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Old 11-04-09, 11:22 PM   #1
mtnbke
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Chainring alignment

I'm mounting up some TA Specialites Alize chainrings to my Zinn custom 205mm crank and I don't know the proper way to mount the chainrings.

The crank is 130bcd so there are five chainring bolts.

In looking at the outer 46t ring it has four little pins that pick up the chain to help it shift. I can't figure out the right way to orient the chainring on the crank so that these pins are properly positioned during the pedal stroke. On the outward face of the TA Specialites rings there is a little "triangle" or "pyramid" is this to aid in setting up the orientation of the rings? There are two "dead spots" on the ring, they are directly across from one another.

On the middle 38t ring it has four ramps with pins to pick up the chain and unlike the outer ring, there is only one "dead spot" on the chainring. Between any two bolt holes there is a ramp/pin, but the best way to describe the distribution is to say that the four ramps/pins are distributed across 23 teeth of the 38t ring.

How do you orient these chainrings to maximize shifting performance.

Peter White's website, which sells the rings is silent about mounting 'em.

Clearly its not any which way works equally well considering that the pins or ramps and pins are not symmetrically distributed.
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Old 11-04-09, 11:35 PM   #2
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A little off-topic, but...205mm!?! How tall are you? What's your inseam?
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Old 11-05-09, 12:22 AM   #3
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A little off-topic, but...205mm!?! How tall are you? What's your inseam?
He's probably 6'4 etc.
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Old 11-05-09, 12:28 AM   #4
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A little off-topic, but...205mm!?! How tall are you? What's your inseam?
tadawdy,

I aint' telling until I get some help with the chainring alignment queston.

However, here's a hint: I could dunk flat footed back in the day...

The funny thing is when I was a competitive basketball player, in the best shape of my life with over a 36" vertical, I was still a terrible cyclist. In the off season I used to do some mountain bike racing on the NORBA circuit, I was ALWAYS in the last ten finishers of every race.

My old cycling friend used to tell me I could be what I was going to be in basketball, or a mediocre cyclist. He was five foot nothin' and a pure climber. God I hated riding with him.

Which is why I have so much respect for Big Mig. He doesn't get enough credit for being a "great" climber. That he was able to minimize the damage on the climbing stages and win Tours on nothing but time trialing is amazing for a big man.

I wonder what Indurain would have used if longer cranks had been available from his sponsors, or were more 'fashionable'.
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Old 11-05-09, 01:09 AM   #5
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Sorry I'm little help to you, OP. I have the opposite problem: tall and thin. Relative aerobic capacity great, absolute fairly low. I climb very well, mediocre on flat rides. Someday I will move away from Illinois!

I agree with you about Indurain's prowess and raw power. If I'm not mistaken, he's the heaviest rider to win the TDF.

I am glad you got some appropriate cranks for yourself. I figured you were either very, very tall or highly experimental.
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Old 11-05-09, 02:07 AM   #6
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If it's an off-the-shelf matched chainring set, like Shimano makes, you align all the chainrings with the tabs under the crankarm and call it done.

That isn't what you have, so you have to orient them experimentally, by trial and error.

Take a short length of chain and wrap it around the middle chainring, outer sideplate catching a pin on the outer chainring, up the ramp onto the outer chainring -- like it would on an upshift. A "good" shift is when the chain flows up from middle to outer, remains taut, and settles in between the outer chainteeth without riding on top of them. a "bad" shift has the chain riding on top of the outer chainteeth. Check this twice for each pin -- once for each polarity of the chain (outer sideplate vs. inner sideplate). Keep score of how many good shifts you find. Then rotate the chainring by one bolt and check again. Pick the relative orientation of chainrings that has the most "good" shifts. Same deal for orienting the inner chainring vs. the middle.

I like to keep the middle chainring with the tab oriented to the crankarm. You could do the same procedure starting with the outer chainring with the tab oriented on the crankarm. It depends whether you tend to make the inner-middle or middle-big shifts under more torque.

I'm about the size of Big Mig, myself. Actually a little taller and a little skinnier. However it seems a crank more than 180mm isn't good for my knees, and I don't seem to be any faster on 180s than 175s.
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Old 11-05-09, 02:56 AM   #7
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I have the exact combination on one bike - 38, 46, 130mm, TA chainrings (this bike also has a 26 ring inside, but that is irrelevant). Anyway, if the 46 is made for the outer position then it should have a hole near the edge somewhere, and there should be a small nut, bolt, and spacer that came with it (TA also make a 46 tooth ring made for the inner/middle position on a 130mm BCD, which does not have this hole and bolt - I actually have one of those on a different bike which has a super-compact crankset: 28 & 46 tooth rings in the inner and middle positions of a triple crank). Put the bolt in the hole, and the line up the bolt behind the crank so that the bolt prevents the chain from slipping between the crank and chainring. Depending on the crank, you may or may not need to put the spacer on before the nut - only use it if there is enough room for it.

So, that takes care of the orientation of the outer ring. I would then assume that the rings inside that should be aligned so that the writing and graphics on all of the rings are in the same orientation as the outer ring.

If anyone is wondering why someone would want to use a 205mm crank, then read the extensive info on this site.

Last edited by Chris_W; 11-05-09 at 03:01 AM.
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Old 11-05-09, 09:00 AM   #8
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If your outer ring has the chain-drop pin as Chris W noted, that takes care of it's orientation.

Shimano marks their inner rings with a ^ and says that mark should be aligned with the crank arm. Perhaps the mark on your TA rings should be oriented the same way if there is no chain-drop pin to use as a guide.

Incidentally, Shimano rings are installed with the name and tooth count engraving facing outward on the big ring but to the inside on the small and granny rings. Campy has the name and tooth count engraving facing outward on all of their rings.
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Old 11-07-09, 11:37 PM   #9
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The 46t outer ring does NOT have the pin to prevent the chain from overshifting and dropping between the crank arm and the ring, so that doesn't really help.
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