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Lengthening rear dropouts to 2.5 cm, possible?
Is it possible to tell, just by the pictures below, if the rear dropouts in the Giant Coldrock can be made longer (to a minimum of 2.5 cm)?
Here are some clipped versions of the best pictures of the bike's rear dropouts I could find: https://cimg0.ibsrv.net/gimg/bikefor...517eb6da0b.jpg Giant Coldrock rear dropouts https://cimg3.ibsrv.net/gimg/bikefor...5e09a1d54b.jpg Giant Coldrock rear dropouts More pictures of the above frame setup can be found at: http://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=184090133650&category=22679&pm=1&ds=0&t=1586797660449&cspheader=1 I have an offer for a complete bike and want to run it with an IGH at times which requires semi-horizontal dropouts to be at least 2.5 cm in length. I know there are other solutions but I want this particular one. If the above is feasible and safe, any advice on how to do it best in the home shop without special tools will also be greatly appreciated. If possible I'd rather not file away at the dropouts manually but I don't want to damage anything either (apart from manual files, I have access to an angle grinder and battery-operated driver). |
Drill/file is the only way I can see. I assume you would have told us if you had a milling machine. And that would require a lot of work to get it fixtured properly
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My 1988 Diamondback Ascent also had partially-filled dropouts to begin with (though not quite to the same degree, see the PS.) It's something that was done toward the end of the horizontal dropout era to help put the freewheel in the best position for indexed shifting.
To gain a little more runway, I propped up the frame on its back end so that I could file straight down with a round file and some oil. I checked my work frequently to make sure I wasn't going above the line made by the upper portion of the dropout. BTW, your dropouts don't need to be 2.5cm+ long to run an IGH. All that you need is to be able to get (almost) all of the slack out of the chain when installing the rear hub. Instead of filing anything, you could just get a half-link for your chain. That would give you finer adjustability in the space you have. :thumb: P.S. Not my picture, but here's what my dropouts originally looked like: https://forums.mtbr.com/attachments/...ack-ascent.jpg |
I wouldn't hesitate to drill a slightly undersized hole a bit farther back and then cut the slot to it with a hacksaw and then clean it up with files.
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If an inch (2.54cm) is the goal I think you'll find these dropouts lacking in enough material to do this. You might get another 1cm of more slot length after some work with a hacksaw and file (or milling machine but the fixturing will be the key. One doesn't want any vibration with spinning cutters
Henry James has offered replacement horizontal dropouts in the past for replacement. But that's a whole other ball of wax. I suspect one of the other options you rejected is a chain tensioner hanging from the der tab. They do work but can add a bit of chain run noise. BTW an adjustment range of slightly more then a half inch can be enough to account for chain tensioning unless some odd cog/ring spec. Is there some other factor we don't know about yet? Do you know about half links (the KMC HL710 is an example of a complete chain with all half links). Andy |
Thanks for your replies.
Originally Posted by ThermionicScott
(Post 21416227)
My 1988 Diamondback Ascent also had partially-filled dropouts to begin with (though not quite to the same degree, see the PS.) It's something that was done toward the end of the horizontal dropout era to help put the freewheel in the best position for indexed shifting.
To gain a little more runway, I propped up the frame on its back end so that I could file straight down with a round file and some oil. I checked my work frequently to make sure I wasn't going above the line made by the upper portion of the dropout. BTW, your dropouts don't need to be 2.5cm+ long to run an IGH. All that you need is to be able to get (almost) all of the slack out of the chain when installing the rear hub. Instead of filing anything, you could just get a half-link for your chain. That would give you finer adjustability in the space you have. :thumb: [...] The user manual for the IGH specifically says that the rear dropout length must be I didn't know about half-links though. Question: do you need to buy a specific chain of half-links only, or is it possible to add, for instance, a couple of half-links to a chain you've already got instead of a regular link? I find it quite difficult to find a retro cro-mo MTB/ATB frame setup with semi-horizontal dropouts, let alone the 2.5-cm-long-or longer ones, are they in some way inferior to vertical dropouts, which are almost ubiquitous on this type of frame setups from the '90s? *Update: the manual actually says 'longer than 25 mm', which I suppose directly corresponds to what Andrew R Stewart is saying in his post, i.e. an inch (2.54 cm) - a length of two standard chain links. Makes sense when you want to shorten your chain.
Originally Posted by Andrew R Stewart
(Post 21416952)
[...]BTW an adjustment range of slightly more then a half inch can be enough to account for chain tensioning unless some odd cog/ring spec. Is there some other factor we don't know about yet? Do you know about half links (the KMC HL710 is an example of a complete chain with all half links). Andy
https://cimg4.ibsrv.net/gimg/bikefor...db346b2976.jpg |
There is no reason to not file out the filler on those dropouts. It was added to make aligning the rear wheel easier in a time when no one cared about single speeds or slide tensioning a chain.
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Ah, more data. Rohloff does have a few methods of establishing the reaction force arm/washer that other IGHs don't have. But I did note the possibility of a chain tensioner and that instruction sheet recommends one when the drop out slots are what you have. So I fail to see how modding the frame is the easiest and most simple way to use the Speedhub. I think your decision to move on from this frame is smart given your requirements. Andy
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Originally Posted by Thomas1
(Post 21417282)
Thanks for your replies.
I guess I'm going to have to pass on this one. Pity as I like this frame setup (it's got all the nice braze-ons I need for an expedition bike and it's cro-mo). The user manual for the IGH specifically says that the rear dropout length must be I didn't know about half-links though. Question: do you need to buy a specific chain of half-links only, or is it possible to add, for instance, a couple of half-links to a chain you've already got instead of a regular link? I find it quite difficult to find a retro cro-mo MTB/ATB frame setup with semi-horizontal dropouts, let alone the 2.5-cm-long-or longer ones, are they in some way inferior to vertical dropouts, which are almost ubiquitous on this type of frame setups from the '90s? *Update: the manual actually says 'longer than 25 mm', which I suppose directly corresponds to what Andrew R Stewart is saying in his post, i.e. an inch (2.54 cm) - a length of two standard chain links. Makes sense when you want to shorten your chain. I don't know if there is something else to it. Have look at the manual: https://cimg4.ibsrv.net/gimg/bikefor...db346b2976.jpg The section of the manual you have circled doesn't say anything that is uniquely true of the Rohloff Speedhub. It just says that you may need a chain tensioner if your horizontal dropouts don't allow for a convenient chain length. With a standard full-link chain, adding a (full) link moves the axle back 1/2", removing a (full) link moves the axle forward 1/2". If you add a half-link to your chain (you would only need one if you think about it), you can adjust the axle position by 1/4" either way. The dropouts on your frame would be plenty long for that. (I suspect that their reasoning for 25mm dropouts is to avoid upset customers who ran out of room for adjustment as their chain elongated from wear.) But if you want to use a different frame to follow "the letter of the law", it's up to you! :thumb: |
it's silly, but all surlys have horizontal dropouts for fixed gear. Might want to look for one.
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I am with ThermionicScott (great name) on this one and recon it will be fine.
As well as the half links you can move the wheel by changing the ring or sprocket size. You might have to play around a bit when you first get it, but once you get the correct set up so with a new chain you have some room for wear, you are sorted. If you can fit a sprocket to each side of the rear wheel (I believe such wheels exist) you could put a 1 or 2 tooth larger one on the non used side. So if you run out of adjustment on an epic long ride just flip the wheel over - you might be pleased of the lower ratio too :-) |
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