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Old 09-03-11, 04:55 PM   #1
Arrowana
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Shimano Nexus 8-speed coaster brake hub with vertical dropouts. Possible?

I guess it's about time I come in here and ask for some help on this. I'm trying to build an all weather commuter on the cheap, and I've run into an issue. The frame I picked is a 1994 Barracuda A2E, a 26" hardtail MTB with vertical dropouts. The rear wheel is a Nexus 8-speed coaster brake hub. I can't find a good way to get proper chain tension. Chain Tensioner won't work, as the chain will go slack when using the brake. Ghost ring won't work, the shift cable is in the way. I've got a few different chainrings and cogs, and can't find a magic gear ratio, even with a half link. Filing the dropouts is a bad idea, as the IGH requires anti-rotation washers. Eccentric Bottom brackets are expensive.

Anything else left to try? If not, any idea what kind of frame I should look for? Here is some info about the parts I want to use:
Nexus 8-Speed Coaster hub, 130mm spacing
Clearance for up to 26x2.35 tires with fenders
Front Disc Brake, Threadless Fork and headset (I suppose I might consider going with a drum brake if there isn't anything way to use the disc.)

I know a Schwinn Varsity can take 26x2.35 tires, any other old road bikes that can do this?
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Old 09-03-11, 05:38 PM   #2
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Forward Components EBB fits regular bb, made for just this situation:
http://www.forwardcycle.com/
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Old 09-03-11, 08:05 PM   #3
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If it has vertical dropouts, no EBB, and no way to slide the dropouts back and forth, I assume there is a derailleur hanger, yes?
http://surlybikes.com/parts/singleator/

(I've seen a full regular derailleur mounted on an IGH bike, and it looks awful... really!)

--

oops, missed the part about tensioner and coaster brake... sorry

Last edited by dchsueh; 09-03-11 at 08:12 PM.
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Old 09-04-11, 10:54 AM   #4
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Can you install a second chain-tensioner on the upper run of chain? Sheldon Brown makes reference to a type of tensioner which clamps onto the chainstay tube - if you can find one it might be suitable.
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Old 09-05-11, 09:52 PM   #5
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Ok, looking at chainstay mounted tensioners, the Dimension one seems common, but I don't think it would do much to help in this case, as it does not move at all. Kore has one that might work, although it is made to be mounted on the underside of the chainstay, where I'm guessing I need it up top. Any thoughts on this?
http://www.bikewagon.com/2010-KORE-S...-p6622355.html

Also, looking at my Raleigh Record, I could probably fit a 26x2.35 up front, but it looks like anything much larger than 26x1.5 won't fit in the rear. I'd probably be ok with a 26x1.9 back there, anyone know of an old road frame that could fit that? I also found someone on Craigslist who might have a MTB frame with semi-horizontal dropouts as another option.
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Old 09-05-11, 10:20 PM   #6
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I second the EBB suggestion. Besides the Forward Components example mentioned above there is also the Tr!ckstuff Exzentriker, and the Halo BB Adapter by Yess Labs. At $50 the Halo is by far the cheapest option.
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Old 09-06-11, 12:05 AM   #7
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I don't see a good choice for a EBB, the Forward doesn't seem to be available, and needs a bottom bracket and crankset that I don't have, making it quite pricey. The Exzentriker is way too expensive, and the Halo is for one piece bottom brackets.
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Old 09-06-11, 05:45 AM   #8
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Vintage bike/frame off of CL with correct dropouts?
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Old 09-06-11, 10:19 AM   #9
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Quote:
Originally Posted by Arrowana View Post
I don't see a good choice for a EBB, the Forward doesn't seem to be available, and needs a bottom bracket and crankset that I don't have, making it quite pricey. The Exzentriker is way too expensive, and the Halo is for one piece bottom brackets.
Where did you get that information? According to Yess Labs, the adapter "fits on Standard BB frames, it allows you in [sic] install Euro bottom brackets". From what I understand, "Euro bottom brackets" is BMX slang for an ISO BB, as opposed to a one-piece crank.
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Old 09-06-11, 10:33 AM   #10
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Originally Posted by irclean View Post
Where did you get that information? According to Yess Labs, the adapter "fits on Standard BB frames, it allows you in [sic] install Euro bottom brackets". From what I understand, "Euro bottom brackets" is BMX slang for an ISO BB, as opposed to a one-piece crank.
You are understanding not what say they even though clearly written is it.

The Halo looks to me to be an adapter for frames with Ashtabula (one piece) bottom bracket shells to use a 'Euro' (English thread) bottom bracket. For some reason the web page refers to Ashtabula as a 'standard' bottom bracket... but if they don't mean Ashtabula, then what do they mean by "allows [you to] install Euro bottom brackets"? If the frame is already threaded for an English BB, nothing is needed to 'allow' an English BB to be installed. Also: the threads inside the unit, presumably for threading in an English BB, are obviously smaller diameter than the outside, which looks to be a press or slide-in fit for some other larger diameter BB shell.

