austex9000

Start with a stock 1987 Trek Cirrus 520. You all know where the specs are published. You've got the following spare parts to work with:
24T chainring, 74 BCD, non-bio pace.
NOS 14-34 Z-012 Shimano freewheel.
NOS Suntour Cyclone GS
New Shimano LX RD-M531 SGS
New Uniglide 6 speed chain UG-CN51

and as head mechanic in charge, you can sell me what you've got on hand to achieve a sub 20" gear for an upcoming ride in a mountainous area in southern Appalachia


I asked this question because I thought I had it all worked out, but the LBS here in Austin, TX says...can't be done because....well, that's your quest: Can a sub 20" gear inch be achieved?

auchencrow

Assuming 700c wheels, 24t / 34t gets you 18.6 gear inches with a regular 170mm crank.
I trust that the rear derailleur you chose will swallow it.

CroMo Mike 

We used to ride in the Blue Ridge Mountains with 42 chainring and 32 freewheel. It gave easy climbing at 6 mph, about as slow as anyone was willing to go.

jimmuller 

Man, a 20" low is so slow you'll fall over! Or at least I would every so often.

One question is whether the big cog will clear the RD guide pulley. Another is whether the second largest cog could hit the outer cage plate when you shift to the big cog. (I have a RD, a Vx-GT I think, which clears the second largest cog only because I chose the chain length carefully.) A third question is whether the RD has enough take-up capacity to handle the accidental shift to both big-big and little-little combinations. The only way to know the answers is to put it together and see.

So, like, why did your LBS guy say it wouldn't work?

austex9000

Yes those questions are important and the published specs for both RD's will dictate the choice you'd make. That Suntour you've got might work here because it is spec'd as 34 for largest rear cog and 38 total capacity (If my memory serves me well). The total capacity in this example is 46T. While 36T is not 46T no experienced rider will shift into the highest gear on a steep grade.

You're right a 20" gear is low. But the route includes a 20% grade starting at 625 ft rising to 1395 ft over 0.7 miles.

Why did the LBS guy say it wouldn't work? Let me wait and see if anybody gets it first.

jimmuller 

An experienced rider may not intentionally shift into "high gear" (which I assume you mean big chainring while running a big cog). But I can think of at least experienced one rider who occasionally shifts to the big cog while on the big chainring, usually because he has forgotten what gears I, oops I mean he is on. Better to have the chain long enough to accommodate big-big and be loose'n'floppy on little-little than to have it too short for big-big.

I'm betting they said you'd lift the front wheel too easily.

austex9000

HAhaha! Nope. They said something else. ...something to do with the chain width.

jonwvara 

Whatever the people at the LBS said, they're wrong. It's pretty easy to get a <20" gear, though it may take some fiddling around and, as Jim pointed out, you won't be able to use the small-small combinations. Be sure to use a chain long enough for the big-big that you'll in theory never use.

How useful it will be is another question. One of my bikes has a 28 chainring and a 38 big cog, for a 19.7" gear with 700C 28 tires. I do use that combination sometimes on mega-long climbs but could easily get along without it, and do on my other bikes.

I've thought about setting up the same bike with a 44-32-22 mountain-bike triple I have just to see what a 15" low would be like. But it would be basically an academic exercise. I'll probably won't ever take the time to actually do it.

pastorbobnlnh 

You know, based on the clues given and the responses to other posts, I don't get why you took it to the LBS in the first place. You appear to have more than the basic knowledge needed to solve this on your own.

Having ridden on the Blue Ridge Parkway in NC, I can attest that approach roads to the Parkway are beyond steep and could be classified as HC climbs if they were included in a sanctioned UCI race. So I agree with you, a 20" or lower gear is needed.

I was going to say the LBS said, "They no longer make 6 speed chains." But I went back and reviewed post 1 and you are providing the UG 6 speed chain.

I'm not up to speed on the UG chains, but do they require the special pin which breaks off after it has been installed? Maybe they didn't have the pin and didn't think they could still use the chain breaker tool to reinstall an old pin? Or maybe they didn't think your old chain had enough side to side "give" to work, i.e. it had too much lateral stiffness.

