So I decided to try to re-build my road bike, mostly so I could learn how to do it. I didn’t do everything but I replaced the bottom bracket, crank, cables, chain, and stem. Tried to do it all by the book (Zinn). It mostly went well but this weekend on a ride, I noticed a problem.
Although I try to avoid cross chaining, I occasionally (briefly) find myself in the small ring up front and in the back. But when I do that with the new build, the chain wants to almost “catch” on the big ring as it goes by it. It is slightly rubbing it in this one gear combination and every rotation or two it just misses catching. I’m afraid one time I’ll inadvertently land in that gear combo and break the chain. This does not happen on any of my other bikes nor did it happen on this bike before.
I am not sure how to fix this. There is no amount of derailleur adjustment that can help me (that I can see) since the chain is going directly from small cassette cog to small crank cog, rubbing large crank cog.
This was originally a 2005 9-speed Trek 2100 with Shimano 105 triple up front. I had a shop replace the triple with an FSA double and new 105 derailleur for the double. When I put the new crank in, I went to a 105 compact crank. The cassette is 12-25 (either Ultegra or 105, can’t remember) and the chain is Ultegra. 9 speed.
I made the chain length match the recommendation that Zinn gives (derailleur pulleys vertical when in big ring up front and small ring in back).
Your bb may be too short which would mount the chainrings further toward the frame thus angling the chain to much to the outside when using the small rear cog. A tad longer bb and this would move the chainrings out a tad from the frame, changing the chain angle slightly and may stop that rubbing.
Sounds like you should just avoid that combination in the first place.
You can try a 10 speed chain, it’s narrower than the 9 speed. I’m not 100% sure if it’s compatible with a 9spd cassette though.
The chain rings are probably closer to the CL of the bike now than they were before with the triple, creating a more angled chain line in the little - little.
It seems the bike should certainly be able to take this combination. This is a pretty generic Trek from 2005 and one of the most generic of Shimano groupsets. It’s never been in an accident so I don’t think I’ve bent the frame or anything.
Is there some generic way to re-align things? Do bike mechanics ever use something like a spacers or anything like between the bracket and the crank to keep the rings slightly farther out from center?? Or perhaps there is some sort of hub I can buy which allows the cassette to ever-so-slightly closer to the center of the wheel?
The chain rings are probably closer to the CL of the bike now than they were before with the triple, creating a more angled chain line in the little - little.
What’s odd is that the FSA was a double and it had no such problem
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Not a realistic solution. I’m trying to get the bike right, not “almost good enough”. I’m staying out of the gear as best I can but I’d like something a bit better than that.
I guess I’ll have to take it to the shop. Of course a real mechanic can fix this, I was just wondering if anyone here knew how they would go about it.
Bringing it to a shop might not accomplish much, you aren’t supposed to cross chain like that. Even the best of bikes and perfectly tuned machines can’t be ridden in that combo.
From time to time everyone needs to do so, if only to avoid a big-ring change. The gear combination is valid to use. Not good to use much but a valid combination.
Most importantly,the chain is also not supposed to do what it is doing. I want to fix it so that it does not so that if I accidentally (or of necessity) briefly find myself cross-chaining, I don’t have a problem.
My guess is that when you changed your standard 39-52 (I’m assuming) for a compact 34-50 you increased the difference in dimensions of the two rings. Initially you had 52-39=13 teeth, now you have 16 teeth of difference.
So, even if the chain now has the same angle when in cross gear, the big chainring will hit the chain. You can visualize that by imagining looking at the bike from the top, keeping the same small chainring and “growing” you big chainring. It will eventually touch the chain.
Maybe you really have to avoid this combination with the compact crank.
I appreciate the replies, I hope that comes across. But I have a hard time believing I’ve somehow hit upon the magical, invalid combination for compact cranks. Everything here is relatively generic. Frame, components and combination.
There are a million 12/25 and 50/34 setups out there.
Joe, if you got a new off-the-shelf crank it’s a 10speed crank and it will have 10speed spacing between the rings (which is narrower than a 9-speed). This puts the big and little rings closer to each other.
You are still running your 9-speed chain.
If you get a 10 speed chain (narrower) it should clear just fine since you seem to be describing a condition that’s already almost OK.
Joe, if you got a new off-the-shelf crank it’s a 10speed crank and it will have 10speed spacing between the rings (which is narrower than a 9-speed). This puts the big and little rings closer to each other.
