8 speed chainring: 9speed chain

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stevegreen
Posts: 15
Joined: 25 Feb 2011, 11:49pm

8 speed chainring: 9speed chain

Postby stevegreen » 24 Jul 2020, 10:37am

I want to replace the rings on a TA Cyclotouriste chainset*, I have nine sprockets.

The packets that the rings come in says eight speed. I've measrued the thickness of the teeth at the route. And the internal width of eight and nine speed chains. I get (roughly) tooth thickness and nine speed chain = 2mm and Eight speed chain= 2.2.

Is continuing with nine sprockets a bad idea? Would It be better to fit eight?


* i bought the bike second- hand and it suits me very well. The gears are as set up by the original owner. I want to keep the cranks partly out of a spirit of pervesity, but mosly because they are 185mm long.

Brucey
Posts: 39884
Joined: 4 Jan 2012, 6:25pm

Re: 8 speed chainring: 9speed chain

Postby Brucey » 24 Jul 2020, 10:52am

once an eight speed chainring has worn slightly it will usually work OK with nine speed chain. However there are exceptions;

- if the chain is still tight (and not all 9s chains are exactly the same BTW) and the chainring is new then it can be a bit reluctant to shift

- if the chainring gets burrs on the teeth they don't need to be large before they can cause problems

- you may get 'skating' when downshifting onto smaller chainrings

- if the chainring is a middle chainring of a triple, an 8s chainring and a 9s chain can be the source of middle-to-small chainring shift problems

A 'cyclotouriste' chainset has no provision for ramps that guide the chainring from the big ring to an inner/middle ring, and was (of course) originally designed for 3/32" fully bushed chain. Whenever an older chainset design is used with a more modern chain there is a danger that the chain will sometimes sit on the tooth tips following a downshift ('skating') and that this will cause problems. 8s chainrings are sometimes differentiated from older 5s/6s chainrings by the exact centre position of the teeth and the presence of a one-sided chamfer on the tooth tops. Often this is enough to make an older design work OK with 8s chain, but of course there is a limit to how far you can go with this approach.

I guess trial and error will tell you if 9s chain has pushed things too far or not. 9s chain can be about 0.5mm narrower than 8s chain; this could be enough to make a difference. If it works OK apart from 'skating', filing a more aggressive chamfer on the tooth tops and/or reducing the spacer thickness slightly may provide a solution.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

stevegreen
Posts: 15
Joined: 25 Feb 2011, 11:49pm

Re: 8 speed chainring: 9speed chain

Postby stevegreen » 24 Jul 2020, 12:21pm

Thanks!

I am aware that I'm dealing wih an ancient design,but;
I first used a bushless chain with six speed friction shifting in the eighties. Therefore, I'm used to nothaving inedxed gears.
Recently the indexing became unreliable (sometimes not changing gear at all) so I reverted to friction gear levers. I don't miss indexing... And I can trim the derailleurs to suit.

I'll put it together and see what happens. I have enough eight speed parts to chang if i need to....

I'll know by Sunday.

LollyKat
Posts: 2996
Joined: 28 May 2011, 11:25pm
Location: Scotland

Re: 8 speed chainring: 9speed chain

Postby LollyKat » 24 Jul 2020, 12:36pm

I think 531Colin uses 8-speed chains on 9-speed sprockets, as the 8-speed chains last longer. Some monhts ago my husband put an 8-speed Sedis chain on his 9-speed Tiagra set-up and hasn't had any problems. Such chains are cheap so you could try it and see.

stevegreen
Posts: 15
Joined: 25 Feb 2011, 11:49pm

Re: 8 speed chainring: 9speed chain

Postby stevegreen » 26 Jul 2020, 11:00am

Thank you both.

Plan A:- I've got eight speed chains (and cassettes) for other bikes in the family. Having offered up one of them to my cassette and derailleur, I think that it's a definite maybe.

Plan B:- If not, i'll try the empirical approach; it may turn out to be error and trial.

Plan B.1:- Otherwise, rethink the gearing and find a suitable eight speed cassette.

Plan B1.1:- Re-read Brucey's comments on gearing and work out a 3x8 set up (currently it's 2x 9)*


* an aside; the recent thread on cross-chaining is disturbing! I'm lazy and stingy. The idea of wasting effort and money does not appeal to me.

stevegreen
Posts: 15
Joined: 25 Feb 2011, 11:49pm

Re: 8 speed chainring: 9speed chain

Postby stevegreen » 28 Jul 2020, 6:16pm

Plan A works! (I'll see how it goes in the mefium to long term)

Thanks to Lollycat for the idea and to Brucey for the background information.