thateling

Hi,
Just started the process of adjusting the front and rear derailleur, trying to find where the scratching sound is coming from.
I've got 2 front chainrings and 10 on a cassette. The sound comes from the chain rubbing against a big chainring when the chain is on a smaller one (crankset) and 1-2 smallest gears (cassette).
Is it possible to align chainrings or it makes more sense just to buy new?

rccardr 

No need to run small/small, you have the same or a similar gear ratio available in big/middle.
Mosr bikes are not designed to run in that gearing combination.

JanMM

If you only have a problem when on the small chainring and 1-2 smallest cogs, then try not using that combination.

79pmooney

The chain is probably hitting the teeth of the big chainring. Ths is basically a fact of life on any bike with lots of cogs in back unless the chainstays are very long. It is made worse when the chainrings are very different sizes. On bikes with compact gearing (say 50-34 in front) and the short chainstays of a performance bike, the two small cogs in back are often completely unusable when in the inside chainring because the large chainring pins (or the teeth themselves) will try to pick up the chain and shift it to the big chainring.

Most of us simply consider those gear combinations unusable.

roadfix

Just don’t crosschain. Chainrub occurs whenever you crosschain. Small ring, small cog combo is a no no with most drivetrains. Same goes for big ring, big cog combo. Also, they cause unnecessary wear and tear.

Kontact 

New parts won't fix this. It is built into the geometry of the frame and is acceptable because the drivetrain manufacturer did not intend that you would ride in those gears.

choddo

You don’t need to buy anything.

To give a specific example
If you’ve got 50/34 chain rings
and a 10 speed cassette covering 11-28 which is 11-12-13-14-15-17-19-21-24-28

then your small/2nd smallest is 34:12 which is pretty much the same as 50:17, the large ring and 6th smallest cog

so there’s a big overlap.

soyabean

A LBS can verify if the crankset/chainrings are bent or need replacing.

It appears you have no idea what you ar doing, but you can still DIY after it is correctly diagnosed by the LBS.

SoSmellyAir

Shimano Dealer Manuals for its 2x11 drivetrains say to expect chain noise when riding on the smaller chain ring and the 3 or 4 smallest cogs, so that phenomenon is just part of its 2x drivetrains, which also apply to your 2x10 drivetrain.

Kontact 

Always charming, I see.

XxHaimBondxX

See https://www.bikeforums.net/bicycle-m...hain-ring.html 😂

oldschoolbike

Probably any 2 x 10 drivetrain on any road bike with relatively short chainstays will do this in one or two small/small gears if it has a 16 tooth chainring difference and a standard chainline. You can fix it, though if you really want to use those gears and can accept compromise elsewhere.

Some things to try:
1. Reduce the tooth-size difference of the chainrings. If you have a 50/34 chainset, maybe 46/34 would do it, if you are willing to give up the top end.
2. Shift the right crank outward 2-3 mm to reduce the chain angle in small/small. This will make the big/big gears rougher and maybe unusable, and it may be easy or hard to do depending on your bottom bracket type. For square taper use a spacer or two under the right cup, moving both cranks to the right, or install an axle 4-6 mm longer, moving both cranks outward. Check first that the front derailler can reach out the 2-3 mm further. Choosing a suitable new front derailler might be messy.

Good luck with this. You should have the freedom to set up and use your bike the way you want to.

oldschoolbike

79pmooney

I considered saying some of what oldschoolbike said but felt it was better to keep my post above simple. I agree. The bike should do what we want it to do.

I like the ability to run small-small (even on triples) because I love doing hard and long climbs. Many of those have stretches where the grade levels out in the middle. Not using small-small means either staying in too low a gear or double shifting, only to have the double shift back as the steep grade resumes.

Another trick that will allow more extreme small-small combos to run smoothly, if not silently is to trim the front derailleur so the outer cage rubs on and slightly pushes the chain in. (Not possible with all indexing systems. I use friction shifting so it is easy. In the earlier days of brifters, racers were known to use friction downtube shifters for the front for lighter weight and reliability. That also included the trim option.)

