lineinthewater

So, I have new triple crank, new cassette, new FD&RD. All 5700 105, except for the Sram cassette, which is a 9-speed PG950. The chain is a new Sram 9-speed chain.

I have the system mostly dialed in, except for this odd behavior on the middle-chainring, small-cog combo. In this gear, the chain is slightly rubbing the inside of the large chainring, most specifically where the chainring has small rivets. Just to be clear, the FD is absolutely not rubbing. The chain is well clear of the sides of the FD.

OK, halfway through this post, among other remote possibilities, I was thinking that it's almost behaving like the chain is too wide. Then I started doing some searching, and think I might be on to something.

Does the FC-5603 crankset only work with 10-speed chains? Did I just buy a crank that won't work with my 9-speed shifter/cassette? Will the Sram PG950 cassette handle a 10-speed chain?

jimc101

You post is a little confusing, saying you have all 5700 (less the cassette) then saying you have a 5603 crank, either way, it should work with a 9 speed cassette/chain with no major issues.

Have you set up the spacer supplied with the crank correctly? This is noted in the Bottom Bracket fitting instructions https://techdocs.shimano.com/media/te...9830692365.pdf

lineinthewater

Sorry for the confusion. It is a 5603 crank, which based on additional searching is "less forgiving" of 9-speed chains. RD-5701-GS and FD-5703 for derailleurs.

The triple spacer is installed on the non-drive side, between the crank arm and the BB bearings.

TiBikeGuy

Try installing the spacer on the drive side, this will bring the crank slightly further out and may shift the chainline clear of the big chainring.

pierce

frankly, the small cog in back should ONLY be used with the big chainring in front. using it with a smaller chainring increases the load on the teeth, and those small cogs never have enough teeth, especially if they are 11t.

lineinthewater

I know it is borderline crosschaining ... but it shouldn't be rubbing the crank. And, yes, it is 11T.

cny-bikeman

See my signature below. It all depends... If you have a shorter chainstay, a middle chainwheel that is significantly smaller than the large or your chainwheel chainline is slighly inboard from the cassette chainline, it certainly can rub protruding chainwheel nuts.

I don't consider the middle/small borderline. It's still a very high gear (39/11 is slightly higher ratio than 52/15) and therefore creates much greater wear (37%) than riding a similar gear ratio with the large chainwheel. Of course any time you are at the end of the cassette you can only go in one direction w/out a double-shift.

lineinthewater

The 5603 has a 50 large chainring .. one of the reasons why I chose it ... it minimize delta across FD shifts.

It may not be borderline in your book (totally respect that), but should it be rubbing the chainring? Rubbing the FD maybe, but not the chainring.

And, yes you are very insightful ... the chainstay on this bike is slightly shorter than the other bike I have ... which is running 105 10-speed (that bike runs fine - but also a complete 10-speed system).

pierce

can you measure the chainline?
https://sheldonbrown.com/chainline.html#front


measure it from the centerline of the seat tube to the tips of the teeth of the middle ring... this is a 130mm wide rear hub, locknut to locknut ?

if your chainline is a little short, that gives you a better 'Q' (your feet are closer together), but increases the chance of chain ring scraping like you're seeing.... one solution is to favor the big ring, and only use the middle or small rings when you are at the other end of the cassette.

With a larger front sprocket, there is less force on the chain, and less drive train friction.

HillRider

Cranks with a fairly large diameter difference between the small (or middle) chainring and the large chainring are prone to just what you are experiencing. Compact (50/34) cranks are particularly prone but your 50/39 can be too. The 9-speed chain is making it worse due to it's greater width than a 10-speed. However, I consider this a very minor problem as the small-small combination is not good for the chain and has no need in the gearing sequence.

FBinNY 

This is getting fairly common as they narrow the spacing between chainrings for 10s, 11s .....

As the chain comes from an outside rear sprocket it brushes larger chainrings on the way to smaller ones. If your bike does this, it's inherent in the system and has nothing to do with derailleurs. It's simple geometry and comparable to how a smaller building can find itself in the shadow of a taller one as the sun gets lower.

There two remedies. Increase the chainring gap, though that can cause problems of the chain jamming on downshifts. Or move the entire crankset outboard a bit, which changes the chainline to more inboard angles. Or leave bad enough alone, and avoid the problem combinations.

lineinthewater

I (briefly) attempted to do exactly this prior to you posting, but had trouble getting an accurate (to the mm) measurement. Attempting to do this with calipers. On second thought, it's probably easier to measure from the opposite side of the seat tube, and then subtract half the diameter of the seat tube. I will try again this morning. Of course, I don't know what is the normal distance .... need to search for that.

lineinthewater

Would not using a 10-speed chain be a potential solution as well? Of course, this is only if a 9-speed cassette can handle a 10-speed chain?

