Derailleur choice problems - High Capacity?
 

I'm currently renovating a 1970's French Tandem (See http://gitaingaves.blogspot.co.uk/ and THIS forum thread, if you're interested), and am having a little bit of trouble picking derailleurs...

The proposed setup for the gearing is:
Front: 52-42-28 (Existing cranks)
Rear: 11-13-15-17-20-23-26-34 (This cassette)

This presents an overall (rear DR) capacity of ((52-28)+(34-11))=47 As far as I'm aware, the highest capacity any rear can officially handle is 45? We are very unlikely to every use the small/small combo, so a bit of slack shouldn't matter too much, my really question is, due to budgetary constraints, do you think we can get away with a 43 capacity (excluding the smallest 2 at the rear, whilst on the smallest at the front) without any problem? This one seems very reasonably priced...
For the record, I will need a claw adapter (included in the linked one, but around £5 separately).

At the front, It's a similar situation; (52-28)=24 is a larger capacity than most are rated for, and 52 is quite a large outer chainring! Does anybody know of a system that would work? The Seat-tube diameter (for clamp_ is 28.6mm

Thanks in advance for your help, which will doubtless be fantastic : D

Will

What you're proposing should work just fine. With a triple, there's some leeway in the RD capacity since, as you mentioned, you shouldn't use the inner chainring with the smallest one or two cogs. Size the chain using the big/big + 1" method. For the FD, a road triple FD should work just fine; many have reported even a 52 to 26T spread working well. There are shims to mate the more modern 31.8 mm or 34.9 mm FD clamp to your 28.6 mm seat tube.

do the ratio math .. and write up a grid of those numbers..

avoiding cross chain combinations by using the outer ring
with just the rear gears above, say, the 42/15.

the granny gear will come into an overlap range at about the 42/20
with the larger cogs on the middle..

those will be double shift points where you change both to get to the next ratio.

print out the grid of ratio/gear-inch numbers and tape it to your handlebars.

I will be using a friction bar-end, the thing that worried me, was that the chain might rub on the bottom of the cage on the granny, if I had a double setup, or might not clear the middle with a triple cage... All the 52-Curved cages seem to be very long, or very shallow?

Phew.

This is very sound advice - Works well with the handle-bar-pannier, too. : )

I'm using a 50,39 & 26t crankset with a 11-32 cassette without a problem. I could install a 11-34 and I am confident that it would be fine. I'm able to use all combinations without any issue.

Derailleur manufacturers add a large safety margin when publishing chain wrap and cog size ratings. I've exceeded both without any problems. Just check to make sure that the chain is long enough for the big chainring and the big cog combination without stressing the derailleur.

http://i289.photobucket.com/albums/l.../IMG_09611.jpg

If you go with an adaptor band + a braze on FD you can add wedge shims between the two
to change the FD angle between it and the seat tube.
+ add a K edge chain catcher on that bolt. to not drop over-shifts around the rear BB shell .

+1

http://i289.photobucket.com/albums/l...CGpart2004.jpg

I am running a 52/42/24 front triple and a 11/12/14/16/18/21/26/32 eight speed cassette. I can't use the 24t front when I use the 11 or 12 rear, as the derailleur will not take up the slack. I am not sure what the specifications are for the derailleur, I think it is a long cage XT M739 or perhaps some other M73_ model? I have enough links in the chain so that if I accidentally cross chain and shift onto the big gears (52t front and 32 rear) that it will not jam, as I wanted to make sure that if I did something stupid by accident that I cause no damage.

I try to avoid using the two gears that are most cross chained on each chainring: when on the 52t front avoid the 26 and 32 rear; when on the 42t front avoid the 11 and 32; and when on the 24t front I obviously do not use the two rear gears 11 and 12 when the drive train makes funny noises when the derailleur won't take up enough slack.

