Shimano Chainring Types & Preferred Shift Points

CrankNFurter
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Joined: Mon May 07, 2018 7:19 pm

Shimano Chainring Types & Preferred Shift Points

Postby CrankNFurter » Sat May 12, 2018 9:29 am

I hope this subject hasn't been done to death previously but I couln't find anything in the archives. As many of the tech-heads here know well there are specific pairs and triplets of chainrings labelled as compatible by Shimano. A type, B type & E type etc. This is NOT a question about which ones are compatible with which - that is covered by quite a few websites - such as this very helpful one:

http://www.thetallcyclist.com/2013/01/the-truth-about-the-shimano-a-and-b-type-chainrings/

My question is not about compatibility, but the consequence of having specific shift-aids placed at particular points around the circumference. If there are particular points where a shift-aid (ramp, pin etc as well as recesed teeth) exist - logically does that imply shifts should be attempted only when the crank is passing that exact point during the pedal stroke? IE should you reserve shifting up or down when the matching up-shift vs down-shift aid is coming into alignment rather than just shift at random?

These features are NOT spaced evenly around the ring - eg on the A-Type DA 7900 crankset the 53 ramps aling with the FD at 12 & 5 o'clock positions of the DS crank (not opposite each other). This implies the rider should shift up to the big ring just as the DS crank is approaching TDC, or just as its passed TDC.

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Tim
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Re: Shimano Chainring Types & Preferred Shift Points

Postby Tim » Sat May 12, 2018 10:11 am

CrankNFurter wrote:This implies the rider should shift up to the big ring just as the DS crank is approaching TDC, or just as its passed TDC.


Maybe, but my take on this is that it isn't an issue.
Chainring ramps and pins are just an assistance to smooth shifting.
Unramped and unpinned rings, as I have on my touring bike, still change within about a half turn of the cranks.
On my 6800, 7900 and 9000 ringed road bikes the shifting is quicker and smoother. Probably achieved within a quarter turn of the cranks, regardless of crank position.
Spinning along at a cadence of 80-120 it's neigh on impossible (and unnecessary) to time front shifting with crank location.
Last edited by Tim on Sat May 12, 2018 10:46 am, edited 1 time in total.

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Duck!
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Re: Shimano Chainring Types & Preferred Shift Points

Postby Duck! » Sat May 12, 2018 10:20 am

There are multiple shift points around the rings, so you're never going to be too far from one in your crank cycle. For best shifting, ensure the alignment marks on both (or all if it's a triple) rings are lined up with the crank arm. It'll still work if they're out of whack, but can slip a bit as the chain tries to catch the ramps.
I had a thought, but it got run over as it crossed my mind.

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