Derailleur capacity
 

Hi, I'm trying to find out what freewheel I can replace a Suntour winner/new pro with. The bike is all Suntour Edge, 6-speed Indexed-Accushift and oval chainrings (not sure if it's relevant to rear derailleur or not) and is pretty nice to ride, though it's rather highly geared.
The freewheel has a broken sprocket, the very first one which is also a lockring. Broken as in it's split and just spins if any load is put on it.

Anyway there are plenty of 6-speed freewheels out there, but all the new ones seem to come with 28t as the big sprocket. The one currently on there is about 19 or 20 (haven't got it with me) max. What I would like to know is if the derailleur can handle a large rear sprocket or if I need to keep it small and just look for a replacement sprocket. The bike is quite highly geared so I'd rather be able to replace it but if I can't well it's no big deal.
I found this page http://www.worthpoint.com/worthopedi...ur-7-117470766 which seems to discuss the correct derailleur, but I don't necessarily trust that as it's from an auction.

Has anyone encountered this?

Saw an old bike recently in my stand... didn't have a label; It'd been repainted orange, yellow, green fade. I think it was some older Bianchi maybe. It had some Suntour Edge components. He used friction cyclone downtube shift levers and a 26T max shimano FW and it shifted fairly well in that mode. What I've heard on the older Suntour index was 24T in indexed, and 28T in friction mode. The shifting doesn't work in indexed if you have Suntour/Suntour RD and Levers together. It a bit off either at the big cogs or at the small cogs in terms of spacing. But I have gotten Shimano shifters and Suntour RD to work with Shimano FW. Not sure if that helps.

Given Suntour is no longer in business the accushift went under with them.
you can still get 6 speed freewheels 13 to 34t for widest range.

friction shifting is a universal common .
long cage RD will have the big cog cap and big difference wrap up.
cog + chainring tooth count
[big+big] - [little + little] is how much chain slack has to be taken up.

If the edge is a short cage it should be able to handle 28 teeth with a standard road double as this affects capacity while the biggest cog a derailleur can handle refers to it's physical limit which is determined by cage length.

As the spacing on Suntour and Shimano and Shimano compatible freewheels is slightly different you may find that the indexed Suntour does not play well with the new freewheel and Suntour and Shimano indexed components can sometimes be incompatible as well due to different geometries on the rear D that affects shifting.

Suntour freewheels can still be found on the used market and some shops (like mine) have the capacity to rebuild Suntour freewheels as we have managed to retain the service boards and cogs that were once common in many shops.

Ah right, so even if the derailleur will take a 28t cog, it'll cause shifting problems with the spacing of the cogs. Hmm, I guess it'll just be cheaper to find a 13t sprocket and keep it running like that. It's not my main bike or anything, but I like fixing things up:)
Are the new freewheels labelled 'Sunrace' at all related to Suntour or is it just a naming thing? Is there any chance that they would have the older Suntour spacing or is everything made to Shimano spec. now?

I'm curious to see the answers the pro's give ya, I just did something very similar but with friction not index, and it worked perfect (going to a 14-28 freewheel that is)

There are no compatibility issues with friction... just when you mix and match earlier generation indexed parts and when you try to get modern Shimano, SRAM, and Campy to play together in indexed modes.

With travel adjusters and alternate cable routing you can sometimes get these differently spec's components to play together and every once in a while they will do it on their own.

The later generation Suntour indexed shifters often has settings for regular and ultra (narrow) spaced freewheels and these can often work well with modern narrow cassettes.

Sunrace is not Suntour , they are (were ) two different companies . Yes Sunrace is made to Shimano spec . Sunrace is not made of the best . Try Ebay for a Suntour 's freewheels , they do show up there from time to time .If you just need a cog maybe Thethirdhand.com they carry New Old Stock (NOS ) .

Too bad it's a 6, I've got a suntour perfect 5 just collecting dust you coulda had.

^^Thanks for the offer:)

Ok, I'm just going to go with looking for a 13t cog. I see loose screws has a few though the position-designating letter is different (this has an E) so if I get desperate I can use a 14t as a lockring.