Understanding Suspension: Cavitation

How does a shock with no reservoir (like an old fox vanilla) deal with shaft displacement during compression?

Great information here!! What's your opinion (if any) on BOS shocks?… I have a Kirk on my AM bike and I think its flipping brilliant, although I am not a technical suspension geek. I also have a CCDB Air on my DH bike which I really like as well.

Hard to have an opinion on a whole brand or line of products, but for the most part I like their stuff. It's all very well made stuff, with very low friction, although the spring and damping curves work extremely well for some people on certain frames, and not so well for others. Again though, pretty solid stuff and typically good if not great.

But if you already own one, you know exactly what it's like, so no need to ask my opinion :)

How does a shock with no reservoir (like an old fox vanilla) deal with shaft displacement during compression?

They have an IFP inside the barrel that separates the damping oil from a nitrogen/air charge.

Hard to have an opinion on a whole brand or line of products, but for the most part I like their stuff. It's all very well made stuff, with very low friction, although the spring and damping curves work extremely well for some people on certain frames, and not so well for others. Again though, pretty solid stuff and typically good if not great.

But if you already own one, you know exactly what it's like, so no need to ask my opinion :)

They have an IFP inside the barrel that separates the damping oil from a nitrogen/air charge.

Thanks! Always curious how that worked!

I saw a similar animation elsewhere on the internet, but it's not G rated! ;)

@Vorsprung Suspension

thanks for taking the time to answer my question, I certainly learnt a good deal from your information

from own experiences working as a wrench, I've found a good number of customer have gotten confused with their DB shock setup, due to the wide range of adjustment and number of adjusters on that shock

Is a simpler shock with a good tune, correct spring rate and only perhaps rebound adjustment, more suitable for many riders?

From your experience do many bikes come with specific tunes for the suspension design? (this is something many manufacturers will claim).

Or do many bikes come with a generic tune, and the rider would benefit from a specific tune?

one last question, some years back one of the German MTB mags did quite an in depth suspension test where they took something like a dozen Fox piggyback coil shocks, dyno tested them and found wildly varying results even though each shock had the same specification.

Have you seen this during your experience with different shocks?

@Vorsprung Suspension

thanks for taking the time to answer my question, I certainly learnt a good deal from your information

from own experiences working as a wrench, I've found a good number of customer have gotten confused with their DB shock setup, due to the wide range of adjustment and number of adjusters on that shock

Is a simpler shock with a good tune, correct spring rate and only perhaps rebound adjustment, more suitable for many riders?

From your experience do many bikes come with specific tunes for the suspension design? (this is something many manufacturers will claim).

Or do many bikes come with a generic tune, and the rider would benefit from a specific tune?

one last question, some years back one of the German MTB mags did quite an in depth suspension test where they took something like a dozen Fox piggyback coil shocks, dyno tested them and found wildly varying results even though each shock had the same specification.

Have you seen this during your experience with different shocks?

I wouldn't say removal of the adjusters entirely (so that you only have say a rebound adjuster) is a good thing. What is a good thing is a smaller but more usable range for your adjusters - like what Ohlins are trying to do with their shocks, and like BOS have always done (the adjustment range on those is really quite small).

What Fox claim as say a "Medium" tune can vary quite a bit, esp from year to year. Unless those guys actually pulled the things apart and verified that the valving was the same, I would say they've simply missed that. From running them on the dyno, Fox stuff is typically very consistent between one shock and another. Where Fox shocks in the past have not been so consistent is with heat - because the Boost Valve is dependent on the air/nitrogen pressure in the shock, when the oil heats that air/nitrogen up it increases the pressure, all the while the oil is getting thinner as the temperature increases (although the stock Fox oil is one of the most thermally stable oils on the market FYI). As a result you end up with increased end-stroke compression damping, and decreased low-speed rebound damping. This is one of the legitimate drawbacks of position-sensitive damping.

one last question, some years back one of the German MTB mags did quite an in depth suspension test where they took something like a dozen Fox piggyback coil shocks, dyno tested them and found wildly varying results even though each shock had the same specification.

I have to say I was pretty surprised to read that Fox only implemented full dyno testing for quality control and consistency last year… Up until then just a guy with a hand dyno going "yep, feels okay to me"…

http://www.pinkbike.com/news/fox-36-float-rc2-talas-first-ride.html

@Vorsprung Suspension

thank you for your continuing replies to my questions

another question.

since suspension appears to be a lot more complex than many layman (or laywomen) may assume, does the shock tune / setup actually play a larger role in the overall experience of riding a full suspension bike, than the suspension design itself does?

in other words, would a simple single pivot design with a dialled setup ride "better" than a short-link virtual pivot design with a bad tune or incorrect setup.

Or does some inherent advantage in the second example, overcome or mask to some degree a bad tune or setup?