mrshinsa

I have a Motobecane cafe noir, which I use as a daily commuter.
I got fed up with the flex from the FSA vero crankset, so I upgraded to a Shimano Tiagra FC-4603.

On the middle 39t chainring and the smallest 11t sprocket in the rear, the chain rubs against the large chainring up front, especially on the pins.
My guess is that its because the FC-4603 is a 10speed crankset, and the chain is a 9speed?

Is this normal?

Would upgrading to a 10speed chain solve the issue?

dsbrantjr

Depending upon the throw of your derailleur you might be able to put spacers behind your large chainring and avoid the rub. 1.2mm spacers did the job for me in a similar situation.

FBinNY 

The diffrence between 10s and 9s cranksets is chainring separation. So it should be no surprise that when the chain comes from the outside to the inner ring, it brushes the outer ring. Increasing the separation by about 0.5mm or so may be enough, but be aware that it often isn't.

I call this effect "shadowing" and it's become common as ring separation is reduced & chainstays are shorter.

One other thing that might work, if it's practical for your bike is moving the cranks out slightly. Don't get carried away, but if the set uses BB spacers, and you can move 2-3mm from the left to the right, it's an easy fix.

OTOH, you can accept that 39-11 is just about the least efficient gear combination on your bike, and join the bulk of riders who simply avoid the combination.

DMF 

[strike]What chain are you using? 9 or 10 speed?[/strike]

Do you have a 10-speed chain you can try?

cycle_maven

I bet the old crankset had a larger middle ring, like 42. The angle needed to make that one rub is further out than the 11 tooth cog.

Don't worry about it. I never use the small cog with the middle ring.

TallRider

I think the narrower spacing of 10-speed cranks is a function of the chainrings, not the cranks themselves. So you could use the original 9-speed chainrings on your newer, stiffer crankset.

You can also get super-thin washers/spacers for chainring bolts, to set your outer chainring very slightly further outboard.

However, I would recommend (like everyone else) that you simply avoid 39/11 combination.

wheelreason

Banning 11T cogs should have been part of ObamaCare...

Drew Eckhardt 

It's not abnormal and in extreme cases you can have rub on the last few cogs.

LeTour makes 0.6mm spacers specifically for pairing 10 speed cranks/rings with 9 speed chains.

mrshinsa

Thanks for the reply everyone.

I'm now under the assumption that 10speed cranksets are different than 9speed crankset, whether it be the chainring thickness or the spacing between the rings.

I'm kinda bummed out because with the FSA Vero triple, I just kept it in the middle ring and I could reach the every cog in the rear.

It looks like even Shimano admits the middle ring + small cog combination may rub.

https://www.shimano.com.au/media/techdocs/content/cycle/SI/TIAGRA/SI_1MG0A/SI-1MG0A-001-00-Eng_v1_m56577569830746319.pdf

I though about going the spacer route, but I might try the 10speed chain first when the current chain wears out.

fietsbob

shim washers should spread out the spacing ..
10speed chain may not be a great fit on the 9 speed cassette.


sorry about the compulsory upgrade by the industry pushing more speeds as a panacea

to all cycling needs , which they are not.

FBinNY 

The ONLY difference is the chainring separation. The actual tooth width is the same. Using a 10s chain may help, and the only reason not to is that 10s chains cost more and tend to wear out faster.

IMO, the least expensive (over the long haul), is to restore the separation to 9s specs.

However, be aware that this may not change anything, so if it's only the 39/11 combination, simply ignoring the "problem" is probably the smartest solution.