You are still running your 9-speed chain.
If you get a 10 speed chain (narrower) it should clear just fine since you seem to be describing a condition that’s already almost OK.
Also, these Shimano instructions say that you can’t use the small front ring with the last 3 cassette cogs or it could rub.
Ding, ding, ding, ding! Narrower chainring spacing PLUS larger difference between the chainring sizes spells highly likely “tickling” of the chain on the teeth of the large chainring when severely cross-chained like that. Put on a narrower chain…but STILL don’t DO that. Seriously, just shift your chainring…what’s so hard about that?
Son of a b… I stand corrected. My apologies for doubting any of you. When I went to buy the crank, I asked for a 9 speed compact Shimano compact crank and I never even bothered to check. In fact, I admit thought all 105 stuff was still 9 speed.
I’m guessing the fact that this crank is 10 speed might mean that the rings would be slightly closer together. That would account for the rub that wasn’t there before.
Odder still, on my tri-bike (a 10 speed dura-ace all around with compact crank) there is no rub whatsoever in any combination. It comes awfully close but nothing rubs
I still wish there was some way I could just position the rings out ever so slightly farther or the cassette in ever so slightly. But I guess I just have to avoid this as best I can.
If I were to decide to go all-ten speed with this a few years down the line, that would mean i need new shifters, derailleur (front, and back), cassette and chain, right? Will that be enough?
Son of a b… I stand corrected. My apologies for doubting any of you. When I went to buy the crank, I asked for a 9 speed compact Shimano compact crank and I never even bothered to check. In fact, I admit thought all 105 stuff was still 9 speed.
I’m guessing the fact that this crank is 10 speed might mean that the rings would be slightly closer together. That would account for the rub that wasn’t there before.
Odder still, on my tri-bike (a 10 speed dura-ace all around with compact crank) there is no rub whatsoever in any combination. It comes awfully close but nothing rubs
I still wish there was some way I could just position the rings out ever so slightly farther or the cassette in ever so slightly. But I guess I just have to avoid this as best I can.
If I were to decide to go all-ten speed with this a few years down the line, that would mean i need new shifters, derailleur (front, and back), cassette and chain, right? Will that be enough?
Why not just put a 10 speed chain on now and be done with it?
You also need to be a little less “picky” when you’re mixing components like this
Ding, ding, ding, ding! Narrower chainring spacing PLUS larger difference between the chainring sizes spells highly likely “tickling” of the chain on the teeth of the large chainring when severely cross-chained like that. Put on a narrower chain…but STILL don’t DO that. Seriously, just shift your chainring…what’s so hard about that?
Agree not hard. But I do occasionally inadvertently cross chain. I did it twice on a ride this weekend which was how I discovered the problem. I’m just worried that one day I’ll do it and the “almost” catch will be a little farther than “almost” and will mess something up.
(I also occasionally ***intentionally ***cross chain but that’s usually big ring to big ring and just momentarily to avoid a front ring switch on a briefly steep section. I know I’m far from the only person to do that!)
Why not just put a 10 speed chain on now and be done with it?
Is that a good idea with a 9 speed cassette, derailleur, etc?
You also need to be a little less “picky” when you’re mixing components like this
OK, now you are really confusing me. I thought that component groups were fairly well matched. That you weren’t supposed to mix 9 and 10 speed stuff. Are you saying I should?
Ding, ding, ding, ding! Narrower chainring spacing PLUS larger difference between the chainring sizes spells highly likely “tickling” of the chain on the teeth of the large chainring when severely cross-chained like that. Put on a narrower chain…but STILL don’t DO that. Seriously, just shift your chainring…what’s so hard about that?
Agree not hard. But I do occasionally inadvertently cross chain. I did it twice on a ride this weekend which was how I discovered the problem. I’m just worried that one day I’ll do it and the “almost” catch will be a little farther than “almost” and will mess something up.
(I also occasionally ***intentionally ***cross chain but that’s usually big ring to big ring and just momentarily to avoid a front ring switch on a briefly steep section. I know I’m far from the only person to do that!)
Well…then take the noise to be a “warning” that you shouldn’t be doing that
BTW, I can’t imagine what damage could occur if your chain did end up going onto the large chainring while in the small cog in the back…although I highly doubt the front derailleur would allow that to happen anyway.
