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Bottom Bracket Height and the effects/causes...

drumondrumon Posts: 175
edited April 2008 in MTB workshop & tech
I have picked up a reasonably priced mountain bike at a police bike auction.

I am concerned that the bottom bracket height is rather low.
It measures 8".

Can you advise me the correct (approx) bottom bracket height for a mountain bike used for light trails and commuting?

I reckon the original suspension fork was replaced by a rigid fork (400mm axle to crown) as this bottom bracket height feels rather low..... hence a sus. fork would raise this bottom bracket somewhat wouldnt it?

Should I consider getting a longer fork to raise the bottom bracket? A rigid fork will suit me fine.

The bike is a Diamant (norwegian) Extreme Zero Degree

Looking forward to your replies.

Posts

  • nicklousenicklouse Posts: 81,520 Lives Here
    do you have a picture of your bike.

    A low BB on its own just means a low center of gravity.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • drumondrumon Posts: 175
    I'll get a picture up soon....

    But does the low BB also mean the pedals are closer to the goround eg when on corners? thats what concerns me,.....
  • drumondrumon Posts: 175
    edited April 2008
    sorry, big mistake
    the BB Height has been measured wrong, it is in fact 12".... more than satisfactory i suppose.

    however as I expect the current fork is not original (its a different colour from frame) and was probably a cheapo replacement for a sus. fork.... would having a longer rigid fork anyway be an issue or an improvement?

    I have read that it could make steering light? what else?
  • nicklousenicklouse Posts: 81,520 Lives Here
    Ok still pictures so we can see what it is all about.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • drumondrumon Posts: 175
    here's thepicture

    bike is 18" frame.

    Fork is 400mm axle to crown.

    BB Height is 12"

    [/img]mybikewebsize.jpg[img][/img]
  • nicklousenicklouse Posts: 81,520 Lives Here
    dont think i would be wanting to put a longer fork on that.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • drumondrumon Posts: 175
    Thanks for your advice.

    For my own curiosity and knowledge, what is the drawback of having a longer fork, eg up to 420 or 430mm?
  • nicklousenicklouse Posts: 81,520 Lives Here
    slower steering that falls over in corners. also that look slack enough already. Typical Scandinavian geometry.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • AnonymousAnonymous Posts: 79,692
    nick, what do you mean "falls over in corners"?
  • nicklousenicklouse Posts: 81,520 Lives Here
    when the head angle get too slack you can get a feeling of the wheel wanting to flop over when steering.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • AnonymousAnonymous Posts: 79,692
    It's got to be really, really slack for that though, right?
  • nicklousenicklouse Posts: 81,520 Lives Here
    i know one bike where just an extra 30mm does that when you are standing on the pedals. when pointing down hill it is okish but...
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • AnonymousAnonymous Posts: 79,692
    Wow. which bike is that then?
    The angles are really relaxed on mine, casuse it was NEVER designed for a fork that tall, but I've never realised that effect.
    I do have to make a conscious effort to shift my weight forwards on fast tight bends, but it's worth it for the "ready for anything" stance everywhere else.
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