Bicycle Mechanics - upgrade 6 speed to 7?
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07-13-10, 03:02 AM
I have a shimano 600 ex rear and front derailleur and the rims are 27 inch with a 6 speed freewheel on it. I'm wondering if upgrading to a 700c rim with a hub and cassette would be possible. I would switch to a 7 speed cassette. I have read that the shimano 600 ex would be able to accept 7 even 8 cogs, but i would like to know first hand before i go out and spend some cash on new wheels. It's a 87 schwinn super sport (i believe).
I have a shimano 600 ex rear and front derailleur and the rims are 27 inch with a 6 speed freewheel on it. I'm wondering if upgrading to a 700c rim with a hub and cassette would be possible.
700C rim depends on your brake reach. Sometimes they're adjustable enough, sometimes they require the change to long-reach calipers.
Have a look at rear dropout spacing and frame material while you're at it. You're probably looking at going from 126mm to 130. This is doable in pretty much any material, but steel is the most forgiving.
I have read that the shimano 600 ex would be able to accept 7 even 8 cogs... If it's a freewheel hub, it'll take anything that can be screwed on - and the standard for freewheel threads is one of the most stable ones in the bicycling industry. A new and longer axle might be required.
07-13-10, 07:31 AM
its probably a very easy switch if you keep it as a freewheel. I just took a ten speed with 27" wheels and easily put 700c on there and went with a 7 speed freewheel, no issues, just had to force the wheel in a little bit but i suppose I could get the frame "cold set" to that same width. I had diacompe brakes with plenty of room to adjust the pads to make them work. best place to start is by simply taking a 700c front wheel and putting it on and see how the brake reach is.
07-13-10, 10:27 AM
Agree, just get a 7 speed freewheel , but i question where that added cog will be used? have a 13-28 and want a 34t granny gear, then the new cog is added, in the middle replacing a 17 with a 16 and an 18 will be less significant .
gap between cogs narrows , 7 speed goes in a 126 dropout overlocknut width so that need not change..
Adding #8 forced the frame specs out to 130.. its 7 speed spacing add 1 more ,
9 otoh further compresses the distance between cogs, without making the overall width much more .
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07-13-10, 10:51 AM
If it's a 600, are you guys sure it's not a Uniglide cassette? The solution could be as simple as scoring a new fh body off ebay and buying one of the better grades of 27" tires.
07-13-10, 11:14 AM
at first i was thinking of buying a newer set of wheels, because the ones with the hub are much easier to find than a 700c wheel with a screw on freewheel. I already have 700c tires and tubes. i don't feel like buying a new set of tires. but perhaps that's just exactly what i'll do. Thanks.
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