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Gear Rattles

Old 06-08-07, 02:16 PM
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daowned
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Gear Rattles

Hi all.

I am abit confused about the stories I have been told about chain rattles from the gears when on the small chainring and large gear and large chainring in small gear.

One story I am told is that you get this because you are at the max limit of the chainline and you shouldn't be going in to these gears anyway if you can help it as it causes the components to ware out more quickly, I know it does lead to ware and as a rule I don't use those gears unless I have a big climb and need the gears, but I don't agree with the rattle is normal.

Last year I had a Spesh Sirrus with Shimano Sora triple chainset and it was a great bike you could use any gear and never get any rattles, now a friend of mine has got a new bike with Shimano Sora triple chainset and he is getting rattles when he is at the max limit of the chian line and is upset about it, and no matter what the LBS does it cant be sorted.

So when I mention the gears about the Sirrus I am told that it isn't so and there must have been some rattle?

Now what I think is: If you spend the time and effort setting up the gears and they are in good condition then you shouldn't get any rattle and maybe the Sirrus was just set up good and the components were in better condition?

Don't really know what to think, is it just all about the setup and quality of the components or is rattles normal when you use the far out gears?
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Old 06-08-07, 02:30 PM
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The chain itself can rattle if it's radically cross-chained (your first story). It can also rattle if it's hitting the front dérailleur. Sora triples seems to have that problem a lot, based on the complaints here.
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Old 06-08-07, 02:40 PM
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The 'rattles' are generally caused by the chain rubbing on either plate of the front mech - a very annoying grating noise. It's entirely possible for a bike to be set up such that this never happens, but it's not a key aim when you're tuning up because it wouldn't lead to quite as crisp shifting as the mech wouldn't be moving far enough. Do any of the bikes you mentioned have a 'trimmable' front shifter, as in, are there points between 1, 2 and 3 so you can tweak the position?

Another cause of rattling can be the chain hitting against a larger chainwheel - I get this on my compact double if I'm on the small chainring and a small sprocket, even if I trim the front mech to be further to the right than is normal for running on the small chainring. If the alignment between the front and back gears of your friends' bike is different to your sirrus, this might lead to the difference in behaviour you've noted.

The two noises are decidedly different though - the second is more of a rattling, so seems to better fit what you describe, although I've never come across the problem on a triple (as the difference in size of the chainrings is smaller, so a greater angle of the chain can be tolerated without contacting the neighbouring chainring). You also get noise from the chain when it's cross-chained, as the plates are rubbing together abnormally as they rotate.
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Old 06-08-07, 03:39 PM
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You are missing (possibly because most people don't mention it) an important reason for avoiding cross chain. All multispeed bikes have overlap between the gears for each chainwheel. Go to Sheldon's gear calc page sheldonbrown.com/gears/ and put in your bike for an example. That cross chain combo has a near-equal somewhere else in your drive train that is not such a radical angle. Avoiding the combos where you are using smaller rear cogs is especially advisable, as those cogs already wear faster than the others.
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Old 06-08-07, 03:39 PM
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If I remember correctly the Sirrus had a 9spd so has a thinner chain so thats why no rattle maybe, my friends bike is a 8spd.

I understand about the setting up because if you have a larger gap between the chain and the front mech you get less rattle but you may have problems shifting on the chainrings because of the large gap, so you have to make a compromise I can understand that.

It has barrel adjusters yes, I have set up the high and low limits using my limit knowledge I'll let him know he can give it a quarter if hes not happy with the gears but it isn't gona sort the rattle, right?
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