Chain rubbing against outside ring after new Chain Rings fitted - advice welcome

[cool_hand]

Just replaced my chain-rings with TA Zephyr 34 / 50. Great quality but after fitting the new rings the chain now rubs against the large ring when the chain is in the small/small position. I am aware that you should not cross gears at the extreme however I did not have this issue with the previous rings and ideally I’d like to avoid this. Looking at the rings they both have a chamfered edge and the teeth are slightly off-centre - my previous inner ring was pretty much flat - no chamfer with centred teeth. I’m assuming that the TA Zephyr 34 is designed for use as a middle in a triple with the option to be used as an inner and it’s the offset teeth that is causing the chain to rub. Is there a fix/workaround for this? BB is Shimano UN55 Square Taper 68 x 110 mm, cassette is Sora HG50 12-25, chain is SRAM PC870 8 speed, crank is Truvativ Touro Compact. Is there a spacer available that I can put between the crank and the BB or would I need to change the BB? Or should I just give up on the inner-ring and replace with something that is flat? Thanks in advance.

 

[Ming the Merciless]

Yes, you would need to push the chain line out further from the frame. In other words you'd want a wider BB say 113mm or 115mm x 68. If you bring the chain onto the second smallest ring on the cassette, do you still get rubbing? That’ll give you a clue as to how much further out the chain rings would need to be to straighten the chain angle in small / small to avoid rubbing.

or you could just recognise if you’ve ended up in small small, it’s time to change to a lower gear at back and shift to big at front. I don’t like compact doubles as you always seem to end up in these double shift situations. I like my triple where I’ve never had to shift both back and front same time to find the right gear.

 

[cool_hand]

Yes, it rubs on the second smallest ring but not on the third.

 

[Sharky]

or you could just recognise if you’ve ended up in small small, it’s time to change to a lower gear at back and shift to big at front. I don’t like compact doubles as you always seem to end up in these double shift situations. I like my triple where I’ve never had to shift both back and front same time to find the right gear.

I also got fed up with compacts for the same reason, particularly commuting in the dark.
So ended up just getting rid of the front gear and replacing the 50/34 with a single 40t.

 

[Heigue'r]

This popped up on another forum yesterday,chain rubbing on big ring when in small/small.This was on 3 different bikes all running campagnolo.I'm not sure if this is common and neither was the owner of the 3 campag equiped bikes..I have not seen any replies to the query.

 

[fossyant]

You shouldnt be running it like that. Could be a slight change in chain line plus shifting ramps can be different. Nothing wrong with it.

 

[Ajax Bay]

Maybe experiment with a 9 speed chain, but the issue is chain line which the OP can adjust with BB spindle length, as @YukonBoy says, so a UN-55 113mm would sort it. ETA: Personally I would not worry, and if I actually hear the noise, I'd take it as a welcome indicator that it's high time I shifted into the large ring.

 

[cool_hand]

Maybe experiment with a 9 speed chain, but the issue is BB spindle length, as @YukonBoy says, so a UN-55 113mm would sort it.

The bike is actually spec'd 34/50 by the manufacturer as new but for some reason it came fitted with 36/50 - don't know why the spec was different but it's possible the BB used is not suitable for 34/50 and a 113 mm will sort.

 

[Ajax Bay]

Yes, the angle small/small which didn't touch with 50-36 might with a 34t on the inner. The chain joins and leaves the ring 2mm further forward (cf a 36t). The top chain run is about 390mm

 

[cool_hand]

Yes, the angle small/small which didn't touch with 50-36 might with a 34t on the inner. The chain joins and leaves the ring 2mm further forward (cf a 36t). The top chain run is about 390mm

Thanks, good advice, I'm going to try changing the BB to 113 - I assume I will have to adjust the front front derailleur at the same time?

 

[Ajax Bay]

Seems a very reasonable assumption. The rings will both have moved 3mm -->. Maybe worth checking that, with the H limit screw right up (count how many turns that takes so you can reverse it) the FD cage swings out at least 3mm more thn current correct setting for outer chainring..

 

[cool_hand]

Seems a very reasonable assumption. The rings will both have moved 3mm -->. Maybe worth checking that, with the H limit screw right up (count how many turns that takes so you can reverse it) the FD cage swings out at least 3mm more thn current correct setting for outer chainring..

If the BB goes from 110 to 113 would the rings not move out by only half that amount - 1.5 mm?

 

[Ajax Bay]

You're right and apologies for getting it wrong. 43.5mm out to 45mm.

 

[cool_hand]

You're right and apologies for getting it wrong. 43.5mm out to 45mm.

Thanks. Difficult to know for sure if that'll be enough - I'd take a guess that it will be but tomorrow I'll try and have a good look. The chain-ring only needs to move a small amount to address this.

 

[Ajax Bay]

Sheldon: "In the case of derailer geared bicycles, the chainline is not perfect in most gears. Chainline mismatch can cause the chain [when on a smaller chainring] to rub against the side of an outer, larger chainring "