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Old 05-29-07, 08:24 PM   #1
TallRider
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importance of large chainrings with ramps/pins designed for specific small ring?

So ramped/pinned/variably-shaped-teeth chainrings have improved front shifting significantly, and made front indexing viable if still a frequent PITA for many folks.

In nearly all instances I've seen, the smallest chainring (granny ring of a triple, inner ring of a double) has all of the teeth shaped the same. Ramps and pins are ususally to aid in shifting up to a larger chainring, or down from the larger chainring, and in both cases the special shaping of teeth, or ramps and pins, are useful on the larger chainring. Hence middle and large chainrings on triples, and large chainrings on doubles, are ramped and pinned and sometimes have variably shaped teeth, but the smallest chainring doesn't have anything of the sort.

But non-smallest chainrings can be designed specifically to shift best with the chain coming off a certain tooth on the inner ring. Which means that the tooth should be in a specific spot on the inner ring to best catch the ramp or pin to the outer ring.
Which means that while inner rings needn't have shaped teeth, ramped/pinned large rings are designed for a specific number of teeth on the inner ring, combined with specific rotational matching of that inner ring to the outer ring (so the teeth on the inner ring are in the spot which was expected when the ramps/pins on the outer ring was designed).

Now, the big question: how much does it actually matter that you use the inner ring that an outer ring was designed for? For example, a Shimano XTR 46t chainring may have been designed for its ramps and pins to shift from a 36t Shimano chainring. But will shifting be much compromised if the 46t ring is used with a 34t inner ring?
Likewise, an FSA 50t outer ring may have been designed for use with a 34t inner ring on a compact double setup, but how much worse will it shift when coming off a 36t Shimano chainring?

This is an interesting technical case where it makes sense that design differences actually matter, but it's not clear that they matter very much. Manufacturers have an incentive for chainrings to be paired, so that consumers will buy two chainrings at once instead of replacing just one. How much practical reason is there for buying chainrings that were designed as part of a system?
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Old 05-29-07, 09:22 PM   #2
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DA 7700 55t VS 56t rings. I suppose they will work like unpinned/ramped rings if they are not matched with the right shimano inner rings.
http://harriscyclery.net/images/libr...odl/CR1795.jpg

http://harriscyclery.net/images/libr...odl/CR1793.jpg
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Old 05-30-07, 03:08 AM   #3
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I've ridden the matched Shimano rings for years on mountain bikes. About a year ago I switched my stumpjumper middle and outer rings to a different brand and have noticed no difference in shifts between the old Shimano small ring and the new middle ring.

When I built up a new road bike I went to a TA tripple. The rings are not matched as Shimanos are, but it shifts very well. I don't think it's as good as the Shimano, but the difference seems small.

Al
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Old 05-30-07, 06:24 AM   #4
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http://www.sheldonbrown.com/dura-ace.html#chainrings is his take on the matter.
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Old 05-30-07, 07:56 AM   #5
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Quote:
Originally Posted by victoon
DA 7700 55t VS 56t rings. I suppose they will work like unpinned/ramped rings if they are not matched with the right shimano inner rings.
http://harriscyclery.net/images/libr...odl/CR1795.jpg
http://harriscyclery.net/images/libr...odl/CR1793.jpg
Those rings are labeled "56-44" and "55-42" with the second number presumably corresponding to Dura-Ace inner ring for which they're designed. Which just begs the question that I was originally asking. I suspect they'd still worked better than old unramped/unpinned chainrings, but not quite as good as when used with the chainring for which they were designed. That is, how much of a difference is there?

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Originally Posted by vpiuva
Thanks, Here's Sheldon's take on the matter, apparently specifically about 10-speed Dura-Ace stuff:

Quote:
Newer "Superglide" chainrings from Shimano use similar features to the rear Hyperglide system to improve front shifting. The outer rings have special shaped teeth here and there, called "gates" which make it easier for the chain to climb up. There are also steel pins rivetted into the sides of the larger rings to help the chain climb.

When this system is working as it shoud, the chain makes a very smooth transition from small to large chainring with no slippage. For this system to work as smoothly as it is designed to, the locations of the teeth on the smaller ring should be specifically placed with regard to the positions of the teeth of the larger ring.

This requires that the chainrings be used in matched sets. Shimano has two "road" sets, designated "A" and "B".
  • Set "A" uses a 42 tooth small ring, and a corresponding "A" type 53.
  • Set "B" uses a 39 tooth small ring, and a choice of "B" type 52 or "B" type 53
Only Shimano is this fussy about chainwheel matching, and this is by no means mandatory. In particular, if your bike currently has an "A" set 53/42 and you decide you'd rather have a 39, this doesn't mean you need to replace the 53 as well. It will still shift, and shift well, just, perhaps, not quite as well as the designated set.
The italicized part (emphasis added by me) is closer to a specific answer.

Al.canoe's experience is about what I expect.
I'm especially curious at this point about where these differences matter. Is it just for front shifting under major load?
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Old 05-30-07, 08:45 AM   #6
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My guess is it'll be slightly more of a pain to get it tuned, but that you will be able to get it to shift reasonably (as Sheldon mentions). Most likely, I'm guessing you'll have to make some tradeoffs with the indexing and limits to get it to shift up well that might add some extra chain rub in the marginal gear combos, or might end up slowing your downshifting a bit. All in all, probably not a big deal.

Naturally, if you're losing the advantage of pinning/ramping AND increasing the tooth difference, that will exacerbate the problem.

