Viewing 40 posts - 41 through 80 (of 84 total)
  • The Grim Donut finally tested!
  • Premier Icon 5lab
    Free Member

    the head angle means that flat hits (like the huck to flat) there’s a lot of sideways load on the bushings – so they perform badly – but whilst riding along and hitting a log the force comes from the front – it could easily be that angles like that are more perpendicular to the force hitting the wheel and thus actually work better (same for the force going through the headtube)

    Premier Icon molgrips
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    but as this has been done without all that (from what I can see from the various videos and articles on it), then I’m more sceptical.

    They did the FEA and the rig testing on it according to the vid.

    Premier Icon thisisnotaspoon
    Full Member

    Im sure Cy talked about it in his lectures at Sheffield (10 years ago?). The loading in the CEN test for pulling the fork forward is actually mimicking a landing so hard your legs would buckle.

    Premier Icon thisisnotaspoon
    Full Member

    Here you go,

    The CEN test is 1200N pulling horizontally away from the rear axle, 50,000 times.

    At 2012 geometry (yes slacker will be a bit less) that was 50,000 9G landings to flat.

    Premier Icon mick_r
    Full Member

    Not just forward – it loads in both directions alternating 1200N fwd and 600N rwd iirc.

    The loads are set to get a balance of short (cheap) test without overdoing it (plastic failure). Fatigue cycles add up – if you want to test at smaller loads then crack on but it might have to run for a million cycles. Mixed load cycles would be best but that needs more complicated rigs and control. It is basically a stake in the ground to show you’ve tried to makes a safe bike.

    Premier Icon greyspoke
    Free Member

    I would like to see someone try to separate length from head angle. That wheelbase looks long enough to have a normal head angle and the bars far enough behind the steering axis to be connected by a backwards stem. Then it would be interesting whether that behaved well or whether a remote steering linkage would be required.

    Premier Icon chiefgrooveguru
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    A backwards stem would cause quite a lot of steering instability.

    Premier Icon joefm
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    I know some brands like Nicolai are pushing the limits of whats available but it’s good to see what PB have done.
    I think the industry just likes to do incremental changes for their next model bikes so they can do the same again for the next model. rinse repeat.
    No one seems to do any empirical data collection and just work out what is actually fastest.

    I like the grim donut though.

    Premier Icon matt_outandabout
    Full Member

    A backwards stem would cause quite a lot of steering instability.

    Aft of steerer mounted bar pivot point with linkage to steerer needed then….

    Premier Icon maxtorque
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    Problem for me is there was no A-B-A type test.

    Watching the video,there are several very significant sections where on the second run (on the GD) that YB is hitting much faster / straighter lines. However, without a second run on his normal bike, we don’t know if he was able to hit those lines due to additional familiarity (due to it being his second run) or actually because the long/slack bike ENABLED him to hit those lines without crashing……..

    Premier Icon 5lab
    Free Member

    A backwards stem would cause quite a lot of steering instability.

    out of interest, why? the steering geometry itself would be the same (for the same frame), just the arc in which your hands move would change (I think?). As we’ve moved from 150mm stems to 40mm stems, that arc has changed quite a bit already, why would it all go wrong if we went backwards (say) 40mm?

    Premier Icon the00
    Free Member

    I think the article says it’s a track he knows well. Sure, it’s not a double blind randomised trial, it is interesting and it is entertaining, and I don’t doubt the result.

    We’ve been hearing for a while that many manufacturers don’t make the enduro bikes that racers would like.

    Premier Icon moonsaballoon
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    I wonder how commencel feel about it 🙂  To be fair they have probably won more world cup DH and EWS rounds than most other brands so i doubt to bothered .

    Premier Icon greeny30
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    I can see Yoann asking Max to knock up a 60° head angle prototype.

    Premier Icon chiefgrooveguru
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    “out of interest, why? the steering geometry itself would be the same (for the same frame), just the arc in which your hands move would change (I think?). As we’ve moved from 150mm stems to 40mm stems, that arc has changed quite a bit already, why would it all go wrong if we went backwards (say) 40mm?“

    I wrote a reply but the internet ate it…

    It’s because most destabilising inputs to a MTB cause deceleration. And that causes the rider’s mass to apply a forwards force to the grips. The longer the stem, the more that force has a self-centring effect on the steering. A negative stem will do the reverse unless both hands are equally weighted.

