How slack is too slack…

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  • How slack is too slack…
  • wiggles
    Member

    Managed to ‘borrow’ a 140mm yari to try on my fuse, it is 20mm more travel than the Reba that came on the bike but a2c is about 25mm longer meaning it now sitting at a seriously slack 65.5° HA.

    Which is slacker than my previous bike which was a 150 travel 650b FS.

    Can’t ride it yet to find out as I don’t have enough headset spacers to take up the excess steerer (might have to give it back so can’t cut it)

    Rorschach
    Member

    chiefgrooveguru got to 64.3 on his Bird zero.
    I’m contemplating putting a -2 on my Scout which would take it to 63ish (with 150 fork).
    Bare in mind with a hard tail that the ‘static’ head angle is a good bit steeper than when your ass is sat on it and the fork sags (but not the rear…unless you are REALY fat).

    duir
    Member

    65.5 is not seriously slack.

    That sounds about right, I think it’s now the same as a Whyte 909 and they ride amazingly well – though you have plus sized so a little more circumference effectively slackening the head angle further. I reckon you’ve probably turned a decent bike into a great trail bike.

    Stevelol
    Member

    Just using a longer fork raises your bottom bracket height too which isn’t ideal for handling, unless you smash your pedals a lot then it would be a bonus.

    thepodge
    Member

    Meh, my 29ers are slacker than that.

    Things like the Geometron and Pole bikes are sitting around 62 without much issue

    Premier Icon convert
    Subscriber

    Shoving a bigger fork on a frame than intended might not be a bad thing for the HA and what that does to the bike handling/feel. But as said previously it also raises the bottom bracket AND changes the seat angle. It’s the later two that I would be focussed on not the HA as they can both add a significant degradation of the bike’s performance . Slack seat angles especially are not nice.

    qwerty
    Member

    66′ on a 120mm HT feels like a trail friendly angle for me, it feels just right and not extreme for xc ups and downs. I’m sure you could go slacked, pretty sure Brant goes along with this.

    Premier Icon brant
    Subscriber
    duir
    Member

    It’s the sum of all the geometry that really counts, just changing one angle can make a decent bike feel rubbish. The Geometron is not a good comparison with a hardtail but the reason it works so well with seemingly extreme geometry is all the angles have been adjusted and it’s not just longer and slacker. My Orange P7 is supposed to be long and slack and is a lovely hardtail but does not climb anywhere near as well as my Geometron because they failed to steepen the seat angle or lengthen the chainstay so you just feel stretched out rather than in the bike.

    I would say to slacken a hardtail an angle set would be better as you will keep the bottom bracket height. That would however shorten the reach slightly so you may need a longer stem which will in turn slow up the steering.

    So you see it’s hard to just change one angle without adversely affecting everything else.

    deviant
    Member

    I ride my Trance SX with a standard 66 degree HA but with a HT for general trail duties I’m considering making the Trance very single minded with one of those -2 degrees Superstar headsets….hmm, 64 degrees you say….with the 155mm back end from the 200×57 shock instead of the standard 200×51 it came with it’d be a beast!

    Premier Icon kayak23
    Subscriber

    Just using a longer fork raises your bottom bracket height too which isn’t ideal for handling,

    This is true.

    Premier Icon julians
    Subscriber

    I’m about to try a -2 deg superstar headset (they were/are selling at 15% off) in my orbea rallon which according to the geo charts has a headset of 65.5 deg in the lowest setting, which would take it to 63.5 deg. However I expect I will also move the shock into the high setting , giving approx 64 deg head angle.

    I’m not sure it will be all good but willing to give it a go. When I reduced the head angle on my Mojo HD by 1.5 deg, it made the down hill handling better, but you really had to make sure you had your weight over the front or it would wash out.

    wiggles
    Member

    I’ve ridden a geometron and had a quick ride on someone’s pole (wahey) so know what super slack bikes are like bit obviously they are very different beasts to my short travel hard tail, will give it a go tomorrow.

    If I like it I would probably change the rear tyre for a smaller one to drop the bb a bit to counteract the longer fork.

    gonzy
    Member

    OP i assume that the head angle measured is while off the bike. depending on how much air pressure and sag you run, once you’re on the bike the head angle should steepen…even if its by half a degree
    you will end up with a slightly higher bottom bracket but nothing that will adversely affect the bike
    as for the seat angle…this will depend on the original angle and the top tube length..if it was already slack then this will slacken more but if the top tube was on the short side then it will feel more stretched…which may be a good thing

    i’ve fun a 150mm fork on a 130mm travel HT frame…the front end was very slack and the seat angle meant that the saddle was more over the rear wheel which was great for grip and climbing…the slack front made descending a hoot too

    the angles on your bike dont look as extreme so you should be fine

    thepodge
    Member

    wiggles – If I like it I would probably change the rear tyre for a smaller one to drop the bb a bit to counteract the longer fork.

    I cant see that making enough difference to be worthwhile. With a slack hardtail you’ll be hitting stuff harder so a large volume tyre on the rear would make more sense.

    IME 65.5 seems to be as slack as you need for a balanced bike you still want to pedal up! Obviously it will need a steep seat tube 73-75 to go with it.

    It does depend on the frame. In general terms if it already has a high BB and you jack it up further with a longer travel fork it will start to feel tall and unwieldy in tight switchbacks. If it has a slack seat tube about 72-71 degrees, you effectively tilt it further backward resulting in floppy steering and front wheel lift on seated climbs (if you stand and mash you won’t notice it) as you will be near enough sat over the back axle.

    Depends how compromised it feels to you. Some people run massive forks in frames not designed for it and love it, compromises and all. 10-20 mm more on a modern progressive geometry frame often doesn’t make a massive noticeable difference.

    if it takes more than 3, then leave her be..

    Oh, wait.

    Sorry.

    Wrong answer.. 😉

    Premier Icon julians
    Subscriber

    Just fitted superstar slackset.

    Numbers before
    Head angle 65.6degree
    Bb height 343mm
    Wheelbase 1175mm

    Numbers after
    Head angle 64 degree
    Bb height 340mm
    Wheelbase 1195mm

    That may be too slack but if it is I’ll try it in the higher shock position

    wiggles
    Member

    Tested it out todsy, just a quick spin at cwmcarn but it appears to have improved the bike enormously. Climbing wasn’t any worse, not lifting the front like I have had on other long forked hardtails, if anything I prefer the slightly higher front end.

    Descending was way better, so much more stable and I was hitting rougher lines rather than avoiding them. Obviously ive gone form a 32 to 35mm fork so some of the effects are more down to stiffness in the fork than angles, but very pleased so far. Might have to permanently borrow them…

    wl
    Member

    65 degrees is spot on on my P7.

    deanfbm
    Member

    As soon has your weight is on the bike and the forks sag, you won’t be a 65.5*, it’ll steepen by atleast a degree to two on flat ground, even more on anything pointing downward.

    Comparing to a full sus, apples and oranges, especially like myself running more sag on the rear than the front.

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