• Hey all,

    So I've had this problem for a while and I'd be interested in putting it out there for all you bike nerds to discuss. I guess ideally I'd like to find out if there's anything I can do about it but I imagine it's something inherent to the frame at this point. Anyway I've had this 58cm Dawes Super Galaxy for about 11 years now, cycled many places between Ireland and Istanbul on it and most recently 3,000km in Eastern Canada in 2019. On that most recent tour, I got a lot of speed wobbles - only, they weren't even speed wobbles, they were just wobbles. They would occur sometimes going pretty slow actually, as well as at higher speeds, the frame oscillating back and forth under me, sometimes pretty violently, despite changing grip on the bars, position on/off saddle, or hugging the top tube with my legs. Weirdly enough, at a certain point they seemed to be really bad in the morning and then fade a bit throughout the day (again irrespective of speed). It was bad enough though that I've been thinking before I do another tour I might want to get another frame. But also, I love my frame, and I'm a cheapskate and don't want to buy another. Is there anything I (or an experienced frame-repairer) could do to mitigate this problem? Or is it just down to the flexibility of an old steel frame?

    I generally don't get the wobbles when the bike is not loaded, so I imagine that's also a major factor. But what use is a bike frame you can't load down with a ridiculous amount of stuff?

    Oh yeah and also before that tour, one of the seat stays popped off the seat tube - I got that repaired by a frame-repairer in Edinburgh.

    Cheers for any thoughts, here's a photo of the steed


    1 Attachment

    • IMG_0803.JPG
  • I can’t help I’m afraid but I would like to know about the brass (?) dog perched on the bottom bracket shell.

  • Eagle eye! That was my faithful companion, it's actually a leopard/lion/little big cat.

  • There isn’t really a straightforward answer as to why speed wobbles (also called tankslappers in the motorcycling world) occur. Essentially something knocks the front wheel off line and the self-correcting nature of the front wheel in the fork moves the wheel back towards the midline but overcorrects and the wheel goes the other way where the reverse happens, thus setting off a to and fro motion.

    There are many factors that can lead to this including speed, road surface, frame material and geometry and weight distribution. How the various factors interact is not well studied but certainly situations where the front wheel is unloaded and has less traction seem to make wobbles more likely. In your case, having loaded rear panniers plus one or more of the other factors could cause it.

    Personally, I’ve never experienced it on any of my bikes in 50 years of cycling but there is always a first time.

    If you fancy seeing a really good speed wobble:
    https://youtu.be/G7Lw0x0vnGA

  • That video's really interesting, the slow motion makes it look like the progressive worsening of the front wheel oscillation is partly due to the rear wheel losing traction and the rider having to counter-steer to negate that. On a bike that's obviously not going to happen, since you wont get the rear wheel to break sideways so easily, so the physics might be different. I have seen speed wobbles on bikes, in fact I managed to snatch mini_m off their bike before one took them into a pillar.

  • The physics of bicycles and motorcycles are essentially the same but with more speed and power in the latter, the effects are going to be magnified. You can counter-steer on a bicycle but if you try it, do it gently.

  • Do you always travel on such a minimalist set-up?

  • Not always...


    1 Attachment

    • 1390460_552854831451482_1866910350_n.jpg
  • Wow yeah that's pretty crazy.

    For the record I get it when I have a good amount of weight on the front as well.

  • I’m pretty uneducated when it comes to steering geometry but just from reading your post I’d wonder the following:

    If it never happened before the seatstay/seattube failure and repair, it would seem to point to either that having changed something or could something else be coming loose or be cracked?

    The bit about it being worse in the morning makes me wonder if it’s load related. Like, you use water or food throughout the day so that weight is removed (or at least shifted) or what’s in your bags settles into a different position shifting the weight?

  • Is that a boat at the back?!

  • Or is it just down to the flexibility of an old steel frame?

    It's probably this. The weight you're carrying probably makes the frame flex. Add into that the weight distribution and a slightly uneven centre of gravity and it probably hits a sweet spot, causing the frame to oscillate.

  • Bouzouki, juggling clubs, accordion, pannier on the other side. And I think a sleeping bag I used to have that was really big. I made this bamboo extension to the rack to get it all in.

  • Yeah that seems likely. Surprising in a way though because sometimes weight can be a stabilizing force too.

  • Weirdly I have this problem on both my bikes; a Raleigh 531Club usually with a single rear pannier on for commuting, and a Holdsworth path racer with a front rack. Happens cycling no-handed (look mum!) at v. low speeds, and gets quickly worse with speed.

    Seems to be pivoting around the seat tube. I've gone through various bar, stem, wheel and rack set ups and the problem is always there.

  • accordion

  • The physics of bicycles and motorcycles are essentially the same but with more speed and power in the latter, the effects are going to be magnified

    I'm not sure about "magnified", I think having the power available to spin your back wheel and make it drift sideways is something that just doesn't happen on a bike other than in really specific conditions

    . I don't think that's the cause of all, or even most tank-slappers on motorbikes, but it's worth considering that the physics of those is potentially qualitatively different from similar-looking problems that you might get on a bike.

  • Awesomely interesting physics chat aside, I think you’ve earned a new frame if nothing else....
    Those loaded pics are both awe inspiring and fearsome. I pack heavy for a weekend away but that’s bold.

  • Fuck me. Next level bike packing.

  • I had this on a tourer whenever I had loads higher up and just on the rear rack. Front low racks helped (and careful weight distribution of bags, heavier things low), but even happened with a trailerbike attached after adding some firewood to the rear load.

  • I would buy a sturdier bike, a Nomad or similar.

  • Yeah, a bit like Skully I get it when the front is not loaded but the rear is.

  • Ha ha. Mind blown.

  • Sounds like one or possible mix of issues: out of alignment frame or fork, high-up and/or too far back weight loading, and a rear rack with a little too much flex for the load allowing oscillations to magnify.

    What is the rear rack?

    I'd suggest checking frame alignment, trying a stiffer rack set up and how you place the weight. I like to split my heaviest kit at bottom of front and back, or if light touring just front loading.

  • I got wobbles on my road bike a few times. Always descending fast with deep carbon wheels and strong crosswinds. Relaxing the grip and having a leg pushing against the frame solved it, pretty terrifying at over 40mph.

  • Post a reply
    • Bold
    • Italics
    • Link
    • Image
    • List
    • Quote
    • code
    • Preview
About

Speed Wobble when Touring on old Dawes Super Galaxy

Posted by Avatar for KayneC @KayneC

Actions