I will probably experiment to find just how much of a BB spacer is required to stop the rubbing.

pierce

road bikes, with 130mm rear axle locknut widths are about 42mm, and hybrid/mountain bikes with 135mm rear axles are about 48-50mm.

lineinthewater

For a triple crank?

pierce

same for triple or double. with a double, its measured at an imaginary midpoint between the chain rings.. for a triple, its measured at the middle ring.

Fun Fact! shimano measures to the inside of the middle ring, while everyone else measures to the tip of the teeth. makes about 1mm of difference.

reality, a couple-3 mm either way is OK. I setup one 2x7 bike so the big ring was in the middle, and the small ring was inside. I used it with the big ring (a 50T) like it was a 7-speed. when I used the 34T, I only used the larger half of the rear, gears 1-4...

lineinthewater

Ah, I misunderstood. I thought it was 42mm to the large chainring (on a double), but you were saying it's 42mm to the (inside of the) middle chainring (triple).

Thanks! I will see how it lines up in a few hours and report back. That will be one more variable to eliminate.

bradtx

lineinthewater, Because you stated the chainrings are rivited you can either space the drive side outwards or simply not use that combination. While I think a middle chainring should work with any gear, sometimes it won't and in this case isn't advisable anyway.

Brad

lineinthewater

The chainrings are individually removable (chainring bolts). The rivets to which I'm referring are not true rivets - they are, I'm guessing, to aide in shifting gears?? Clustered in groups of two - about 4 sets evenly spaced around the outer ring. I assume they are designed to help lift the chain from middle to large ring. Maybe on this bike I can call them suggestion rivets.

lineinthewater

I measured 45.8mm, center-seat-post to inside-middle-chainring. However, I had to figure this from 3 measurements, because that was the only way to get the calipers in there:

(opposite-side-seatpost to large-chainring-outside) MINUS (large-chainring-outside to medium-chainring-inside) MINUS (seatpost-diameter)/2

I believe this is slightly on the high side since it is impossible to get the calipers entirely square on the surfaces, so I think it is well within the 42mm +/- 2-3mm tolerance. Regardless, the middle chainring is almost certainly farther out than 42mm.

cny-bikeman

There is one other possibility that I did not mention. Just as the cranks may be inboard from ideal the cassette may be too far outboard if the rear triangle is not centered. What you need to know is their relative position - again, not what it should be, but what it is.

First, check rear triangle alignment. Use Sheldon's instructions under "The string method" at https://sheldonbrown.com/frame-spacing.html, but don't go by the awful photo. Instead, tie the string to the right seat stay above the dropout, run it first to the inside and then to the outside of the dropout, up to the seat tube, back to the outside of the other dropout and then back across to the right dropout. Make sure it's taut and tie it off wherever handy - bottom of dropout, deraiiler hanger, etc. You can of course leave the derailleur on.

Once you have confirmed the rear triangle is centered (we hope so!) go through Sheldon's method for measuring rear chainline (it is more accurate to measure with calipers from the right side of the seat tube and then add 1/2 seat tube diameter. If the rear chainline is greater than the front that will be part of your problem.

lineinthewater

That was one of the "remote" possibilities I was originally considering - well, not the triangle centering, but the cassette itself not being all the way "on" the hub. FYI, I inspected the cassette and there are no gaps in the cogs or spacers, and it looks snug against the inner hub.

Conceptually I understand your instructions, and the reasoning. I will take a look at Sheldon's explanation. I have some other non-bike repairs that I need to get to today, but I will definitely make this measurement either tonight or tomorrow. I will report back. Thank you.

cny-bikeman

You're welcome. I know you would like to be able to run that combo without rubbing, but i don't see the advantage or need. Assuming your small chainring is 39 teeth and rpm's of only 80 (quite low for performance riding) that gear is 23 mph. if you really are motoring along around or over 20mph I would question using the small chainwheel, as both the 11 and 12 will wear pretty quickly.

bradtx

Go to the LBS and buy some chainring spacers to move the big chainring outwards. They're available in .5 and .6 mm widths.

Brad

ThermionicScott 

Your bike is just telling you to shift into the big ring. In your heart, you know it's right.