Originally Posted by
oldbobcat
The combination of short chain stays, a wide cassette on a 130mm axle, and a wide size difference between chain rings, like 50-34 or 53-39, will often cause the chain to rub on the inside of the big ring when using the small-small combination. This is quite normal. My Felt F5 did it. My Giant TCR did it. My Trek Madone does it. My 42 year-old Masi Gran Criterium doesn't do it, because it has a 7-speed cluster on a 126 mm axle and longer chain stays. It didn't happen with your steel rings because the teeth were probably a little bit narrower. When you fudged with the inter-ring spacing it stopped shifting properly because the derailleur is designed to work with a center-to-center chainring spacing that is proprietary to Shimano (and copied by FSA, SRAM, and others).
Small-small is your sacrificial gear combination. Just don't use it. For me it results in too much chain slap against the stay anyway, and with a 10-speed cluster I know there's a combination on the big ring that's close enough. I know some guys compensate by inserting a 1mm shim behind the drive side bearing or cup to shift the whole crank to the outside a bit. If you're really hung up on this you might give it a try, but it might result in too much cross-chaining the other way on big-big. And some guys say big-big is against their religion, so they don't mind.
And I apologize to the topic border patrol, but I thought I could just put this to bed. I promise not to do it again.
I see. It must be the odd spacing that the aluminums have over the steels, PLUS, I just figured out that someone may have changed the chain on this. The factory specs say this was supposed to come with a shimano hg40 chain, but that's the chain I just threw on there that caused all this ruckus. The chain that was on there was an odd KMC Z chain, with slightly buldged side plates. By throwing that shimano hg40 on there plus adding the aluminum rings (the exact same company and shape) it caused all
sorts of crap. So I put the original steels on there and it was a tad better but still rubbed. So I took the shimano chain off and put the kmc back on there and it's ok now. The chain BARELY touches the inside of the big ring but she's really nice now. Then, for science, I threw the aluminums back on and she's like 99% now. Overall it was the hg40 that was the main culprit. Though it sucked; how could the factory use it?
It must be a combination of the short stays because I have/had a TON of road bikes, and NOT A SINGLE one of them ever had this problem.
Ever. And not any of countless road bikes I built when I worked at a shop. JUST this one lol. (this new stuff will be the death of me. C'mon powder coaters, hurry up with my old bianchi frame so I can ride some old school stuff again) I know it's 'cross chaining' but besides hills, I've
always rode the smallest cog and the next 3 or 4 cogs up and never rode the big ring except in some situations where I was racing my brother. Not my first Schwinn Varsity in 1984 nor any other bike has the small/small combo been trouble for me. Weird.
I was thinking about the rear spacer option but it has sealed hubs with these odd aluminum collars and set screws (kind of like crupi bmx race hubs) so the distance the cassette has to the drop outs is kind of stuck, unless I want to grind some off of there. Then the dish will be a tad off. I'm going to get a 4mm wider BB and see what pushing the drive side out 2mm's does to the final alignment. Maybe that will allow me to use the shimano chain, which I feel downshifts a tad better than this one.