Gioworld

I'm changing the chain on my road bike and trying to size it correctly. The old chain was sagging while in the small rear sprockets and the small ring in front. (2x 10, 11-36t Shimano DT) I sized the chain using the big ring to largest cog method and added 2 rivets as was shown on the Park tools web site. When I do this however the lower 4 cogs in the rear allow the chain to sag considerably while on the small ring. If I set the gears to smallest to smallest then size the chain for that then the chain does not sag, or only slightly. When set like this though I can not reach the top 3 cogs in the rear when on the big ring in the front. Hmm.

I realize these extremities are probably not important and maybe not needed. So I'm wondering if I should leave it as is and not use the lower cogs while on the small ring to avoid the sagging chain; or set it for a tighter chain and not be able to access the larger cogs while in the big ring? (I don't like the sagging chain)

I know this sounds finicky but I want it to be set up well. Ride style; I live in Vermont and do a lot of decent climbs. I like to be able to have many options with gear combinations depending on the road. Thanks for any insights that the community can provide. Ride on.

Steve

Crankycrank

What model rear derailleur do you have and short, med or long cage?

HillRider

It sounds like you rear derailleur doesn't have the "wrap capacity" you need for your gearing. You don't give your chainring sizes but for a 50/34 crankset you need (50-34)+(36-11) = 41 teeth of capacity and that's long cage road or MTB territory.

It is essential that the chain is long enough to allow you to shift into big-big. Yes, you should avoid it but someday you may inadvertently try to shift into it and the chain must allow it or the damage can be significant and dangerous. Slack in small-small is annoying but not normally a hazard. So, either studiously avoid small-small or buy a rear derailleur with an adequate wrap capacity.

Andrew R Stewart 

It seems that your bike gear range has exceeded the der's ability to wrap chain, hence Cc's question. I strongly suggest that you don't run a chain length that won't allow the big/big combo. In the heat of the moment you will forget and try shifting into one of the no no combos and do some serious damage to your bike.

As long as you don't ride in the sagging chain combos for long, of do so in a rough and aggressive manor, this is the "side of fence" to be on. Best is to end up with all parts of your gear system that agree with your range needs. Andy

Gioworld

Thanks all for the quick responses. I didn't even think of the cage length but that makes sense. It is a medium I believe so since it is an older derailleur maybe I should splurge and get the correct size. This one came with the bike and I have been ridding it for years. Never really noticed the slack until I moved back to VT from CO. Smaller hills here so different shifting combos. Seems I have the chain sized correctly but the longer cage should make the difference. Thanks again for the tips.

Andrew R Stewart 

I'll bet you shift more frequently nowand wouldn't be surprised if the average slope is steeper back east than out west. (I know I just opened myself up to flaming) Andy.

squirtdad

I have moved to this small/small sizing method it works well for me on both vintage and modern setups

Gioworld

Thanks Squirtdad. This is exactly what got me here. I sized for the big to big method and it looks great for the big ring range. But when I checked against the small small it sags a lot. So I think I need to either compromise or get a new derailleur with a longer cage. Fortunately road bike components last much longer than mountain bike components to it is not a tough pill to swallow on cost as this is the original derailleur.

Andrew, I don't know what flaming is, but up hill is uphill. The difference being that the uphill's were much longer in Colorado Vs VT. So I used the lower gear range more.

Camilo

I do agree with the others who have said it's most likely the wrap capacity which is determined by the cage length. I also agree that it's always best to set the chain to accommodate the large/large combination because failure to do that could result in a catastrophic failure.

The best way to tell if it's actually the derailleur or something else is to simply find the model number of the derailleur and look up the wrap capacity. If you find the specs for that model number, you should see two capacities: the largest sprocket capacity and the wrap capacity.

The wrap spec is based on (the difference between large and small sprocket) + (difference between large and small chain rings). Example: (36-11) + (50-34) = 41. Plug in your own chain ring numbers)

If you have a double 10 speed road set up with 10 speed road derailleur, I can almost guarantee that no Shimano road rear derailleur that I'm familiar from that era with will wrap a common road double with a cassette that large (11-36). Theyre generally designed to wrap maybe a 11-28 with a double crank. Maybe there's exceptions for the road derailleurs I'm not aware of but it's easy enough to find out.

There are easy and not expensive solutions to getting a rear derailleur you need. Any Shimano 8 or 9 speed mountain bike rear derailleur will work with Shimano 10 speed road shifters and they're plentiful on Ebay as well as new. 10 speed Shimano MTB derailleurs will not work with road shifters, nor will any Sram rear derailleurs. But be aware that many of the Shimano MTB options are only rated to a 34t large sprocket even though they might have adequate wrap capacity. Most will go up to 36t anyway, but not guaranteed. If you're looking at Shimano, the Deore level or even lower, is not expensive and works perfectly.

A 8 or 9 speed Microshift long cage MTB rear derailleur (other than 9 speed "Advent" which is proprietary) will also work. And there's options for very inexpensive options there, just look at the specs and make sure they have a large sprocket capacity of 36t you need and the wrap you need based on your crank, which you didn't mention. Some are designed for 1Xs systems so arent designed to wrap a 2X crank. You can find a long cage Microshift RD for less than $30. Check their website for examples and there's lots of online sources. I bought a couple Micoshift RDs from REI recently.

HillRider

Yes it does, IF AND ONLY IF your rear derailleur wrap capacity is adequate. If it's not enough than big-big won't work with bad things to follow.

Kontact 

Except that method would destroy the OPs bike.

