Random thought: Idler Pullys

metadave
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metadave
So, I don't know enough about kinematics to think this one through and this isn't for any particular reason, just chasing a random thought, but...

With all the new high pivot bikes coming out with idlers to compensate for chain growth, what would putting one on any bike do? Would to help free up smaller chain growth and pedal feed back?

In theory, if you made a type of chain guide that attached onto you current ISCG taps that was designed to handle the forces, how would this affect say a normal non-hig pivot bike? Would it be a positive or a negative effect?

Lets not bring added weight and possible drivetrain drag into this, just stick to the above.
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bermslapper69 2/10/2021 8:44am
2/10/2021 8:44am
metadave wrote:
So, I don't know enough about kinematics to think this one through and this isn't for any particular reason, just chasing a random thought, but... With...
So, I don't know enough about kinematics to think this one through and this isn't for any particular reason, just chasing a random thought, but...

With all the new high pivot bikes coming out with idlers to compensate for chain growth, what would putting one on any bike do? Would to help free up smaller chain growth and pedal feed back?

In theory, if you made a type of chain guide that attached onto you current ISCG taps that was designed to handle the forces, how would this affect say a normal non-hig pivot bike? Would it be a positive or a negative effect?

Lets not bring added weight and possible drivetrain drag into this, just stick to the above.
This is actually a pretty interesting thought and I’d love to hear some more educated people’s thoughts on it too. Never thought of this before but might have to 3D something to roughly try it out
willsmooth18 2/10/2021 9:05am
2/10/2021 9:05am
In my eyes the idler pulley is necessary to make a high pivot working well.

But the idler pulley alone will make a negative effect, for sure, on any well-conceived non-high pivot suspension design (unless you can put an idler pulley concentrically to a "standard" pivot... which is not possible without a ridiculously small chainring).
1
joelsman
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joelsman 2/10/2021 9:09am
2/10/2021 9:09am
You want the upper chain line very close or slightly below the pivot for the best pedaling. This is for a single pivot frame, dw, vpp, etc change things.
If the chainline is away from the pivot, this creates a triangle, the pivot, the point where chain leaves chain ring and the point where chain connects t cassette, are the 3 points. With the chain under tension it is trying to shorten one side of the triangle. High pivot will pull tire into ground/ lift yourself with each pedal stroke. Low pivot will sag with each pedal stroke. Bikes used to have 3 front rings so pivots were lower to pedal best in granny gear. Now we mostly only have 1x drivetrains.
1
bermslapper69 2/10/2021 9:10am
2/10/2021 9:10am
willsmooth18 wrote:
In my eyes the idler pulley is necessary to make a high pivot working well. But the idler pulley alone will make a negative effect, for...
In my eyes the idler pulley is necessary to make a high pivot working well.

But the idler pulley alone will make a negative effect, for sure, on any well-conceived non-high pivot suspension design (unless you can put an idler pulley concentrically to a "standard" pivot... which is not possible without a ridiculously small chainring).
What negative effects exactly would be experienced?
brash
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brash 2/10/2021 12:40pm
2/10/2021 12:40pm
I think Scott did this when they were prototyping the new gambler, obviously never made production.

36T front chainwheels and ridiculous speeds mean pedal kickback is a moot point now. The proto must have had a higher pivot point I'm presuming to require the upper idler, but if you have ever ridden a supreme, it's a very surreal feeling having the rear end grow on compression, I personally love the confidence it inspires when hitting sketchy shit.
4
jfkusa
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jfkusa 2/15/2021 12:12am
2/15/2021 12:12am
brash wrote:
I think Scott did this when they were prototyping the new gambler, obviously never made production. 36T front chainwheels and ridiculous speeds mean pedal kickback is...
I think Scott did this when they were prototyping the new gambler, obviously never made production.

36T front chainwheels and ridiculous speeds mean pedal kickback is a moot point now. The proto must have had a higher pivot point I'm presuming to require the upper idler, but if you have ever ridden a supreme, it's a very surreal feeling having the rear end grow on compression, I personally love the confidence it inspires when hitting sketchy shit.
I tried finding the picture of it in old pit bits but came up with nothing. I remember a few years back someone had a pulley that mounted to the uscg tabs. I also remembered it being scott but i haven't been able to find photos.
willsmooth18 2/15/2021 2:27am
2/15/2021 2:27am
willsmooth18 wrote:
In my eyes the idler pulley is necessary to make a high pivot working well. But the idler pulley alone will make a negative effect, for...
In my eyes the idler pulley is necessary to make a high pivot working well.

But the idler pulley alone will make a negative effect, for sure, on any well-conceived non-high pivot suspension design (unless you can put an idler pulley concentrically to a "standard" pivot... which is not possible without a ridiculously small chainring).
bermslapper69 wrote:
What negative effects exactly would be experienced?
Negative anti-squat essentially, aka. squat.

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