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Old 10-27-10, 01:33 PM   #1
stevegor
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53/38 chain rings and chain questions

Hi

I'm restoring a Reynolds 531 steel frame bike with a Dura Ace crank set using a 53/38 rings and DT shifters.
1: Is the jump too much between the 53 & 38?
2: I measured my 116 link chain by the Park Tool method: Large chainring to Large rear cog, then 1 link and it seems too slack on the 38 in the smaller cogs, what am I doing wrong?
3: The RD seems to pull forward too much, why?
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Old 10-27-10, 01:38 PM   #2
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Quote:
Originally Posted by stevegor View Post
Hi

I'm restoring a Reynolds 531 steel frame bike with a Dura Ace crank set using a 53/38 rings and DT shifters.
1: Is the jump too much between the 53 & 38?
2: I measured my 116 link chain by the Park Tool method: Large chainring to Large rear cog, then 1 link and it seems too slack on the 38 in the smaller cogs, what am I doing wrong?
3: The RD seems to pull forward too much, why?
The issue is Chain Wrap and the capacity of the RD may not be great enough. See: http://www.sheldonbrown.com/gloss_ca-g.html#capacity

"For rear derailers, the capacity relates to the amount of chain slack the derailer can take up, and is equal to the front range (15 in the example above) plus the rear range. Thus, if you have a 53/38 crank set, and a 12-28 (16 tooth difference) cluster, the total capacity required would theoretically be 31 teeth (15 front difference + 16 rear difference).

Manufacturers specify this fairly conservatively. They must do so, because they have to assume that some of their derailers will be sold to incompetent cyclists, who will abuse their drive trains by using the smallest chainwheel with the smaller rear sprockets.

Competent riders can considerably exceed the official rated capacity, since they will not misuse the granny ring by running it with the smaller rear sprockets, so it doesn't matter if the chain hangs slack in those gears".


What size cassette (or freewheel) is installed? What make & model RD are you using?

You could solve the problem with a new set of chainrings, or not. Knowing the chain wrap of the RD and the cassette range is needed to answer the question.

Last edited by Barrettscv; 10-27-10 at 01:52 PM.
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Old 10-27-10, 03:06 PM   #3
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Ok, I'm using a 12-25 cluster with Dura Ace 9 spd DT shifters and an 8 spd Dura Ace RD..... According to Sheldon Brown the 8 spd RD should work for 9 spd shifters because it's the shifters that are indexed not the RD, it should just obey the shifters, as long as there is enough scope to handle the cluster, which there should be as 8 and 9 are basically the same width.
Is this right or should I just use a 105 9 spd RD I have spare?
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Old 10-27-10, 03:28 PM   #4
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Originally Posted by stevegor View Post
Ok, I'm using a 12-25 cluster with Dura Ace 9 spd DT shifters and an 8 spd Dura Ace RD..... According to Sheldon Brown the 8 spd RD should work for 9 spd shifters because it's the shifters that are indexed not the RD, it should just obey the shifters, as long as there is enough scope to handle the cluster, which there should be as 8 and 9 are basically the same width.
Is this right or should I just use a 105 9 spd RD I have spare?
Both 9-spd shifters using the 8-spd DA RD will result in movements matching an 8-spd cluster. To use 9-spd cluster, you'd need to get more modern 9/10-spd DA RD or any non-DA RD.

No problems with FD shifting between 53/38t chainrings. Personally I would swap the 53t to a 50t chainring since I would never ever use the highest 3-4 gears with the 53t chainring anyway. Unless I'm just soft-pedaling down a hill.
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Old 10-27-10, 03:34 PM   #5
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Quote:
Originally Posted by stevegor View Post
Ok, I'm using a 12-25 cluster with Dura Ace 9 spd DT shifters and an 8 spd Dura Ace RD..... According to Sheldon Brown the 8 spd RD should work for 9 spd shifters because it's the shifters that are indexed not the RD, it should just obey the shifters, as long as there is enough scope to handle the cluster, which there should be as 8 and 9 are basically the same width.
Is this right or should I just use a 105 9 spd RD I have spare?
Not correct. Shimano 9-speed shifters will work with Shimano 8-speed cassette if the rear derailleur is a Dura-Ace 8-speed.
This is a Shimano peculiarity because cog spacing for 8-speed and 9-speed cassettes is different.
The distance that a derailleur travels (pitch) depends on two variables- shifter cable pull and derailleur actuation ratio.
Here is a link to some charts that help explain this: http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3946 Where it says "Old D-A" it means pre-9-speed Dura-Ace.
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Old 10-27-10, 03:39 PM   #6
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Originally Posted by DannoXYZ View Post
Personally I would swap the 53t to a 50t chainring since I would never ever use the highest 3-4 gears with the 53t chainring anyway. Unless I'm just soft-pedaling down a hill.
I agree.
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Old 10-27-10, 04:24 PM   #7
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It's a little strange that you are having this issue. The required capacity based on the chainrings and cogs are only 28. You RD should have a rated capacity of 29 and Shimano is very conservative on this rating. I've used a similar RD with a compact crankset and an 11-28; this set-up required a capacity of 33 and the short arm Ultegra RD was able to take up all the slack.

