Take it to Living Car Free (see the Drinking Water thread).

Ugh. There's 5 minutes I'll never have back.

You must be in health care. So was I. Of course, there's also «Système Internationale» aka "metric system."

International System of Units (SI, abbreviated from the French Système International (d'unités))

he responded in a build your bike thread in mechanics he meant SIS so shimano indexed

Oh, ---- ok.

Si is the Spanish word for yes. It is also the French word for yes if in response to a negative question.

That's incorrect:

7 speed chain bushing - .092" 10 speed chain bushing - .090"
7 speed side plate thickness - .049" 10 speed side plate thickness - .030"

The bushings can't have gotten narrower because chainring teeth haven't gotten narrower. You can run an 11 speed chain on a 1980s six speed chainring.

Thank you for that. All is now clear and my mind is at rest.

Yes, you can. But then you risk jamming the chain between the rings when shifting between them. Better to use a 7-speed chain with a vintage crank, if at all possible.

If you say so. Campy's chainring spacing only shrunk by .25mm, and Shimano's 11 speed chainrings are spaced wider apart than their 10. People have been claiming something like this since 7 speed came out, but there doesn't appear to be much to it.


None of which has anything to do with bushing width, which was the point I was making - 11 speed chains will work fine on any multispeed crank's chainring tooth profile going back to those for 5 speed chains. The chains got narrower by thinning the plates, which necessitated different pins because of the decreased contact.

FWIW, I have personal experience with this happening, using a TA Pro-5 crank and a 9-speed chain.


Point taken. Signing off.

You can jam a chain of any width in the open gap between spider arms. I just don't think the danger of doing so with 11 speed chains is that much greater than it was with your 9 speed chain or a 7 speed chain.

When SIS came out We called it sissy shifting.

The wider chainring spacing of today's compact cranksets is not an issue since the big ring now has it's inner surface heavily ramped and thus further offset from the plane of the teeth than on traditional chainrings.
The actual space between the small ring's teeth and the inner surface of the big ring at the outer radius of the small ring is what will affect the possibility of the chain slipping between rings.

I've retrofit modern 9s chain to a lot of very old bikes, some work perfectly while some allow a narrower chain to jam between rings or to merely skate along the tips of the teeth, depending on the model of crankset and to a seemingly lesser degree on the size difference of the two rings.
I once had a new 9s chain almost immediately get stuck between shimano 600 6s-era chainrings and gore the chainstay of a brand new Cannondale frame, so won't easily forget that.

I have yet to see a modern chain fit too tightly on a vintage bike's chainring teeth, but some "semi-modern" chains (from the 7s era) did actually have that issue because of too-narrow bushings. Those were brands no longer offered so of no concern today, and I suppose they were having difficulty maintaining a large enough inside width as they had to redesign the outside width for the then-new Ultra or 7s cog spacing.

This is a bit like the command line unix/linux guys refusing to use a GUI editor. and VI is a terrible editor (fighting words for some )

Isn't that more relevant to crank length?......

Maybe so, but vim is pretty awesome, with context sensitive syntax highlighting, etc.

Hmmm that's a new take on laterally stiff and vertically compliant...

When I started this thread I was actually expecting a technical response. Its like being back at university, where every double-entendre is seized upon, and the original question is lost.

As I think everybody knew I should have typed SIS, but clearly no-one has a credible explanation. Please prove me wrong

No, none of us knew you meant SIS, because no one uses that term to refer to indexing any more. And then you didn't respond to your own thread. Where you back in 1988?

Despite that, a few of us did have technical discussion about shifting accuracy and chain length. Did you read it?

This was not a question about shifting accuracy, although the conversation went that way. It was about why chain length, not its specification, was the sole factor in preventing access to all gears in such a major way, by reducing the throw distance of the derailleur.

Since I deal with vintage bikes in the main, SIS is considered modern. Mostly I build with friction shifters, although I do like to replace the downtube shifters with handlebar shifters. Since mostly, I am restoring the frame, then brazing a double guide on the frame downtube, and cutting off the old stubs is my preferred route.

The SIS technology may now be superceded, but that does not impact on its name, unless you want to start calling SIS a "legacy" product.