High-speed (velocity, not size of bump) descending on rough ground….getting too much vibration

Is the first step to fettling it to increase rebound damping?

What do you mean by vibration?

Are you feeling ‘twangs’ and ‘judders’ as you hit stuff at high speed? Or do you mean the bike feels like it’s bouncing up and down after a hit at high speed?

And what sort of rough ground – is it pebbly, rutted, rooted, etc?

If it’s more of a buzz from pebbles or a similar surface it might just be a simple of dropping tyre pressure a bit on the front, which brings up another question – what pressure do you run the front at?

If you mean the fork /shock isn’t absorbing fast repeated hits well, it’s probably ‘packing down’ and your first step should be to reduce rebound damping (i.e. speed the return up). If that doesn’t help then you probably have too much high speed compression damping, which on most forks/shocks needs internal adjustment.

Is the first step to fettling it to increase rebound damping?

Sounds like it needs reducing, you could try this

https://books.google.co.uk/books?id=_2wkch1SE3QC&pg=PA39&lpg=PA39&dq=mark+fitzsimmons+bracketing&source=bl&ots=u4Z-iwkRzM&sig=sYz7Q1QktawCun-rOw5UPiHnnEo&hl=en&sa=X&ved=0ahUKEwj9ivCz99DQAhUqB8AKHeEWBQ0Q6AEIOTAE#v=onepage&q=mark%20fitzsimmons%20bracketing&f=false

Yes, reduce damping.

You need less damping for lots of small hits (ie fast rough ground), to allow the fork to move quickly. You need more damping when you have big hits, because when you compress the fork a lot it’ll kick you off on rebound.

When I got my first FS I ran it with fast rebound cos it felt great. Then on some innocuous trail there was a rain gulley I hit sitting down and the rebound almost boinged me off the bike. That’s when I learned about compromise in suspension 🙂

Sorry – work and real life got in the way here

Cheers for the replies…yep, it’s just pebbles and loam and twigs n stuff. Vibrations rather than boinginess. So I’ll give the rebound a bit less damping, and maybe see how that feels before checking the HSC

I’ll have another look at the Lopes book too – good reminder there

You have to accept that your MTB is not meant to be a limo. If you try and set it up super plush to soak up ‘pebbles and twigs’ then it’ll wallow around like a mad thing and bounce you off as soon as you hit a bigger bump.

Softer tyres to soak up the little stuff.

Hehe – think I’m only trying to get a view on where to start fettling

I’m not a big jumper and not normally too fast – so happy to have a bit less stiffness and a little bit more boing on the odd occasion that I do let it go. Fork and shock were set up by mojo so I don’t want to go mad on it but just need some advice on which little bit to tinker with first

Cheers molgrips

Btw – was 26psi front and 30psi rear on advice from CP

I’d normally ride 20 front / 24 rear so yeah, there’s probably something in it there too

I’m not a big jumper and not normally too fast – so happy to have a bit less stiffness and a little bit more boing on the odd occasion that I do let it go

It’s not about that. You just need to roll into a rain gulley sitting down, like I did. I was on a 24 hour race at the time, so hardly smashing it…

Have you got too much pressure in your shock and/or forks? Check the ‘sag’ is roughly what you want and then ‘fiddle’ with pressures to see how it affects your suspension feel. In a similar way, sounds like you could play with tyre pressures. Just going on psi isn’t the be all and end all though. It obviously depends on your weight, the volume of your tyre and the side wall stiffness of the tyre as to what you can get away with and what feels right.

That’s part of the ‘fun’ though. GMBN have some good youtube guides to setting stuff up – start there and evolve to your preference. There are no rules; some people like to ‘feel’ the trail, others like to ride a marshmallow and I guess there are many in between.