BTW, I have a Cannondale hybrid with a 3X3X9 81 speed transmission and can claim I've achieved a One Foot Gear (actually 12.3 inches), and I can keep it upright on steep trails.

auchencrow

If you plan to use Suntour's Cyclone Accushift indexed shifting with that Shimano rear set up, I don't think the spacing will be "quite" right.
Making that jump to the big cog could be iffy - But I don't see what that has to do with any 3/32" width chains.

bradtx

austex9000, The only thing I can think of is the RD may require a narrower chain?

My touring bike's low is 19.8 GI. I haven't had to use it yet, but it is fun to play with. There are some hills in Ingram that could put it to use.

Brad

repechage

Whenever I have encountered super wide triple drivetrains, the workability always hinges on the total range and chain length. As the original Chain mentioned is a Uniglide, my questions would be is the freewheel acceptable for that chain, Uniglide chains had "swollen" outer plates and way back in the five cog era not all freewheels liked them.

I know this as Shimano America came by the shop and gave us a handful of chains to use for a month free, just please give them back and fill out the comment form. (even provided prepaid return packaging) I rode the chain for a week, could use only one freewheel (the others never allowed the chain to settle in some cogs- the distance between the cogs on a few freewheels was too close) It also began skipping on the one freewheel that it did work on by the end of the week. I had stretched the chain out in one week! True, it was a 350 mile week and included many hills but I never suggested a Uniglide chain ever when they later came out.

Road Fan

Setting up a 42/26 11/28 2x10 friction system on my Terraferma, I found that when on the granny and the 11 or 12 tooth rear cogs the chain can drag a bit on the large chainring. It could cause ghost shifting or just noise. After perfecting the chainline the problem went away. I use a 10-speed chain in this setup, but with a wider chain there would be more rubbing.

Another solution in my case is to go with a larger granny that raises the chain and reduces the free length in the front. Same chain angularity but the chain is less likely to interfere with a rising tooth on the big chainring.

Too wide of a chain can cause the chain to try to engage adjacent cogs. I'd imagine a 5-6 speed chain to not play well on a 10 speed cassette.

austex9000

Thanks for your comments! None of you, or Sheldon, seem to agree with the LBS :" You can't use that RD-M531 SGS because its a 9 speed and your 6 speed chain is too wide"If you're wondering why I don't ditch the UG system, it's because I want to keep a working example of this technology. The Bike came stock with the UG system and it is one of my favorite "innovations" in shifting.

pastorbobnlnh 

Not meaning to be contrary, but not stating the specs on the M531 RD as being a nine speed, is a bit misleading. And, if you "...want to keep a working example of this technology...," how is this the case with a modern 9 speed RD?

If you are just throwing the M531 RD on there for the NC mountain tour, try running an 8 or 9 speed SRAM or KMC chain (for just this trip), then switch back. That should do the trick.

austex9000

Well, the RD spec's are widely published. As far a keeping an example; the RD isn't a part of the UG system...just the freewheel and chain. But, the LBS is wrong. the 6 speed chain will work. Thanks!

pastorbobnlnh 

At least I feel this way.

himespau 

Don't feed him.

austex9000

HAHA, I think I know what you mean Himespau. Thanks!

austex9000

Yes I hear that. I hear many people who say UG system is not the best, but my personal experience has be very good. The freewheel in this example is an UG to match the UG chain.

Bill Kapaun

He also posted this in the Mechanics Forum!

auchencrow

shelbyfv

another for the "ignore" list

WNG

You hear, but you don't listen.

pastorbobnlnh 

I've never heard that the UG system "is not the best." Only that the HG system was an evolutionary improvement. But then I don't spend any time in the Mechanics section or the Road Forum and I can see a few of those guys being critical of anything over 2-3 years old.

We here in C&V even appreciate the lowly Huret Allvit RD and plastic Simplex bits. We like to resurrect and maintain 50+ year old freewheels and SA IGA hubs. We have no qualms about cleaning, de-rusting, and restoring a 60 year old chain. We like and appreciate the sharing of tips and techniques and work arounds to vexing challenges.

When someone asks a basic question, we like to help that person, not belittle or ridicule or make them feel stupid. So when a 20 post BF member comes in with a legitimate question about achieving a low gear for an upcoming ride in the NC mountains, we make suggestions and find answers and occasionally brag about our particular achievements (but only with the hope it might inspire the OP or others).

But we don't mislead with the intention to make those who respond appear to be stupid or inadequate.

End of my Saturday morning sermon.