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Lahar Lovers.

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
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borcester rhymes
The great thing about high pivot idler bikes is that there is little to no effect on the drivetrain from pedalling. unlike a VPP or a mid pivot bike, there's no lockout or [extremely limited] chain torque on the suspension. This creates an ideal setup because only rider movement has an effect on the bike's vertical motion. If you're a good pedaller, there's no effect. If you suck, the bike will bounce.

I think, and this isn't really based in science, that the pivot itself has something to do with it. Since the pivot is not near the center of your weight (the BB) you're further from the fulcrum, which makes for less suspension action. Ride a concentric pivot bike and you'll see what I mean. Every movement you make goes straight into the suspension on those bikes. On a high pivot bike, the effect of the weight's motion is minimized because it's not on the axis.
 

no skid marks

Monkey
Jan 15, 2006
2,511
29
ACT Australia
There is actually an affect from the chain,it's not noticable but to be perfectly correct without a doubt there is a miniscule affect. Same as on your Racelink,the chain sitting up on sprockets means that the chain is elevated above the pivot and rear axle,therfore trying to pull it up as you pedal,yes I'm being a Hyperchondriac again but otherwise flyingfatman that was will come and break my balls,well yours.Compared to most other bikes though it's not even on the scale.
I wouldn't say cornering is worse,just requires a different style.
The bennefits of a high pivot is not only the pedalling,a concentric pivot will offer that.It's the more consistent geometry,that when it changes,normally changes for the better(longer wheelbase off drops etc),but mainly it's square edge hit absorbtion. Over 90% of hits would come from ridding the wheel into stuff,a high pivot enables the suspension to track with the impact and absorb it,rather than the bike just having to bounce up over it.
They do take a bit more finesse to manual though.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
we've been over this before...and i'm not arguing it. The question of pedalling was brought up, and I just wanted to try and explain it as best I could.
 

no skid marks

Monkey
Jan 15, 2006
2,511
29
ACT Australia
we've been over this before...and i'm not arguing it. The question of pedalling was brought up, and I just wanted to try and explain it as best I could.
Fair enough.I'd just made the same statement in the past and got grilled by the flyingfatman and was trying to avoid you that encounter. I like your idea about the pivot hight in relation to bobbing,I'd not really thougt about it like that before.
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Basically high pivots (assuming chainline is parallel to the swingarm) resist squatting/bobbing under power because the force that accelerates you forwards (that's the tyre's traction being transferred to the frame via the axle) creates a moment about the pivot that tries to extend the suspension, while your weight being shifted backwards simultaneously tries to compress it. If you calculate this stuff right so that the rearwards weight shift is the same as the extension force, they cancel out and you get no movement.
 

dhkid

Turbo Monkey
Mar 10, 2005
3,358
0
Malaysia
Basically high pivots (assuming chainline is parallel to the swingarm) resist squatting/bobbing under power because the force that accelerates you forwards (that's the tyre's traction being transferred to the frame via the axle) creates a moment about the pivot that tries to extend the suspension, while your weight being shifted backwards simultaneously tries to compress it. If you calculate this stuff right so that the rearwards weight shift is the same as the extension force, they cancel out and you get no movement.
that was what i was wondering about, great stuff.
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Question for everyone who thinks rearward axle paths are the way to go: What happens in rebound? Is the advantage somewhat negated?
You mean because now the wheel is moving in the direction of whatever bumps are coming towards it (ie forwards)? Doesn't really matter unless there is an obstacle there, in which case it will have to move backwards to absorb the bump again anyway.

As far as pedalling performance and bump absorption (including traction) go, rearwards axle paths are as a general rule superior (of course, if you have a high pivot bike with a conventional chainline it's going to pedal like crap, I'm talking about well-designed ones) - those two things are quantifiable. Not to say you can't make a bike pedal extremely efficiently with a relatively vertical (or only slightly rearwards) axle path, but you don't have - on paper at the very least - the same benefits regarding very low chain pull effects. However, there is most definitely a point where chain pull becomes negligible/insignificant and according to the figures I've punched out and the bikes I've ridden, most low/mid pivot bikes are fine when it comes to pedal feedback... 222s and the like are pretty bad on most bikes it's realistically not much of an issue.

However, rearwards axle paths can make bikes handle strangely (how good/bad this is depends on who you ask, so obviously it's pretty subjective) and often the bikes end up having very long chainstays. Again, some people say this is good, some people say it's bad, my personal opinion is that it depends on the speed you're traveling at at the time... going flat knacker I've never ridden anything that felt as planted as a Lahar (including in fast open corners) but by the same token, stability is the inverse of agility - anything that is super stable at high speed tends to be slow handling at lower speed, and the reverse is also true - bikes that handle quickly at 15km/h (like say XC bikes) are not good at all when you're doing 3 or 4 times that speed, they're just sketchy.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
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borcester rhymes
Just curious, how does the lahar do in slow speed situations? Picking your way through a rock garden? We all know it destroys things at high speed, but the slack angles and long wheelbase sketch me out when the going gets tight.
 

