Which brands/models chainsets / chainrings have perfect centering?

[silva]

Since my newest bicycle I'm plagued with serious chain tension variation.
First a Sugino now also a Stronglight.
Other causes have been eliminated, I replaced chainring/chain/rear cog with new, still directly a tension variation of 2 cm up and down, which is said to result from a 0.5 mm offcenter bottom bracket part (crank/spider/chainring).
On a previous fixed gear, with a French brand TA Specialities Alize Piste, I never had that tension variation, yet I came across a forum post where some1 ranks TA as number 1 worst on this centering issue.
Since this variation is a pain when having to retension, and it is also felt while cycling (alot less fluent), I want to get rid of it, and go for brands/models that are better machined than this crap.
So who has a chainset / chainring that is (near) perfectly centered?
It's a question for people without derailer, because a spring compensates for the tension variation.

 

[Deleted member 1258]

Since my newest bicycle I'm plagued with serious chain tension variation.
First a Sugino now also a Stronglight.
Other causes have been eliminated, I replaced chainring/chain/rear cog with new, still directly a tension variation of 2 cm up and down, which is said to result from a 0.5 mm offcenter bottom bracket part (crank/spider/chainring).
On a previous fixed gear, with a French brand TA Specialities Alize Piste, I never had that tension variation, yet I came across a forum post where some1 ranks TA as number 1 worst on this centering issue.
Since this variation is a pain when having to retension, and it is also felt while cycling (alot less fluent), I want to get rid of it, and go for brands/models that are better machined than this crap.
So who has a chainset / chainring that is (near) perfectly centered?
It's a question for people without derailer, because a spring compensates for the tension variation.

I've never come across one thats perfect or near perfect. Have you tried centering the chainring on the spider?

 

[Yellow Saddle]

Since my newest bicycle I'm plagued with serious chain tension variation.
First a Sugino now also a Stronglight.
Other causes have been eliminated, I replaced chainring/chain/rear cog with new, still directly a tension variation of 2 cm up and down, which is said to result from a 0.5 mm offcenter bottom bracket part (crank/spider/chainring).
On a previous fixed gear, with a French brand TA Specialities Alize Piste, I never had that tension variation, yet I came across a forum post where some1 ranks TA as number 1 worst on this centering issue.
Since this variation is a pain when having to retension, and it is also felt while cycling (alot less fluent), I want to get rid of it, and go for brands/models that are better machined than this crap.
So who has a chainset / chainring that is (near) perfectly centered?
It's a question for people without derailer, because a spring compensates for the tension variation.

This sounds interesting but I'm confused. Are you saying that the chainring has a run-out of 2cm? In other words, it isn't concentric?
Then, what do you mean by 0.5mm BB off-centre?

 

[Pumpkin the robot]

General tolerance in the machining I do is +/-0.25mm I find it hard to believe that they accept something being half a mm out. Pay peanuts, get monkeys I guess.
You may find that the chain ring has an error and the chainset has one, causing a compound error. You would be able to rotate the chain ring to eliminate some of that if that is the case .

 

[Yellow Saddle]

General tolerance in the machining I do is +/-0.25mm I find it hard to believe that they accept something being half a mm out. Pay peanuts, get monkeys I guess.
You may find that the chain ring has an error and the chainset has one, causing a compound error. You would be able to rotate the chain ring to eliminate some of that if that is the case .

I'm not convinced those figures are right. Something else is going on there, but let's wait, maybe Silva will respond. Stronglight and Sugino have been in the business for a long time, I'm sure they can machine a concentric circle.

 

[silva]

This sounds interesting but I'm confused. Are you saying that the chainring has a run-out of 2cm? In other words, it isn't concentric?
Then, what do you mean by 0.5mm BB off-centre?

1) That 2 cm refers to the distance one can push the chain up and down, so related to the chains tension.
A difference/variation of 2 cm thus means that for ex in a tightest spot of 1 cm up and down, is accompanied by a 3 cm up and down at the most slack point.

