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Single Ring chain angle???(4 posts)

Single Ring chain angle???highcamp
Jul 29, 2003 8:17 AM
Here's a question for all you Single Ring-ers: when using double guards, does the required effective lengthening of the spindle (either by using a spacer on a 109mm BB or a full on 118mm) result in really bad chain angles? Intuitively I would say yes, given that the single ring already sits in the "big ring" position on the cranks and spacing it out even further would force the chain to make an even more acute angle to reach the larger cogs. How well does the set-up function when in the larger cogs?

Not bad at alltriangleforge
Jul 29, 2003 9:45 AM
I've got a 118mm BB on my VooDoo & double TA guards on a 105 crank. The chainring (a 42, fwiw) is in the "small ring" position on the crank, with the inner guard held off with spacers and the outer guard in the "big ring" position. I checked the chainline with a straightedge, and it falls pretty much right in the middle of the cog, maybe a couple of mm outboard. The chain just barely rubs the inner guard when I'm in the lowest gear -- I've thought of grinding the guard ring just a little to eliminate it, but its sometimes handy to have an audible reminder that you're done downshifting and it might be time to hop off and run.

If anything, I'm likely to grind a tad off the other side of the inner ring, since it's not very far off the chainstay -- close enough that if things get a little muddy I can make it rub slightly under hard pedaling.

I was wondering the same thing about the chainline before I put everything together, but for me it turned out not to be an issue.

Why on inner ring?highcamp
Jul 30, 2003 6:27 AM
Thanks for the reply. I was wondering why you opted to mount the chainring on the "small ring" position? Perhaps I'm totally off on this, and believe me it wouldn't be the first time, but I thought the setup was meant for the single ring to sit in the "big ring" position, with the inner guard in the "small ring" spot and the outter guard set further to the outsie with spacers. I understand that your method brings the chainring more inline with the cassette, but it also spaces the inner guard closer to the chainstay - which was what you were trying to avoid by moving to a longer spindle in the first place.

I'm not too bothered by a little chain rub now and again, but I'm spooked about that inner guard doing a number on the chainstay. Aluminum frames aren't too thich-walled and I have visions of that thing amputating the back half of my bike mid-race.

As a side question, while riding with double chainrings did you drop the chain a considerable amount?

Why on inner ring?triangleforge
Jul 30, 2003 11:00 AM
If you look at most double-guard set ups, it's normal to use the outer ("big ring") position for the outer guard. It's:

1) cosmetically a much cleaner installation,

2) a MUCH better chainline (as you note)

3) on some (most?) cranks it's the only way a guard will fit; look at some of the add-on MTB bash guards, and you'll usually see a great big notch cut in them (sometimes all the way through the ring) to clear the crank arm.

In fact, if you look at some of the kits at, you'll notice they are set up to run with a guard in the outer position, a chainring on the inner, and a 3rd Eye Chainwatcher on the inside. If you're worried about spindle length or the inner guard rubbing, that might be the way to go (though I had a bad, bad experience with a 3rd Eye, so would recommend the Jump Stop or other design for that job).

The clearance off the chainstay on my bike is tight, but not that bad at all -- and nothing that wouldn't be cured by a 2mm spacer at the bottom bracket or ten minutes with a hand file to knock the square edge off the inside of the ring -- both easy enough that I would have done them by now if it was really an issue.

I used to drop the chain a fair amount, until I learned to set the bike down gently ALWAYS, even when you're completely knackered. I still lost the chain occasionally, especially in really muddy races where things got gummed up with clay and wet leaves. I then got a 3rd Eye which didn't work out so well for me (a search on this site for "triangleforge" should turn up three or four renderings of the sorry tale), though they've worked fine for others. I went with the single ring & double guards, and have been happy since.