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7-speed cassette to 8-speed

stfc1stfc1 Posts: 505
edited September 2008 in Workshop
Hi all,

I have a neglected old Raleigh that I am thinking of sprucing up to function as a winter bike. It currently has a well worn 7-speed Shimano cassette that needs to be replaced. If I replace it with an 8-speed, will the current and original RSX shifters be able to cope? The more bits I'm likely to have to replace, and the less cheap the spruce up option becomes, the more likely I will be to just dip into the second-hand bike market.

Sorry if this is a stupid question but I'm a total novice when it comes to bike mechanics, and thanks in advance for any help.

Posts

  • maddog 2maddog 2 Posts: 8,114
    7 to 8 is a bit messy, You need a new freehub, new cassette and becasue the 8 speed cassette+freehub is wider then you'll need to re-dish the wheel to get the new freehub on and keep the rim central.

    Plus your shifters only have 7 clicks so getting the extra gear might be tricky. I know 7-speed thumbies could be made to go 8-speed but I'm not sure the shifting was spot-on.

    For a winter bike I'd just keep the 7 speed on. You can still get hold of cassettes last time I checked.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • redveeredvee Posts: 11,920
    7 speed casette is narrower than 8 speed so you can either change the freehub body and redish the wheel or buy a new wheel, plus new shifters. Be cheaper in the long run for new bike IMHO.
    I've added a signature to prove it is still possible.
  • stfc1stfc1 Posts: 505
    Thanks to you both, sounds like a job too far to me. Perhaps I'll see if I can find a new 7-speed cassette on Ebay...

    The reason for wanting an extra gear is that my chainset is a 53-42 and my legs aren't as young as they were. I'm not sure whether fitting a compact would cause problems with shifting, but could swapping the inner ring to a 39 be a fairly hassle-free option?
  • I have a 15 year old Cannondale road bike with 7-speed cassette and down tube shifters. Plenty of life left in it yet for winter rides and daily commuting. 7-speed Shimano cassettes are still available on Wiggle in different ranges. I have a number of them which I swap around depending on how fit I feel.

    I have also replaced the 42 inner with a 39 (old legs). The only problem can be getting enough range on the rear mech. The set up I'm using at present is 52/39 with 12/28 and it works OK and will take me just about anywhere.
  • alfabluealfablue Posts: 8,497
    There's plenty of 7 speed cassettes here on Dotbike, upwards from £11.

    I have 7 speed on my Dawes Audax, I can't say I am really hankering for any more gears. As long as the shifters and wheel last, I'll stick with it.
  • nicklousenicklouse Posts: 81,520 Lives Here
    if you really want 8 gears you can and keep your current wheels.
    8 Of 9 On 7
    If your 126 mm frame is carbon fiber or held together by glue, you probably shouldn't try to spread it. That still doesn't mean that you're stuck with 7-speeds!

    Any 7-speed Shimano Hyperglide Freehub will actually work with 8 sprockets, without any modification! What you need to do is to use 8 of the sprockets from a 9-speed cassette, with the 9-speed spacers.

    To make this work, you'll also need to use a 9-speed chain and shifters. Your old 7-speed derailer should work OK if it isn't too badly worn. The limit stops on the derailer will cause the useless 9th position on the shifters to be locked out, so this will work as a perfectly normal 8-speed rig.

    http://sheldonbrown.com/k7.html
    near the bottom.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
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