Randybb

I just set up my old 7 speed bike with a new 11 speed rear wheel with an 8 speed cassette. I'm noticing my chain rubs on the FD in the highest gear, even at its maximum reach.

I'm trying to figure out how my chain line was affected by the new wheel -- there's a few things going on -- respacing the dropouts from 126 to 130, the different length of the 11 sp freehub body, adding an additional cog, adding a spacer behind the 8sp cassette...

I could just try putting in a shorter bottom bracket, but I want to figure this out. I started to do some measurements, but I'm not sure if I'm precise enough to get it -- does anyone know the dimensions of a 7 speed freehub vs an 11 speed freehub?

ThermionicScott 

Chain rubs on the outer part of the FD cage in top gear, or inner?

From what I've read, 11-speed expanded the cassette a little bit in both directions over 10-speed (similar to what happened going from 7- to 8-speed), so the official chainline spec is around 42mm.

Might be good to double-check that the dropouts moved out equally when respacing the rear.

Randybb

Chain rubs on outer part of FD in the top gear (smallest cog, biggest ring). Looks like I still have a a few extra mm retraction on the FD for the low end though, so a shorter spindle could definitely help, assuming my chain line is in fact off. Rear triangle is aligned. I did have to add a spacer behind the cassette (it came with the hub), but I didn't measure the thickness.

ThermionicScott 

Okay. If you can't get any more FD travel by letting out the high limit screw (and it's otherwise adjusted correctly), a shorter BB may be what you have to use.

What crank and BB length are you using now? I use 6/7/8-speed era double cranks on most of my bikes, and while they typically spec'd 113-116mm BBs, I've had good results with 107mm units -- this helps get the big ring centered on the cassette so that I can use the big ring with the whole cassette.

Homebrew01

You don't mention if you have tried to adjust the FD.

Randybb

Yea, it's maxed out, I took out the high limit screw.

Randybb

I have a 68x118 BB on there now -- but I had previously replaced the original BB which was 117mm with the DS 2 mm longer than the NDS.

I'm not sure if I should step down to a 115 or a 112. I want to make sure my chainline is good, or it might make more sense to replace the FD instead.

AnkleWork

A shorter spindle will only make your chainline worse -- swapping a small problem for a medium sized one. Maybe try dremeling the high limit?

ThermionicScott 

A road FD ought to have enough swing for what you're after. I'd use Sheldon's chainline article to measure yours before making any changes.

Just speaking in terms of Shimano's UN54/55 bottom brackets, the 115mm is 1.5mm shorter on each side than the 118, so if you've got at least that much clearance from the chainrings and crank arms to the frame, I'd go for it.

ThermionicScott 

Let's think about this -- to throw out ideas like dremeling the high limit stop, wouldn't that mean that his chainline is already way too far out?

Randybb

How do you know if my chainline is good now? Maybe it will fix my chainline.

Randybb

My initial thought was to just get a 115 BB, but it also looks like I have the clearance for a 112 mm spindle. And then I was wondering *why* exactly the new wheel would cause this problem in the first place...

AnkleWork

Try to follow:

Maybe. The original complaint appears to be high side chain rub, which dremeling could solve. Apparently nobody knows whether the OP's chainline is good -- or how bad.

I don't know about your chainline except that you say you have rub that can't be adjusted away with the high limit. Note my use of the word 'worse.' [Dude this is your deal -- only you know what you have.]

Randybb

Well that's why I made this post -- I'm trying to figure out why drivetrain went from a good chainline and a properly functioning FD with 7 speed hub and cassette, to a FD that doesn't reach enough with the new wheel. There are two options 1) My chainline is the same (good), but the outer cog is just farther out, causing the problem, or 2) that the center point of the cassette is also farther out messing up my chainline.

For option 1) shortening the spindle could be a decent compromise. For option 2) shortening the spindle would make the chainline go from bad to worse. I don't really have the tools to measure any of this precisely enough.

Anyway, I'll probably just go with trial and error on this, but I'm curious what exactly is happening, in case I run into this again. Also, because learning things.

ThermionicScott 

In engineering, we try to find and fix the "root cause", not apply band-aids. Which is why I've been trying to coax out part information and measurements before proposing hack fixes.

AnkleWork

Good for you. Of course, dremeling the high stop has a history of sometimes working well and no one yet knows if the problem is just that the FD does not work with the new setup. Would you consider shimming the FD out to be a hack?

The OP seems to begin to grasp some of the issues.

ThermionicScott 

Given that road chainline hasn't changed a lot over the last 60 or whatever years, my money says that just about any road FD should have plenty of adjustability for a crank used with the right BB. If it turned out that the OP was already at 42-43.5mm chainline and just couldn't move the crankset in any farther, I'd still be curious but would be more open to shimming or grinding. But again, only as a last resort.

Randybb

Anyway, seems the issue with the FD can't be fixed by dremeling anything, the top of the spring attachment point is running into the cable clamp arm. It has nothing to do with the stops. I'd previously posted that I removed the limit screw entirely.

Are there any other specific pieces of info you'd like me to provide that would help you grasp the crux of my question? As I said before, I have limited measurement capabilities, but I could try my best.

Bill Kapaun

You know what it does on BIG:LITTLE
What does it do on LITTLE:BIG?

Maybe you can rotate the FDER a hair without messing up the low gears?

ThermionicScott 

I think @AnkleWork and I agree that the very next thing you need to do before anything else is whip out that ruler and measure your current chainline:



You could either measure to the tips of the teeth on each chainring and average the two values, or try to aim the 0 point on the ruler to the middle of a crank spider arm.


(both images pilfered from the Sheldon Brown article.)

Randybb

In little:big there's definitely some spare room, I could loosen the low screw by 1-2 mm if I wanted as well. That's why I was thinking a shorter spindle could be the ticket. I think I'd have to rotate it quite a bit for it to fix the problem on the big ring, but maybe I'll mess with that.

Randybb

Ok so just measured it really carefully, and getting 45mm for the chainline, weird since I thought I'd had it right before... maybe I'm thinking of a different bike!

So now the question is, is the chainline for the new hub supposed to be 43.5 or something less or something more?

I measured from the inside of the dropout to the line in between cogs 4/5 and got 23.5 mm. With a 130 mm hub that'd put the chainline at 65-23.5 = 41.5 mm .

Maybe the new hub needs an even shorter chainline, and that problem is exacerbated by my already too long chainline?

EDIT - just measured the old rear wheel and getting 43 mm from frame center to center cog.

ThermionicScott 

Excellent -- I'm cautiously optimistic that a 115mm BB would clear everything up, then. Since I'm kind of a tinkerer with lots of BBs in boxes anyway, it would be tempting to try even shorter sizes, but 115 would be a good place to start.

Randybb

Yea, unfortunately for me I'd have to shell out a whole $20 for a new one... Looks like I have 4 or 5 mm of clearance between my small chainring and chainstay -- think that's enough to step all the way down to 112 mm spindle?

ThermionicScott 

Probably! Those $20 sealed-cartridge BBs last so long -- with no maintenance -- that I consider them money well-spent, though.