2) That 0.5 mm offcenter is the result of a given equation:
- assuming a chain spans (hangs over / distance between sprockets) a distance of 40 cm, then a vertical chain movement in the middle is due to 0.5 mm offcenter of a sprocket.
The equation is
dh= L*sin(arccos(1-dL/L))
dh (deltaHeight) is the tolerance in the middle, total tolerance from highest to lowest point.
L is the tensioned length in the case of a tolerance of 0, so from the rear tooth that engages on the chainring till the front tooth of the rear sprocket.
dL (deltaLength) is the difference in tensioned length in other words the degree of excentricity.

 

[Yellow Saddle]

1) That 2 cm refers to the distance one can push the chain up and down, so related to the chains tension.
A difference/variation of 2 cm thus means that for ex in a tightest spot of 1 cm up and down, is accompanied by a 3 cm up and down at the most slack point.

2) That 0.5 mm offcenter is the result of a given equation:
- assuming a chain spans (hangs over / distance between sprockets) a distance of 40 cm, then a vertical chain movement in the middle is due to 0.5 mm offcenter of a sprocket.
The equation is
dh= L*sin(arccos(1-dL/L))
dh (deltaHeight) is the tolerance in the middle, total tolerance from highest to lowest point.
L is the tensioned length in the case of a tolerance of 0, so from the rear tooth that engages on the chainring till the front tooth of the rear sprocket.
dL (deltaLength) is the difference in tensioned length in other words the degree of excentricity.

Aha. Glad you're still here. Lemme just confirm.

1) You say the chain, at a given position on its drive cycle (upper run), for a given pedal tension, can be pushed up or down with a variance of 20mm, depending on pedal position?

2) OK, I get it, the chain moves up and down as you pedal. Number 2 is just a different expression of Number 1.

Is my interpretation correct?

 

[Yellow Saddle]

One more thing. What you don't say is how often viz a vie say, crank rotations, this oscillation happens. Can you clarity that please?

 

[silva]

General tolerance in the machining I do is +/-0.25mm I find it hard to believe that they accept something being half a mm out. Pay peanuts, get monkeys I guess.
You may find that the chain ring has an error and the chainset has one, causing a compound error. You would be able to rotate the chain ring to eliminate some of that if that is the case .

I've had 2 chainrings of different brands (the one of Stronglight itself that came with their crankset and a UK Velosolo one) and with both I had/have that tension variation, both with 144 bcd.
Before, I had a Sugino XD crankset with a 110 bcd, and also that tension variation.
This all on the same bicycle, that tensions the chain along a bottom bracket eccenter.
My last chainring replacement started with all 3 drive components new, eliminating remaining components as cause.
At the time of the Sugino XD, the tension variation started with 2 cm, then gradually grew (due to wear) to 4 cm, likely due to another reason, a gear ratio of 48/16=3, integer, causing same chain links "hunting" same sprocket teeth, exaggerating local wear and thus wear delta.
The last chainring replacement was a move from 48/16 to 47/16, to avoid this wear concentration within the chain.

 

[Yellow Saddle]

At the time of the Sugino XD, the tension variation started with 2 cm, then gradually grew (due to wear) to 4 cm, likely due to another reason, a gear ratio of 48/16=3, integer, causing same chain links "hunting" same sprocket teeth, exaggerating local wear and thus wear delta.
The last chainring replacement was a move from 48/16 to 47/16, to avoid this wear concentration within the chain.

You don't say how that tension (actually tension inferred by a distance) was how do you a) measure the 20mm and b) ensure that you use the same finger pressure each time you measure?

You are absolutely right that even tooth combinations are problematic and that it is always better to have an uneven number of teeth in one of the sprockets.

 

[silva]

Aha. Glad you're still here. Lemme just confirm.

1) You say the chain, at a given position on its drive cycle (upper run), for a given pedal tension, can be pushed up or down with a variance of 20mm, depending on pedal position?

2) OK, I get it, the chain moves up and down as you pedal. Number 2 is just a different expression of Number 1.

Is my interpretation correct?

Test situation: bicycle upside down on the ground, with me slowly rotating the cranks, one 360 degrees rotation.
With little force I move the other hand holding an allen key that touches the underside of the upper part of the chain, up and down, with the chain following a certain distance up and down.
At one point the allen key lifts the chain 1 cm up, at another point that is 3 cm, ie a variation of 2 cm.