You may need to look at the adjustments on the RD, be sure that the limit screws allow the RD to rotate as needed.

There is nothing wrong with using a 50t chainring, too. I have a 50t & 39t standard crankset and really enjoy having a fully usable big ring. But your initial problem can be solved with an adjustment in the RD.

Last edited by Barrettscv; 10-27-10 at 04:28 PM.
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Old 10-27-10, 05:21 PM   #8
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I agree with Barrettscv that something sounds strange. I actually have the Dura-Ace RD-7400 (spec'd capacity of 29) and I've run it with 13-30 and 50x34 which requires a capacity of 33 and it worked fine. I sized the chain to just make the big-big and it still was not slack in the small-small (but just about).

#1. The 38-53 jump should not be too big. The front derailer (assuming that's Dura-Ace, too) is meant for big ring between 50-56 (which can be exceeded by a few either way) and handles a difference up to 15 (which can be exceeded by a couple).

#2 and #3 in your post almost sound contradictory. #2 might indicate the chain is too long. But #3 sounds like the chain could be too short (I assume you mean the cage pulling forward when in big-big). Keep in mind you used a "minimum" chain length sizing method. That's OK but the RD will pull very far forward in the big-big combo. As for the chain being slack, perhaps the spring in the RD is broken, deformed, or weak. Or maybe there is something (dirt?) impeding the movement of the derailer or cage and it isn't wrapping all the chain it should.
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Old 10-27-10, 05:52 PM   #9
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Thanks guys for the info,

I will still use the 53t as my riding usually consists of high speed hammerfests where it is not unusual to ride 53/14-13-12.

Sorry to labor the point I can be dumb sometimes, but am I wrong in thinking that my 8 spd DA RD's pitch should still match a 9 spd RD's pitch because it is the shifter that indexes so the RD simply obeys? Remember I'm using 9 spd shifters and cluster with the 8 spd RD.
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Old 10-27-10, 06:09 PM   #10
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Originally Posted by stevegor View Post
Sorry to labor the point I can be dumb sometimes, but am I wrong in thinking that my 8 spd DA RD's pitch should still match a 9 spd RD's pitch because it is the shifter that indexes so the RD simply obeys? Remember I'm using 9 spd shifters and cluster with the 8 spd RD.
There are no dumb questions.
Due to the geometric shapes of the derailleurs the pitch is not the same for 9-speed and Dura-Ace 8-speed rear derailleurs. All other modern Shimano derailleurs do have the same pitch (actuation ratio). D-A 8-speed is different. The D-A rear shifter has the same cable pull as all Shimano 9-speed rear shifters. This is why any Shimano 9-speed rear shifter working with a D-A 8-speed rear derailleur is compatible with an 8-speed Shimano cassette.
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Old 10-27-10, 11:41 PM   #11
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Originally Posted by Al1943 View Post
There are no dumb questions.
Due to the geometric shapes of the derailleurs the pitch is not the same for 9-speed and Dura-Ace 8-speed rear derailleurs. All other modern Shimano derailleurs do have the same pitch (actuation ratio). D-A 8-speed is different. The D-A rear shifter has the same cable pull as all Shimano 9-speed rear shifters. This is why any Shimano 9-speed rear shifter working with a D-A 8-speed rear derailleur is compatible with an 8-speed Shimano cassette.
Ok, I think I've finally got it, many thanks.

I see I have the choice of using all 9 spd DA (or whatever), OR swapping the rear 9 spd cluster for an 8 spd

IMHO the DA 8 spd RD is one of the nicest looking ever made..... apart from Campy!
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Old 10-27-10, 11:56 PM   #12
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Yup, IMHO the DA 8 spd RD is pretty nice.
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