Chainline out by 5mm (hubgear) - too much or doesn't matter?

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LancsGirl
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by LancsGirl »

I got the impression that an advantage of hub gears and single speed is that you can run a dead straight chainline, thereby reducing wear on various components. Also being able to use a 1/8" chain/sprocket/chainring. Which might wear better, that is, slower.

It could be that Rohloff's advice refers to their hub, rather than components outside the hub.
Last edited by LancsGirl on 21 May 2022, 9:28pm, edited 1 time in total.
Jdsk
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by Jdsk »

LancsGirl wrote: 21 May 2022, 8:44pmIt could be that Rohloff's advice refers to their hub, rather than components outside the hub.
That's what I concluded.

Jonathan
Galactic
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by Galactic »

I think it's a case of just because you can run the chain at a 1 degree angle, that doesn't mean you should do.

I think for the moment I'm going to try to find the right match between spacers and longer bolts/sleeves to try to narrow that 5mm gap. And the next time I have to mess with my bottom bracket or cranks, I'll add a spacer in there since that seems like the better solution (and gives my trouser legs a few extra mm before they come into contact with a greasy chain).

Thanks for all your tips and advice - very useful and appreciated.

PS thinking about it more, my current crankset and bottom bracket has only been on for about 3000 miles, and I was surprised at the wear on the rear sprocket and the chain but put it down to a bad chain (don't remember what it was, but it was a basic Shimano 8/9 speed) but perhaps the angle had something to do with it? Who knows how it was set up before that.
PH
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by PH »

Galactic wrote: 22 May 2022, 6:02am I think it's a case of just because you can run the chain at a 1 degree angle, that doesn't mean you should do.
Indeed, from the same link Rohloff also say
"Generally the goal is to create a chainline with as little offset as possible."
LancsGirl
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by LancsGirl »

Galactic wrote: 22 May 2022, 6:02amPS thinking about it more, my current crankset and bottom bracket has only been on for about 3000 miles, and I was surprised at the wear on the rear sprocket and the chain but put it down to a bad chain (don't remember what it was, but it was a basic Shimano 8/9 speed) but perhaps the angle had something to do with it? Who knows how it was set up before that.
In a derailleur drive train a worn chain at 3000 miles wouldn't be thought of as excessive, from what I've read. I just replaced my chain (9 speed KMC) at 1202 miles. Though it only measured 0.4% worn (against a new one, measured over its full length) so I replaced it a little sooner than most people would.

But a badly worn (however you judge that) sprocket at only 3,000 miles seems early to me.

As I said, I thought an advantage of hub gears was that you could get a straight chain line. If that was my bike, I'd be replacing the BB and/or chainset to get a dead straight drive chain, and putting a nice beefy 1/8" chain on, if possible. It seems a waste not to exploit the advantage of that lovely hub gear you've got. But maybe that's just me.
slowster
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by slowster »

Galactic wrote: 21 May 2022, 1:33pm the easiest solution seems to be spacers with extended chain bolts. My current bolts are m8/8.5 and are 1mm too long, the chainring is 2mm thick and if I use 5mm spacers then presumably I need to find some bolts and sleeves that are about 12 to 14.5mm long?
It is possible to buy longer chainring bolts and nuts, e.g. https://www.sjscycles.co.uk/chainsets/i ... pack-of-5/, and Spa sell spacers in various widths which would enable fine tuning of the front chainline. However, I suggest you measure the current clearance between the chain and the inside of the crank arm, because I suspect that moving the chainring as much as 5mm further outboard may be likely to result in the chain touching the crank arm.
Last edited by slowster on 22 May 2022, 7:22pm, edited 2 times in total.
Galactic
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by Galactic »

I suspect that moving the chainring as much as 5mm further outboard may be likely to result in the chain touching the crank arm.
Yes, I checked that today - there's 5mm to spare after moving the ring out 5mm, and from that point the crank arm is straight, so theoretically there should be the necessary clearance.

I was also looking at the crank shaft (is that what it's called? The spindle that goes through the bottom bracket), albeit from the outside and with the help of some random videos on the internet ("how to remove and re-fit a Shimano FC-S501"). There's a wee dimple at the end for the loose crank arm to be guided onto (don't know the correct terminology, the video I was watching wasn't in English). That makes me wonder whether I can actually fit a spacer on the spindle because if the dimple isn't long enough then thingummy on the crank won't slot into it once I've fitted the spacer on the other side (since that'll effectively shorten the spindle on the port side).

First stop: get the longer chainring bolts and see if my measuring and maths fit with reality.
slowster
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by slowster »

Galactic wrote: 22 May 2022, 7:03pm with the help of some random videos on the internet ("how to remove and re-fit a Shimano FC-S501"). There's a wee dimple at the end for the loose crank arm to be guided onto (don't know the correct terminology, the video I was watching wasn't in English).
I suggest you watch the Park Tool video, even though it is generic rather than specific to your particular model.

https://www.parktool.com/blog/repair-he ... on-slotted

Shimano state that the chainlines for the chainset are 49.2mm for the double chain guard and 42.7mm for the single chain guard. Since the difference corresponds to the 6.5mm spacer fitted to the spindle of the double chain guard version, that suggests that the crank arm and spindle units are the same for both versions, and that the 6.5mm spacer could be fitted to the single chain guard version to increase chainline.

According to the exploded diagram I linked to in my earlier post, the double chainguard version also has an extra spacer on the non-drive side, item 6 in the diagram, which presumably is to reduce the asymmetry of the relative position of the pedals with the 6.5mm spacer fitted. It is also available from SJS:

https://www.sjscycles.co.uk/chainsets/0 ... y1md14100/

However, before buying the spacers I would remove the LH crank arm fixing bolt (bearing pre-load cap) and see where the end of the spindle was inside the crank. With the spacers fitted the crank will move further outboard, so I would want to try to see if the splines on the crank and spindle meshed for a sufficient length. Similarly with the spacers fitted I would also check carefully how far the LH crank was on the spindle before riding the bike. If the LH crank arm is not properly seated on the spindle of two piece Hollowtech II chainsets, the crank is likely to be ruined by the inevitable damage to the splines.

As with all these things, you do them at your own risk. I am not a fan of Hollowech II chainsets and bottom brackets, having read too many stories of people wrecking their LH crank arm, bottom brackets lasting a very short time, and the RH crank of some models coming apart.
Jupestar
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Re: Chainline out by 5mm (hubgear) - too much or doesn't matter?

Post by Jupestar »

As mentioned earlier In the thread I would try and determine the location of the 6.5mm spacer (item 11). I always assumed it was needed for 68mm shells but not 73mm although this is 1.5mm out…. I’d never measured it.

Mine are both 68mm shells and I certainly need this spacer, or the crank is not secured. I can install it on either side depending on the chainline/chainstays. To try and get the right clearance. Paired with the alfine hub I find installation on the drive side with the chairing on the inside of the spider gives me a bang on chain line. (68mm BB shell).
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