Author Topic: Chain Rings  (Read 3287 times)

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Offline peterswim

Chain Rings
« on: June 20, 2010, 07:56:13 pm »
This is a much discussed subject, but most of the comments are too general to be helpful.  I'm talking about gear inches and the experts are always complaining that most touring bikes (I ride an old Cannondale T-2000) are not geared low enough.  Well, that's fine, but please then give me suggestions on components to use that will function seemlessly and be dependable.

My bike has chain rings of 52, 42 and 30 and my rear 9-casette runs 34-11, so I have a low end of 24 gear inches.  The rear derailleur is a Shimano XTR.  I would like to swap out the 30 tooth chain ring (and lower the 52 and 42 too), but the mechanic at my bike store is worried that my derailleur couldn't handle the gaps and I could end up with chain drops and other shifting problems.

I'm a strong enough rider I can handle most hills with the gearing as it is, but as I age (I turn 60 next month) I'd rather have mechanical advantage on my side and work less.

Any recommendations?  I appreciate the input.

Offline CastAStone

Re: Chain Rings
« Reply #1 on: June 20, 2010, 09:26:46 pm »
You will have chain drops and other shifting problems, but they'll be with your front derailer, not your rear derailer. A gap of even 12 teeth like yours came stock can be too many, and bringing that to 14 is almost certainly going to kill it. The chain will end up getting stuck between the chain rings, and even if your mechanic can shim that issue away, the shifts will still be slower and you'll have to slow your pedaling to get it to catch. And you would then almost HAVE to use friction shifters of some sort; indexed shifters like STIs cant handle a shim kit.

As to your options that won't be more trouble than its worth, you can get a 11-36 cassette like the SRAM Apex or the 2011 XT or SLX, which will drop you to 22.5 gear inches, but to drop below 20, you'll need to replace all of your chain rings. Your current top gear ratio is 127, which is unnecessary. Anything above 100 and your really reaching a point where you should only use them on a hill so steep that you could gain speed faster by tucking than you ever could from pedaling. So you can afford to replace your big chain ring. With that cassette, you could run a 46-36-26 or a 44-34-24 and never miss the loss on the high end. I see no reason that you would have to replace anything but the chain rings ($15-35 a piece, depending on quality), but your mechanic will understand what your options are better than I can.
« Last Edit: June 21, 2010, 12:52:10 am by CastAStone »

Offline jfitch

Re: Chain Rings
« Reply #2 on: June 21, 2010, 12:32:55 am »
I run a 20-34-46 front end (a 94/58 BCD TA Carmina crank) with a 12-34 cassette (Sheldon Big Dozen with a 34 in place of the 32) with Shimano bar end shifters and derailleurs. My Tiagra front and XT rear derailleurs handle this just fine, so long as I respect the no big-big combination and no little-little combination rules. I do have a dog fang chain watcher on the front. I've never thrown the chain, or lost it between the chain rings. FWIW.

Offline whittierider

Re: Chain Rings
« Reply #3 on: June 21, 2010, 02:01:04 am »
My wife is anything but a climber; so after the first time we did a climb of 4,000 feet in 8 miles on the tandem, I changed the 11-28 cassette to a 13-34, and the 28T granny ring to a 24T, so now the crankset has 24-42-52.  Yes, there's an 18T jump from the granny ring to the middle ring, and we don't have shifting problems and it does not drop the chain.  There's a trick to setting it up correctly though, and a lot of bike-shop mechanics don't have it down.  The 24/34 low is about a 19" gear.  (I've never needed the granny ring at all when riding with either of our sons though!  We just fly up the hills!)
« Last Edit: June 23, 2010, 09:52:49 pm by whittierider »

Offline paddleboy17

Re: Chain Rings
« Reply #4 on: June 23, 2010, 05:01:06 pm »
You can swap out chain rings if you want, but I think you will find it cheaper to just replace the crank with a compact drive mountain bike crank.  I am sure you will be very satisfied with a 22-32-42 front crank.  You will have to lower the front derailleur, and it may need a new compact drive compatible front derailleur if the old front derailleur does not shift well. 

I would just try your existing front derailleur to see if it works or not.

Check you chain for wear as you may want to replace the chain at the same time.
Danno

Offline rvklassen

Re: Chain Rings
« Reply #5 on: June 23, 2010, 05:49:46 pm »
My bike has chain rings of 52, 42 and 30 and my rear 9-casette runs 34-11, so I have a low end of 24 gear inches.  The rear derailleur is a Shimano XTR.  I would like to swap out the 30 tooth chain ring (and lower the 52 and 42 too), but the mechanic at my bike store is worried that my derailleur couldn't handle the gaps and I could end up with chain drops and other shifting problems.

I'm a strong enough rider I can handle most hills with the gearing as it is, but as I age (I turn 60 next month) I'd rather have mechanical advantage on my side and work less.

You could in principle change the 30 to a 26 or even a 24.  Given that you currently manage with a 30, dropping to a 26 is enough that you would really notice it: a change of 10% is enough to notice, and this is more than 10%.  If you only did that, you would have trouble shifting, as your mechanic says.  But if, as you say, you lower the other two as well, by the same number of teeth, the only additional changes you will have to make are 1) to lower the FD mount on the seat tube so it lines up the same on the new rings as it does on the old; and 2) potentially shorten your chain.  With a 48-38-26 you will have pretty much the same shifting performance.    The curvature of the FD won't match as well, but that's not a biggie.

