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Old 04-19-07, 06:47 PM   #1
Motorad
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Any Issues From Using Smallest Cog With Smallest Compact Crank Chainring?

TRIPLE CHAINRING:
I forget the term, which describes how it can be a problem with triple chainrings ... if you have the chain on the smallest chainring and the smallest cog at the same time ... or if you have the chain on the biggest chainring and the biggest cog at the same time. What is that term, which refers to the extreme angle of the chain when using the smallest/biggest cog with the smallest/biggest triple-chainring?

At any rate, is the rule of thumb to never have your chain at such an angle ... or is it okay to have the chain at such an angle for a few minutes at a time?

COMPACT DOUBLE CHAINRING:
With compact double chainrings, is it even an issue if you have the chain on the small chainring and the smallest cog at the same time ... or if you have the chain on the big chainring and the biggest cog at the same time ... since there should be less of an angle being put on the chain?

If chain-angle is still an issue with compact double chainrings, can you at least ride on these chainring/cog combinations longer than you could with triple chainrings?

The reason why I ask is to know how useful the biggest cog would be with a compact crank ... to compensate for not having a granny gear.
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Old 04-19-07, 07:30 PM   #2
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"Cross chaining" can occur when you use either the largest front cog with the smallest rear, or smallest front with the largest rear. The chain is stressed to cross that larger of an angle, which puts too much lateral stress on the sprockets.

You can do it for a short period with little damage, at least usually. Some bikes will begin complaining immediately.

If you do it a lot, the consequence is kinda like sharpening your sprockets. The chain begins to wear them down, leaving them thinner and more pointed. It damages the chain too.

For the most part you don't need to do it. There will be gears off of the middle crank, or the smaller crank on a double, that will be near duplicates of the large front to large rear.

As to question about the lack of a granny gear, that's more a question of your own riding condition. A lot of cyclists do fine with compact doubles, where the lowest gearing is around 39:26 (assuming a 12-26 rear cassette). That's a reasonably low climbing gear for many. For others of us it isn't nearly enough. My hybrid's lowest gear is 26 in the front and 34 in the rear - a great grandmother gear.
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Old 04-19-07, 07:35 PM   #3
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You can probably get away with it (my wife will do it all day long with a triple if I don't remind her), but what's the point? It does put a little strain on the chain, and you'll find another gear very close to that combination by going to the other chainring and a larger cog. There's just no reason to do it.
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Old 04-19-07, 08:17 PM   #4
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Quote:
Originally Posted by Motorad
TRIPLE CHAINRING:
I forget the term, which describes how it can be a problem with triple chainrings ... if you have the chain on the smallest chainring and the smallest cog at the same time ... or if you have the chain on the biggest chainring and the biggest cog at the same time.

COMPACT DOUBLE CHAINRING:
With compact double chainrings, is it even an issue if you have the chain on the small chainring and the smallest cog at the same time ... or if you have the chain on the big chainring and the biggest cog at the same time ... since there should be less of an angle being put on the chain?
It doesn't do a lot of harm doing what you've described for short intervals but try and avoid it. You really don't need to be in smallest chainring/smallest cog (go to middle chainring/larger cog) or in the Compact-biggest chainring/biggest cog (shift to smaller chainring and larger cog). You can find the same cadence and speed on those other gears and generally have a quieter less stressed drivetrain. It's pretty hard to get a front derailleur spaced so it doesn't have any chain rub in the situations you've described-particularly on a triple.
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Old 04-19-07, 08:40 PM   #5
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I have two thoughts on the topic.

How much are you willing to worry about wearing out your chain a little bit sooner? I mean a chain costs $20.00! Besides, how often do you cross chain anyway? If your gear selection was purely random, you'd only be cross chaining 8 to 10% of the time. In real life it's probably a lot less than that. I'll agree that cross chaining isn't the best thing to do but I think that it's a problem that's over rated.

