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Forks

(8 posts)
  • Started 11 years ago by amir
  • Latest reply from amir
  • This topic is not resolved

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  1. amir
    Member

    A tricky question this one:

    I am buying new forks for my weekend bike after the crash. The old had 43mm rake - the frame has a 73 degree head angle. I ordered a new fork with a 43 mm rake to be consistent but one with 45mm has been sent to me.

    My Q is - might this be a good thing? It should make the steering a mite more responsive - would this help on the descents as I can be a nervous descender esp around corners. I am more confident on my other bike, a Ridgeback Horizon - don't know the geometry for this.

    Posted 11 years ago #

  2. Cyclingmollie
    Member

    There's a good article on Dave Moulton's blog. Elsewhere he states:
    "... fork rake (Offset) ... seems to have increased in recent years to around 45mm. A shorter rake, as much as a centimeter, bringing it down to 35mm would increase the amount of trail and would make the bike more stable, and hold a tighter line when cornering."

    Edit: I had a frame/fork combo on my old winter frame which never felt right. It was slow to corner giving a feeling that I was falling over as I went round corners. I think it was a 73 degree head tube with a 43mm fork rake. My current summer bike has a 72 degree head tube and 45mm rake as far as I can remember and feels much better to me.

    Posted 11 years ago #

  3. amir
    Member

    I also posted this on the CTC forum. The advice is that I am unlikely to notice 2mm difference. 45mm also seems to be approximately neutral with an hta of 73 degs according to some tables I found on t'web.

    Posted 11 years ago #

  4. amir
    Member

    @cyclingmollie

    trail tables are here

    According to these, my setup with 73 degs and 43 mm rake gives 5.9 trail whereas 45mm rake gives 5.69.

    Your setup of 72 degs and 45 rake gives 6.31

    In the linked article, it says that

    "a more stable bike will help the rider stay upright, but cannot be steered with as much precision"

    Somewhere else it says that a trail between 5.5 and 6.0 is "neutral" however that is defined.

    Anyway the shop is not acting quickly on having sent the wrong rake and given little diff between 43 and 45, I might just risk it. Pity you can't test forks before you buy!

    "a more stable bike will help the rider stay upright, but cannot be steered with as much precision"

    Posted 11 years ago #

  5. Uberuce
    Member

    I don't understand how there can be a difference in precision; even including front suspension the fork/handlebar/tyre unit is effectively rigid with respect to rotational motion, isn't it?

    Posted 11 years ago #

  6. amir
    Member

    It's somat to do with geometry, init. Don't forget that the bike leans on turning.

    Posted 11 years ago #

  7. chdot
    Admin

    "It's somat to do with geometry, init."

    Yep, all here -

    http://citycyclingedinburgh.info/bbpress/topic.php?id=10915

    Posted 11 years ago #

  8. amir
    Member

    In the end I kept the 45mm forks and tried them out at the weekend. The combination of the new forks and wheel seemed to make the handling around downhill curves better than I remember - more secure and precise.

    The additional good news is that CRC gave me a voucher for sending me the wrong size.

    Posted 11 years ago #

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