Edit:
To the OP: I think you need to start looking for either a frame with chain tension adjustment built in (horizontal*/sliding dropouts or an EBB), or for a hub without a coaster brake. Are you able to disengage or remove the coaster brake on the Nexus hubs like you can with their roller brakes?

*Horizontal dropouts are super common in older, low-end steel frames, so just about any dirty old MTB you pull out of a dumpster is a possible frame doner.

Last edited by DCB0; 09-06-11 at 10:39 AM.
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Old 09-06-11, 10:37 AM   #11
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Don't think the OP wants a fabulous bling kit, just function.

Quote:
I'm trying to build an all weather commuter on the cheap,
A coaster brake has a separate strap for the braking ,
chain tension is what you have to get straight.

your magic chainring / cog ratio , that feels right, with a chain half link
so to get get within a 1/2 inch, doesn't leave too much chain slack,
that will work.

some sloppy chain tension coaster brake cruiser bikes are out there, they stop ,
just may take a bit longer. anticipate your stop.

Vertical dropout frame probably has rim brake mounts too,
fit both, to be extra safe.

Last edited by fietsbob; 09-06-11 at 10:50 AM.
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Old 09-06-11, 10:46 AM   #12
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You can take the poor man's approach and fit a spring chain tensioner to either the chainstay or the derailleur hanger. You have to make sure that the tensioner has enough travel to rise enough to allow a straight lower loop when braking.

This is a limited solution, and how well it works depends on the amount of chain slack. Depending on your particulars, using a half link to get the chain closer will help. Then, understand that there'll be greater pedal throw (dwell) when applying the brakes because of the need to take up the lower loop first. If it's close you might not even notice, but otherwise you will.

Whenever you brake the upper loop will go slack and sag, but this shouldn't be an issue because the chain is stationary, and should pick up again when you pedal forward (maybe not on a bumpy track depending on how much slack.

Given that you want to stay on a budget, you should consider this option, especially if you've fitted a chain and it's only a bit slack as it is.
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Old 09-06-11, 11:20 AM   #13
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You are understanding not what say they even though clearly written is it.
Thank you, Master Yoda!

Quote:
Originally Posted by DCB0 View Post
The Halo looks to me to be an adapter for frames with Ashtabula (one piece) bottom bracket shells to use a 'Euro' (English thread) bottom bracket. For some reason the web page refers to Ashtabula as a 'standard' bottom bracket... but if they don't mean Ashtabula, then what do they mean by "allows [you to] install Euro bottom brackets"? If the frame is already threaded for an English BB, nothing is needed to 'allow' an English BB to be installed.
I stand corrected! I remember having a BMX bike when I was a kid that had one of those "Ashtabula" BBs (or I assume it did since it also had a one-piece crank). Of course that bike also had horizontal dropouts, precluding the need for an EBB.

If one can justify the cost, IMHO the aforementioned Exzentriker would offer the best-looking solution:

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Old 09-06-11, 05:00 PM   #14
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Another thought: since you've got a half-link, you can adjust the chain length in 1/2" steps. That means you can adjust the rear-axle-to-BB distance in 1/4" steps, and consequently your rear axle must be within 1/8" of a suitable position - possibly less. Can you grind that much out of the drop-out slot without fouling the axle fixings? The idea is not to widen the whole dropout-slot, but just to grind away a little material where the axle sits so that the slot is "L" shaped. With care a simple circular file might do the trick.
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Old 09-06-11, 05:05 PM   #15
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Can't find the magic ratio? It's there, somewhere. You might have to adjust the rear axle a little bit to get the correct chain tension. Meaning, you won't be able to just slam the wheel into the vertical dropout like you would with a derailer bike. The "perfect" magic ratio is the one that gets the chain too tight with the wheel in the normal position, but lets up just enough when moving the wheel down a bit.

This is the cheapest way (free) and the way I do my SS/FG conversions on bikes with vertical dropouts. By the way, once you find it you have other ratios that will work too. For example, if you find that 42/18 works, any ratio 4 teeth away will also theoretically work. Like 42/22, 38/18, 40/20, etc.

I've done this on 3 bikes now and never had to use a half link. A pile of old loose cassette sprockets and wheel is helpful for finding it.
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Old 09-07-11, 03:03 PM   #16
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Well, I'm going to the co-op tonight to see if there are any frames that will work better. I got my first taste of bike polo Sunday, and might build up the Barracuda as a bike for that if I do find a frame for the IGH tonight.

Edit, found a Trek Cruiseliner frame, made for a coaster brake and IGH. Score!

Last edited by Arrowana; 09-08-11 at 12:28 AM.
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