almost full sprocket utilization and engine efficiency (possible dumb question) =D

[FurryOnTheInside]

I've used both in industry.
Spring idlers are for single direction steady loads. No reversing, power in one direction only, no shock loading.
The best were rubber cored tensioners like pictured below.
The rubber adds some damping to the arm. Spring tensioners are typically quieter.

On a reversing, shock loaded, variable load system (like most bikes are) a fixed tensioner would be a better choice "by the book".

A light/soft spring tensioner with travel limited to minimum would be an ideal solution, I agree.
Have not seen one yet. Maybe something like this could be made into ideal?

Steve

My thoughts are that a spring being constantly compressed wastes (some) power, but a fixed idler makes no allowance for the eccentric HT drive sprocket and/or wheel sprocket. That is why I thought a light spring is best. When the chain is at it's tightest spot in the cycle (once every 220 revolutions of the rear wheel with 44t rear sprocket) and when it's function is reversed, the soft spring would be compressed as far as it's (adjustable screw?) limiter, but when the chain is slackest it should be only compressed by the weight of the returning chain, so applying almost no load to the chain.
The picture appears to show an adjustable preload, great for switching from bumpy roads to smooth racetrack; but no limit to the spring's movement other than it's own. The part it would like to see when I look at the picture you posted is a bolt poking down next to or inside the spring.
I thought maybe there is something for "fixies" and single speed cycles built on bike frames with dropouts (lacking the proper rear facing forked wheel mount that you generally see on BMX bikes) but the idlers that I have seen so far appear to favour quick wheel installation over maximum efficiency so they are just sprung with lots of preload and really no limit until the chain pulls tight (so it does allow the top to go slack during pedal braking, eek!) just like an ordinary derailleur. Which does lead me to question the actual amount of power loss and whether it really is worth worrying about, whether it is fixed by the spring strength and preload or varies with the power put in.. and I really dont know.

 

[HeadSmess]

no worry about getting the sprocket concentric...i am yet to find a chain that wears evenly anyways. after 10,000km or so...kachunk ka chunk kachunk.


nope, the whole thing isnt worth worrying about. you can run an amazing amount of slack on a chain before it starts spitting. just set the fixed tensioner so you get 20mm or so slack in the tightest spot, then forget about it until it starts flinging off, breaks, or has worn enough to mandate checking...

never have a tensioner on the tight side. a guide, maybe, but no tensioner. it has to take the pressure of engine power driving the load. they never hold up, add to the wear, blah blah.

 

[FurryOnTheInside]

10,000km on one chain?!
That'll make your sprocket concentric.

 

[HeadSmess]

just replaced my moto chain after 20,000... thats about the standard life of a motochain bit less, bit more, depends on the bike and the maintenance.

and no... the sprockets get WORSE with the amount ive done on them. might be time to change em, as youre meant to when replacing the chain.... cost more than the freaking chain does though!

 

[FurryOnTheInside]

just replaced my moto chain after 20,000... thats about the standard life of a motochain bit less, bit more, depends on the bike and the maintenance.

and no... the sprockets get WORSE with the amount ive done on them. might be time to change em, as youre meant to when replacing the chain.... cost more than the freaking chain does though!

Crikey, I've never had a bicycle chain last that far. I just replace when ten links measure more than 25.55cm (new is 25.4cm).. I couldn't say how far that actually is. Sprockets AFAIK only need replacing when they seem to be accelerating chain wear, or if chain replacement was delayed too long (25.7cm) then run the worn out chain and sprockets as long as possible then replace both together.

 

[skyash]

I got that tensioner in the pic at work i have takein one home to try but will the rubber in sides hold up? And I like how thay have a kg on them. Mine is 0 to 15 kg and have a hard and mid hole.

 

[skyash]

At the moment. Hard to see but it's a stock tensioner with a kick stand spring to the top back wheel fork adjustable.

 

[Steve Best]

I like your ideas Furry, but as usual, I think Headsmess has it pegged.
Chains can run efficiently with huge slack. A light spring tensioner with limits might let it run quieter however. Is it worth the bother?

The picture shown was a stock one from off the internet as an example and Headsmess is right, you'd never want to run it on the drive side.

Steve