[DNW]

The question is in the title, does a shock's performance degrade over time, either riding hours or during a long ride, and how does this happen?

This came up after some observations on a couple recent rides and some feedback from both a shockwiz and riding feel. I ride a Yeti SB130 with a DPX2 Performance rear shock. I weigh about 205 geared up, and have run the DPX2 with about 245 psi. I have about 115 hours on the bike and shock, a lot of that in terrain that is chunky with a lot of descending. Single black diamond type trails, no park or big drops/jumps. I have performed regular air can service on the shock but have not done the 125 hour full factory service yet.

I have been playing with a shockwiz for the last week, and on the last two rides, I have seen a rise in air pressure of about 10 psi after a couple miles of chunky descending, with in increase in the perceived spring rate, the back end feels less forgiving and more stiff towards the end of the ride. The shockwiz says remove air and or remove spacers, but after some time the pressure goes back to where it was before.

What is happening? I assume there is some heating going on, based on the pressure changing, but what else is happening? I dont feel like I am pushing the limits of this shock, would the full factory service improve the performance? Has the oil degraded?

 

[fredcook]

Does Shock Performance Degrade, and How?

Are you asking about degradation over long periods of time, or between service intervals?

Assuming required maintenance takes place on said shock, I don't think much will degrade performance wise until actual metal wears and structural integrity begins in take place. I have an old FS bike still laying around with thousands of miles on it, and it's original rear shock still performs like the day I bough it new in 2003. Yes, it's had many oil and seal changes over the years.

I've never had a noticeable seat of the pants change in performance between service intervals with any shock or fork, other than a little sticktion when an oil change was due.

 

[DNW]

I guess the two questions I have are:

Does it degrade between service intervals? What does the full factory service do to refresh the shock that regular air can service does not address?

Does is degrade on long descents, under heavy active use, say 1000+ feet of descending in rough terrain? If so, what is the mechanism/cause?

 

[Lone Rager]

1. IMO, no until something goes wrong like air/oil leaking, surfaces getting scored.... Air can is just air can seals/glides and oil. Factory service is that but also disassembles the damper and replaces damper wear parts (seals, glides), damper oil, and recharges the IFP (or bladder, etc.)

2. It changes, not necessarily degrades. The shock heats up somewhat affecting oil viscosity and air spring pressure. If you tune cold, then hot will be "degraded". If you tune hot, then cold will be "degraded".

 

[JohnnyC7]

In your case, the main thing happening is the seals are dry which creates extra friction, and therefore heat. A fresh service and oil should reduce that problem

The other thing is the damping oil loses its ability to resist change in viscosity with temperature, ie will become thinner as it heats up than it did when it was new. How big this change is depends on the exact oil used

 

[karpiel]

Will nitrogen seep past seals over time and therefore loose pressure behind the IFP and thus increasing cavitation ? Obviously oil does wear and looses its lubricity over time, experts please chime in to add or correct this.

 

[JohnnyC7]

Nitrogen can leak out for sure which leads to the shock cavitating or sucking air in to the damper. Some shocks do this worse than others and its kind of luck of the draw whether it happens or not, so that is another good reason to get it serviced regularly

 

[jasonp22]

Interesting topic as my shock is in need of a full service and I could swear the rear of the bike starts to get stiff and less forgiving toward the end of long descents.

 

[Dougal]

Pretty much all air shocks suck air into the damper and foam the oil. This results in damper oil that resembles a milkshake more than a liquid. Your damping becomes mushy, adjusters stop behaving like they should, the oil volume increases and it can even be difficult to get full travel.

This is the biggest single reason for damper service. The next is oil leaks which are usually less common (some brands and models are exceptions here).

Surprisingly oil viscosity (once unfoamed) doesn't change much with bike damper use. Even when oil has turned black from use it's viscosity doesn't measure much different to new.

This is different to say engine oils which can suffer significant viscosity breakdown due to higher temperatures more often.