head angle vs wheel size?

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  • head angle vs wheel size?
  • Premier Icon mattjg
    Subscriber

    my 29er*** trailsy HT has 68 degrees head angle, 120mm travel, I like it lots but am a bit 650b curious too. with a smaller wheel will I need to go slacker to get comparable feel or is it the same-ish?

    I note the Whyte 90x 650b builds have 66.5 degrees HA, that’s pretty slack but they’re still positioned as trail bikes.

    *** FAO wheel size fundamentalists – this is not a wheel size thread, nobody cares what you ride, 26 will be here for decades and there is no industry conspiracy. hope that’s all covered for you and we can move on.

    asterix
    Member

    Is this right?

    for any particular wheel size, steeper head angle = faster more twitchy steering

    keeping all other things the same, smaller wheel = quicker steering

    so I think you’re thinking is going in the right direction.

    (ps. just checked and I am riding a 26er with a 71 degree head angle :lol:)

    Hob Nob
    Member

    I dont pretend to understand the reasons why, but I have read historically, (predominantly when talking 29″) they don’t need to be as slack as a 26″ wheeled bike for the same feel?

    Which does make sense, I went from an SB66C with a HA of around 65.5 to my Enduro29 which is 67, and they feel very similar. Jumping onto a 26″ bike with a 67 degree HA felt scary by comparison, but then head angle is probably my one fussy sticking point when riding bikes.

    Premier Icon Northwind
    Subscriber

    There could be more to it than this, but for the same head angles, a taller wheel/tyre gives you more trail, so more stability/steering correction.

    mallorcadave
    Member

    Also 650b and 29er forks have more offset as well, which makes the head angle feel slacker

    Premier Icon roverpig
    Subscriber

    If you want to keep the same trail then as the axle gets closer to the ground (i.e. smaller wheel) then the head angle does indeed need to get slacker. Not sure by how much though.

    I guess you also need to look at how the HA is measured. Your 68 degrees at 120mm (Yelli?) is static (I think) so would be around 69 degrees at ride height (e.g. 25% sag).

    Edit: beaten too it 🙂

    robinlaidlaw
    Member

    Northwind has it, more trail for a given angle and it’s the stability created by the trail that you feel.
    On an only partially related note, It always surprises me that people reckon a 1 degree or even 0.5 degree steeper head angle makes a bike feel scary twitchy, I don’t know if I’m doing it right or wrong but I’d have to pay close attention to feel 1 degree difference and it certainly wouldn’t make me perceive the bike as difficult to ride.

    What northwind said, it’s all about the trail. The distance between the wheels contact patch and an imaginary line drawn down from the headtube.

    By manipulating head angle, wheel size and fork offset you can make 2 different bikes feel similar. There’s a bit more to it than that 2D reprisentation (otherwise there’s all sorts of angles/wheels/offsets which give the same trail figure), as you turn the bars they change, which is why wheel sizes have matched fork offsets and designers only have one remaining variable to contend with, the head angle. Or you can f*** it up, which is why some bikes feel like they fall over into corners then take a lot of effort to get back upright again. Thankfully bad bikes are rare these days.

    [edit, took a while typing that]

    Northwind has it, more trail for a given angle and it’s the stability created by the trail that you feel.
    On an only partially related note, It always surprises me that people reckon a 1 degree or even 0.5 degree steeper head angle makes a bike feel scary twitchy, I don’t know if I’m doing it right or wrong but I’d have to pay close attention to feel 1 degree difference and it certainly wouldn’t make me perceive the bike as difficult to ride.

    I recently put an external headset on my El-Mariachi, so the front end is ~15mm taller, ~1 degree slacker, and the BB up by ~5mm. The bike feels far slacker/stable than it’s old nimble self.

