A handling question- Single pivot designs

[McPete]

Hi all,

Today I've been doing a bit of messing around with a few different DH bikes, and seeing how they corner. This is also helping me cast around, looking for my own DH bike (I currently ride an STP for reference).

Of particular interest was a Cove Peeler, in the way that it cornered. Attacking a flat corner with any gusto at all would make the rear end step rather dramatically, as it skipped and juddered across the ground. This was fun, produced some pretty cool rooster tails and made a lot of noise, but it didn't strike me as the fastest way to get around a corner. The fact that the bike did this so easily surprises me.

So, do all single pivot bikes handle like this, or have I been riding some sort of mutant?

 

[bighit05]

its all in the shock settings... normally when a bike is juttering along like that its the rebound is to fast and/or the bike is to upright when drifting


it happened with me when i had my old shock ( had no rebound in it was some crappy x-fusion thing) and it used to jutter along.. but now i got a new rear shock and slowed the rebound up enough and it doesnt do it anymore its much more controlled... but yeh... its on a single pivot bike... so i doubt it would be the suspension design as ive seen it happen on 4 bar designs aswell

 

[NH_]

how did you come into teh corner though, foot off, foot on, sideways or railing

alot of it is suspension settings but you just cant come into a corner sideways with a foot off and expect the bike to rail

 

[McPete]

We've made the bike rail. Once. I'm not sure what I did differently, but it just just squatted in and went.

I'll see if I can dig up a video.

 

[S.]

Nothing to do with the fact that it's a singlepivot, and everything to do with bike geometry, axle path (pivot height), stiffness, tyre pressure, tyre wear, and suspension setup. Your riding technique also plays a pretty big part in determining how much grip you can get out of either end of the bike at any one time.

 

[McPete]

Perhaps I should qualify; It's not just my riding that makes the bike do this, everyone who has ridden it has had the same, juddering slides and almost instant loss of rear traction.

From that, would it be safe to assume, for now, that this is an individual bike problem?

 

[S.]

Perhaps I should qualify; It's not just my riding that makes the bike do this, everyone who has ridden it has had the same, juddering slides and almost instant loss of rear traction.

From that, would it be safe to assume, for now, that this is an individual bike problem?

Yeah, what that is usually caused by is the tyre gripping and then slipping again as it slides. This usually means that the bike has quite a bit of flex in it somewhere, in my experience usually in the swingarm or the rear wheel. Check the spoke tension, see if you can flex the swingarm a lot, and try pumping the tyre up to a much harder pressure, then try again and see if it does the same thing.

 

[Tazed]

Yeah, what that is usually caused by is the tyre gripping and then slipping again as it slides. This usually means that the bike has quite a bit of flex in it somewhere, in my experience usually in the swingarm or the rear wheel. Check the spoke tension, see if you can flex the swingarm a lot, and try pumping the tyre up to a much harder pressure, then try again and see if it does the same thing.

Second that - if the frame's flexing sideways under load.
It'd also be good to know more about the shock settings:

That's a pretty decent shock, but could easily set up wrong, as some setting combinations could easily make the shock work badly.
Too high a spring rate (stiff spring) or over-damping, compression or rebound, can cause the same effect.
Anything that packs up the back end could explain why everyone (presumably of different heights, weights and riding style) might have felt the same thing.
The same bike just won the US Open DH Championships and Canadian National Champs, so it can't be total crap!

 

[mayo]

hey guys

this peeler mcpete is talking about mine..

the chainstay does not flex, but the rear wheel needs to be constantly trued and spokes always need to be tightened/checked after every ride.i have the bike setup with a 450 pound spring with 150psi in the boost vale (the shock is a dhx3) the rebound is set at medium to fast speed

the rear tyre is about 75% wear (maxxis minion 2.5 60a compound) it is inflated to around 34psi

hope somebody can help clear this up as it is a very disturbing noise everytime i hook into a drift

kind regards zac

 

[jrewing]

i'm with you on needing to tighten rear spokes all the time on my peeler. i run a 400 spring on my 5th. i'm 83 kg plus gear.
the rear on mine is pretty reliable handling wise. the front always seems abit vague on flat loose coners, but thats more me i think

 

[NH_]

60a compound and 34psi arnt doign you any favours

how much do you weigh?

 

[mayo]

85

and only got the 60a as that was the only set left before a race and theyve held up just fine

 

[Donkey-boy]

i'm with NH

i run a 60a minnion on the rear of my 222 but i run about 28-30 psi with a DH tube, doesn't sound like much on paper but you will definatly feel a differance.

 

[chops]

peeler

i had a peeler(its mayo's now) i had that problem when i first got it but fixed by low pressure minion super tacky's 2.35-2.5 with dh tubes and slowed the reboud down on my vivid(on fox shox's slow the rebound down and also the propedal)
hope it helps thier top bikes

 

[Gruntled]

G'day Mayo and all,
My bike (the La Bruja) is a single pivot. If you can get it to shudder/skip when drifting you can have it. But it will skip when the shock is too stiff and the rebound is set wrong. The shock on Skippy the Orange Peeler might have issues (I'm not sure Mayo is very kind to it....) or might just be set up wrong- too much rebound or too stiff or a number of things. Single-pivot designs don't inherently behave like this when running properly.
Never fear Mayo, you can fix it. Play with your shock, or even pull it out and service it (manuals are online, get McPete to help ya- he's a tech wiz).

 

[mayo]

ill have a fiddle around this afternoon with tyre pressures and rebound and what not and see if i can correct the skipping

cheers