That said, I wouldn't worry excessively about riding with a compact crank using the little/little combination because your bike will tell you when you do it. The chain will rub the inside of the big chainring and make an annoying scraping sound. Then you'll find another gear combination to make the noise go away.
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Old 04-19-07, 09:07 PM   #6
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IMO, crosschaining happens at times to most of us but why make a practice of it? Always a good idea to make a gearing chart for yourself (you can go to Sheldon's at http://www.sheldonbrown.com/gears/). Learn your gear patterns. You'll get a handle on your shifting habits and needs, recognize where duplication is, and have a label to put on gears you use in different situations (e.g. climbing the local Mount Doom in 46 inches is a good day for me, etc.)
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Old 04-19-07, 10:21 PM   #7
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This is a common issue with most compact setups, cross-chaining. The holy grail is a triple that does not rub in any gear combo.
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Old 04-19-07, 11:22 PM   #8
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Quote:
Originally Posted by oilman_15106
This is a common issue with most compact setups, cross-chaining. The holy grail is a triple that does not rub in any gear combo.
Not so much the rub with a triple...just an inefficient, radical and potentially worrisome chain line-- especially with a short chain stay bike.
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Old 04-20-07, 03:32 AM   #9
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I do it often for brief periods.
My 21 year old bike has friction shifters. The majority of my riding is flat, city stop & go.
It's just easier to leave it on the Big Ring and push the rear shifter all the way against the stop (28T) then trying to push 2 friction shifters into the proper position while doing a quick stop.
Taking off, I shift after 2-4 pumps, try to shift 1 gear, repeat? depending on how many gears I skip. Sure wish I had HG!
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Old 04-20-07, 04:08 AM   #10
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Thanks everyone. The discussion helps me to know the possible damage that could be done to the chain ... and a damaged chain could lead to damaged gears ... from cross-chaining. The reason I ask these questions, is that I've read more than once that a 50/34 compact crank is suited for older riders who are less aggressive bike riders, and I'm guilty on both of these charges.

After I re-read the title of my message, I see that I should have used the title: "Any Issue From Using Biggest Cog With Smallest Compact Crank Chainring?" I guess this wouldn't really be considered cross-chain ... since both gears are the ones closest to the respective front and back wheel.

To rephrase my question: With a compact crank, you do without a granny gear. So with a 50/34 crank and a 12/27 cassette, it would be nice to rely on a 34-27 combination ... to get as low a gear as possible. The thread of this message is to address using the lowest available gears on a compact crank. So my actual question: How often can I get away with using the 34-27 combination on a compact crank ... and what are possible consequences from using the lowest available gear on a compact crank?
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Old 04-20-07, 08:04 AM   #11
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Quote:
Originally Posted by Motorad
. The thread of this message is to address using the lowest available gears on a compact crank. So my actual question: How often can I get away with using the 34-27 combination on a compact crank ... and what are possible consequences from using the lowest available gear on a compact crank?
Assuming your chain is the right length-- none........except perhaps happier knees.
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Old 04-20-07, 08:09 AM   #12
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Quote:
Originally Posted by Motorad

To rephrase my question: With a compact crank, you do without a granny gear. So with a 50/34 crank and a 12/27 cassette, it would be nice to rely on a 34-27 combination ... to get as low a gear as possible. The thread of this message is to address using the lowest available gears on a compact crank. So my actual question: How often can I get away with using the 34-27 combination on a compact crank ... and what are possible consequences from using the lowest available gear on a compact crank?
I thought that is what you had intended to ask but when you mentioned the size of the cogs it went a different direction.

For sure, use the Heck out of a 34/27!!!! It's a terrific combination. I love that gear on rides with long climbs. It's a very smooth little operator!!!
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Old 04-20-07, 09:30 AM   #13
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If your bike is set up properly, you should be able to use any gear combination except possibly large chainring to one or two largest cogs and small chainring to one or two smallest cogs. The lowest (small/largest) and highest (large/smallest) combinations should be fair game on any bike, unless it has severe chainline issues. My only caveat in using the largest rear cog is to shift into it at low speeds only, and only from the adjacent rear cog, to avoid the off chance of throwing the chain into the spokes. I always set up my gears so that I will seldom have to use my lowest gear, but it is always reassuring to know it is there for that 17% grade or for even a mild climb at the end of a long ride.
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Old 04-20-07, 09:34 AM   #14
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Quote:
Originally Posted by jppe
I thought that is what you had intended to ask but when you mentioned the size of the cogs it went a different direction.

