cvcman

Ok lets assume you have NO chain on the bike or have just chgd the rear cassette to a bigger large cog...I have read to put the chain on the front sprocket...smallest IF you have more than one...and thread it thru the rd and around the smallest cog with the derauiler under the smallest cog...pull the chain tight enough that it is away from the cage and not touching it for about 1/2"....is this the best way ?

bradtx

It is simply one of about three ways to size a chain. Not to be rude, but search this forum for the pros and cons of each method.

Brad

1 Miyata Biker

The method you describe is a bit off. You want the largest chainring of the front derailleur to the largest gear on the rear derailleur without threading the chain, through the derailleur. Snug the two ends together, and then add two links to the length. The next rivet point beyond that spot is where the chain should be separated. This length should be about an inch for the two links +. There are a couple of other methods if you want any possible variables in the equation. Here is the Park Tools instructional. Park Tool Co. » ParkTool Blog » Chain Length Sizing

FBinNY 

So the OP has described the small/small method which is what Campagnolo suggests. It works fine to end up with the longest chain. it works fine as long as the Gear combination is within the RD take up capacity.

Miyata Biker has described the big/big +1" method which Sram suggests. It measures the shortest chain possible, and I consider this the absolute minimum, since shifting into a combination that the chain can't loop will have serious consequences.

Shimano suggests a method in between the two.

So those are the three bears of chain measurement, subject to being longer than the minimum, any method is fine.

Andrew R Stewart 

I like to first try the longest chain possible. One can always shorten a chain far easier then lengthen it. Andy.

FBinNY 

+1, instead of using the shortest chain possible and carrying spare links, I use the longest possible so the "spare links" wear the same as all the others. I got into the habit in the days before bushingless chains, when failure of an inner link wasn't that rare.

Also extra length translates to extra life.

Anyone racing or wrenching for a racer should also opt for the longest chain possible. There's always the change that you'll grab a borrowed or neutral support wheel during a race. If your chain was measured as short as possible, and the borrowed wheel has a larger cassette the combo could lead to disaster.

scott967

I recently went though this. Thanks to all the good advice on this forum I first did big big + 1 to establish the min length. Then I did small small to get the rd to take up all slack while ensuring I was at least meeting the min I established (I did by a link). This is on a touring setup with 50/45/28 up front and 14/28 on the back.

scott s.
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headloss 

The most important thing isn't to choose one method over another, the most important thing is to know the pros/cons of each method and understand why they are used. I like small-small for the longest possible chain without damaging anything (my cousin's bike had a chain that was too long b/c he took his bike to shop that didn't know what they were doing). I still have to verify that everything shifts smoothly across the gears regardless of what chainring and cog sizes I'm using.

Understanding, that is all that matters in order to get the correct size (regardless of method).

Reynolds 

Big ring front - small cog rear, vertically aligned derailleur pulleys is what I use.

LastKraftWagen

Assuming if you were changing th size of the cassette (or chainrings for that matter) and had the old chain one could simply add (or subtract) the number of links by the change in gear teeth???

I know this isn't fitting a new chain, but I think OP mentioned elsewhere swapping to a larger low-gear cassette.

KDC19561954

I do it the same way you do and it has work out great for me too.