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Old 09-27-06, 08:55 PM   #1
wild animals
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Changing Sprocket on Nexus 8 Hub

Hello again

I had a question for you guys... I have a Bianchi Milano with a 44t chainring and a 20t sprocket in the back. I have to go up steep, steep hills, and I'm not super-athletic at this point (plus my bike and luggage and I are, shall we say, robust), so the low gearing is at times totally inadequate. The high gearing is okay, and I'd prefer more high end than less, but I can survive with lower high-end gearing.

So, what I was wondering is, what do I have to consider to change the rear sprocket?

I think I have about a 30" first gear right now. I don't know a lot about that, but here's a page about Nexus 8 hubs, with a chart at the bottom: http://sheldonbrown.com/nexus8/pages/05.htm I feel like I need at least one and more likely two or more gears below what I have now.

What does this involve? Should I leave it to a bike shop? I read that it could mean I'd have to change the chain length and move the wheel back further. If I pick a bigger rear sprocket, do I have to get a smaller chainring? (Is that super-expensive?)

Hope that isn't too many questions but I'd never thought of changing the rear sprocket before, and it could save me from hurting myself and/or having to buy a new bike in order to ride to work every day
Thank you!(!!)
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Old 09-27-06, 09:16 PM   #2
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A larger rear sprocket or a smaller chain ring will give you a lower gear. The sprocket is cheaper, the chainring is arguably easier. In any case you will most likely have to change your chain length if the difference is more than a tooth or 2. A 1 tooth increase in the rear cog is approx. = to a 3 tooth reduction in the chainring. You should be able to get a shp to change the cog for $20ish if you dont want to do it yourself. If you can remove & reinstall the rear wheel you can change the cog, it is held on by a snapring & preety easy to change out.
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Old 09-28-06, 12:07 AM   #3
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how much of a difference do you think going up one tooth in the rear sprocket will make in terms of climbing a hill? is it worth the effort or do i need to pick a much bigger rear sprocket? do you think that would make the bike useless for going over 15mph or so?

thank you for your help!
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Old 09-28-06, 12:11 AM   #4
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Not much really.
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Old 09-28-06, 12:22 AM   #5
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how big of a rear sprocket do i need to make a difference?
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Old 09-28-06, 01:28 AM   #6
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Your current gear of 30" would be 26" if you add 3 teeth to the cog. I find that 4 gear inches is pretty noticable. The drop in your top end probably more so. Your current top gear is 92" add 3 teeth in back you get 80". Spin spin spin!
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Old 09-28-06, 07:39 AM   #7
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If it is like a 3-speed Nexus, the rear cog is held in by a simple spring clip, easily removable by a small straight bladed screwdriver.
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Old 09-28-06, 09:45 AM   #8
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I have lots of these internal hubs. I haven't seen rear cogs bigger than 24. You may need to change both for a huge difference (and pretty much any change will need a new chain length). If your front cranks have a 130 BCD you won't get anything smaller than 38 teeth. But combine that with a 24 rear cog and you'll have a 22 G-inch low gear. That's pretty low, but you'll have lowered your top end to 68 G-inch.

I have a touring build where I put 53/38 front cranks mated to a 22 th nexus 7 rear (requires a fixed rear derailer to take up the chain) with a friction shifter on the downtube to a front derailer. My range is 29 to 100 gear-inches.
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Old 09-30-06, 12:05 AM   #9
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thanks guys! i was out today pushing down a hill and realizing i probably didn't have a lot of room to spare on either end, especially if i'm going to lose so much from the top. i'll probably have to wait to mess with the gearing until i have another bike. thank you though! it was helpful and now i have a better idea of what to do if i can change gearing later.
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Old 09-30-06, 09:47 AM   #10
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I like my Nexus 8, but it has problems with steeper hills. As you indicated, if you set it low for up hills you are going to loose the high for the down hills. I found that toe clips or clipless pedals will give me a boost for the up hill sections leaving more of the gearing for the down sections. Right now I'm using Power Grip straps as a sort of "virtual low gear".
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Old 09-30-06, 11:20 AM   #11
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hey, thanks! i've been meaning to get power grips or some other strap for my feet but i have such a long list of stuff to get. haha. i didn't think about them helping me climb hills though. that's a great point!
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Old 09-30-06, 11:27 AM   #12
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I run mine with a 42 on the front and a 19 tooth cog on the back. Even for flat riding I don't feel the bike is geared too low; it's good for you to spin if you can do it.

Apropos changing the sprocket - what people said is correct but expect that it'll be pretty annoying getting the spring clip back on. Two flatbladed screwdrivers and plenty of patience will get it done though.
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Old 09-30-06, 09:43 PM   #13
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Quote:
Originally Posted by bjkeen
Apropos changing the sprocket - what people said is correct but expect that it'll be pretty annoying getting the spring clip back on. Two flatbladed screwdrivers and plenty of patience will get it done though.
You can pop those suckers in quickly with as much practice as I've recieved. You slide the screwdriver blade under one side, ease it into place, then jam the blade on the other half, popping it into place.
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