    Premier Icon TiRed
    Full Member

    I thought that was amazing. And there is no way I’d be mincing down that track. But the bit that I found most impressive was not the bike. No, it was the calm cool commentary on both runs. Just remarkable. Bike seems like it could compensate for even my skills deficiencies.

    Premier Icon thisisnotaspoon
    Full Member

    Not just forward – it loads in both directions alternating 1200N fwd and 600N rwd iirc.

    The loads are set to get a balance of short (cheap) test without overdoing it (plastic failure). Fatigue cycles add up – if you want to test at smaller loads then crack on but it might have to run for a million cycles. Mixed load cycles would be best but that needs more complicated rigs and control. It is basically a stake in the ground to show you’ve tried to makes a safe bike.

    If you watch the video he makes that point. 600N seems like a high number, but achievable in the real world.

    1200N pulling has no real world application and broke the original Soul in about 1/4 the required cycles (and everyone elses frames it seems).

    Premier Icon orangespyderman
    Full Member

    No, it was the calm cool commentary on both runs. Just remarkable.

    Yeah – and he calmly says at the start he’ll be going about 80% of capacity and then proceeds to shoot down it at unreasonable speeds and takes 15 seconds or something off the Strava KOM 😐

    Premier Icon singlespeedstu
    Full Member

    Yeah – and he calmly says at the start he’ll be going about 80% of capacity and then proceeds to shoot down it at unreasonable speeds and takes 15 seconds or something off the Strava KOM 😐

    Have a look at some of Yoann’s other videos…
    Rides tech like he’s riding to the shop for a pint of milk.

    Premier Icon weeksy
    Full Member

    There’s an unrelated Finn Isles vid this week where he’s training too, again, the same…flying down, destroying the trail like he’s strolling for a sandwich.

    Premier Icon stevextc
    Free Member

    My <b>35kg</b> kid has been playing with a measured static 62.1 deg HA on a correspondingly long frame for his size and 142mm cranks.
    Goes downhill VERY fast… uphill … a bit of a pig. Seatpost is very slack though.

    Premier Icon 5lab
    Free Member

    It’s because most destabilising inputs to a MTB cause deceleration. And that causes the rider’s mass to apply a forwards force to the grips. The longer the stem, the more that force has a self-centring effect on the steering. A negative stem will do the reverse unless both hands are equally weighted.

    that interesting, I hadn’t thought about it.

    Based on this – if I flipped my 35mm stem (I’m not actually going to..) – that would have a similar difference from going to that 35mm stem from a 100mm stem – that is to say, it would be gradually less stable, rather than suddenly unstable? on a 35mm stem and a bit of backsweep, the riders mass is applied pretty much in-line with the head tube?

    Premier Icon chiefgrooveguru
    Free Member

    I think you’ve got four main systems providing stability to a bike:

    1. Trail
    2. Jacking (head tube rising when you turn the bars)
    3. Gyroscopic
    4. Handlebar weighting

    Trail and jacking increase stability with decreasing head angle and offset. Gyroscopic stability increases with rim+tyre mass. Jacking has the same effect at all speeds, the other two increase with increasing speed.

    The handlebar weighting (tiller) stability does nothing if the grips are in line with the steerer (typical bars and 30mm stem). As the stem length increases it adds stability. As the stem length decreases it deducts stability. It isn’t proportional to speed but is to input force.

    Premier Icon 5lab
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    so if you have enough trail and jacking (by using a 58 deg head angle) – the instability caused by reversing the stem could (maybe) be offset (no pun intended)?

    Premier Icon richmtb
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    I still can’t get my head round how decreasing offset increases trail.

    Does anyone have a diagram 😉

    Premier Icon wzzzz
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    Watching all those SIDs waggle around on the huck to flat is, er, educational.