Now that's assuming you can find rings of those sizes with the same BCD (bolt center diameter) as your crank has.   Otherwise you would need to replace the crank.

Offline biased bohemian

Re: Chain Rings
« Reply #6 on: June 24, 2010, 08:21:42 pm »
Everybody that has posted to this comment is very experienced, whereas I am relatively new to touring, so take this for what it is worth.  I have a 48-36-26t crankset and find that, going uphills on the lowest gear with a bike weighed down with front panniers for a long tour, the bike at that speed is somewhat difficult to control, especially under high traffic conditions and with a narrow road shoulder.  This may not be an issue for more experienced bikers, but there must be a point that one crosses with lowering the gears that it becomes unsafe for long tour traveling.
___________________________________
www.biasedbohemian.com - an unabashedly biased look at the world from one small unapologetic man

Offline rvklassen

Re: Chain Rings
« Reply #7 on: June 28, 2010, 12:45:33 pm »
Everybody that has posted to this comment is very experienced, whereas I am relatively new to touring, so take this for what it is worth.  I have a 48-36-26t crankset and find that, going uphills on the lowest gear with a bike weighed down with front panniers for a long tour, the bike at that speed is somewhat difficult to control, especially under high traffic conditions and with a narrow road shoulder.  This may not be an issue for more experienced bikers, but there must be a point that one crosses with lowering the gears that it becomes unsafe for long tour traveling.
Your effective lower limit depends on a) the inherent stability of the bike (i.e. does it have the long wheelbase of a bike designed for touring); b) your preferred cadence while riding up hill; c) how your load is balanced; and d) to a lesser extent, experience.

You mention front panniers. Ideally those should be mounted as low as possible, as weight below the front axle enhances stability.  If you also have a bar bag, try to keep the weight in that as low as possible.

For most people, there will be a threshold speed below which it is just too hard to keep the bike upright and going in a straight line.  On my single, based on an experiment climbing a very mild hill at the lowest speed I could manage, I could probably get away with a 22 in front and a 34 in back, without running into any difficulty.  On our tandem, we have 24 on the front, and 34 on the rear, and yes, we use that combination, and stay upright just fine.  Could use a 22 if it would shift easily enough without giving up the other end (a 48, which we rarely, but sometimes top out, and could go to a 50 or 52, if it weren't for shifting issues).


Offline Tourista829

Re: Chain Rings
« Reply #8 on: June 28, 2010, 10:08:26 pm »
I agree with Paddleboy17, I would switch out the front crank. I have a Race Face Crank, not cheap, but I really like the gearing. 24,34,46.  I was climbing the Barge Canal Bridge, in Florida, a mama of an incline and a very narrow shoulder. With big logging trucks speeding by, one needs to have control, especially with full gear. I feel one can never go too low. 4.5" is another gear. I was glad I had a 19.5" gear. You might have to increase your cadence, but climbing at 4.5-5.0 mph all day and saving your knees is worth it. FYI, on the way down, I could have hit 40 mph, but 30 mph was my limit with full gear. On my last bike, I had a 26, 44, 50 crank and the setup I have now shifts better and is a better ride. That's my 2 cents. 

Offline DaveB

Re: Chain Rings
« Reply #9 on: July 04, 2010, 07:56:12 pm »
You could in principle change the 30 to a 26 or even a 24.
You can do it in practice too.  I've converted numerous 52/42/30 Shimano 7, 8 and 9-speed triple road cranks and even a Campy 53/42/30 10-speed triple crank from the stock 30T granny to a 26T granny with universal success.  They all shift well with the only somewhat sluggish shift being from the granny back to the 42T middle ring.  You are rarely in a rush for that shift anyway. 

I do recommend fitting a "chain watcher" to keep the chain from derailling inside on a hurried shift to the granny.  The Third Eye Chain Watcher and N-Gear's Jump Stop both work well.     

Offline briwasson

Re: Chain Rings
« Reply #10 on: July 05, 2010, 11:14:20 am »
Lots of good advice already! Some more thoughts/addendums:

I have several triple setups running on my bikes, and all work pretty well:

1. Our triplet has Ultegra cranks (130/74 BCD) with 48-39-26 rings (FSA for the two biggest rings), Ultegra STI levers, Ultegra FD, XTR RD
2. Our touring tandem has White Industries cranks (110/74) with 48-36-24 rings and same as above other components. Rings are XTR 5-arm 110/74 that I got NOS on Ebay (nice).
3. My Cannondale touring bike has TA Carmina cranks (110/74) with 50-36-24 TA rings, Dura-Ace FD, Ultegra STI, XTR RD. This chainring setup is near perfect for me on a single touring bike and shifts just fine using the DA FD. The TA cranks and rings are crazy-expensive, though, and the only reason I have them is I got a killer deal on Ebay for the setup.

Would my life be simpler with barcons? Probably. But I really like STI, especially on the tandem and triplet.

All bikes above also have a chainwatcher gizmo installed.

Ultegra FDs are designed for a 10-tooth jump between large and middle rings. Dura-Ace are designed for a 14-tooth difference. This only matters if you are using STI shifters. Also, if you are using STI shifters, beware that FDs designed for MTBs/compact cranks (e.g., XT, XTR) won't work well (or at all) with STI levers due to differences in cable pull.