OGRipper

back alley ripper
Feb 3, 2004
10,647
1,116
NORCAL is the hizzle
You mean because now the wheel is moving in the direction of whatever bumps are coming towards it (ie forwards)? Doesn't really matter unless there is an obstacle there, in which case it will have to move backwards to absorb the bump again anyway.
Great post, but isn't the above a little too convenient? Seems there are times when your bike is rebounding in bumps, otherwise (for just one example) you'd be bottomed out after the first few hits on a washboard. Just curious, it's something I've always wondered about when people tout the benefits of a rearward path.
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Just curious, how does the lahar do in slow speed situations? Picking your way through a rock garden? We all know it destroys things at high speed, but the slack angles and long wheelbase sketch me out when the going gets tight.
The only time I really noticed it not wanting to do what I wanted was in those kinds of corners where you come down something steep and have to square off at the bottom - when you g-out like that the back end gets really long and doesn't want to snap around, it sits your weight a long way forwards or something. Honestly though, I rode the bike a year ago (and only got one day of runs on it) so I can't be much more specific than that. Never had any issues weaving through stuff in a relatively straight line though... just tight corners where you want to be aggressive but kind of can't.

Be interested to hear Dazz's and xy9ine's opinions of the tight-corner thing... I'm wondering if it's possible to change your technique to suit, I didn't get enough time to really try that.

Great post, but isn't the above a little too convenient? Seems there are times when your bike is rebounding in bumps, otherwise (for just one example) you'd be bottomed out after the first few hits on a washboard. Just curious, it's something I've always wondered about when people tout the benefits of a rearward path.
Well yeah the wheel has to rebound at some point between bumps, but I'm not understanding how it's necessarily going to be any different to a normal low pivot/vertical wheelpath bike there... or do you mean just the extra inertia/momentum of the wheel moving "forwards" towards the next bump as it rebounds? Don't think that'd be much of a horizontal speed difference between a low pivot and high pivot bike's rear wheel there, but there is a big difference in the vertical wheel speeds required to get over a big bump between a low and high pivot bike - high pivots can take a lot longer to move the wheel out of the way, which means lower shaft speed and far less of a jolt to the rider.
 

dhkid

Turbo Monkey
Mar 10, 2005
3,358
0
Malaysia
socket, if you dont mind me asking, what did/do you study at uni? and what do you do for a living? you seem to know loads about vehicle dynamics and damping and everything really. i am doing aeronautical engineering right now but i am getting pretty interested in the whole vehicle dynamics/damping thingy.
 

OGRipper

back alley ripper
Feb 3, 2004
10,647
1,116
NORCAL is the hizzle
Well yeah the wheel has to rebound at some point between bumps, but I'm not understanding how it's necessarily going to be any different to a normal low pivot/vertical wheelpath bike there... or do you mean just the extra inertia/momentum of the wheel moving "forwards" towards the next bump as it rebounds? Don't think that'd be much of a horizontal speed difference between a low pivot and high pivot bike's rear wheel there, but there is a big difference in the vertical wheel speeds required to get over a big bump between a low and high pivot bike - high pivots can take a lot longer to move the wheel out of the way, which means lower shaft speed and far less of a jolt to the rider.
I am merely an e-enginerd and I'm not entirely sure I understand everything you're saying. I just keep thinking that the benefits in compression might be somewhat negated in rebound, particularly in really rocky conditions. But maybe not.
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
socket, if you dont mind me asking, what did/do you study at uni? and what do you do for a living? you seem to know loads about vehicle dynamics and damping and everything really. i am doing aeronautical engineering right now but i am getting pretty interested in the whole vehicle dynamics/damping thingy.
Automotive engineering... currently doing Praktikum (internship/work experience stuff) at Continental Teves in Germany, working on automated braking functions for cars (eg ABS, traction control, ESC, cruise control braking etc). Still got another year of classes to go though once I finish this.

