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How to keep the back end down

tofu21tofu21 Posts: 359
edited February 2012 in MTB workshop & tech
:D:D:D Hello,

I'm starting to make some real progress in getting used to the new Pivot Mach 5.7 Carbon.

A mixture of me learning how to ride it and some tweaks to the setup seem to be making a huge difference.

I went round Llandegla on Saturday and had a scream on it. It's a brilliant bike but seems to be far more tempramental to setp and ride than my old Stumpy. I don't know if that's just the way it is when you go from 120mm bike to a 150mm bike.

What I have noticed is that the back end seems to pop up on me which caused me to almost deck it. It was most evident on rollers. I'm not trying to grab loads and loads of air just wanting to get to the bottom as quick as possible and having a great time doing so :D

I've got the rebound set quite quick, about 3 clicks off quickest as per the Pivot instructions. Having the rebound set quick seems to be the key to reduce peddle bob and going through all the travel.

I'm thinking it's my lack of ridding ability that's the problem. :oops: Any tips on what I can do to keep the back end in place?

Thanks
Simon

Posts

  • nicklousenicklouse Posts: 81,520 Lives Here
    Slow the rebound down then.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • tofu21tofu21 Posts: 359
    Slowing the rebound means that the rear shock develops a lot of peddle bob and blows through it's travel very easily.

    I'm thinking it's a ridder skill issue more than a bike setup issue.

    Is it just a matter of getting my bum over the back end more?
  • benpinnickbenpinnick Posts: 4,148
    Pedal bob is better controlled through the low speed compression damping, as using rebound tends to be reactive, and will cause the bike to squat more. You'll find that the 'anti-squat' characteristics of your bike do make it prone to more agressive rebound from mid stroke to fully extended. This is the opposite reaction to what makes anti-squat work (a rising rate as you accelerate to counter the increased loads that acceleration puts on the shock over and above absorbing bumps). You're going to find it happens no matter what you do, so you need to work around them with your riding style.

    If it were my bike, I would invest in a CC DB air, assuming they are as good as they should be. This will give you much better control over these aspects.
    A Flock of Birds
    + some other bikes.
  • nicklousenicklouse Posts: 81,520 Lives Here
    tofu21 wrote:
    Slowing the rebound means that the rear shock develops a lot of peddle bob and blows through it's travel very easily.

    I'm thinking it's a ridder skill issue more than a bike setup issue.

    Is it just a matter of getting my bum over the back end more?
    It can not do that. All it does is slow the speed at which the suspension extends.

    Bob is more to do with compression and any low speed controlls that the shock may/not have and are normally seperate to rebound.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • tofu21tofu21 Posts: 359
    nicklouse wrote:
    tofu21 wrote:
    Slowing the rebound means that the rear shock develops a lot of peddle bob and blows through it's travel very easily.

    I'm thinking it's a ridder skill issue more than a bike setup issue.

    Is it just a matter of getting my bum over the back end more?
    It can not do that. All it does is slow the speed at which the suspension extends.

    Bob is more to do with compression and any low speed controlls that the shock may/not have and are normally seperate to rebound.

    Sounds like I need to understand the rear shock more!

    Will faster rebound help stopping the shock blowing through all of the travel on smaller hits?
  • cooldadcooldad Posts: 32,601
    Depends whether it's bottoming after one bump or a succession. One needs compression stiffening up. Series needs rebound speeding up ie less rebound damping.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

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    Parktools
  • benpinnickbenpinnick Posts: 4,148
    What shock do you have on the Pivot?
    A Flock of Birds
    + some other bikes.
  • styxdstyxd Posts: 3,234
    Sell your bike & buy a hardtail. Not only are they a more appropriate bike for langdegla, they are also much cheaper, easier to understand and they'll tech you how to ride a bike properly.
  • cooldadcooldad Posts: 32,601
    styxd wrote:
    I am a troll.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • tofu21tofu21 Posts: 359
    benpinnick wrote:
    What shock do you have on the Pivot?

    It's a RP23 with adaptive logic.
  • tofu21tofu21 Posts: 359
    I think that it could be a case of RTFM.
  • benpinnickbenpinnick Posts: 4,148
    Lol. Not much to read on rp23. You've have 3 controls : spring, rebound and low speed compression (also known as propedal).

    The spring controls the sag and spring strength via the air (you know this so I will skip ahead). Propedal controls the pedal bob, and is either off (0) or 1,2 or full. On the AL
    version (0,1 & 2) are controlled via the dial when the lever is one way (cant remeber which) and the other way is 3/full to reduce pedal bob run it on 3, but you should really be able to get away with 1 on a buke like the pivot. Rebound controls the rate at which the shock returns after hits via the red dial. This is what you want to stop the bucking. I suggest riding the same section over and over until your happy it's tuned out. You might want to consider less air in the can and more propedal if you can't find the right balance. This will slow the return and add sag, but you can compensate for te softness with the added propedal.
    A Flock of Birds
    + some other bikes.
  • bails87bails87 Posts: 13,317
    I think the OP needs to understand what everything on the shock does, as it sounds like there's a little confusion.

    Also, to sounds to me like the OP is possibly a bit too stretched out on the bike. Would a shorter stem help? I know that I get the same thing when riding a bike that's too long for me.
    MTB/CX

    "As I said last time, it won't happen again."
  • tofu21tofu21 Posts: 359
    bails87 wrote:
    I think the OP needs to understand what everything on the shock does, as it sounds like there's a little confusion.
    I totally agree with this. .
    bails87 wrote:
    Also, to sounds to me like the OP is possibly a bit too stretched out on the bike. Would a shorter stem help? I know that I get the same thing when riding a bike that's too long for me.
    I was thinking the same thing. I've swapped a 70mm over from the HT to see how it compares to the original 90 that I had on the bike.

    At the moment I seem to be going for a unscientific approach and changing lots of things at the same time so it's hard to know what differences they are making.

    I think I need to find a shortish loop with a bit of everything in it and spend Saturday morning doing laps and tinkering with the settings one by one until I get them right.
  • The RookieThe Rookie Posts: 27,748
    +1, backing off the rebound to reduce bob is all wrong, I too have just changed the stem to 80mm from 100mm on my HT as the new bars (from Bails - cheers) move the grips forward relative to the clamp and was making the rear feel a bit 'kicky'.

    Other then the pro-pedal he should be stiffening the rear spring (air) to reduce bob and then using the rebound to control the spring rate (so increment them in turn).

    Simon

    Simon
  • styxd wrote:
    Sell your bike & buy a hardtail. Not only are they a more appropriate bike for langdegla, they are also much cheaper, easier to understand and they'll tech you how to ride a bike properly.

    is that right hard tail more appropriate for llandegla?? gonna go next week on mine?? thought about going to coed y brennin but mate blew his cheeks out and said ON A HARD TAIL GOOD LUCK!!! LOL
  • tofu21tofu21 Posts: 359
    Its ridable on either but I think its more fun on a full sus. But its all down to personal preferance.
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