In the end, it shouldn't matter much unless you switch chainrings a lot, which I try to avoid.
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Old 05-30-07, 09:17 AM   #7
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Quote:
Originally Posted by Mr. Underbridge
My guess is it'll be slightly more of a pain to get it tuned, but that you will be able to get it to shift reasonably (as Sheldon mentions). Most likely, I'm guessing you'll have to make some tradeoffs with the indexing and limits to get it to shift up well that might add some extra chain rub in the marginal gear combos, or might end up slowing your downshifting a bit. All in all, probably not a big deal.

Naturally, if you're losing the advantage of pinning/ramping AND increasing the tooth difference, that will exacerbate the problem.

In the end, it shouldn't matter much unless you switch chainrings a lot, which I try to avoid.
I have experienced no difference in adjusting the shifting. On my atb, I tune while riding. Shifts under load are about the same best I can remember. On the TA, tuning is about the same as the Shimano matched atb rings but I have no adjusters to tweak while riding.

My "differences" on the TA are 22/36/46. The 22/36 shifts are surprisingly good, but I really don't shift all that aggressively on a road bike compared to the atb. The atb is 22/32/42 where the 22 is shimano and the 32/42 are Blackspire.

I have no additional chain rub though I've always had that with Shimano rings and Shimano derailleurs. That occurs at angles I don't use anyhow. I chose the particular TA rings to provide a group of close ratios (plus some ultra-low) the old fashioned way using logarithm paper. That advantage was more important to me than the Shimano slicker shifts as I used to ride some in the old days before matched rings. Back then, you could also select the cogs and either assemble them yourself or custom order. Life was good!

Al
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Old 05-30-07, 09:58 PM   #8
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Quote:
Originally Posted by Al.canoe
I've ridden the matched Shimano rings for years on mountain bikes. About a year ago I switched my stumpjumper middle and outer rings to a different brand and have noticed no difference in shifts between the old Shimano small ring and the new middle ring.

When I built up a new road bike I went to a TA tripple. The rings are not matched as Shimanos are, but it shifts very well. I don't think it's as good as the Shimano, but the difference seems small.

Al
that's very comforting news to me. I will have to start to use unmatched rings soon. but my experience with the rings came with the ritchey wcs compact crank (with FSA C-16 FD) wasn't good at all anyway.

but in order to give Tim's question a fair answer, I do think we have to know how well people rate the shifting of unpinned/unramped and unrotationally matched rings. if people think they shift well enough, I am sure the improvement margin provided by technology won't be that significant no matter what.
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Old 05-31-07, 12:36 AM   #9
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Quote:
Originally Posted by victoon
I do think we have to know how well people rate the shifting of unpinned/unramped and unrotationally matched rings. if people think they shift well enough, I am sure the improvement margin provided by technology won't be that significant no matter what.
My crankset is TA Zephyr with 20/34/46 rings. 34 is TA and 46 is Race Face, both ramped. For a moment, I went down to TA 33 in the middle. 33 has been unramped, but bolts close to its teeth were supposed to take on the role of ramps. In my riding, I shift often in the front and it was bad with the unramped 33. After few weeks of suffering, I kicked 33 out and went back to the ramped 34.

Otherwise, my overall quality of front shifting has depended on tweaking the orientation and shape of the derailleur cage. After tweaking, it has been very good, but each time I had to move the derailleur, for one reason or another, it must have taken me 2 weeks to get back on track.
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Old 05-31-07, 07:49 PM   #10
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My personal experience is that ramping/gates/pins are all very well and good, but the thing that really matters, to the point where the rest of it is down in the noise, is how accurately the derailer is positioned relative to the chainrings.

A dime-width of clearance between cage and big ring, everything's perfect. More than that, and you're not a happy camper. So my instinct is to hypothesize that a perfect match between middle and big chainrings w.r.t ramp/pin/gates gives you more slop in getting the FD on to still allow indexing there to work.

But, admittedly, I only have one bike that has indexed front shifting and in general indexing there is an answer to a question I'm never asking. I don't like not being able to trim.
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Old 05-31-07, 08:10 PM   #11
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Quote:
Originally Posted by bjkeen
But, admittedly, I only have one bike that has indexed front shifting and in general indexing there is an answer to a question I'm never asking. I don't like not being able to trim.
Gripshift is sort of like indexed friction. You can push it farther if the intended stop does not work. This is helpful when you are still tuning the derailleur. I found that bending the cage also helps in reaching an optimum with the front shifting.
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Old 05-31-07, 08:35 PM   #12
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I have a 2007 Deore LX with a black 48T big ring that I wanted to swap with a silver 48T big ring from a last year Deore crank. However, when I compared them, the pins and ramps were in very different places plus the older Deore had very little ramp built into it while the newer Deore LX had a lot of tooth and ramp shaping built into it. Apparently technology flowdown from higher models into the current production LX. I did not make the swap because it looked to me like I would be giving up the alighnment built into the stock Deore LX crank set. I suspect it would still work OK but would lose some smoothness in shifting. I wanted the color change but not bad enough to downgrade my shifting performance.
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Old 06-01-07, 12:05 PM   #13
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I've done many chainring switches and the only time I have noticed any decrease in shift performance is when I tried ones with no shift aids at all.

BTW, the biggest reason for the ramps & pins is current front derailleurs are designed with less vertical movement then older models. The older units would actually lift the chain during an upshift; newer ones just give 'em a shove sideways.
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Old 06-02-07, 05:41 PM   #14
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Originally Posted by rmfnla
BTW, the biggest reason for the ramps & pins is current front derailleurs are designed with less vertical movement then older models. The older units would actually lift the chain during an upshift; newer ones just give 'em a shove sideways.
I think that has a lot to do with seat tube diameter. nowadays the tubes are bigger. so the shift happens at the more horizontal part of the swing.
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