[roborovski007]

So I just changed the inner chainring of my crank (52/36) to 39T, however I got this issue that the chain wouldn’t shift to 52T from 39T. Is there anything that I have missed out?

Thank you.

Topic

[Drinfinity]

I agree, although my

I agree, although my challenge is usually shifting from small to large. The ramps catch the plates of the chain and lift them smoothly up on to the teeth. You can watch this happening. The simple peg on the replacement flat rings is much more agricultural.

[Welsh boy]

I am not sure if that is

I am not sure if that is casting doubt on my observations but from experience I can say that my SRAM shifting from large to small ring is so much better than in the bike with Stronglight after market (flat sided) rings of the same size also on SRAM cranks.

[Dave Dave]

“Cheap (flat sided rings) don

“Cheap (flat sided rings) don’t have this problem but they don’t change as well as profiled and matching combinations “

According to sellers of fancy bike parts and their groupies, anyway. It’s a bit like gold-hyperloop-atomic-powered audio connector cables: the credulousness of punters knows no limits.

[roborovski007]

sorry it is originally a

sorry it is originally a Shimano 105 R7000 52/36 crank swap in a 39T Ultegra R8000 chainring.

[Hirsute]

50-34 ma
50-34 ma
I have learnt something new as I thought just the gap between them had to be within the derailleur max.

[Welsh boy]

My Force and Ultegra outside

My Force and Ultegra outside rings have sloping inside faces which guide the chain down on to the inner ring, the profile of this is designed to line up with the inner ring. Changing the size of the small ring will mean that this ramp will be at the wrong height so, at best the change might not be as smooth as expected and at worst, there may be a lip which will catch the chain and hinder the chain moving from the inner to large ring. Yes, rings can be changed independently of each other but the size of the new ring should be the same size as the old one or matched to each other. Cheap (flat sided rings) don’t have this problem but they don’t change as well as profiled and matching combinations 

[Welsh boy]

I don’t know what you are

I don’t know what you are riding but it says that on my Ultegra and Force chainrings. Hirsute, have you got after market rings on your bike and maybe lost the original markings?

[Hirsute]

Still don’t follow where you

Still don’t follow where you are getting these combinations from or what manufacturer you refer to.

[matthewn5]

Sorry, I mean there are

Sorry, I mean there are usually several ‘permitted’ combinations, and they’re usually marked, so both the 53 and the 39 will have ’53/39′ marked on them, as will the 52 and 36 of a ’52/36′ combo… that said, things like this normally work fine, if not quite as effortlessly as the ‘matched’ combinations do.

[Hirsute]

You need to say what the make

You need to say what the make/model/variants are of your setup for a start.

Have you put the chainwheel on the right way round ?

[Secret_squirrel]

matthewn5 wrote:

Chainrings come in matched pairs

Are you sure about that? That *may* just be true for Shimano oems sold with a crank but not for anything retail where it’s not unexpected for rings to wear out at different rates.

[matthewn5]

Chainrings come in matched

Chainrings come in matched pairs, so if you have a 52/36 crank, and add a 39, unless you get the right 52 tooth – made to work with a 52/39, not a 52/36 – then shifting might be less than utterly perfect. But I would have still expected it to work, even if it’s a bit rough!

The other possibility is that you’ve managed to change the stop on the front mech so it doesn’t move inward far enough.

Could you upload a video of the problem?

[Author]

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