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Double crankset question

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Double crankset question

Old 05-24-20, 07:36 PM
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hybridbkrdr
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Double crankset question

I was told on a triple crankset you should avoid "big-big" & "small-small". If I'm on the lower chainring on the crankset, can I use any gear in the back? (Like on a 11-32T cassette.)
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Old 05-24-20, 07:39 PM
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Generally avoid big-big and little-little. It’s called cross chaining. You can ride this combo but it will cause some extra wear and typically these gear combos are redundant anyway.

So avoid it but if you find you need to be in this or inadvertently end up there, it’s not a big problem short term.
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Old 05-24-20, 07:47 PM
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As well it’s not uncommon on doubles that are 50/34 ring setups, to get rub from the chain on the inside of the big ring when using small ring and small cog, especially on road bikes with typical 40cm chai stays.
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Old 05-25-20, 01:31 AM
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Just make sure the chain is long enough. If the chain is too short, shifting into the big/big rings can damage the rear derailleur, hanger, dropout and even the wheel, causing a crash. I've seen it a couple of times on group rides.

Some folks will say they prefer to keep the chain as short as possible and simply won't shift into the big/big. Well, the problem is that under pressure eventually we can all make that mistake. Yeah, in ideal circumstances you can actually hear cross-chaining -- it'll get a little noisier. And there's a slight increase in drivetrain friction. But on a noisy road with wind and traffic drowning out our bike noise, huffing it to close a gap in the group or stomp up a short, steep climb... we can all make the mistake of shifting into the big/big. And if the chain is too short it's gonna be a bad day.

When installing a new chain I always leave it a little long, check the bike on the stand or on a trainer, do several shifts to the extremes of cross-chaining to be sure it's safe. I'll remove one link at a time until it's as short as it can safely be. Or, if I had already done that with the chain I'm replacing, I'll use it as a guide (allowing for elongation from chain wear).

The problem with leaving the chain a little long is increased chain slap, dinging the paint on the right side chain stay. I need to replace the old plastic chainstay guard on my old steel bike for that reason. I noticed the other day the paint is chipped where the old plastic protector has fallen off. I think some folks recommend helicopter tape as a replacement for the chainstay protector.

That's a common issue with some chainring combos. I have mine set up with 52/39 now, and have gone with 38T small ring on some occasions. That means there's a bit of chain slop when I'm in the small chainring, especially with the short cage rear derailleur. My bike with long cage rear derailleur seems to have enough takeup to minimize chain slap.
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Old 05-25-20, 11:09 AM
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Assuming everything like chain length is okay and there is no interference causing the chain to rub on something it shouldn't, (the DR cage is okay, many have a skid plate.). Then it's not really a big deal for the few moments you might need that gear combo. IE, getting over that tough part of a climb where the grade suddenly but briefly increases to double what you are used to.

If you find that those are the gear combos that you would normally be in for a lot of your ride, then you need to consider a whole new front and back gear size. And I think that true for 1x, 2x, or 3x.
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Old 05-25-20, 04:52 PM
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Originally Posted by hybridbkrdr View Post
I was told on a triple crankset you should avoid "big-big" & "small-small". If I'm on the lower chainring on the crankset, can I use any gear in the back? (Like on a 11-32T cassette.)
In general, chains last longer if they are in the ring/cog combination which uses the largest ring/cog combo available to get that same gear. So for example, say you're in the middle ring, smallest cog. You can approximately duplicate that gearing in the big ring and a cog somewhere in the middle of the cassette. The larger the rings/cogs in use, the lower the chain tension. Thus small-small is the worst possible combination.

That said, of course in trying for a certain cadence at a certain speed, there may only be one ring/cog combo which yields that cadence, so fine, use that.

And that said, In general when in the big ring, don't use the 2 largest cogs in back. In the middle ring, you can use all the cogs, In the granny ring, only use the 4 largest cogs. That totally avoids the small-small business. There's never a reason to use it. Honest. Been riding triples for 25 years in the mountains and on the flats. Still use triples on all my bikes.

Modern chains are narrower and built differently than trad chains. Thus the old advice about not cross chaining to avoid chain wear no longer really applies. Thus it's OK to run the whole cassette from the middle ring if your FD cage and FD trim allows it without rubbing. I will occasionally find myself in the 2nd largest cog in the big ring, though I'll quickly change out of that, and I never use big-big, well because that is cross chaining and I just don't feel right about it.

The trick with triples is to use the smallest cog you can get away with for the granny, and thus the closest ratio cassette that gives you the low gear you need. I have one bike with 53-39-26 in front and 12-25 in back. Very nice as long as I'm not doing a lot of climbing.

Since you're new to triples, I might mention that over time, you'll wear out chainrings. Either the chain jumps on the ring when you're out of the saddle, or it won't shift to the next larger ring, or you get chain suck when shifting to the middle ring. So, new rings: an ordinary double big ring will work with a 39T middle, but not with a 42 middle and vice versa. You have to have a special triple ring for the middle, and any ring will work for the granny. If your current rings are 30-42-52, know those 42-52 rings are the only combination that'll work together. Thus if you can't find a 42, you'll need to go 39-53.

You might want to print this and save it somewhere, just in case.
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Old 05-25-20, 07:06 PM
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I have no problem using any of the cassette's gears with my smallest of 3 chain rings should the need arise. But I do avoid it for extended periods. I don't normally use the small chain ring anyway, So the few times I use it isn't a problem.

I too think you can safely use the big - big and small - small gears in pinch. When I got my bike I avoided those combo's, But later I tried out the small - small combo. Despite cross chaining, I feel comfortable using it from time to time. The big - big combo just seems more stressed, Perhaps because the chain is so tight now, So I do avoid that combo.

Last edited by xroadcharlie; 05-25-20 at 07:13 PM.
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