Road chainrings compatibilty?

Alek

Can I run the middle chainring as outer?

I'm currently on 50/34 but would rather have 44/34 as I'm switching to 11-34 cassette and I super rarely use 12t with 50t.

seamus

Short answer is yes, but it does depend on your crankset and you will find that shifting is a good deal less reliable.

Seems like a bit pointless though going 44/34 with an 11-34 on the back. You will basically only have a very narrow range of actual gears to choose from, so little that you may as well run a single chainring on the front.

Removing the 50T chainring won't really accomplish anything except to leave you high and dry for those "super rare" times you need it.

Alek

I used to have 47/38 with 12-34 that I was really happy with - used the big ring with 5 gears (90% of time) and switching to 38t plus three largest cogs for serious hills only (>8%)

After the upgrade (5700 compact groupset with 12-27) I find the steps are too small for my liking and the gearing is generally too high. Also, jump from 50 to 34 is massive.

I may think about 46/34 instead, but I really don't find I need to go faster than 50kmh by any other means than gravity ;-)


My biggest concern is if I can install the middle chainring with no extra washers/bolts on the outer position and if it will not drop the chain or something

mirv

50/34 compact cranks don't have middle chainrings. Can you be a bit more specific about what chainring goes on what type of crankset?

seamus

The chainrings should all be the same thickness, but you can get chainring bolts and spacers in a variety of lengths so you can tweak it till it works.

Dropping the chain is a very real concern because you will lose that little nipple which catches the chain. However, once you drop your front mech lower and set it up correctly to not go over the top, you should be fine. Because the difference between the two chainrings is smaller, changes will be more reliable, so you can work with tighter tolerances - in a 50/34 setup you sometimes have to risk going over the top in order to get a really good gear change.

One concern would be that an inner double chainring is not ramped to accept gear changes from the left, so if you can get a small outer rather than a big inner, that would be best. You may be able to get a triple outer to fit, that would be ideal.

mirv

seamus wrote: »

One concern would be that an inner double chainring is not ramped to accept gear changes from the left, so if you can get a small outer rather than a big inner, that would be best. You may be able to get a triple outer to fit, that would be ideal.

He's talking about a middle chainring, which should be ramped and pinned for shifting. The confusing part is how he's planning on putting a 44T (130bcd road triple middle or 110bcd 4 hole mountain outer ) middle chainring on a compact crankset (110bcd).

You'd just be better off buying a 46T CX chainring and forget about any compatibility issues if you've got to ask.

Alek

50/34 compact cranks don't have middle chainrings. Can you be a bit more specific about what chainring goes on what type of crankset?

I have the original Shimano compact double 50/34 now (5700). I want to buy 44t chainring, most likely Stronglight, but the smallest one described as "outer" is 46t. Sorry, I guess I meant "inner" then

However, once you drop your front mech lower and set it up correctly to not go over the top, you should be fine.

I have a band-on FD so I will lower it as required.

so if you can get a small outer rather than a big inner, that would be best.

34t is the smallest in 110BCD.

You'd just be better off buying a 46T CX chainring

Its my plan B :-)

mirv

Inner chainrings won't have ramps or pins, as described by seamus. The teeth aren't shaped either - look at the forward edge of the teeth on the 50T and you'll see that they're almost pointing forwards, compared to the very square symmetrical teeth on the 34T.

They're completely different to middle chainrings, which are effectively the same as outer rings except they might have slightly different alignment idiosyncrasies depending on the brand and ring in question. Except that 110BCD middle rings are pretty rare.

Buy a Shimano 46T and enjoy optimal shifting.

Alek

This inner chainring's teeth do not look too square?

mirv

The teeth of the ring you posted are most definitely square/symmetrical.

Look at this outer chainring for comparison. The teeth are shaped so that it's easier for the chain to fall onto the inner ring.

Alek

Thanks!

Stronglight's outer is also more round:

mirv

It's not the pointiness of the teeth. It's the fact that the teeth aren't symmetrical.

Also, using an middle/inner ring in the outer position would mean that the recessed drilling for the bolt is in the wrong place.

Alek

Is the asymmetry of teeth necessary for the chairing to work? Shimano ring's teeth above look quite sophisticated , but 52t Stronglight's seem symmetrical to me.

I had a Stronglight previously (it was the outer one though) and I don't remember it being fancy about the teeth shape. It shifted very smooth on a 8sp setup, having no pins or ramps, too.

mirv

It's not strictly necessary, but it helps you change from the outer chainring to the inner with less movement of the front derailleur. So it means you're less likely to drop the chain to the bottom bracket. Same as ramps/pins - they're not strictly necessary, but will improve shifting.

Alek

Cheers for your help, I need to think it over now :-)