Doing aero engineering you will most certainly study mechanical vibrations at some point, which is the basis of everything to do with suspension. If you can understand how a damper works and why it's necessary to have one (rather than just running nice big top out and bottom out bumpers), it's not a big step to understand the different aspects of suspension tuning IMO. No doubt you'll pick it up alright.
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
I am merely an e-enginerd and I'm not entirely sure I understand everything you're saying. I just keep thinking that the benefits in compression might be somewhat negated in rebound, particularly in really rocky conditions. But maybe not.
I can kinda see where you're coming from (I think) but the wheel is only rebounding when it's not hitting an actual bump (ie between bumps) and so the axle path during the rebound stroke is nowhere near as important as during the compression stroke. Once it hits another bump, the wheel will have to change direction from rebound to compression stroke - as you say, you could end up with bottoming issues on really fast bumps if the bike was unable to rebound enough, but that's why you have to run your rebound sufficiently fast that it can extend enough before it takes the next hit... that's universal for all bikes/vehicles though.
 

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
On my Demo which has a long front end as well, you have to manual the bike and whip it around tight corners if you can or just go easy.

You have a Sunday now Socket, right? How do the 2 compare as far as medium-fast speed conditions and when it's chattery/loose?
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Sunday? Nah... got ye olde 04 SGS :)

Interesting that you say that about the demo though, from the Demo 8 I rode I found it to be quite a good-cornering bike - because the front end is longish (keeping in mind I'm fairly tall and most bikes are too small for me) and the rear end is short, I found it easy to get over the front end and just shove the rear end around wherever you want it. Definitely the easiest bike to do cutties on that I've ever tried.

Depends on ya riding style I suppose... honestly I don't even think it matters anymore. 95% of riders adapt to the bike, 4.9% have a placebo-induced buying disorder, and the other 0.1% have a genuine reason to say "X bike is not good enough for me because it's too ____ and not ____ enough"... don't think I'm in that 0.1% personally.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
Agreed...

I could probably ride anything and have a good time if it were properly tuned, but I'm too picky for my own good. I will say the turner I rode for a day sucked over choppy terrain...whether by shock or design, and that spoiled my appetite. So maybe I do know what I'm talking about....maybe...

Although I will say that many of that above .1% described probably frequent this and other boards...
 

KnightChild

Chimp
Sep 17, 2006
48
0
Noo Zealund
I am merely an e-enginerd and I'm not entirely sure I understand everything you're saying. I just keep thinking that the benefits in compression might be somewhat negated in rebound, particularly in really rocky conditions. But maybe not.
If you've ridden a Lahar through a rock garden, you'll know that weaving through rock gardens isn't the correct method on this bike (no matter how rough it is). Straightline it at speed and it'll feel like you're riding a few tiny treeroots.

I think I understand what you mean about the rebound stroke of the suspension - that the wheel moves forward?
Consider this: The rear wheel of the lahar is designed to move at the same angle as the front wheel (think of the headangle - 65deg?).
Do you have any issues during the rebound stage of your front forks?
In fact it gives you more grip since the wheel is moving towards the next bump as you're going forwards, maintaining as much contact as possible. (and as Socket says, the advantage of a slack wheel path is that your forks and shock have more time to deal with the impact.)
 

xy9ine

Turbo Monkey
Mar 22, 2004
2,940
353
vancouver eastside
Just curious, how does the lahar do in slow speed situations? Picking your way through a rock garden? We all know it destroys things at high speed, but the slack angles and long wheelbase sketch me out when the going gets tight.
the numbers worried me a bit, as my previous bike had a 2º steeper ha, and a stubby rear, but its actually surprisingly capable in the tight tech stuff. even works fine on slow speed ns skinnies. ride off the back & the front can push; a more centered / aggressive position works well, and the bike carves tight radius stuff nicely. it took a bit of an adjustment coming off the pdc, but its feeling dialled now. i like it lots. as socket mentions, we're adaptable beasts; most of us can easily adapt to variations in geometry - almost all modern dh frames are in the ballpark.
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
Agreed...

I could probably ride anything and have a good time if it were properly tuned, but I'm too picky for my own good. I will say the turner I rode for a day sucked over choppy terrain...whether by shock or design, and that spoiled my appetite. So maybe I do know what I'm talking about....maybe...

Although I will say that many of that above .1% described probably frequent this and other boards...
For sure - most riders can tell the difference between one bike (or suspension type/setup) and another... whether or not that's the difference between having fun or not (or winning a race) is up to you. The 0.1% of people I was referring to as pro racers where the bike might actually make a difference to their result. However, at the end of the day, nothing ever feels as good as your own bike - cos you know exactly how to ride it, and when you're used to it nearly any bike is decent.

All that said... when you're paying a few grand for a bicycle FRAME it's fair to want it to be as good as possible!
 

no skid marks

Monkey
Jan 15, 2006
2,511
29
ACT Australia
I dunno about that,I think it makes alot more difference for us punters than it does the pros,anything is fun though. A mate just recently went from ridding his DH Comp to a Glory and knocked seconds off his times imediatly.