It is my preferred method, IF I know that the derailleur has the capacity for the installed gearing.

squirtdad

agree that Big Big needs to always work


I found that when pushing capacity (i.e by 2 teeth) this give max possible chain length, but I also have checked specs and know how close I am to capacity and double check that big/big works

Gioworld

Ok, I've looked a bit closer and found that my Front is 50-34, Rear is 11-28. Rear Derailleur is Shimano Ultegra short cage 10 speed and Shifters are Shimano 105. Wrap capacity is 33 based on the provided information.

What I would like is to install this new chain and not have it flopping around at any gear combination. I agree that it is important to go Big Big.

I'm good with buying a new derailleur but would like to avoid spending on new shifters. But if I must... Just a much bigger job for me right now. As I search around there are compatibility issues that creep in the more I change and being an old setup makes it harder. There are not a lot of options for 10 speed derailleurs.

Any suggestions for setting this up with the existing derailleur? Thanks for the help.


.

Jeff Neese

I have always used Large-Large+2 and it's always worked for me.

Before you go changing derailleurs, check these conditions. Ensure that the cage is not at the end of its limit on Large-Large, and isn't causing the chain to double back on itself in Small-Small. If both of those are true, your chain length is probably OK.

What this sounds like is maybe a weak spring. What exactly do you mean be "sagging"? Does it just seem that the spring doesn't have enough tension? Is the spring even engaged correctly?

Gioworld

When set to Big Big the rear derailleur is almost at its forward limit. Has a bit of room to go but not much. When on the small small or even the 12 or 13 tooth it sags down. Like swaying in the breeze. Like the chain hangs far below the mech. As I said before I could just leave it and never go small to 14, 13, 12, or 11 but this just seems like a bad set up. Even though I have been riding like this for some time now I feel like it is apart and I should set it up correctly.

Seems like just getting a medium or large cage derailleur would solve this but I don't want to just throw money at it without a known outcome.

Bill Kapaun

You ask.
Question is answered correctly.
You persist.
Ignore List.

squirtdad

if these specs are correct then you are not exceeding anything,but are exactly at max. 10 speed ultegra short cage is speced at 33 wrap, 16 tooth front rings difference, max rear cog 28 min rear cog 11

if your derailler at low/low is not al the way back it suggests the derailler may be not functioning correctly, picture would be a huge help.

Hard to diagnose without pics, but I really am thinking your derailler is not working right

otherwise try the low/low sizing posted before

Jeff Neese

The chain shouldn't hang down below the cage. Are you saying the derailleur is not taking the slack out of the chain? It sounds like there is something wrong with the derailleur. You may or may not need a different size cage. Post pictures.

maddog34

then, from your First post... (2x 10, 11-36t Shimano DT)... busted.

Jeff Neese

As has been pointed out, your current derailleur has (just) enough capacity to handle your 50-34 and 11-28 gearing.

Your chain should not be hanging down as you seem to be describing. Is there a reason you're not posting pictures, so that maybe we can actually help you?

Hondo6

OP: although you can't insert images into your posts until you have sufficient total posts (10 or more, if memory serves), you can post them to a personal album. Once you've done that, someone else with enough total posts can give a "pic assist" and post them on your behalf.

Edited to add: unfortunately, as I recall they're also a 5-posts per day limit for new members until they've achieved enough total posts (also 10, I think). So you may need to wait until tomorrow to let people know that photos are now available.

These restrictions are to combat spammers, not to harass new members.

Kontact 

The max possible chain length is when it is dangling with no tension in the small/small. That's how my 8 speed triple MTB with short cage derailleur is set up. It can handle any gear combination, but there is not tension in granny/7or8. And that's okay for me because shifting to granny is always a methodical process, unlike rapidly using up the cassette on a hill. I wouldn't like a dangler on a double set up like the OP's, though.

Gioworld

All, thank you for all the great information. Sorry I didn't take pics but I am short on time to go back to this. I believe I will benefit from a medium or long cage but at this time I haven't found an equivalent Ultegra derailleur to replace it with. So for the time being I will set it up as big big length and run the existing derailleur. Just won't use the small to small gearing. Pretty much how it has been. Good thing is the whole bike is cleaner than it's been in a couple of years and the weather is changing to spring. Time to get off the rollers and onto the road. _As a side note. My wife has the exact same bike but smaller. Hers does not have the same chain issue so I think the smaller stay comes into play as her chain was shorter and an equal length for the replacement worked fine.

Thanks again for all the good information. Enjoy your coming season.

Steve

Camilo

As others have said, from what you've described, it's not the cage length. You don't need a longer caged derailleur. Your current derailleur has both the large sprocket and wrap capacity you need for the common road components you have: 50-34 crank and 11-28 cassette. Therefore, it isn't cage length that is not working, it's something in the derailleur.

I get the feeling that you haven't understood this. It doesn't seem so based on the above post. Yes you might need a new derailleur because the current one is not working right, but it's not because of the cage length.

Sorry to be repetitive.

It won't hurt to get a compatible longer cage derailleur though but it's not your problem!

If you've decided that the current derailleur just isn't working right in the chain -wrap department (again, not because of the cage length!), Microshift makes compatible10 speed ROAD derailleurs. If you're looking to save money, they're inexpensive and well regarded.

In my previous post, I suggested Shimano or Microshift MTB derailleurs, but that was because you posted that you had a 11-36 cassette (a MTB sized cassette), not the 11-28 (a road sized cassette) that you actually have.

tFUnK

You can fine tune by adjusting the B screw on the current RD. Like said, it should work on paper (unless there's something else going on that were not aware of), you just need to tinker it a bit.