My front is a vintage Suntour high normal derailleur, model is Le Tech, but they made several other similar models. Friction front shifter is needed for shifting between the 24 and 42, as this is not a smooth shift.

http://bikeforums.net/attachment.php...hmentid=272697

For some of these component issues, it might be best to just try what you have and see what works. If for example, your front derailleur did not have the clearance, you can measure how much more clearance you need and you have something to judge competing components against. I am a big fan of vintage Sunour front high normal derailleurs and have them on most of my bikes.

Sir, is THIS your derailleur?

Forgive my (probable) ignorance, what is the advantage of being able to do this?

Thanks for the illustration, it was very helpful! what's the story with that crazy tube section?

The Existing derailleur is, none other than, a vintage Suntour! (See, the blog, HERE and HERE)
You're right, the shifts are not smooth at all, and there is minimal clearance in all areas. Are you of the opinion, that to stick with it would be better than to "upgrade"?

Your crankset looks like it is not ramped and pinned, that makes it a bit less smooth. (My older bikes built in the 1970s and 1960s do not shift very smooth either.) In my case, the 24t granny chainring is not matched to the 42 ring ramps and pins, as the 24t is an aftermarket one, so that hinders shifting somewhat. Also, you can't really expect a jump from 24t up to 42t to be very smooth, as that is a big jump. It actually looks like a big jump in the photo.

I think a different derailleur may not help, so I would not bother trying to upgrade that. But a crankset that has ramped and pinned chainrings might be smoother. If it was me I would not upgrade. But, I have never ridden a tandem. Your riding partner might not agree with me, they might want smoother shifting.

I do not know if an older crankset that was designed for use with a 5 or 6 speed freewheel will work smoothly with an 8 speed chain, that may be another issue. Since I have never tried this combination, I am quite ignorant of potential incompatibility with the narrow chain.

My preference for the older Suntours are specific to the high normal derailleurs. Only some of theirs were high normal. With my bar end shifters, pushing both shifters all the way forward puts me in the highest gear. I am not pushing on one shifter and pulling on the other to upshift. I found a local store that had some new-old-stock ones, I bought a lifetime supply of them. From your photos, I think yours is not high normal.

The bike shop I worked in carried Gitanes, but that was many many years ago. I assumed an old Gitane had Simplex equipment, I am surprised you have Suntour.

SHELDON suggests, that "Shimano 5-speed and 6-speed shifters are made to index with the 5.5 mm spacing between sprockets on older 5- speed and 6-speed freewheels", and I know that Shimano 6/7 Speed shifters are compatible with 8 speed cassettes, so, hopefully the indexing should work. On top of this, he says "Up through 9-speeds, all cassettes use very nearly the same wdith of sprocket teeth, and will work with 7/8 or 9-speed chains." I'm hoping that this means the 8 speed chain that I propose to purchase, to go with my 8 speed cassette, will be of the same with (minus the protruding rivets on the old one).

You're right, it's not HN... I may have scout around E-Bay for one, but since I won't have it on my solo (which I ride much more), I expect I'd just get a bit confused...

You are almost certainly correct in this. The cranks (cotterless, post 1982 since the crank-extractor threads worked) and the rear derailleur (Shimano!) are definitely not original, so I wouldn't be surprised if the front DR was not as well.

Possibly worth mentioning, just in case, is that There is a third (proper) (and probably final, at least until Christmas) post on the *NEW LOOK BLOG*
Check out that background...


Much love to you all, and thank you for supporting me thus far,


Will

Given it is a tandem another possibility exists,

Crank set with the crossover, triple crank on the front BB,
then you can add another chain slack control in between. there
are rollers from long WB recumbents and spring loaded 2 pulley tensioners from
other sources.. some frame fitting braze ons may be required..

means to an end, they say..

It's a mop handle...:-)

This pretty much rules it out for me I'm afraid, nice idea though!

Of course it is; why didn't I think of that?
It's a very nice colour, for a mop handle!