Bicycle Mechanics - 7 Speed, Single Chainring Set-up
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08-06-10, 02:39 AM
Here's my idea: I'd like to run a 7 speed cassette with a single chainring up front on my commuter bike. I'm seeing that I've got two options here: 1. Seek out older Shimano 600 parts and throw them on. 2. Run a new cassette, such as a Shimano HG70.
I'm leaning towards new parts, which puts me in a bit of a bind. I cant seem to get a straight answer on compatibility. Does anyone know if a Shimano HG70 cassette will fit on a current Ultegra hub (assuming that it requires a spacer)?
Conversely, any suggestions on a lightweight 7 speed cassette/hub combo? Ideally one that allows me to use a 36 hole Open Pro.
08-06-10, 03:00 AM
The stack height is greater for the higher number cassetes so with a 7 speed cassete on a new wheel you will need a spacer. And if you choose to run a MTB cassete with an 11T small ring then you're stuck with the spacer being on the inner end and that'll mess up your chainline to some extent.
What about checking with the LBS's to see if they can get you a 7 speed freehub to transplant over to the hub? With the freehub and a shorter or shotened axle you'll be back to normal for the chainline issue.
08-06-10, 03:07 AM
Hmm, freehub...not a bad idea.
I wasn't aware of the chainline issue when running a spacer on the hub. That's a problem that I really don't want to encounter. So considering that, I will start looking into freehubs, I suppose. The dropouts are at 130mm but I can't see why they wouldn't accept a 126mm freehub.
08-06-10, 01:24 PM
As long as it's not one of the 10-speed only, aluminum freehubs, a 7-speed cassette will work. If the cassette has rivets holding it together, I suggest removing them or they'll butt up against the 4.5mm spacer and can make the cassette sit unevenly. There was noise and bad shifting on my setup until I removed the rivets.
I wouldn't worry about the potential chainline issue. It's common to put a 4.5mm spacer before the 7-speed cassette.
08-06-10, 01:55 PM
I'm not sure why you are limiting it to 7. If you already have the shifter you can use an 8speed cassette. The spacing is almost the same and close enough that I have never had a problem making it work. 8 speed stuff is easily found new and cheap.
I put together a 1x7 commuter last night myself. I used 7 because I had a 7 speed freewheel and a 7 speed lx thumb shifter gathering dust. I mounted the shifter on the tops of some drop bars, we'll see how it works out. Like a poorman's Paul thumbies.
08-06-10, 02:08 PM
You want the chainline in line with the middle of the rear, cog #4 of 7..
for 126 hub, add a spacer to the axle on the left, longer axle, and re-dish the wheel to the better , then add chain-ring spacers as needed to get the chain-line optimized .
But a Modern Internal gear hub makes life so simple, as there is no derailleur to hit and crud up.
There is this Brifter http://www.sussex.com.tw/versa.html for shimano's Allfine .
so You could build up a nice road machine with those Internal gear hubs.
08-06-10, 03:34 PM
You don't say if you have the wheel or not, if not, why limit yourself to 7 speed, especially a freehub, when you already spaced for 130? Buy a nine speed and go 1X9.
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