Random musing: why not use a shorter chain pitch for 1x?

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jever98
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by jever98

I was wondering why the bike industry is not for a shorter chain pitch - i.e. distance between chain rollers for MTB and gravel. At the moment, its half an inch (12.7mm), which seems like it just a historic choice.

When riding a 1x on the road or gravel, you have the issue that where you have to have bigger gear jumps than you want because you are shifting between 10T, 11T, 12T instead of 15T, 16T, 17T more often, because you make use of 9 or 10T cogs to avoid riding around with dinner plates on your back wheel.

If one were to go for a shorter chain pitch, say 10mm, as Shimano tried in the 70s-80s with Dura Ace (but got shut down), then you could have smaller cassettes and chain rings at the same number of teeth, because the distance between would be smaller. So you could end up running a 53 front with 12-50 that are roughly the size of a 47 at the front with the current chain pitch, and of a 10-40ish (under current chain pitch) at the back but still have a higher tooth count.

Of course it would be a PITA to switch over, but I'm curious why no one is going that way.
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mattr
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by mattr

jever98 wrote:
Tue Jan 08, 2019 12:49 am
but I'm curious why no one is going that way.
Because shimano got badly burned on D-A 10mm?

And 1/2" chain pitch is an industrial standard, so machines/parts/tooling is widely available. 10mm (as far as i know) was a special, so add 500% to the cost. ;)
IIRC most of the "metric" pitches are actually just a metric equivalent on an imperial pitch, so the 9,525 triplex i've specced before now for a drive chain was actually just a 3/8ths" pitch.......

Marin
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by Marin

I don't think it would be more painful than switching to a new groupset with the same chain pitch.

Also, manufacturing a smaller chain can't really be a problem - I'm sure tooling up for a new derailleur or crank is much more expensive.

mattr
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by mattr

Yes, all the other tooling costs are more expensive, cranks and so on. So why add unnecessary expense on a smaller chain pitch, when 1/2" is the pretty much the only remaining standard in the bike industry. And works extremely well.
Oh, and decreasing the chain pitch by 20% would reduce the strength (cross sectional area) by about twice that as far as my 2 second calculation goes, and have a similar effect on durability/wear.

Marin
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by Marin

mattr wrote:
Tue Jan 08, 2019 10:41 am
So why add unnecessary expense on a smaller chain pitch, when 1/2" is the pretty much the only remaining standard in the bike industry. And works extremely well.
Gearing.

Also, I don't think chain strength is an issue - we don't produce a lot of torque, and with bigger cassettes and thus larger chainrings the forces are much lower now than they were on an old MTB with a 22-36 low gear.

mattr
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by mattr

Nothing to do with torque, we could probably go down to 1/4" pitch on a track bike with no major issue.
But people already snap chains by shifting badly. Reduce strength by 40% and you *might* be into snapping chains all the time.

Gearing, yeah, smaller steps would be nice. But there are trade offs.

basilic
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by basilic

I am not sure I follow. With 1x and wide ranging cassette, there are no 1-tooth jumps, you'll never see 10 to 11, and much less 15 to 16. By necessity you'll have uncomfortable jumps, eg 12 to 14 is almost 17%. If you dislike that use 2x.

Marin
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by Marin

Hmm you're right. Actually, I don't really mind the jumps myself, I don't notice much of a difference between my 10-42 and my 9-46 cassettes.

And when I ride with fast groups, I put on a 3T 9-32 because for some reason the fast groups never want to ride steep gravel roads?

-> http://ritzelrechner.de/?GR=DERS&KB=40& ... 6&UF2=2135

mattr
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by mattr

basilic wrote:
Tue Jan 08, 2019 4:11 pm
If you dislike that use 2x.
Already on it ;)
Trying a 1x experiment on another bike and aleady getting pissed off with the "missing" ratios, at the current rate i'll end up up using a road cassette on the MTB......... which will be shit for other reasons.

jever98
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by jever98

You're right on the small marginal benefits: I just played around with in excel, and by making every cog about 20% bigger the only benefit you really get is that the 10-12 jump goes down from 20% to 17% at 12-14. Most gear jumps are in the range of 17%, with a few going down to 13%. If one would have a 13 speed cassette, 10-39, like Rotor showed, then it becomes pretty nice: most gear jumps below 14%, with the biggest 3 only in the 17% range.

Would a shorter pitch chain not make it easier to squeeze more gears into a cassette? I.e. a shorter pitch matched with a narrower chain and smaller cogs?
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mattr
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by mattr

Yes. If you just shrink the chain ~20% you'd be able to shoehorn another 2 or 3 sprockets in there.
They might be so thin they'd fold up with poor chainline though ;)
Shifting really would be taking a risk, more like the old 7 speed friction stuff, than the rapid, loaded shifting you can do these days!

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Marin
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by Marin

Come to think of it, I'm actually pretty happy with 11x as it is now. If only the TRS cassettes weren't so expensive!

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