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Prototype Commencal DH V4

peecee

Monkey
Apr 27, 2012
232
42
Australia
An idler pulley interesting nothing new but they have won races and on a bike that Max was involved with back in the day and which would probably still kick as on a track today aka the VProcess they were miles ahead of everyone else its a shame they never went into production

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ianjenn

Turbo Monkey
Sep 12, 2006
2,499
286
SLO
Just guessing that was about 3% bike and 97% the man on board..

For the kids on here he is the Alien or DH's GOAT .
 

norbar

Turbo Monkey
Jun 7, 2007
9,564
345
Warsaw :/
Just guessing that was about 3% bike and 97% the man on board..

For the kids on here he is the Alien or DH's GOAT .
Probably though Nico was really anal about his bike setup and he was really involved in the process. Still I'm surprised they went that way.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
16,028
1,040
01776
it's a very clean setup, and very polished if it's not being put into production. I've started to appreciate commencals, the single, mid-high pivot and rising rate linkage are pretty nice...but they're just so french. Definitely some Vprocesz influence, but that bike is also 17 years old now? I've also never been a terribly big fan of the way super high pivots corner...there has to be some compromise with axle path between bumps and corners.
 

RayB

Monkey
Jan 31, 2008
745
94
Seattle
Can somebody explain this like I'm a 5 year old...?

If you're using a narrow-wide ring and clutch rear-mech... why do you need an idler pulley?
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,738
843
Because you don't have 650b yet, and if you don't have 650b you need to be punished with all kinds of terrible sacrifices until you give in.

Not sure if you're joking but at the risk of taking the bait, the idler pulley has nothing to do with chain retention, it's just to correct the huge amount of chaingrowth you'd otherwise get (and resultant excess antisquat to the point of substantial suspension extension under pedalling + pedal feedback under compression) due to the higher main pivot location.
 

no skid marks

Monkey
Jan 15, 2006
2,514
26
ACT Australia
I've also never been a terribly big fan of the way super high pivots corner since I read it on the internetz. there has to be some compromise with axle path between bumps and corners.
BMW with 24s experience? Seems your are trying to get in on some of UDIs slippery rear end comments.
Pivot doesn't seem super high. So obviously a compromise they were happy with. Not everyone has the same balance of compromise ideals. I know For DH I and many others prefer high pivot bikes that make you faster overall and more confident. Most people are riding smooth over rough off camber corners anyway, this is were high pivot bikes need a neglegable amount more sensitivity. Far from outweighs the gains though.

Anyone got photos of the linkage on it. Looks like they're using the bump compliance to get away with a docile lighter air shock. I myself don't mind the feeling of air shocks in a high pivot bike, I run one in my Zerode. Not as plush as a coil but still plush in A high pivot bike.
 
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demo 9

Turbo Monkey
Jan 31, 2007
5,911
45
north jersey
I did, I went back to the jedi. Owned every gen so far including the now 650b.

Which hasnt seen dirt yet...

I think this is a cool bike. High pivots are awesome, hopefully it makes it out to production.
 

norbar

Turbo Monkey
Jun 7, 2007
9,564
345
Warsaw :/
I did, I went back to the jedi. Owned every gen so far including the now 650b.

Which hasnt seen dirt yet...

I think this is a cool bike. High pivots are awesome, hopefully it makes it out to production.

How much agility did the 27.5 Jedi loose due to a longer end?
 

demo 9

Turbo Monkey
Jan 31, 2007
5,911
45
north jersey
I have no idea, i have not ridden it yet. So much snow outside...

The bb stayed the same but the axles rose, so i think it will still be plenty nimble, just a different sort of nimble.

It was bonkers last year in the tight stuff, even if it does decrease a little i am sure it will still be great.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
16,028
1,040
01776
It's a really smart design. I love that the pulley is fully enclosed along the axle. It should never bend or come loose. Shock packaged nice and low...definitely one of the best examples of the design so far.
 

frango

Turbo Monkey
Jun 13, 2007
1,456
5
Can any1 tell me whether it is good or not, to have this angle so narrow?

 

bismojo

Monkey
May 5, 2009
271
36
nicely executed, clean design... but with pulley at the main pivot location (technically a bb main pivot / prosquat, chain tension wise) will it bob like crazy?
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,738
843
Seems like a cleaner-than-most excecution of high pivot. I like
I was thinking the same, looks like it won't carry a 3kg weight penalty over a normal bike which is a good start, and doesn't use ugly/heavy non-standard components.

The other big issue with high pivot frames is that a lot of manufacturers go "well we're making a behemoth of a bike to do this high pivot thing, so we may as well put the pivot 3m above the BB and really make the most of it" and then you end up with some pretty undesirable dynamic geometrical characteristics as @Sandwich very correctly points out.

I think the ideal maximum CS growth for the required predictability at Elite/WC speed riders is around ~25mm, which is more than current mid-pivots, but substantially less than current high-pivots. It'd be good to see more elegant designs like this out there though, because it'll make idlers more widely accepted, and then someone can make an optimised racebike out of one. @buckoW
 

4130biker

PM me about Tantrum Cycles!
May 24, 2007
3,904
442
Lizard Town
This PB article says the chain is in line with the pivot.
I'm having trouble envisioning how this pulley placement produces anti-squat... Oh wait...

Sorry typed question too soon, am I correct in thinking that the pulley being above and behind the pivot when pedaling (under sag) would produce anti-squat?
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