Chain rubbing on chainring (105 w FSA chainset)

mikeeye

I've replaced various components on my bike after an RTA. Since I needed new gears, I took the opportunity to switch from 105 5600 gears to 5700 for the new cable routing. Everything is assembled and working well except for a minor niggle...

The chainset is an FSA Gossamer - compact. Wheels are Planet-X model B. Shifters and both derailleurs are Shimano 105 5700.

If I run the gears in small chainring to small sprocket then the right side of the chain rubs very slightly on the inside face of the large chainring. In practice, this doesn't really matter since it's not a gear I'd use - nobody on here would, right ;-). However, I wonder if this is indicative of some other issue. E.g. I can see some of the splines of the freehub as though the cassette ought perhaps to be slightly further in. But if I omit the spacer, then the cassette wont lock into place - it wobbles around as you'd expect if the spacer was missing.

Any ideas?

Thanks,

Mike

John.T

That rub is quite normal for a compact on small/small. It can be worse and rub on the next sprocket too.

Ouija

Two options.

1) Use a chain for a model with more gears than yours (if 9 speed, use a narrower 10 speed chain etc.)

2) Increase the space between the two rings. This is easier than it looks. Simply take the outer ring off and put some helicopter tape (or anything the same thickness as a piece of serial box cardboard) on the front of the four or five arms on the spider where the ring attaches and then put the ring back on and tighten up. This can separate the two rings by 0.5mm, preventing rub from the outside edge of the chain. Experiment with different thickness of materials and by also placing the it on both sides of the screw holes. Just don't use anything squishy or easily compressable as it can cause the outer ring to wobble.

mikeeye

Thanks for the replies guys.

Knowing it's normal is probably all I need. I'm not going to use that gear, so it's not going to cause wear. Having said that, I might experiment with the helicopter tape option - it's already 10 speed with 10 speed chain.

John.T

10mm shim washers do a better job. When I use my Stronglight 52/38 rings on my Ultegra cranks I need 1mm washers behind the big ring to stop the pick-up pins catching on the second smallest sprocket. No problem when using the Ultegra 50/34 rings. I guess all rings are not equal.

tonye_n

What the OP is describing is, and has always been an issue with Compact setup.
Because of the big difference in size b/w a 34t and 50t, the chain rubs the inside of the large chainring when cross chaining small front chainring to smallest cassette cog.

**According to Shimano sale pitch** one of the benefits of the new compact chainsets (5750, 6750 etc) is that the chain-rings are spaced a further about 1mm apart to all but eliminate this problem.

I still would not advocate using small-small or big-big though, as there is no real reason to do so when you can achieve the same range/cadence by shifting early and selecting a different set of gears.

mikeeye

tonye_n wrote:

**According to Shimano sale pitch** one of the benefits of the new compact chainsets (5750, 6750 etc) is that the chain-rings are spaced a further about 1mm apart to all but eliminate this problem.

Thanks tonye_n. That's very interesting and answers some of the questions I'd been mulling over when trying to decide whether I should upgrade to 5700. I was unable to find a definitive statement on the exact spacing between the chainrings so I based my decision to go ahead on there not being info (that I could find) which said that the FSA Gossamer chainset was suitable for 5600 but not for 5700.

I hadn't noticed this rubbing before I switched, but then I'd not had the bike very long before it was restyled for me, so I wouldn't like to guarantee it didn't do it before the switch.

Since Shimano have increased the spacing by 1mm then that does suggest that John.T's spacers would be a good plan since I'd presumably get the intended positioning of the cage relative to both chainrings now that I've got a 5700 FD on the bike.