Cheviot setup - chain length, front derailer

[Jay Lonner]

I'm making slow progress on a 55cm Cheviot build for my wife and am hung up on determining the proper chain length. The Riv website says:

>The chain is the right length when it pulls the derailer cage free of and parallel to the chain itself when wrapped around the smallest cog and the smallest chainring -- i.e., the derailer cage will be flexed slightly.

Try as I might, I'm having a hard time visualizing what this means - can anyone unpack this further for me? A picture would be even better! (The there's also Sheldon's rule of thumb calling for one full link of overlap when the chain is wound around the large-large chainring/sprocket combo, but I'd still like to understand the Riv method).

I'm also a a little stuck on front derailer options. I'm setting this up with the Silver wide-low double (38x24 with chainguard) and the front derailers I have on hand (IRD Alpina-f, Suntour XC-9000) both have a lot of daylight between the bottom of the cage and the chainguard. It looks funny, but would it affect performance? I'm open to buying a new part if needed, but am getting a bit Marie Kondo and would rather declutter my parts stash than add to it.

Thanks,

Jay Lonner

Bellingham, WA

[Joe Bernard]

Here's a not particularly easy to see shot because it's indoors and everything is black, but hopefully explains what Riv is saying.

With the chain on the smallest front and rear cogs, the pulley cage is sitting parallel to the bottom run of the chain. If the chain were much longer it would lead to the rear of the cage kicking up until that bottom run of chain was clanking into the pulleys themselves, and the chain would dangle loosely in that gear. Basically you want your chain as long as you can get it without that looseness/clanking happening.

Yes the derailer up high looks weird, yes it works. It shifts the small/middle rings as designed, and doesn't know that somebody replaced the big ring with a chain guard approximately the same size as the middle ring. How this came about is Grant/Riv originally conceived this crank setup to run without a fd, you would just stop and move the chain by hand. This didn't make it past whoever talked them out of it when bikes were built with them 😬

[Justin Kennedy (Brooklyn, NY)]

Riv had long chains for sale on the site but it appears they're sold out. This one mentions 130 links. I think I have 128 link-chain of my 60cm Chev (two spliced together) but only 8 speed rear derailer, not 9, and no front derailer (using the big ring on the same set up as you with manual shifting/placement on the small when I need it (almost never)).It's probably better to go too long than too short but 130 linx should be a good start.   

[Jay Lonner]

Joe, this picture was incredibly helpful - once I saw it the Riv instructions made immediate sense. This method does result in a few more links than Sheldon's guideline would call for, but I don't see an immediate downside to being able to accommodate a slightly longer chain.

Jay Lonner

Bellingham, WA

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[Joe Bernard]

Yes, it leaves plenty of room for the chain to work in the big/big combo. I've made that mistake before, and you don't want to know what happens when your chain stretches into that situation and doesn't want to come back off it. BAD things 😣

[Sky Coulter]

Joe your picture and brief description is super helpfeul.

thanks,

Sky in new west

[Joe Bernard]

Glad to be of help! 🙋‍♂️

[Benz, Sunnyvale, CA]

On Monday, March 2, 2020 at 2:24:44 AM UTC+8, Jay Lonner wrote:

Joe, this picture was incredibly helpful - once I saw it the Riv instructions made immediate sense. This method does result in a few more links than Sheldon's guideline would call for, but I don't see an immediate downside to being able to accommodate a slightly longer chain.

Jay, a word of caution. This method resulted in a few more links than St Sheldon's method, but only for the cassette/chainring/cage length combo you have now. In other combos, the Riv method may produce the same, or even opposite result from the Sheldon method, and may in fact result in your derailleur getting crunched in big-big if the cage length isn't correct for the cassette/chainring combo. The reason is that the Sheldon method is based on having enough chain, whereas the Riv method is based on having the longest chain that the derailleur can wrangle. In other words, if you ensure your derailleur has enough chain wrap, you will be fine with the Riv method; the Sheldon method will always ensure you have enough chain, but may leave a bit of dangling chain in the small-small.

[Joe Bernard]

Benz is correct, I answered the question as it applies to the crank/derailer combos we know work from Riv. The first step in any new setup is to make sure your chain is long enough for the big/big combo that we're all taught not to use but sometimes it happens.