Martian63

Advice for a novice. Can any of you out there tell me if I should remove one more link in my chain? I recently went from 12-30 cassette to 11-28. When I got home from LBS in noticed in the small - small combination the chain was laying on the chain stay. I have already shortened by 1 link (actually 2 to make the power lock work) but just don't know if I should take one more out. This novice old guy would greatly appreciate any advice. Thanks!

Yan 

Here you go:

Chain Length

FBinNY 

Shortening the chain will not make any difference in the small/small combination (but might cause problems for big/big, though not likely)

Based on the photo, the RD is taking up the slack, but you can confirm by slowly backpedaling as you derail the chain at the bottom to create still more slack. If the RD cage can wind back farther to take some of that slack before hitting the stop, then it's a pass and you can leave things as they are.

For a more detailed consideration, sprockets affect chain length by an amount equal to half the difference in the number of teeth. So going from 12 to 11t would "lengthen" the chain by 1/4", something that would only matter if you were already at the absolute limit for longest possible chain.

The reason you're seeing more chain slap, or close pass above the chainstay is simply because the radius of the 11t sprocket is smaller, and the chain leaves it barely high enough to clear the stay.

HillRider

First be certain you can shift into big-big with out forcing it. This ability is absolutely essential for safety. If you can and there is still enough slack chain to allow removal of 1" (two half links) you can shorten it again. Otherwise leave it alone and avoid small-small, for which there is no use anyway. You have a short cage rear derailleur and what appears to be a compact crank. That along with the wide range cassette may have exceeded the rear derailleur's wrap capacity. If so there is nothing you can do but avoid small-small.

fietsbob

Its not really too long as it is.

FWIW Half Links are only suitable with single speed & IGH drivetrains .. old school 3/32" wide chains went out of favor when they wanted to pack in that 7th Cog.

I have a 3/32nd Half Link on my Brompton's chain.. I chose A Whipperman Full Bushing type Chain.

[pins stick up proud on their sides, and the bushing tube around the pin is a separate Piece, pressed in the inner links as the chain is assembled] .

RoadGuy

Why did you change the cassette?

Were you trying to tightening the spacing between the gears?

Or, didn't need the 30T low gear?

Or, wanted the higher 11T gear?

If you just want to tighten the gear spacing, and don't need the 30T, and if the old cassette and the new cassette are from the same manufacturer, you can swap parts to make a cassette with custom ratios. On Shimano cassettes the two smallest cogs are loose, and easy to swap (after removing the lock ring). On some other brands of cassettes all the rings are loose, and you can swap any ring easily (you can also free the rings that are bolted or riveted together on Shimano cassettes).

For instance, let say you don't need the 11T top gear on the new cassette, but you want the 28T. You could take the 12T top gear (and the next gear 14T? if you want) from the old cassette and swap out the 11T (and 2nd gear 13T?) and make yourself a 12-28 cassette (using whichever 2nd cog fits your riding style better).

Kill two birds with one stone as it were. Top gear will be a little lower and easier to pedal, and you will eliminate your sagging chain in the small-small without shortening the chain or replacing the rear derailleur.

Martian63

Thanks guys! Just amazed at how helpful everyone can be on the BF. I am new to this but wanting to learn do my own work. Whenever i've tried something never done before I've looked to you guys for some positive reinforcement before I screw up. The Sheldon Brown page is excellent. Right now it's shifting good. I don't ride the small-small anyway. So thinking I should just leave it alone until I pull the chain to clean it. Then refer to the Sheldon Brown page method of checking length. My next project will be to replace cables and housing so I'll probably be back looking for that positive reinforcement......LOL..........THANKS

RoadGuy

I would not leave the chain like that if I were you. From the photo, I can see that you have a Trek carbon bike. Carbon parts and chains do not play nice. The chain sagging, slapping, rubbing, or tapping, on the carbon chainstay may cause damage that can eventually ruin the frame.

I would not ride the bike that way. Do whatever it take to prevent contact between the carbon chainstay and and the chain. Some solutions that have been already mentioned: bigger small cog on cassette, or shortening the chain, or replacing the rear deralleur with one with more capacity (longer cage).

ThermionicScott 

Isn't there already a chainstay protector in place (the blue strip)? I'm not seeing any need for alarm.

Number400

All my bike chains are set up to make sure the large/large combo is right and I have never had a chain that sags visually like that, even in the small/small combo.

Oh, and you have already learned that you really cannot shorten a chain by just one link, so be a little careful before you make the next cut.

RoadGuy

Why take a chance on a bike with carbon chainstays?

It actually looks like that frame is not really designed to work with the cassette and crankset that is installed on it. Not enough clearance for my taste.

You don't load a weapon, point it at something, and pull the trigger to see if the safety works.

And yes, I have spoke protectors on the rear wheels of my bikes.

ThermionicScott 

What does a dumb analogy about guns have to do with anything?

