choddo

Hi

Got a 2 month wait for a 52T DA9000 chain ring so I’ve picked up a 50T that happened to be in stock. Should I shorten my chain slightly - one double link perhaps? Seems a sensible adjustment but never had to fettle such things before.

Also - good grief these things are expensive.

ljsense

It's not necessary to shorten your chain. It will be the slackest at 39x12, or whatever your small chainring and second smallest cog is, and those haven't changed.

And I agree, it is ridiculous how expensive new chain rings are. It's not much more to find a whole crankset in excellent condition on eBay, and then while you're at it why not just get a new bike.

choddo

36x13 I think - yeah that makes sense. Cheers, one fewer job always appreciated.

Is there a reason why it’s slackest at the 2nd smallest cog? Just that I shouldn’t be using the smallest / cross chaining that far?

FBinNY 

Pour yourself a cup of coffee, and stop to think a moment.

You KNOW that your system works fine with a smaller chainring. So, why would you need to shorten the chain.

OTOH, if your question is whether the smaller outer ring would allow a shorter chain.....

The chain wraps halfway around the ring, so going from 52 to 50 teeth would allow 1 link less in the chain, which can only be shortened by 2 or more.

choddo

I always prefer to flap my jaw than consume any cognitive energy

Good point about the half circumference, hadn’t thought of that.

roadcrankr

When DA9000 came out, I anticipated the scarcity and cost of replacement 50/34 rings.
So I snagged a complete crankset after the market settled down and parted-out the cranks and hardware.
My net price on the rings came to less than a hundred bucks, if memory serves.
Still in my spare parts bin after logging more than 30k miles. Maybe I will reach 50k? I wonder what others achieve.

ljsense

Yeah, you're right, the chain will be slackest with the small chain ring and smallest cog. I said second smallest because the convention is not to cross chain, but it happens. You definitely want a chain to be long enough to handle the big chain ring and biggest cog, even though that is also cross chaining.

SoSmellyAir

Well, actually, the Shimano dealer manual warns that one would expect chain rub when on the small chain ring and the four smallest cogs.

See, e.g., DM-RAFD001-05-ENG.pdf (shimano.com) at page 4. So best to avoid small small cross-chaining and the next few combos.

ljsense

Lots of great advice in that Shimano derailleur manual, such as this:

"Be careful not to let the hemming of your clothes get caught in the chain while riding. Otherwise you may fall off the bicycle."

FBinNY 

Like everything in life, it depends on the details. Why the manual engages in some CYA, with worst case warnings about cross-chain issues, not all systems are the same.

Important variables include; chain line, chainring gap, chainring size difference, and chain width. Many bikes can comfortably cross chain all but the worst combinations.

So, if you are willing to accept somewhat higher chain wear, feel free to ride ANY combination if/when it makes sense for you.

SoSmellyAir

Agreed, except for chain width; I think the manual assumes that one would install and use an 11-speed chain. Also depends on chain stay length.

I suppose, instead of "avoid", I should have said "minimize duration riding in". I did not imply that shifting into one of those gear combinations would lead to an immediate catastrophic assplosion.

FBinNY 

I haven't checked all 11s chains, but at least up to 10s there was variation in the outside width of "same size" chains.

And, yes chainstay length factors. Then again "includes" is open to addition, unless one adds a limiter such as "only". However, in legalese, one might add "but not limited to", to be more bulletproof.

The key point one needs to remember about cross chain is that it's not a binary thing, ie. OK/not OK.

At most only 2 combinations (3 on a triple) have perfect chainline. ALL others have varying degrees of misalignment. So, using the inner with the 4th outer is only slightly worse than the 5th outer, and so on.

So, as a rider, who's also the engine, use gear combinations that best serve your cadence/torque needs and let the bike worry about itself.

SoSmellyAir

I was not suggesting that we somehow need to keep the chain as parallel as possible to the central axis of the bike, which would be a fool's errand. I was merely suggesting to minimize the gear combos in a 2x setup where the chain would be rubbing on the FD cage and/or the big chain ring as recommended by the dealer manual.

FBinNY 

We don't really disagree, and as one who only uses trimmable FDs, I don't sweat FD rub.

Change the "would be" to "is", and we agree completely.

Not being pedantic, just have spent too much time here on BF reading posts fretting about possible issues, when there are none.