    But that’s just one variable, if you swaped between bikes telling the head angles would be harder as there would be other factors influencing the handling.

    robinlaidlaw
    Member

    Also 650b and 29er forks have more offset as well, which makes the head angle feel slacker

    Not quite that simple. More offset will reduce trail and therefore, at speed it’ll actually reduce stability. At low speed though, it’ll reduce flop, which is where the front wheel wants to fall over because the front of the bike is actually highest with the wheel straight so it’ll make the bike easier to ride straight at low speed. It’s a balancing act to get all the attributes you want.

    Premier Icon mattjg
    Subscriber

    There could be more to it than this, but for the same head angles, a taller wheel/tyre gives you more trail, so more stability/steering correction.

    ok that makes sense ta … broadly, other factors being the same, a 650b at 68 degrees will feel a little less slack than a 29er at 68 degrees.

    Premier Icon mattjg
    Subscriber

    anyone got any opinion about those 66.5 degrees Whytes? pretty slack, non?

    Premier Icon Northwind
    Subscriber

    robinlaidlaw – Member

    On an only partially related note, It always surprises me that people reckon a 1 degree or even 0.5 degree steeper head angle makes a bike feel scary twitchy, I don’t know if I’m doing it right or wrong but I’d have to pay close attention to feel 1 degree difference

    When I stuck the 2 degree head-thinger in my bike, it did make a massive difference- there’s no chance I’d have kept that bike with standard angles. But then later I stuck in an offset-thinger which was about another degree off, and it wasn’t anything like as noticable. So I think it wasn’t so much the fact that it was a degree or 2 degrees, but more the fact that it felt too steep before, and now it doesn’t. Tipping points rather than progressive changes.

    Yup, I’d say a 29er feels 2deg slacker than it’s head angle suggests on a 26″ bike. I guess 650b sits inbetween.

    Premier Icon Andy R
    Subscriber

    thisisnotaspoon – Member
    Yup, I’d say a 29er feels 2deg slacker than it’s head angle suggests on a 26″ bike.

    Maybe some of it is purely visual though, as you have more front wheel and tyre ahead of you, even though the actual contact point on the ground may still be in much the same place.
    I think it’s some of that with me anyway.

    Premier Icon mattjg
    Subscriber

    yeah Andy I think there’s something in that for me too, it’s quite reassuring seeing all that rubber out there clearing the way. especially since I started wearing my prescription glasses for riding, which shorten perspective a lot at less than a couple of metres. basically all I can see is wheel.

    robinlaidlaw
    Member

    Tipping points rather than progressive changes.

    Could be that. I had my 5 Spot feeling fine on a standard headset by means of plenty of sag at the back, not too much at the front and a slightly longer fork than the geometry is quoted for and I can feel the extra degree that a slackset has taken off, but it’s not a big deal, it’s probably gone from 67.5 to 66.5, or maybe 68 to 67. However, before I got the sag set right at both ends, it didn’t feel so nice but I interpreted that more as a problem with the relative heights of the saddle and bars at the time.
    I think your bike history may have an effect to, I learnt to ride off road on rigid steep angled hardtails twenty something years ago, with the bars slammed and the saddle always up, most modern bikes feel very stable.

    Premier Icon jameso
    Subscriber

    if you get the trail the same between a 650 and a 29, the wheel-flop difference between wheels of different sizes means it still doesn’t feel the same imo. flop-factor is tricky to explain but for a given trail figure a bigger wheel has less of that flop weighted-turn-in kind of feel that some feel as ‘slackness’. so a bigger wheel can have equal stability as a smaller one with a more neutral feel in one respect – offsetting the ‘bigger wheel’ feel.

    Premier Icon Northwind
    Subscriber

    robinlaidlaw – Member

    I learnt to ride off road on rigid steep angled hardtails twenty something years ago, with the bars slammed and the saddle always up

    Me too, but I was always pretty sure the bikes were awful 😆

    asterix
    Member

    I think your bike history may have an effect too, I learnt to ride off road on rigid steep angled hardtails twenty something years ago, with the bars slammed and the saddle always up, most modern bikes feel very stable.

    I think this is probably correct too. Switching straight from a ~20 year old, steep-angled, rigid 26er to a more modern, slacker 29er can be too big a change to easily like or get used to

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