For sure, use the Heck out of a 34/27!!!! It's a terrific combination. I love that gear on rides with long climbs. It's a very smooth little operator!!!
34/27 ain't low enough for our hills.- Thats why I went to a triple and now have 30/28- Trying 30/30 shortly though.

On crosschaining- the other thing that has not been mentioned is NOISE. The sound of the chain wearing out the cogs drives me mad- and if there is a strong enough wind to take the noise away from me- I get plenty of reminders from my mates that are looking for the peace and solitude of the countryside.
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Old 04-20-07, 09:49 AM   #15
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I run a 50/39/30 with a 12-27 cassette and I live in a hilly area. I've maybe used the 30 ring once or twice in the past year as I have been attempting to spend the majority of my time in the middle ring. If I am on a tough hill I generally will stay in 39/19 or 39/21. If it's really tough or I'm really tired, I will go to 39/24. I try to never use 39/27. Do those sound like severe chain angles? They don't look like it to me when I observe them while riding.
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Old 04-20-07, 11:17 AM   #16
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Quote:
Originally Posted by jppe
For sure, use the Heck out of a 34/27!!!! It's a terrific combination. I love that gear on rides with long climbs. It's a very smooth little operator!!!
Sounds like a plan! Thanks everyone for input so far. I've purchased a Legend ST a couple of weeks ago, and I needed to make up my mind on gearing soon. Being a cousin twice removed from Bilbo Baggins, I'm setting the bike up with a 165 mm crankset. The smaller arm had me really puzzled as far as compacts, but I've heard good things about Shimano's R700 compact. The R700 is supposed to be at the level of Ultegra, although technically the R700 does not belong to any Shimano grouping and can be used with Ultegra or Dura Ace.

I used Sheldon's online gear chart, and it looks like a compact would be good for a lot of 50+ club ride speeds. I'm more of a masher, but here are some calculated MPH speeds at 80 RPM ... for a 50/34 compact, 165 mm arm, 10-speed 12/27 cassette, on 700 x 25 tires ... on the 34T chainring:
17T = 12.6 MPH ... 16T = 13.3 ... 15T = 14.2 ... 14T = 15.2 ... 13T = 16.4 ... 12T = 17.8 (but don't use 12T or you'll be cross-chaining!).

If my riding improves considerably, there will be the issue when riding above 16 MPH, because I may have to switch back and forth a lot from big chainring to small chainring. For anyone who usually rides between 16 and 18 MPH, they may have to debate on whether a standard double would be better than a compact double. Thanks again everyone. Hope to hear more comments about using compact cranks, especially going uphill ... because Michigan has its share of hills.
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Old 04-20-07, 04:35 PM   #17
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Quote:
Originally Posted by Motorad
How often can I get away with using the 34-27 combination on a compact crank ... and what are possible consequences from using the lowest available gear on a compact crank?
That's what it's there for. There is no reason what-so-ever for avoiding that gear combination.
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Old 04-21-07, 12:50 AM   #18
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You will be surprised at what you will be doing within a few months of riding.

Cadence of 80 sounds about what I use on the MTB. On the road bike I am above 90. I have also found that I am well above or below that cadence- depending on who I ride with and where I am riding- so untill you get used to the bike and settled into it- do not worry about what you might be able to do.

As to the Double crankset. The large ring can be used on most of the rear cassette gears- except possibly the largest 2. The small ring can can be used on all except possibly the smallest 2. Worrying about what gear you will be in is not a problem. Your legs will tell you what is right. And if you are new to riding and have a few hills to go up- I would go with the compact. It will give you a larger range of available gears. In fact if you have real hills- I would go with a triple.
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