Down shift aids on chainring
 

I am running a KMC x8 chain on a Campagnolo Racing Triple 9 sp. 30-40-50 chainset with Racing Triple FD. The down shift from middle to granny is very sluggish due to chain length between cage contact and ring contact points, a fundamental issue with a triple set-up. I notice that the TA rings for this chainset have pairs of shortened teeth. Are these downshift aids? Would filing a few pairs of teeth down help the Campagnolo middle ring to let the chain go?

oldschoolbike

I can't answer your question, but I am interested in what others have to say.

A bike's shifting is really designed like a Houdini level magic trick - the goal is to keep the chain locked in a chosen gear no matter what, until of course it gets the magic touch from the derailleur that moves it easily and instantly at the push of a distant control.

I think the short teeth are UP shift aids

check your chain tension - should not be too tight on the middle ring.

also check the ANGLE of your front derailleur. outer plate should be parallel to the plane of the chainrings.

you MIGHT try bending the "toe" of the cage in just a tiny bit. would need to see the actual problem to give you better guidance.

/markp

Shimano early in their pursuit of better shifting (early 1980s) came up with (knowing Shimano's patent research dept, likely "borrowed" the idea) with what they called "W Cut" ring teeth. The tops of a pair of teeth were cut down in height, reasoning being that the chain wouldn't have to climb up as far to get over the teeth to move sideways to the inner ring. It worked fairly well and a trick/mod I have done to many non shift ramped/pinned rings to enhance their shifting. In my home made versions I increase the number of paired cut down teeth from two pairs about opposite each other to 5 pairs distributed evenly around the rings..

Having said the W Cut helps with shifting is all great it discounts the vastly larger component in the shifting system, the rider. Or more to the point the riders control box between the ears. I don't think I can count on the number of fellow club riders and so many customers who complain about front shifting, double and triples. Those who listen and take advice find that many of their issues go away after they learn and use best shifting techniques. Andy

Another vote for checking your chain tension. Don't know about your short teeth. I always imagined that all the various ways they sculpt teeth on rings is mainly for shifting to the next larger ring.

How loose is your chain when in the small/small combo? If you shortened the chain, then is there enough left to get into the big/big?

It sounds like your version would be even easier to shift than Shimano's, but if you really want easy shifting why stop there? Make five triple cuts - still only 15 shortened teeth. Or do more pairs. At some point, you come to a compromise between shifting performance and power transfer performance. Different riders likely have different ideas about where to make that compromise.

Am I missing something? You are using an 8 speed chain with a 9 speed crank? I might suggest that you try a 9 speed chain and see if that helps. Even if you have an 8 speed cassette - the 9 speed chain will work fine with that.

You probably already know this, but it can't hurt to check the basics: many triples on bikes seem to shift best to the granny when the chain is on one of the innermost sprockets in back. I usually do that shift when the chain's on the biggest sprocket or one of the two next largest ones.

Also, the difference between sluggish and reasonably quick shifts to the granny can be a matter of repositioning the front derailleur so that the rear of the cage is just a degree or two further in toward the frame.

And, of course, make sure to confirm that the vertical gap between the bottom of the cage and the top of the teeth on the big chainring is as it should be. About a nickel's thickness, if I remember correctly.

Here is Shimano's reasoning for the shortened teeth profile in the early SG chainrings (late 80's). Similar to some of their earlier attempts to modify the teeth's shape. These were designed to release mainly in 2 points.

https://cimg0.ibsrv.net/gimg/bikefor...ce250804e7.jpg



A few years later they introduced the SG-X. More similar to what is common today, adding pins, plates, hooks, varying teeth profiles, etc. to aid upshifting. Cranks in this era also began to use chainrings in sets to 'clock' the rings so the distance between the teeths of adjacent rings would match the pitch of the chain. Over the years Shimano and others have modified these ideas in many ways.


https://cimg8.ibsrv.net/gimg/bikefor...b7ff71b4dc.jpg

Very, very cool to see the diagrams.

I did not appreciate that a front derailleur has to work on the tight part of the chain while the rear derailleur can work on the slack part of the chain.

Seeing that I've ridden basic non-pinned/ramped double and triple rings my entire life without issues friction shifting the FD, obviously these "aides" are not necessary. Clever marketing would have you believe you can't live without them... Oh the humanity ! I wouldn't go modifying any chainring teeth. I too suspect either the angle or possibly the height of the FD. I do all my own bike work save make the frame and I've found FD's are highly flexible in their mounting height. I know what the instruction manuals included with the FD's show on paper, but in the real world sometimes a little higher or lower is what works. I'm all about experimenting when what the book says doesn't work. (often !)

Also, more details on your shifting are needed. It's sluggish shifting for mid to small ring in what cogs ? Myself I've never used the tiny ring for anything but 3(of 7) or 4(of 9) cogs or else I'm back on the middle ring. Yet some people as I've read think they can use it on all cogs..... yikes ! Generally when I shift from mid to tiny it's in either the smallest or 2nd cog.

