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Speed shimmy on new hybrid

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  • October 2, 2014 at 8:40 pm #22500
    thebrindo

    So yesterday I collected a new Hoy Shizuoka 001 from Evans on the ride-to-work scheme. My plan was to use it for my daily commute, 3.5 miles each way. Now I’m not so sure. After free wheeling down a reasonably steep and smooth hill on the way from the shop I felt that the front end had a wobble. I checked a few things when I got home and all seemed tight and true. rode it to work this morning and there was still an unstable feeling at the front end so I took it back to the shop after work. They checked it over and gave it the all clear, but on the way home again it was as bad.

    So I’ve done some searching on here and followed some links to some of the Zinn articles and can only assume that this shimmy is down to the combination of bike and rider. It’s an XL frame and I am 6’2″ and the wrong side of 200lbs + VAT.

    So I guess my questions are, is there anything I can do to solve this in the short term? I fully intend to get back to 190-195lbs but that will take some time and I don’t feel confident riding the bike at speed on the road.

    Alternatively has anyone had experience of returning a bike for something so intangible as this? and/or a bike on the R2W scheme?

    Thanks in advance

    Phil

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Viewing 11 replies - 1 through 11 (of 11 total)
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  • October 8, 2014 at 12:06 pm #816577
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    thebrindo

    Not loads as it’s and XL
    Not loads as it’s and XL frame and I’m long bodied/short legged, but it’s as far up as is to be correct for my legs. It is a very upright seating position compared to my other bikes so it may just be that the front is light? There is some room to drop the stem a bit to get me over the front a little more.

    October 8, 2014 at 11:16 am #816575
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    MKultra

    Just out of curiosity how
    Just out of curiosity how much seat post have you got showing?

    October 7, 2014 at 8:29 pm #816573
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    thebrindo

    Well, it’s certainly much
    Well, it’s certainly much better now that the tyres are at the right pressure. I’ve not hit the same steep hill yet but on the commute it feels more stable. Just need to do something about the rider weight now. =))

    Thanks for the help 🙂

    October 4, 2014 at 5:33 pm #816571
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    thebrindo

    50 , can;t see me getting
    50 :O , can;t see me getting above 25 on this one =)) but given the weight it carries the wobble will start at lower speeds I guess!

    Will update on Monday :W

    October 4, 2014 at 4:10 pm #816569
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    Initialised

    I was going to suggest tyre
    I was going to suggest tyre pressure as I had the same experience with a new bike from Evans, it got wobbly at around 50mph, turned out the tyres were way too low.

    October 3, 2014 at 8:06 pm #816567
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    thebrindo

    Thanks for the feedback all.
    Thanks for the feedback all. Really helpful.

    On the way home this evening the tyres felt a little soft so I checked them when I got in. Bearing in mind that they should be between 75 and 100 psi I was a little shocked to find them at 40 (front) and 35 (rear). Not too impressed given that I collected it Wednesday and it was back in the shop on Thursday! Aren’t they supposed to check these things?

    Anyway, since a properly inflated tyre probably goes some way to adding to the structural strength of the wheels it will hopefully help with the wobble. If not I’ll start working through the other suggestions. B-)

    October 3, 2014 at 6:07 pm #816565
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    Leeroy_Silk

    I experience the dreaded
    I experience the dreaded wobble every time I ride through a certain corner on a certain hill. I found the only way to stop it was to slow down.
    One area I did discover had an impact on the wobble related to stem length in relation to the front axle. Imagine a plumline from the end of the stem, the line should sit behind the axle, but if you raise the back wheel to mimic going down an incline you’ll see the plumb line move towards the axle. Once it goes beyond the axle you’ve got yourself an unstable situation as weights now in front of the axle. The longer the stem, steeper the incline the more likely the wobble scenario.
    Might be worth a look.

    October 3, 2014 at 5:22 pm #816563
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    pablo

    Saddle to High? I played
    Saddle to High? I played around with my saddle height and had it set about 20mm above where it is now the front felt light and on a couple of occasions at speed (around 30) the bike would violently shake got to the point i would avoid a certain hill because the bike would always do it. Dropped the saddle in stages and never had a problem since the bike.

    October 3, 2014 at 11:59 am #816561
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    Tjuice

    Do the handlebars turn
    Do the handlebars turn smoothly? If the headset has been done up too tight and the handlebars are not completely free turning, your handling will feel dreadful (and possibly quite scary). However, as DavidC points out, this will not cause wobble unless your physical inputs are overreacting to the fact that the steering is not turning quite as it should. I made the mistake of over-tightening the headset once when fitting a new stem. Won’t do that again!

    Very, very unlikely in a brand new bike, but the other experience I have had of poor steering is if the fork has a bent steerer tube. For me, it took a long time to identify the issue because the damage to the steerer tube was so slight. Was caused by a big crash, but the bent tube was not at all obvious – I could only be sure when I put a ruler up against it – but it made the bike very difficult to ride.

    October 3, 2014 at 10:53 am #816559
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    DavidC

    First, perhaps what you are
    First, perhaps what you are experiencing is not shimmy/speed wobble. You describe it as “an unstable feeling”, whereas wobble is the handlebars/front wheel shaking violently and the bike is out of your control — there is no uncertainty about when it happens. Speed wobble is very dangerous.

    Most of what people believe to be causes/fixes for wobble and post online are not true (eg. headset too tight or too loose is popular). Any caster wheel can produce wobble, given the correct circumstances. The sum of you, your bike, how it is set up, the road surface, the speed, etc., produces the circumstances in which the feedback loop starts. Change one (not a stereotypical anal-rider change of millimeters/grams, but a meaningful, big change) and the loop will not start.

    If wobble does start, clamp your knees on the top tube as far forward as is possible. Do not use the “unweight the saddle” method sometimes suggested as being an instant cure-all — it does not work.

    October 3, 2014 at 1:26 am #816557
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    The _Kaner

    It may be something as simple
    It may be something as simple as a poorly fitted front tyre. Or wheel/tyre deflection due to the rider/weight combo that you mention. That’s where I’d start looking…

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