    Premier Icon kayla1
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    Did anyone else think the Commencal looked really short after seeing the Donut?

    Premier Icon kayla1
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    I would like to see someone try to separate length from head angle. That wheelbase looks long enough to have a normal head angle and the bars far enough behind the steering axis to be connected by a backwards stem. Then it would be interesting whether that behaved well or whether a remote steering linkage would be required.

    I don’t think that would work very well. If you were tall enough to be able to weight the forks straight down through the steering axis it might but for anyone shorter than ideal it wouldn’t be very nice to ride. I have no idea in reality, it’s just a gut feeling that it wouldn’t be quite ‘right’ for some reason.

    Premier Icon DrP
    Free Member

    Are you so sceptical of bridges, aeroplane wings not snapping and the existence of helicopters?

    Speaking of… I’m still awaiting the Brighton i360 to blow over….
    Now I’m no structural engineer, but I’m not fick or nuffink…and it just looks ‘too thin’ to be safe.
    So there. If it blows over, they should have listened to me.

    DrP

    Premier Icon chakaping
    Full Member

    we don’t know if he was able to hit those lines due to additional familiarity

    It was explained that it’s one of his regular test tracks, so not an issue there.

    We’ve been hearing for a while that many manufacturers don’t make the enduro bikes that racers would like.

    We often hear that racers don’t want the longer, slacker bikes that some of us punters are moving towards.

    Premier Icon Rubber_Buccaneer
    Full Member

    Watching all those SIDs waggle around on the huck to flat is, er, educational.

    I got hooked on the huck to flat videos to see forks flexing then I looked at the rear suspension and now can’t take my eyes off the chains and rear mechs flailing around

    Premier Icon hols2
    Free Member

    That wheelbase looks long enough to have a normal head angle and the bars far enough behind the steering axis to be connected by a backwards stem. Then it would be interesting whether that behaved well or whether a remote steering linkage would be required.

    I’m not sure what to make of the “Dangerzone” theory, but surely, someone, somewhere must have tried it.

    https://www.pinkbike.com/news/exploring-the-relationship-between-handlebar-vs-stem-length.html

    Premier Icon Kamakazie
    Full Member

    I’m a big fan of slacker head angles and balanced rear stay length but less so of much longer reaches & lower BBs.

    I could see myself getting a frame with 60 degree ha in a few years.

    Premier Icon 5lab
    Free Member

    Speaking of… I’m still awaiting the Brighton i360 to blow over….
    Now I’m no structural engineer, but I’m not fick or nuffink…and it just looks ‘too thin’ to be safe.
    So there. If it blows over, they should have listened to me.

    have you seen it up close? its all perforated so the wind just goes straight through it. The really crazy thing is how it was built – they built the top section, lifted it up, then built the top-but-one section underneath it, lifted that up, and so on..

    Premier Icon scaredypants
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    I think the article says it’s a track he knows well. Sure, it’s not a double blind randomised trial, it is interesting and it is entertaining, and I don’t doubt the result.

    It’s still pretty odd that he smashes the KoM (which presumably includes many of his own runs) on his first go that day

    Premier Icon the00
    Free Member

    We often hear that racers don’t want the longer, slacker bikes that some of us punters are moving towards.

    Yeah, there’s a mix for sure. The PB video speaks to a bike company, which says that racers are conservative. And to Arron Gwin, who I would say is one of the conservative riders too.

    Jordi at fox has mentioned before how some enduro riders alter their sag front and rear to effectively reduce HA. And I think one of the main drivers for racers trying 29er front ends on their 27.5 bikes was to slacken the HA a bit.

    Premier Icon jamj1974
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    Really like Paul Astons’s bike. Looks great and is probably perfect for what he does.

    Premier Icon DrP
    Free Member

    RE the i360 being built that way…look..you’re right…

    But… I wouldn’t have done it like that. I’d have lay all the pieces down on the beach.. got Norman Cook to have DJ’d a cracking set whilst workers/ravers bolted it all together laid down.. then hired a crane for the afternoon, pulled it up in one go, and then post-creted the base in.
    But like I say..no one asked me, so hey ho..

    DrP

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