+1 9spd chain and adjust the front derailleur. My 3x9 Campy RT shifts just fine

Make sure your derailleur is mounted as low as possible. The outer plate should clear the big ring by 1.5-2.0 mm, and the inner plate should clear the middle ring by at least that amount. Also try easing off the inner limit screw slightly. Try this before doing anything heroic like bending the cage.

You are not alone in not looking at the gear system as an upper and a lower split. I began teaching how to shift classes with this tensioned top half and un tensioned lower half a long time ago. Andy

Bravo for you being the choir that don't have to learn how to shift. But it's too bad that you are the exception. Andy

10 and 10 are not big jumps. The shifting aids on modern chainrings are designed to aid things like 16 tooth jumps, and mostly for upshifting (pins, ramps), but also downshifting (gates, i.e., reduced tooth height) for doing so under higher chain tension than in the past. Way back when, derailleurs were all designed for road bikes. Downshifting while climbing steeps on a mountain bike requires a stronger push. My Microshift 9 speed triple FD which I retrofit for 2X on my folder, the spring is *ridiculously* strong, my hands were not strong enough to use the left gripshift, I had to fit a lever/trigger, and even then I need to push with right thumb inline of pressure, not left thumb swinging an arc. This is WAY stronger spring than I need for downshifting, but it was probably designed for mountain climbs and muck. I only bike on road. The Microshift is the only one that fits my FD adaptor design, Shimano didn't, linkage interferes, I'm still looking for one with softer spring.

They are necessary when using indexed front shifting with a derailleur and shifter that don't allow trimming to eliminate scraping the chain on the derailleur cage. To make indexed front shifting idiot-proof, the shifter does not allow trimming; you're either in one gear or the other. To eliminate scraping, the derailleur cage is made wider to provide more clearance without scraping. But this degrades shifting efficiency, so pins and ramps are added to the chainrings to facilitate shifting even with a wide derailleur cage.

A worn chain can also lead to sluggish shifting up front.

Yes, the wider cage is part of the problem. Maybe I should put my pre-indexed Campagnolo Record FD back on, if it can handle 50-40-26, or look for a pre-indexing triple FD that can. To validate the wide cage theory, I do get an improved middle to granny shift now that I have installed a Deda Dog Fang and adjusted the inner stop inward about 3 mm from almost rubbing in bottom gear. This will work until I arrange a couple of sets of shortened teeth on the middle ring, and won't mess up anything else because I am friction shifting this FD.

It's all about what you want, not what the manufacturers give you. I want a snappy and reliable middle to granny shift and I am on the way to getting it..

oldschoolbike

I have a Campagnolo Racing T with 52/42/30 that shifts great with a Record triple FD. A 50/40/30 was acquired but the high end was too low for down hills. Rear is 9 speed 13/26.
https://live.staticflickr.com/65535/...77aa9e1_5k.jpgP1050228 on Flickr

I have a theory about that. I don't think it's due to stretch, but rather, side-plate-gap, i.e., the gap between the outer and inner side plates on the links. More gap means less lateral stiffness of the chain. Once or twice in the life of a chain, I pull the chain off, clean well, and then, adjust the side plate gap with a chain tool. Not so tight the links bind, but eliminating that gap, doing an even job so the amount of pin protuding on each side is the same. Then remount the chain and lube. I don't know if this helps, if it reduces stretch, if it causes any increase in friction when the chainline is off on crossed-gears. I'll have to remember to look at what the gap is from the factory, the next new chain I buy.

+1 I don't do index shifting so trimming is easy. Many of my FDs are the old, narrow ones. I further narrow the backs of the cages by removing the bushing and replacing it with a shorter stack of very small washers. Also tweak the angle to slightly inboard at the back. Often bend the front of the outer plate in. (All this done with the old SunTours.) A plus about no index - I can leave the cable quite loose to simplify loosening the clamp and twisting to dial in the angle. Leave the chain in the big ring with the lever thrown forward - DT levers.)

I want my FDs to shift reliably from the smaller cogs in back, when I am still rolling fast up that hill. Then, little speed lost and I get to shift just in back as the hill steepens and I slow. Yes, old racer thinking but also using inertia to make the hill easier. As an aging cyclist, why wouldn't I want that?

I rode Cycle Oregon last Sept on that exact combo except 7-speed. Sweet, sweet shifting. My standard forever (starting with the TA Cyclotourist, then Avocet, then Sugino was 52 or 53-42-28m then 24. Recently the 52-42 has shrunk to 50-38 and the like.

Question, [MENTION=124730]SJX426[/MENTION], what are the BCDs of that Campy crankset? I could go out and measure so don't you but if you know off the top of your head, TIA. I need to start ramping down those big rings!

Edit: beautiful bike!

There is no important difference between an 8 and 9 speed crank or chainring. An even narrower chain isn't going to help the derailleur push the chain off the ring any quicker.


I doubt there is much that can be done with ring design. The shift happens over quite a few teeth.

I would want to look at the FD adjustment.

135 IIRC. Campy had to be different.