Mr. Spadoni 

So I’m rebuilding a bike that I put together years ago in the pre internet days when access to specs was limited and at when my access to parts was complicated by the absence of any road bike shops in the place I was living.
Bike was assembled using a Dura ace cartridge BB with a 108 spindle. It’s still going strong.
In the rebuild, I’m replacing the cranks with one of two options that say they need a 113 or 114 spindle. If my math is right, and the spindle is symmetric, that means the chain line will be off by 2.5 to 3mm.
Is this going to make any difference? Keep in mind that this bike will never have indexing or any non friction shifter.

52telecaster

Modern chains make it less critical but you may run out of derailleur travel or room. While it is less critical it's still important.

Andy_K 

I'm not even convinced the "recommended" chainline is optimal for my riding style. The standard 43.5 mm chainline (for a double) is meant to more or less center the rings on the cogs they'll be used with, but it skews towards centering the big ring on most of the range, assuming the small ring will mostly be used for the three biggest cogs. That may be true for most people. I hardly ever use the big ring.

Anyway, as long as your small ring doesn't rub the chainstay and your front derailleur will shift the chain onto the big ring, you're probably OK.

52telecaster

This is how I see it too. When I do half step and granny I try to get the granny very close to the frame because I only use it on 2-3 cogs. For a double I would cheat toward the one I use most. Personally I don't put big rings on anymore. A 50 is kind of pointless to me.

Andy_K 

I know exactly what you mean. I use the big ring to rule out chainring wear as a possible problem when diagnosing chain-related problems. Other than that, it's purely decorative.

52telecaster

They do look cool and manly!

Classtime 

funny.

Kabuki12

I had never really paid attention to chain line with the fixed cup BB’s and the bikes seemed to work fine. Then, I had my Colnago painted which came with a Phil BB and I did not take an end of spindle measurement prior to disassembly….doh! When I put the bike together, I just sort of “eyeballed” without using a straight edge to check and the bike just did not shift properly. It seemed I was at “limits” with either the FD or the RD. I posted about it on the CR list and got some help via the Campagnolo spec sheet for 5 or 6 speed freewheels and two chainrings. . After measuring where I was and comparing where I needed to be , I adjusted the BB to that spec. The bike shifted perfectly and my world got better. I only had to take the crank off twice. It is still a bit of a pain but the nice thing with the Phil BB is that I can adjust for a triple if/when I decide to go that route.

dualresponse

Another 'big chainring' vote here!!!! Go big or go home. If I'm in the Big ring, I'm (feeling ) faster, and I enjoy life more. If it wears out the cogs or chain sooner, so be it. Don't get me wrong, I'll go down to a smaller front gear, but when I hit small front/small back, and it skips, I'm still crossing just as much, and I lose MOJO.

Don't lose MOJO!

sd5782 

I am exposed to mostly mass produced bikes, and I like to keep it to at least mid level ones. Seldom if ever do I see the factory chain line being skewed towards the inside. They are mostly aligned outward. I often change spindles on bikes to “improve “ the factory choices, or at least in my view. I like to err on the side of being closer to the seat tube.

Mr. Spadoni 

Thanks for the input on the spacing. I’m going to set this bike up skewing towards the small ring. Still gonna keep a “big” ring, but it will be smaller than what I used 50 years ago when I got my first good bike.

52telecaster

Just make it work for you. Riding is the goal.

gaucho777 

Another possible concern is that the chain will rub on the inside of the big ring when in a small-small combo. I can ignore this if it only happens in a true small-small cross-chained gear, but not when it happens in a small ring to 2nd cog situation. One of my bikes is set up with a 53-36 T.A. Cyclotouriste in front and it’s tight on that second cog. Obviously, the bigger the gap between chainring sizes, the more likely this will be an issue.

esasjl

Wheels I've built myself have the axles set (cup and cone) so that the chain (small sprocket on freewheel) runs as close as possible to the DS seat stay. This, and an offset rim, helps to reduce dish. The chainline is then the centre of the sprocket cluster (as for all wheels). I then get a BB (square taper) the correct length for my most-used chainring to be on the chainline, usually middle of a triple or outer of a double (logic also being more chain tension wit smaller chainrings therefore more sensitivity to chainline). I have a junk STBB and eye in the chainline in units of sprocket spacing to give the correct spindle length. I'm using modern flexible 9-speed chains on compact 6 and 7 speed freewheels so I'm not sure if any of this makes any real difference, but the tinkering is fun.

79pmooney

A couple of points. One - different cranksets sit different distances from centerline. Yes, there are nice tables to tell you how far off but - square taper BB spindles and their matching cranksets have a fit based on a very shallow slope. So little variances in manufacturing or from prior installations make much larger differences in how far out the cranks sit. Another thing to look at - Shimano BBs now are symmetrical. Were they always? I don't know. In the '70s and '80s most of their competitors were not symmetrical. I haven't done the math (and I'd have to see and measure the asymmetrical ones) but an asymmetrical 108 might be identical to a symmetrical 113 on the drive side. I keep Shimano triple BBs simply to mount prospective cranks on and measure where they sit. Then buy a BB with the spindle to place the cranks where I want them. (And love the adjustability of Phil Woods!)

And last - also probably the most important - think of all the past BF mechanics that will be rolling over in their graves if you do not adhere to a proper chainline. You might even be speeding current BFers to an early grave. (Says Ben whose Sugino 75'd velodrome standard drive fix gear and 1976 racing bike might be the only two he's ever owned with proper chainlines. And who now slides cranks as far inboard as possible for his knees.)

dddd

Generally I'm always trying to get the chainrings in further, with the limits being:

1) Will the front derailer still be sufficiently adjustable so as to still pull the chain down to the smallest chainring with authority.

2) will the chainrings clear the chainstay with minimum ~2mm clearance?


Likewise, at the rear wheel, I'm always trying to move the rear hubshell and smallest cog as far to the right (drive side) as is possible, within the clearance limits of the chain touching the seat stay or the dropout (or any protruding dropout hardware such as axle stop bits or derailer claw-mount nut/bolt). I sometimes take a Dremel grinding stone to any such points of contact with the chain, including said hardware (or even the seatstay itself).
Sometimes it's the freewheel body which might make contact with bits of dropout hardware (but the solution is usually the same as if it was the chain rubbing).

gaucho777 

Out of curiosity,
1) Is the desire to get the chainrings closer to BB related to Q-factor, or some other purpose?
2) Is your reason for getting hubshell closer to dropout an attempt to increase angle of drive-side spokes for added wheel strength? Other reason?

dddd

I'm mainly trying to achieve a better chainline when using the big ring, since I'm in rolling foothills terrain here and trying to avoid frequent use of the front derailer (which usually causes a loss of momentum).

At the rear, again I'm trying for best chainline in the big ring, also keeping the axle better supported, as well as the rim.

due ruote 

+1. I set up a bike of mine with what I thought was perfect 8-speed gearing, and optimized the chainline for the large ring and the couple of cogs I routinely use in my mostly-flat terrain. But the three smallest cogs/small chainring caused chain rub on the big ring.
I resolved the issue by shimming out the drive side with a 2mm spacer.
Also, maybe obvious but worth a mention - the severity of chainline issues correlates with chainstay length.

52telecaster

Longer stays make chain line much easier.... Thanks for pointing that out.