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Old 06-28-10, 06:27 PM   #1
MarkN
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Replacing the middle chainring - 39t to 42t? (Shimano)

I replaced the chain and cassette on my Dawes Discovery 601 (2001) hybrid fairly recently but the middle chaining has also had a fair bit of use in the last decade. Some of the teeth are sharpened or chipped. Also, I've just replaced the wheels and am now using narrower tyres which are quicker but lower than my old tyres, so the gearing is less efficient. I'm finding myself spinning away at the 39t/11t gear a lot more than I used to.

Current setup; 30t/39t/50t Shimano... "Mega drive chain" ? It has 4
bolts. Deore cranks.
The chain is SRAM pc971, the Cassette is also SRAM.

I spend 95% of the time on that 39t middle chainring and would like to replace it with something a little higher, ideally 42t to 44t however I can't find a 42t Deore middle chainring. Is there one? Do I have to use Deore, or could I use a road middle chainring (eg Ultegra)? What are my options here?

I'll also be looking into alternative handle-bar arrangements but that's another matter

Many apologies if this is something I should have found through searching - I had a go but was bewildered at the results



Last edited by MarkN; 06-29-10 at 06:09 AM.
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Old 06-28-10, 06:45 PM   #2
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Four chainring bolts, baby. A road chainring isn't going to work.

Here's my question: Insted of riding around in the 39/11 so much, why don't you just shift into the big chainring?
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Old 06-28-10, 07:09 PM   #3
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Un cheap .. Highpath engineering in Wales will make a chainring in any configuration you need.

as an MTB crank , a 44t outer is common, but its an outer, not a middle , and cannot be flipped over to use as a middle/
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Old 06-28-10, 07:18 PM   #4
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Here's my question: Insted of riding around in the 39/11 so much, why don't you just shift into the big chainring?
My question exactly. A 39/11 combination is cross chained and is hard on the chain so why not use a 50/14 which is the same gear ratio.

I never understood this fixation some riders have for using one particular chainring when another will do the job better.
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Old 06-28-10, 07:38 PM   #5
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I'll second the recommendation to use the 50T more. While I often prefer to stay in the same chainring, using a combo like 39/11 often is going to quickly kill that 11T cog.

The other issue with your proposed gearing change is that even if you could find a 4 bolt, 42T chainring, you'd likely have front derailler clearance issues when shifting from the middle to the big ring. Triple deraillers require a certain amount of tooth differential between the middle and big rings to work properly. With too little differential, you'll have to mount the derailler too high and shifting will suffer. If you really want a 42T middle ring, either search Ebay for an NOS Shimano road crankset from the 9 speed era (all except Dura Ace were 52/42/30) or try Stronglight who makes cranksets with just about any road-sized gearing you could possibly want. The Impact Triple is a good value. You may need a new bottom bracket to go with it though. Link: http://www.xxcycle.com/road-crankset...nglight,en.php
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Old 06-29-10, 03:23 AM   #6
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Well you're right, I would spend more time on the 50t chainring but for a few issues. From the outer chainring the chain occasionally derails outwards onto the crank arm, and that's never an issue on the middle chainring; it only ever goes onto the lower chainring. Then there's the the chain length and angle issue of the big/big combo (50/32) which I was trying to avoid. Does using all 9 speeds on the cassette make me a big girls blouse or something? Now and again I cycle into headwinds or up steep hills so the 50t chainring can be a bit much. The final issue is simply that changing up on the rear derailleur is really, really stiff. I have to crank the shifter dozens of times until it engages, and then sometimes it just half heartedly rubs the chain a bit... but I guess some tuning would fix that? I was thinking a single 42t chainring would be just about perfect for everything... no?
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Old 06-29-10, 06:25 AM   #7
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MarkN,

(1) If the chain occasionally derails to the outside when you're on the 50t ring, adjust the frt derailleur.

(2) Nobody suggested using the 50/32 crossed-chain gear combination; why would you do that? Simple rule: use the outer ring with the outer four or five cogs, the middle ring with the middle four or five cogs, and the inner ring with the inner three or four cogs. That way, you get to use all nine cogs as they were designed to be used.

(3) Yes, if it's difficult to shift, get your drivetrain, derailleurs, and shifters tuned, and lubricate or replace housings and cables as appropriate.
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Old 06-29-10, 06:46 AM   #8
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You are attacking this "problem" from the wrong direction. Spilling the chain can be cured by proper adjustment off the front derailleur's limit screws. Poor rear shifting is either a shifter or cable and housing problem. Have the bike adjusted properly and these difficulties will go away and you can make proper use of the gearing you have. Using all 9-speeds on the cassette is perfectly acceptable but in concert with the appropriate chainrings.
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Old 06-29-10, 06:53 AM   #9
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(1) If the chain occasionally derails to the outside when you're on the 50t ring, adjust the frt derailleur.
I'll have a go.

