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Thread: 7 & 8 Speed compatability

  1. #1
    Mojo Road Warrior TXRAiDR's Avatar
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    7 & 8 Speed compatability

    Curious to know if 8 speed cranks & RD (Shimano Sora) would work with the rest of a Shimano 7 speed group. I'm figuring that the RD would just have to be locked out with the H/L limit screws, a spacer behind the cassette, and everything would work just cherry.
    "As long as I breathe, I attack"-Bernard Hinault
    I've got more skill on two wheels than the majority of people have on two legs.

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    carlos's Avatar
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    as long as teh chain is 7 speed, you should be ok.

    are the cranks a triple or double?

    yeah, block out the limit screws.

    you may want to try it with and without the spacer on the cassette.

  3. #3
    Mojo Road Warrior TXRAiDR's Avatar
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    I thought a chain was really 7/8/9 speed anyway now, except for Campy chains?

    Double Chain ring. 52/39
    "As long as I breathe, I attack"-Bernard Hinault
    I've got more skill on two wheels than the majority of people have on two legs.

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    carlos's Avatar
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    7 and 8 work pretty well when mixed with in their respective drivetrains but 9 is so narrow that it won't even sit on a 7 speed cog or chainring properly.

    if it's a double, make sure your chain line is less that 50mm (center of seatube measured out to the smaller chainring. if it's not, you might want to get a new BB with a shorter spindle.

    but you get about 4 mm of room to play with when you're talking 8 and 7 speed, so you've got options there.

    what bike will this build up to?

  5. #5
    Mojo Road Warrior TXRAiDR's Avatar
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    Chainline, got it. I was going to use a SACHS chain. This is building up to an older Raleigh Super Course TT. I had the rear end & hub respaced to take 7 speed. I didn't know if the frame could make the 120 to 130 jump for 9 speed, but figured the extra 6mm would be okay (from 120 to 126). Thinking back on it now, I could have built up the 120 spacing as a single speed using some suzue hubs, but didn't think about that till after the fact. That brings up another question: would it be possible to move back to 120 spacing? Or, is that just to much fatigue on the metal of the frame?
    "As long as I breathe, I attack"-Bernard Hinault
    I've got more skill on two wheels than the majority of people have on two legs.

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    carlos's Avatar
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    10mm is quite a bit. see where the drop outs sit where the hub isn't mounted. if it's 125....you could go either way.

    spreading open chainstays can cause chain line issues. since one chainstay could move more than another, the rear end gets misaligned.

    5mm is the max you'll want to push. then again, if you're going to be using 6 or 7 speed cassettes, you might be able to get away with it.

    then the only issue is, will the rear wheel still track in the center of the whole frame.

  7. #7
    Mojo Road Warrior TXRAiDR's Avatar
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    I understand what you're talking about. I had the frame widened by a frame builder, so I'm going to say that he knows his job and it's done right. On his recommendation, I did not have him widen the dropouts anymore.

    As for the rear wheel center tracking the rest of the bike, that's what I'm gunning for. I'm building the wheels up myself (damn wheelbuilding is a useful thing to know ), and I'm using 7 speed hubs (Raleigh Brand) along with some Mavic 700CC rims. I'm going to use long reach brake calipers instead of having the brake boss on the frame or fork dropped. I all so saw an interesting article by your boy Sheldon Brown about creating a brake drop that allowed the user to use standard short reach brakes. Not going that route though
    "As long as I breathe, I attack"-Bernard Hinault
    I've got more skill on two wheels than the majority of people have on two legs.

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    carlos's Avatar
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    sounds like it's gonna be a cool build.

    Sheldon Brown? he was potty trained at gun point!

  9. #9
    Mojo Road Warrior TXRAiDR's Avatar
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    On a side note, why is it that a track set up is all most as much, if not more, than a regular build?
    "As long as I breathe, I attack"-Bernard Hinault
    I've got more skill on two wheels than the majority of people have on two legs.

  10. #10
    try explaining the internet to a bum!
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    carlos's Avatar
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    hmmmm.....i would think it comes down to, shops don't do track builds very often....not around here anyway.

    the big issue is the chain line. there's more room to work with but that means that if the rider is big, you'll wanna space out the cranks a bit more to suit a wider stance.

    as for the labor, maybe they don't want to deal with another price tier.

    i've done two track builds. the most time consuming was the bar tape job and the wheels.

    maybe it's easier to lump all builds together.

    there is an issue with frame prep but that's kinda gone now since most frames come alreay preped from the factory.

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