 You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
After not using the bike for 1 year my 2013 Reverb has started sagging a few mm when I sit on it. Is this few mm likely to increase over time and, if so, how quickly and how badly? Also, what's the cure? Off on holiday in 9 days and wondering whether to just leave it well alone. Ta v much.
Have you checked the air pressure?
No, not yet. Is this the likely culprit?
Mine's always been like that, despite working perfectly. It really is only about 3mm, so negligible as far as I'm concerned. But if yours wasn't doing this, and now started, I'd be interested to know what might cause it (assuming it's not just due to low air pressure)....
Post has been 100% fine up until now, and it's been used hard for a couple of years. Pretty sure the new sag (probably between 5 and 10mm) is somehow a result of not using it.
The sagging is due to air bubble(s) in the oil inside the post (not the remote lever / hose, etc, which is a completely separate system).
How it gets there is open to debate - I've never seen a definitive answer (it's the IFP doesn't count! 🙂 ) - but it involves an internal seal somewhere leaking. Certain things, like pulling the seat up (e.g by lifting by the seat while the post is lowered) can be argued to make this more likely, but it's not the definitive cause (IMHO). (Another possibility is one of the 'O' rings acting as a sliding seal 'rolls' occasionally, allowing some air past - maybe more likely if the post has been static for a long time...)
The increase in pressure when you sit on the seat compresses the air bubble(s) and the seat post sinks a little to take up the space. The oil in the post is at the same pressure as the air chamber, so if the air pressure drops, the bubble in the oil gets bigger, making the sagging worse. Pump the air pressure back up and the bubble(s) shrink again, but they're still there.
Given that you've got some sag, there's a path somewhere that's allowed air into the oil, so it will probably continue to do so, making it get gradually worse, but it could take years. (IIRC SRAM have a figure for what is 'acceptable' sag - 4mm??).
I had exactly the same problem with mine. Was worried it was complicated, but the simple solution of pulling the post out, putting the recommended pressure in, has sorted it ever since.
I just assumed that over the years air had at a micro level been getting out ... was down to some very (relative to the right number) low pressure.
Hope that works for you else it's down the more complicated route
Wow, cheers for these answers, everyone. I'm guessing you work in the industry, Tillydog, judging by the detailed knowledge. Very useful anyway, so ta v much.
I'm guessing you work in the industry
No bike industry connections. I work in engineering and have some experience of DIY fettling reverbs - they are quite simple once you understand how they work and are subject to the same generic failures as any pneumatic/hydraulic system.
Just trying to dispel some of the 'mystique' 🙂
Mine has done this too but dropping 15mm. Dropped off at the LBS and I'm hoping it will get fixed under warranty as faffing with pressures etc didn't work. Anyone had theirs fixed under warranty please?
Had two fixed under warranty for this exact problem. They usually send you brand new ones (I ended up with a left hand remote instead of my right hand one and longer overall length posts too, which was a little vexing). However LBS would only send them back once the sag got to about 4mm and was beginning to be annoying whilst riding. My replacements have about a tiny bit of sag but it's not annoying yet. I was off the bike for 9-10 weeks this summer due to injury and the only thing I noticed was that because I store them fully dropped they would "push" out themselves about 1-2cm over 2 weeks of no use. I then got the bikes down off the wall and cycled everything as best I could and they'd do it again over 2 weeks (like air pressure heat expansion or something!). Now back on the bikes and they're both fine with the same tiny sag. I haven't checked the air pressure but when I was told do that on my old posts (which were replaced) it didn't fix it for very long. It's a leaking seal inside and that's that. Annoying.
I was under the impression they need stored at full extension?
I had a little sag in my first one 3-5mm, it was replaced under warranty no problem.
It's like anything else semi-complicated on a bike, it should be serviced every so often.
No need to store them at full extension apparently. Makes no odds.
My replacements seem to be doing pretty well - it's almost a whole year for both now. I've heard just as many sag stories about the new B1 models. Mine have never let me down while riding and I've never had to bleed them either. It was the LBS who wanted to send them away and I was happy to take their advice.
Customer service from SRAM on Reverbs has been awesome for the past few years TBF.
I've found a local service shop who do full rebuilds on them so I will take mine there unless SRAM feels like swapping them out for new ones again if they start to sag too badly eventually 🙂