar Shaker

Mine (a 4.2 on the same bike) doesn't lose 1psi a week where as I expected it to lose some. I have used my shock pump once to set the pressure and once to fine tune it, this year.

I think the 1psi per pound thing is a bit high. You should set your shock by the sag and should get around 25-30% sag when sat stationary on the bike. There is a scale on the shock. Raise the rubber ring, carefully get on, feet up and then carefully get off. See where the rubber ring settled.

As your shock will be running at up to 800psi under riding conditions, some loss is to be expected from each ride. The limit for the shock is 275psi (static pressure) but this will be when the shock is cold. It gets hot during use and your pressure may be up to or exceeding the limit.

I would re-check the sag and see if a lower pressure will work. You want just enough that it doesn't bottom out during a ride. If it doesn't leak from that, all well and good. If it still leaks then ask Halfords to replace it at the six week service. Tell them beforehand so they have one in stock for you.

One last point which you may already know, just checking with out re-inflating will reduce the pressure as removing the pump causes a small amount of air to escape. If you pump up, remove pump and refit the pump, the pressure will always be slightly lower.

http://www.sram.com/en/service/rockshox/view.php?catID=2&subcatID=6

plife

ride_whenever wrote:

how are you measuring the pressure? Shock pump?

Does the seen sag change?


I'd imagine it is leaking when you put the pump on.

Yes measuring using shock pump. Not checked the sag will take a look before and after. I assumed I would lose a small amount of pressure puting and taking the pump off, though not that amount!

plife

Thanks Bar Shaker - was that just luck the bike turned up with a 4.2?

I am pretty sure my sag was around 20% after setting to 220psi. I had it set to medium floddgate for the ride and it was not too far from bottoming out.

I will have a play with the pressure and see how a 25 - 30% sag works out and check pressure afterwards. Thanks!

Bar Shaker

Yep, it was on the bike when they lifted it off the stand in Halfords. My guess is the 3.3 parts bin was empty when its was built. I think its basically the same but has compression speed adjustment as well as rebound and lockout. I spent some time setting it up initially but haven't touched it since.

If you end up getting yours replaced and still have problems, there are 'high volume' versions for bigger riders.

Northwind

Are you sure it's actually losing pressure? When you connect the shock pump air will escape from the shock to "charge" the pump so you'll lose shock pressure every time you do that. (it's not leaking, just that the shock pump volume is high enough to make a big difference when it gets pressurised) Small air springs make it really obvious.

Ride it, best way to tell if it's going soft is to ride it and see if it's going soft really

plife

Northwind wrote:

Are you sure it's actually losing pressure? When you connect the shock pump air will escape from the shock to "charge" the pump so you'll lose shock pressure every time you do that. (it's not leaking, just that the shock pump volume is high enough to make a big difference when it gets pressurised) Small air springs make it really obvious.

Ride it, best way to tell if it's going soft is to ride it and see if it's going soft really

I was not expecting such a big loss each time. I haven't really noticed anything over a 90 minute ride but if it was a gradual loss I am not sure I would over differing terrain. It's the first FS I have owned so is very different anyway!