When I ride the bicycle, I experience it alike the chain "catches up" every rotation. And I feel a oscillating kinda roughness/vibration in the pedal. It's just crap, ruins the ride, and when drivetrain components have had some wear, it just gets worser.

 

[silva]

... b) ensure that you use the same finger pressure each time you measure?...

It's a little to no force, just enough to overcome gravity effect on the chains mass. Hence the allen key held at its end, the opposite effect of a lever.

To add as much info as I can, in the past very occasional, when moving from forward pedaling to pushing back to slow down, it felt like something moved, and before/after the drivetrain behaved (noise, vibration) different.
I think this was due to a chainring moving abit on its position.
Both Sugino and Stronglight chainset spiders had notches on their arms that left the mounted chainring a littlebit space. The Velosolo chainring lastly mounted on the Stronglight spider, fitted with zero space, no tolerance, I had to very gradually tighten the bolts, making sure none stayed behind too far from the others.
This likely means that the Velosolo chainring is totally unable to move on its position (except on the bolts themselves, but that isn't excentricity).
And this would leave the Stronglight chainsets spider, or taper, as cause for the excentricity.

So this story isn't that obvious, there have been multiple causes for excentricity, and wear concentration (ex the new bicycle had a 5 mm offcenter chainline while the dealer had told me a 100% straight line).

And this last touches another so far untold part: my rear cog is mounted on a brake disc mount (IS disc) and I corrected that 5 mm offcenter chainline with 2 x 2 mm 6 bolt flange spacers. But the spacers are flat, and the IS disc mounts protruding center ring doesn't center the rear cog anymore.
But the rear cog rotates due to the gear ratio 3 times for every chainring rotation, so if it gave any excentricity I would see 3 tension variations for every crank rotation, and there is just 1 variation.
Just to be as complete as possible.

 

[Yellow Saddle]

Test situation: bicycle upside down on the ground, with me slowly rotating the cranks, one 360 degrees rotation.
With little force I move the other hand holding an allen key that touches the underside of the upper part of the chain, up and down, with the chain following a certain distance up and down.
At one point the allen key lifts the chain 1 cm up, at another point that is 3 cm, ie a variation of 2 cm.

When I ride the bicycle, I experience it alike the chain "catches up" every rotation. And I feel a oscillating kinda roughness/vibration in the pedal. It's just crap, ruins the ride, and when drivetrain components have had some wear, it just gets worser.

Still a bit confused, but I'm getting my head together. When the bike is upside down, what part of the chain are you tension-testing. The tension run or the return run. And, confirm or not if the high point is just once per crank rotation.

Edit: Forget whether the bike is upside down or not, that confuses the issue. Are you testing the tension run or return run?

 

[Yellow Saddle]

When I ride the bicycle, I experience it alike the chain "catches up" every rotation.

That does sound like some sort of eccentricity. May I suggest you remove the chainring/sprocket and draw its outline on paper as well as the bolt holes. Then rotate until you see the place where it seems eccentric and draw that outline. It will show clearly in the drawing if you manage to keep the pencil vertical all the way round. I use that method to check symmetry of templates all the time.

And I feel a oscillating kinda roughness/vibration in the pedal. It's just crap, ruins the ride, and when drivetrain components have had some wear, it just gets worser.

This is a very typical way that a worn chain on a good set of sprockets presents. If the chain is worn and used on a derailer bike, the derailer spring allows the chain to ride up the sprocket tooth and skate over the top. On a single-speed it doesn't have that escape route and the incoming tooth (front or back) forcibly collides with the chain roller that's in the wrong place for perfect engagement due to chain elongation. That feels like a strong vibration through the pedals.

 

[silva]

Still a bit confused, but I'm getting my head together. When the bike is upside down, what part of the chain are you tension-testing. The tension run or the return run. And, confirm or not if the high point is just once per crank rotation.

Edit: Forget whether the bike is upside down or not, that confuses the issue. Are you testing the tension run or return run?

The upper part of the chain when bike upside down is the return run, but why would that matter, I'm slowly moving the cranks by hand, nearly no force. When I do the test on the "tension" run, it gives just the same result.
And yes, the high (and low) tension point is just once per crank rotation.