Lazarus Short

I just got finished paring back my 5-speed freewheel from 14-38 (Kansas City hills gearing) to 14-28 (high plains gearing). I had even considered 14-24. BTW, I used Mike Sherman's Bicycle Gear Calculator to decide on the exact gearing - it's fast, and informative of any gaps in the gearing - goodbye semi-log paper and gear charts.

My old PX-10 is set up with Huret Duopar rear and Huret front derailleurs. The Duopar did very well on the 14-38, actuated by a Suntour indexed barend shifter - it works! I also have a Sachs-Huret ECO S rear derailleur, and there is a 24 and 28 tooth position for the tension spring, so it should be good to go on the 14-28. My question concerns the chain-wrap capacity. The front TA crankset is 30-46-50, so does the ECO S have sufficient capacity for that? Maybe someone on this forum can tell me.

fietsbob

if not a long cage RD, get one . friction shift, no specifics,

just a long distance for pulley to pull back when extra slack.

ThermionicScott 

Is it this guy? https://www.velobase.com/ViewComponen...108&AbsPos=179 There are other Ecos and DuoPars on Velobase under the Sachs and Huret names.

Lazarus Short

Yeah, thanks! I looked up the ECO S on the www, and it wraps 31 teeth max - not enough. The Duopar is a bit bent, sooooo, since I already have Suntour barends mounted, I'm going to try a Suntour on the rear. I've got these:

7-GT

XC Sport 7000

Accushift -4050

The biggest factor against them is that Suntour rear derailleurs are not at all compatible with Simplex dropout mounts. The PX-10 came with Suntour when I bought it second-hand, and it made wheel changes a challenge. I might try some sort of quick-release skewer...

Lazarus Short

No, it was this site: https://www.disraeligears.co.uk/Site/...railleurs.html

ThermionicScott 

I can tell you that the a-4050 won't like a triple, either. I tried running mine with a 52/42/32 triple and 14-28T freewheel and it didn't have nearly enough capacity.

The 7-GT should get the job done, though! https://www.velobase.com/ViewComponen...108&AbsPos=393

Lazarus Short

Yeah, I thought the a-4050's cage looked a bit short. The 7-GT would do, I'm sure, but it's fugly!

Hey, I recall that to get more chain wrap out the Simplex L.J. Super I once had on the PX-10, I replaced the short alloy cage with a long steel cage from a Simplex Maxy. I wonder if I could make another Frankenrailleur out of the two Hurets? Crazy...

Retro Grouch 

In real life you might not need as much slack take up capacity as the calculations suggest.

Do you use all of your freewheel gears in combination with your granny chainring? I certainly don't. The only time that I use my granny is on steep hills and only in combination with my biggest couple of rear cogs. If I never shift into the 30/14 combination, I don't need enough slack take up to handle that combination.

HillRider

+1. As long as the chain is made long enough to shift safely into big-big, you can sacrifice the ability to use small-small with no problems. All that happens if you forget is that the chain goes slack and it's a bit noisy. As RG notes, there is no need for small-small as the same gear is available elsewhere.

MikeWMass

I have a Velosolex with Simplex dropouts. I was able to cut a notch in the dropout with a Dremel that will catch the B screw from a Suntour V-GT just fine. The axle to pivot distance seems long, so the B screw is backed off pretty far, but it works well, much better than the Simplex derailleur that was originally spec'ed. I have used it with up to 32 tooth, seems like it would work with a bigger cog, currently running 14-28. By the way, this was done in 1976 when I bought it new.

Lazarus Short

I know where Retro Grouch and HillRider are coming from. I looked at the chart of my gearing, and realized that for practical purposes I had five speeds on the 46-tooth chainwheel, plus an overdrive on the 50x14 and an underdrive on the 30x28. That is how I intend to use it anyway.

MikeWMass suggests that I Dremel a place for the "B" screw of a Suntour derailleur, but I still have the problem of the Simplex mount lacking threads (and I think the hole is too big to tap anyway), and the threads of the Suntour are not long enough for a nut on the other side. I still see a quick release, perhaps a seatpost skewer as the answer if I go Suntour.