Fork Steerer minimum length - advice

DW01
DW01 Posts: 66
edited March 2011 in Road beginners
Evening all...

I have a couple of sets of forks but one set i'd really like to use. The fork steerer however comes out of the top of the headtube (as normal) and with the stem on aswell, the steerer does not come above the stem but about 1cm away from the top of the stem.

I shall be using an expander plug and then a top cap with a screw in which can reach the expander plug when i place it in there. However I was wondering if it will matter if the top cap is sat on the stem rather than the fork or a spacer???

There are no spacers under the fork either.

Any help would be much obliged as I am a bit of a bike noobie 8)

Comments

  • Berk Bonebonce
    Berk Bonebonce Posts: 1,245
    The top cap is supposed to sit on top of the uppermost spacer or stem, so that when the bolt is tightened into the bung the effect is one of compressing the steering set-up. But a gap of 1cm is on the large side. Proceed with care.

    Note that the stack height of stems varies from one manufacturer to another, and also across models in any range.
  • Erudin
    Erudin Posts: 136
    The gap is a bit too big I think.

    From http://www.parktool.com/blog/repair-help/threadless-headset-service:

    "It should be about 3mm (1/8") below the level of the stem. The stem needs to press down on the spacers in order to adjust the bearings. If the steering column is level with the top of the stem, another spacer is needed below the stem."
  • Elio
    Elio Posts: 63
    1cm is quite a lot, indeed. If it's an alu or steel steerer, you might get away with it. But if it's carbon, I wouldn't risk it...
  • Dan_xz
    Dan_xz Posts: 130
    Depends on the stem and length of top cab bolt.

    The top cap bolt needs to reach the star nut (or alternative) so that it can tighten against the stem and pull the headset tight enough. All the top cap is for is to set the pressure on the headset, once the stem is tightened everything is locked in place and the top cap doesn't do a lot.

    The important thing is to look at how the stem clamps to make sure it has a good grip on the steerer tube. If it has an internal wedge type clamp, such as Thompson stems then the clamp needs to be completely in contact with the steerer with at least 5mm steerer above it. The top of the stem can stick as far over the steerer as you like if the clamp part is secure.

    With stems that are split down the back and clamped by a couple of bolts you don't really want the steerer more than 5mm below the stem top, but if the highest bolt is quite a way from the top of the stem, and 5mm or more below the steerer tube top you will probably be ok but not ideal. I can't actually thinkg of any stems that would fit that scenario.
  • neeb
    neeb Posts: 4,470
    One possibility might be to get a different headset with a lower stack, depending on how high the one you've got at the moment is.
  • DW01
    DW01 Posts: 66
    Okay thanks alot for the advice all. I have measured the difference between the top of the stem and the top of the steerer and the top of the steerer sits 5mm below the top of the stem, so there is a considerable amount of steerer for the stem.

    The stem is a ritchey WCS 4axis and the fork is an easton slx.

    The stem is basically sat flush against the headset and the top cap would be sat flush against the stem a bit like in this photo (i know its carlos sastre's bike and not mine but we've got to have a dream!)
    http://autobus.cyclingnews.com/photos/2 ... 10stem.jpg
    Just imagine that fork doesnt quite make it to the summit!

    So there is no use of spacers. The top cap with the screw in the middle will still reach the expansion plug, its just the top cap will be sat on the stem rather than the spacers. In theory there should be nothing wrong with this right?

    I mean what "could" go wrong?
  • Ron Stuart
    Ron Stuart Posts: 1,242
    DW01 wrote:
    I mean what "could" go wrong?

    It's quite simple with a carbon steerer and with the top of the stem 10mm above the top of the steerer tube you will when tightening the top stem bolt around the steerer probably crush the top of the steerer.
    Your only hope is locate a shallower head cap (goes under stem).
    Have no more than 3mm gap between carbon steerer top and top of stem. This can be more in the case of steel or alloy steerers.
    Also if you haven't invest in a torque wrench, I use one of these http://www.probikekit.com/display.php?code=T0019 I use it for my seat clamp (carbon seat post) and all stem bolts. :wink:
  • neeb
    neeb Posts: 4,470
    It's quite normal for the top cap to sit directly on top of the stem. The top of the steerer needs to be a few mm below the top of the stem (or stem + spacers) to allow you to tighten it. But this tightening just temporarily fixes everything on place - the whole assembly is held together by the stem bolts.
    I mean what "could" go wrong?
    If there is too much gap between the top of the steerer and the top of the stem, the clamping won't be secure and you are also highly likely to damage the steerer, as the top stem bolt will effectively be clamping on the top edge of the steerer - this can easily crush or crack a carbon stem.

    <edit> previous poster beat me to it!
  • neeb
    neeb Posts: 4,470
    On the other hand, you might just possibly be able to get away with 5mm (as opposed to 1cm as you originally thought) DEPENDING on the design of the stem clamp. But it could easily be extremely dodgy.

    Best to go with a lower headset / head cap.

    If you DID have a 5mm gap (and the steerer is carbon), you would be best to use an expander bung of this design:

    http://www.wiggle.co.uk/deda-expander-bung

    It has a lip that makes it sit right at the top of the steerer, effectively bracing the top edge against compression and adding about 1mm to the height.