Crankycrank

You can also mount some chainring shims between the outer chainring and the spider and the bolts go through the shims. This is an entirely experimental trick for your individual bike as the problem that can arise is that you create too large of a gap between the small and large chainrings which allows (on some bike setups) the chain to get stuck between them when shifting sometimes. You may get lucky and it will work with no issues. Here's just an example and they come in different thicknesses and diameters. Sugino 0.7mm Chainring Bolt Spacers (10 x 14 x 0.7mm) - Set of Five | eBay These are 0.7mm thickness which would be about the thickest I would try. As others have mentioned, most of us just stay away from those gear combos that rub.

Troul 

you could try an 11sp chain to see if the noise goes away. it might create for lazy shifting. ymmv

Russ Roth

On one of my bikes, in order to accommodate the wide spread of gearing 16t difference in the front and 23t difference in the rear, the rear der doesn't have enough spring tension in the small/small to stop the chain from skipping. Although it is possible to mess with things to try to make them work sometimes we have to accept some limitations. Troul mentioned switching to an 11sp chain, my experience has been that the narrower chains are better at cross chaining without having rubbing or issues and its probably not a bad suggestion. I would suspect you'll still have rubbing in the smallest cog but maybe not the second smallest.


Noise-wise I doubt it would be much better, maybe have the advantage of the pick up pins not trying to grab the chain to help it up. Not certain how long it took, though I'd guess a long time from the age of the ders, but I've seen two bikes with worn through front ders from doing this.

79pmooney

Yeah, if you do this a lot, you will kill the FD. Faster if the cage is aluminum. Thick chromed steel cages will last quite a long time. I make it a point to use small-small only for those shortish stretches of levelish grade on long climbs so that isn't a lot of miles. If I was planning to do this on a regular basis, I'd stockpile a few FDs. (In my racing days I'd kill a Cyclone FD in about a season and a half. Narrow cages and I was far more concerned with the proper gear ration than how I had the cage trimmed. I was riding a lot of miles. Plus I worked at a shop where SunTour cost me little.)

Kontact 

Another trick to avoid chain rub is to remove the second chainring entirely, or give up bicycling.

thateling

what can i read on the chain math?

Trakhak

There are several different ways to compare sprocket/chainring/wheel combinations. Some people prefer "gain ratios" or "gear development," but I've used "gear inches" for many decades, so that's what I'm used to. All the methods result in numbers that you can utilize for the comparisons.

(If you're curious, here's a forum thread where the differences between those methods are explained.)

Here's one bike gear chart. You choose your chainring tooth counts, sprocket tooth counts, etc., from the drop-down menus at the top of the page and then click "Calculate."

In the table that the calculation will produce, chainring tooth counts are listed in the column heads, and sprocket tooth counts are listed in the rows.

I just calculated the gears for 49/36 chainrings and an 11/28 cassette, using the default tire and wheel sizes. 36/11 (small to small) gives an 86" gear. So does 49/15 (large to middle or thereabouts).

Your bike may not include a large-chainring/moderate-sized-sprocket that is precisely identical to your small/small combination, but a difference of 2 or 3 inches will be all but imperceptible.

choddo

and for a simple example of ratios, ignoring the other factors that can change gear inches but would involve swapping out wheels or cranks, using the tooth counts I used in the post above, you can see the ratio of front T divided by back T overlap like this between the chain rings. The highest numbers in this chart represent the hardest & highest speed and the smallest numbers are the climbing gears. Big overlap where you don't really need to use the small/small section of the cassette and using big / biggish instead will give you similar effort and no noise.

grumpus

To summarise:
Cross-chaining can be expected to run poorly or even be unusable - just avoid it, it's not useful.
Anything you do to "fix" it will hurt something else, if you don't have a very specific objective then just leave it and live with it.
Look at a gear inch calculator for your specific set-up until you understand it.

oldschoolbike

I have sometimes wondered if some well-placed drops of epoxy on the inside of the large chainring would prevent the chain getting stuck in the gap.

oldschoolbike

Crankycrank

My experience with different types of epoxies is that they would not survive an angry attack by a steel chain. Great for bonding and light duty filler but not great for abrasive/cutting situations.

SoSmellyAir

Several places, but I find this to be the best visualization:

Bicycle Gear Calculator (gear-calculator.com)