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Old 11-09-10, 10:54 PM   #1
FergieGirl
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Swapping derailleur setup for Shimano 8 speed hub. What do I need to know?

Hi there
I have a 1980s 12 speed mixte I'm going to have converted to a Shimano 8 speed hub gearset. I've bought the Shimano kit including cables etc and am waiting for it to arrive.

What I need to know is, what else do I need to replace? Do I need a new chain? A new chainring? If I need a new chainring, how many teeth should the replacement chainring have? Will I therefore need new cranks or crank arms?

I'm no mechanic so any help would be appreciated. I won't be doing the conversion myself (heck, I wouldn't want to ride a bike that I'd worked on! ) but want to be able to source the parts myself to make this little bike look pretty special as well as ride like a dream.

I've put some pics of my bike below so anyone who wants to help can see the existing situation. I believe my dropouts are horizontal enough for the hub setup to work just fine.



Hope some of you can offer advice!
Kind regards
Fergie
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Old 11-10-10, 04:31 AM   #2
dabac
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Ah, OK, you want to put an internally geared hub there. You might need to tweak the dropout width a bit. Not certain about how the cable stop on the chain stay will work out for you, you might want to look for a fulcrum clip. Chain wheel depends on the basic gearing ratio of your IGH, and your preferences. If your chainwheels are bolted you should be able to find something fitting.

I suggest that you start by riding the bike as it is first, and figure out which gears you like. Then head over to www.sheldonbrown.com and use his gear calculator to determine which combo of sprocket/chainwheel that together with your IGH will be the closest match.
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Old 11-10-10, 10:48 AM   #3
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I'm in the process of doing this conversion to my wife's bike right now. I'm having the frame powdercoated, so am removing unnecessary braze ons and drilling/filing cable stops to be cable housing guides where appropriate beforehand.

Hope you checked your rear spacing and number of spokes before you ordered (most Nexus inter 8's are 36 spoke, 130-135mm OLD). If your rear spacing is 125mm or more, you should be fine for spreading it to fit. You won't use the chainstay cable stop--the hub comes with an integrated stop/fixture, but you'll be running cable housing from the shifter all the way to the hub, so cable stops can either be modified into housing guides or ignored (clamp on cable guides or zip ties will work in their place). You'll need to source the proper keyed washers for mounting the hub to your angled drop outs (several sources sell them, Sheldon's site among them). The ones that come with the hub will be for horizontal or very close to it drop outs. There are also ones for vertical and angled drop outs. They are important because the cable assembly won't line up right without the correct ones. You will also likely need a chain tensioner (looks like a modified derailleur without the parallelogram--they run between $20--$100 or so, depending on brand and design). Without it, you will probably not be able to get your chain length and tension just right, and the chain will jump off the rear cog and/or wear out very quickly. The up side of the tensioner is that it will make flat repairs a whole lot easier. Your crankset will probably be ok, if you're happy with the gearing. Since the internal gear ratios are fixed, you adjust your whole range up or down, depending on your strength and terrain, by swapping out the external cog (easy) and chainring. The smaller chainring is unnecessary, unless you intend to continue using your front derailleur (definitely need a double jockey wheel tensioner for that). Otherwise, the derailleur should be removed, along with cabling and shifter, and the small chainring can stay or go, your choice. The big chainring may be fine as is--most Nexus-equipped bikes come with 42-46 tooth chainrings and 18-22 tooth rear cogs.
CC

PS, NICE BIKE!