The bike appears to have a chainstay protector to guard against the very thing you're worrying about, if @Martian63's bike doesn't have one, he can correct me. Since chain slap has been known to happen for a very long time, I'd be very surprised if the bike had bare CF exposed to it.

RoadGuy

You are not experienced with handling guns, are you?

The analogy to guns is applicable to ANY SAFETY DEVICE. Safeties are designed to provide additional protection in the case of an accident. To depend on a safety for everyday protection without practicing safe operation is foolish, and the way that many accidents happen. Just like *** handling accidents.

You're assuming that: #1 the thin decal/adhesive label chainstay protector is thick enough and tough enough to protect against chain rub under pressure, and/or when the chain sags down and makes contact with the chainstay, and that it #2 covers the chainstay all the way back to the dropout and to the inside where the chain will rub if there is inadequate clearance because of the small cog.

My Treks are earlier models, and I can tell you that the Trek supplied chainstay protector/covers do not provide coverage all the way to the dropout, and will not protect the chainstay against anything more than the lightest droop or contact with the chain, and they do tear and wear away.

That's a lot of assuming, considering that if you're wrong at all, the result is a ruined carbon frame (that Trek is not going to replace under warranty).

Martian63

To answer a couple of questions.

The LBS where I bought the bike put the 11-28 cassette on when I had the worn chain replaced. Found I had let the chain get too worn and told me had to replace the cassette. They did not have a 12-30 in stock.

There is a protective strip on the chain stay. I do not ride small-small but have tried it there and don't seem to get any chain slap when I tried.

In the big-big combination I pulled the chain to overlap two more links to get an idea of how much slack I had there. It extends the rear derailleur cage further forward but looked like the chain still had a good "S" through the jockey wheels. Being a rookie didn't know how much that cage can extend forward safely. Below is a pic in the big-big combination.



Thanks again for the help.

ThermionicScott 

A bunch of assumptions on your part, too. Sounds like the OP's bike has a good chain length and no issues with chain slap, so maybe we can all calm down a little.

RoadGuy

My concern is adequate clearance over the chainstay at the rear with the small cog. Does the chainstay protector cover the inside and top of the chainstay where the chain runs over? A single incident with the chain running on the carbon stay could ruin the chainstay. And dropping or slapping the chain on a carbon tube could cut or crack it.

From your photo, it looks like there is very little clearance over the chainstay when in the small cog. If the bike were mine, I would not run that small cog. Even if you don't run the small/small on purpose, one accidental bad shift could cause permanent damage. I'not not sure that shortening the chain would do anything to reduce the risk. Some frames just aren't designed to work with some gears.

At the very least, I'd recommend that you install the 12T small cog from your old cassette onto the new cassette. That would allow you to run the a longer chain and improve the clearance over the chainstay when in the small cog. I doubt if the old 12T cog is worn significantly, even if other cogs were used up. Most people spend very little time on the small cog.

I recently picked up a used 13-23 8-speed cassette from another BF Member so I could assemble a 13-28 (using a new 11-28 cassette for the rest of the cogs) cassette for one of my bikes. The bottom cogs showed considerable finish wear, and I could see exactly wear the previous owner spent his peddling time. The two smallest cogs (13T and 14T) showed barely any use, and were perfect for my purposes.

I'm no expert sizing chains, but I read that a four link overlap was supposed to be correct. Rear derailleur looks pretty stretched out, and the chain looks like it's bordering on too short when in the big-big. I probably would not have shortened it myself. If the rear derailleur does not have the capacity to tension/wrap the longer chain, get a medium or long cage derailleur.

RoadGuy

Were the 12-30 cassette and compact crank original equipment on the bike when you bought it new?

Martian63

Yes it was. Bought it new.

RoadGuy

Then I would use the 12T top cog from the old cassette by the very least to raise the chain up above the chainstay.

FBinNY 

Any difference in chain slap between a 11t sprocket and a 12t sprocket which is a whopping 1/6" taller is going to be marginal. Nothing related to the change in cassette is material in any way, and the OP can rest comfortably that his bike is fine as it.

BTW- since the cassette and chain were replaced at the same time, any change would be more likely the result of a longer chain, than a smaller cassette. However the chain is within guidelines, and need not be shortened, except if the OP wants to save the weight of 1" of chain.

To the OP ----- YOUR BIKE IS FINE AS IS. Stop obsessing over stuff that doesn't matter, and ride it. You can prevent chain slap by pedaling over bumps which will keep the upper loop taught. Or you can add a padded chain protector (as do many mtn bikers) which reduces the sound of slap. A cheap padded protector can be masd of clear PVC tubing, split up it's length and kept in place with wire ties.

ClarkinHawaii

Another fascinating aspect of bikeforums: *** is censored, but its plural, guns, is not.

Martian63

THANKS EVERYONE! i always learn something from you guys. I'M GOING RIDING!