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(2) Nobody suggested using the 50/32 crossed-chain gear combination; why would you do that?
Laziness? My usual journey features a lot of starting, getting up to full speed for a stretch, and then stopping again. I got used to accelerating from 39/32 and switching quickly up through the gears to 39/11, rather than going from 30/32 - 24, 39/21 - 16, 50/14-11, or whatever the correct way to it would be. Mea culpa, I have sinned

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(3) Yes, if it's difficult to shift, get your drivetrain, derailleurs, and shifters tuned, and lubricate or replace housings and cables as appropriate.
Rogger that, I'll see if that helps me mend my shifty shifting ways.

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Have the bike adjusted properly and these difficulties will go away and you can make proper use of the gearing you have. Using all 9-speeds on the cassette is perfectly acceptable but in concert with the appropriate chainrings.
Noted. I'll pay attention to this.

Last edited by MarkN; 06-29-10 at 06:56 AM.
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Old 06-29-10, 06:56 AM   #10
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The final issue is simply that changing up on the rear derailleur is really, really stiff. I have to crank the shifter dozens of times until it engages, and then sometimes it just half heartedly rubs the chain a bit... but I guess some tuning would fix that? I was thinking a single 42t chainring would be just about perfect for everything... no?
Sounds to me like you are trying to avoid the real problems which has to do with poorly adjusted/functioning derailleurs and/or cables. It will probably cost you less to bring your bike in to your LBS and have them adjust and tune it than it would to replace the middle chainring, and guess what, it will actually solve the real problem! I would suspect that a new set of cables and housing will be required but that is a maintenance item, and if you ride much you should be replacing them every year or two at the most anyway.
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Old 06-29-10, 07:06 AM   #11
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Guys, please just humour me on this one, this 27 speed business is a bit much for me. What I really want is the same gear range but with fewer actual gears. All I really want is a 39/32 (or equivalent ratio) gear at the bottom, a 50/11 (or equivalent ratio at the top) and a few gears in between. I don't want the hassel of all this using the cassete "in concert with the appropriate chainrings". Is there a simple, mechanically robust, economically viable solution along these lines?
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Old 06-29-10, 07:27 AM   #12
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MarkN, In stop and go riding I've found that one selection at the rear with a change up or down on the front was often all that's needed. Once you've taken care of the above maintenance items give that a try.

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Old 06-29-10, 07:30 AM   #13
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MarkN, Take a look at the Sheldon Brown links sticky at the top for some gearing info. There's a wealth of info there.

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Old 06-29-10, 08:28 AM   #14
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'I don't want the hassel of all this using the cassete "in concert with the appropriate chainrings". Is there a simple, mechanically robust, economically viable solution along these lines?'

Many people have reported great satisfaction with the newer internal hub gear drivetrains, which are available in various configurations; the 7-speed versions look like a good choice. Low maintenance, simple operation, and only slightly lower efficiency than derailleur gear systems.

That, or replace your right crank arm with a single-chainring setup. Note that the single chainring must be compatible with derailleur chains (i.e., 3/32" rather than the 1/8" track chain standard size). Probably wouldn't cost much more than the single chainring that you may or may not be able to find, and this way, you'd be able to swap back and forth between the triple-ring crank and the single-ring crank with relatively little effort, assuming that the same bottom bracket spindle length works for both.

If you do go this route, you might want to leave the front derailleur in place, since using the single ring in front with 9 sprockets in back can lead to dumping the chain to the inside or outside.

Or, as several experienced posters have suggested, do a little reading on the Sheldon Brown site and practice using the gears the way they were designed to be used. It's easy, once you understand how they work.

Last edited by Trakhak; 06-29-10 at 08:36 AM.
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Old 06-29-10, 03:44 PM   #15
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'I don't want the hassel of all this using the cassete "in concert with the appropriate chainrings". Is there a simple, mechanically robust, economically viable solution along these lines?'

Many people have reported great satisfaction with the newer internal hub gear drivetrains, which are available in various configurations; the 7-speed versions look like a good choice. Low maintenance, simple operation, and only slightly lower efficiency than derailleur gear systems.

That, or replace your right crank arm with a single-chainring setup. Note that the single chainring must be compatible with derailleur chains (i.e., 3/32" rather than the 1/8" track chain standard size). Probably wouldn't cost much more than the single chainring that you may or may not be able to find, and this way, you'd be able to swap back and forth between the triple-ring crank and the single-ring crank with relatively little effort, assuming that the same bottom bracket spindle length works for both.

If you do go this route, you might want to leave the front derailleur in place, since using the single ring in front with 9 sprockets in back can lead to dumping the chain to the inside or outside.

Or, as several experienced posters have suggested, do a little reading on the Sheldon Brown site and practice using the gears the way they were designed to be used. It's easy, once you understand how they work.
Cheers for the suggestions, I'll think carefully about changing the crank arm although right now I'll settle for reading up on what Sheldon Brown has to say about gears. I kinda get how they're supposed to work but I've just got used to the front derailleur being massively stiff. There's no way I could find a smooth gear progression the way it is now, which makes it practically useless. Need to figure out what's making it so stiff.
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