Last edited by Cross Creek; 11-10-10 at 03:42 PM.
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Old 11-10-10, 03:41 PM   #4
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Forgot you asked about the chain. Chains are cheap. If yours is old, go ahead and drop $10 or so on a new one. You can use either 1/8" or 3/32" on the hub, but it needs to be compatible with whatever chainring you settle on. Chains for 6-8 spd casettes/freewheels usually work fine. Also, your mechanic needs to check out your chain line to ensure it isn't too far off. If so, you may be able to move the chainring to the inside of your crank (maybe not, though, depends on the design). The more expensive fix is to change out the bottom bracket for one with the proper length. Prices vary from low $20's to $50's or so for this application. If your bottom bracket needs replacing anyway, don't automatically order the same size without checking the chain line first.
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Old 11-10-10, 03:44 PM   #5
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Thanks, dabac.
I've had the bike a couple of years. I live in a hilly area so need the low range to be pretty low. A friend built up a similar mixte conversion and used a 46 tooth chainwheel which she says works pretty well for her.
Typically when I ride it as a twelve speed I use the middle gears in both high and low range. I resort to the lowest two gears on hills when necessary but can go up smaller hills in 3rd or 4th.
The Sheldon Brown site is brilliant - I'll check out the gear calculator before I talk to my bike shop
Cheers
Fergie
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Old 11-10-10, 03:52 PM   #6
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Hi Cross Creek
Thanks for all this info - very helpful from someone who's done what I'm about to do. I suspect I'll need a new chain but that's not an expensive thing. The gears come with 36 spokes which match my existing wheels and the spacing looks about right. However, my brother-in-law is trying to persuade me to change my rims to 700C as I'll have to have the rear wheel rebuilt anyway. A bit of an extra cost but it 'futureproofs' the bike. I'll see what the budget is looking like once the gears appear magically in my letterbox.
Brother-in-law also thinks that the keyed washers should come in the box with the rest of the kit, which will make life easier.
I didn't know about the gear tensioner - thanks for that tip.
Cheers
Fergie
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Old 11-10-10, 04:05 PM   #7
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you're dropouts are horizontal enough that you won't likely need anything for tension. If the box comes with anti-rotation washers, they may not be the proper ones. Judging by the picture, you'll want the brown ones, but it may be the grey ones. Best bet is to measure the nagle at which the dropouts intersect the chaionstay, and compare with Sheldon's page.

hth,
-rob
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Old 11-10-10, 04:10 PM   #8
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Quote:
Originally Posted by FergieGirl View Post
Hi Cross Creek
Thanks for all this info - very helpful from someone who's done what I'm about to do. I suspect I'll need a new chain but that's not an expensive thing. The gears come with 36 spokes which match my existing wheels and the spacing looks about right. However, my brother-in-law is trying to persuade me to change my rims to 700C as I'll have to have the rear wheel rebuilt anyway. A bit of an extra cost but it 'futureproofs' the bike. I'll see what the budget is looking like once the gears appear magically in my letterbox.
I like brother-in-law's advice re: the wheels. You're likely to need new spokes as well as this hub you got, and the rim is probably borderline ancient by now, plus it will grant you access to about a million more tire choices. I think you'd enjoy that. On the other hand, it'd add expense cause you'll likely wanna do the front wheel, too.

hth,
-rob
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Old 11-10-10, 04:44 PM   #9
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The anti-rotation washers packed with your hub will be for horizontal drop outs. You'll need to order the correct ones. Surreal may be right about your chain tension adjustment. I haven't worked with angled drop outs and IGH's, just horizontal and vertical.

+1 on the 700c recommendation--lots of rim and tire choices. I just picked up a nice wheel set on sale from VO--red line (premium) Nexus 8 hub, built into a 650b wheel, and a matching front wheel on a Shimano 105 hub, for $320, total. I had anticipated brake issues, but they were a drop in fit on my Milano (559 wheels--MTB standard, originally). I just moved the brake pads on my front V-brake up 12mm and added a roller brake to the hub--as the bike came originally, anyway. I had to re-mount my fenders to clear the tires, but that was easy. The whole thing looks and rides great--larger wheels actually fit the frame better (700c's wouldn't have fit), and the BB was only raised about one cm, which I can handle. That left me with a Nexus 7 set to move to my wife's smaller frame when it comes back from the painter. I'll post pics of the pair when done with the project.
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