Speed Wobbles

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Speed Wobbles

Postby James Quinton » Wed Oct 22, 2008 5:58 pm

Hi,

Anyone ever get speed wobbles? Any suggestions on fixing it other than changing body position. (Ive changed position more times than an 'X'y with a budget.)

It happens when I go over 60km/h.

I've heard its common on all bikes over a certain speed. That right?

Thanks
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by BNA » Wed Oct 22, 2008 6:20 pm

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Postby sogood » Wed Oct 22, 2008 6:20 pm

No. Some bikes are more prone. Some bikes with some riders are more prone. At the end of the day, it's all about the natural frequency of the system. Irrespective, to get speed wobble at 60km/h is rather unusual and bad. Have you checked if your headset bearing and other major bearings are in good order?
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Postby Kalgrm » Wed Oct 22, 2008 10:33 pm

+1 for sogood's response, but you might also find you are tensing up at those speeds, enhancing that "natural frequency harmonic" which sogood mentioned. Try loosening your grip on the bars to help your arms relax somewhat. It's going to be hard to do that though - you'll need to overcome natural (and sensible) fear.

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Postby wintal » Wed Oct 22, 2008 10:45 pm

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Postby CB » Wed Oct 22, 2008 11:08 pm

just lift your bum up just a little bit, so your bum is rest on the seat but all you weight is on your feet.

this puts you more in control of the bike, and gives you a bit more confidence at high speeds.

combine that with a fairly relaxed grip on the bars and you'll be fine
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Postby Mulger bill » Thu Oct 23, 2008 1:04 am

Clamp the top tube between your thighs and decelerate without braking, as Sogood said there's a certain combination of rider, bike, speed and terrain that'll bring on the wobbles, change one of them and voila.

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Postby uncle arthur » Thu Oct 23, 2008 8:55 am

I set my new top speed yesterday - 74.3kmh. Fortunately - no wobbles, but a fair bit of tail end clinch. :shock:
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Postby winona_rider » Thu Oct 23, 2008 9:07 am

are your tyres pumped up enough?
i find that i get death wobbles if my tyres get under 60psi
(tyre not beading with rim properly)
:oops:
but i don't know much about stuff...
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Postby fatherofmany » Thu Oct 23, 2008 11:18 am

Haven't experienced them yet and my bike computer says I've maxed at 88. (Now that was a rush and lots of wind noise too)
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Postby bowie » Thu Oct 23, 2008 11:34 am

yes more noise then wobbles.. but i did just replace all my bearings... and Mr Brown says not to worry about it :P
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Postby beauyboy » Thu Oct 23, 2008 4:56 pm

To tell the truth I would be a little worried
Back in 1994 a girl died when the front wheel of her BMX failed under her at speed. They said the reason for the wheel failure was due the Bike developing speed wobbles, all bmx bikes of a certain brand were recalled.

I remember this Cos I was 9 and had a BMX.

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Postby RideLikeTheWind » Thu Oct 23, 2008 5:34 pm

Yeah I would be worried too.

I have hit 90+ with no wobbles. It does bother me though the damage that I would do when (if) i came off. I have come off before at 60km/hr and that was bad enough - took some major skin off legs, hands, arms and a huge gouge out of my side. But 90 will hurt, if there is anything left to hurt.

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Postby lukas » Thu Oct 23, 2008 5:58 pm

Joe wrote:I have come off before at 60km/hr and that was bad enough
Joe


Ouuuchh :shock:

I've never had the speed wobbles.. I only learned about them by reading online. I try and stay as relaxed as possible on descents now though.

Fastest I've been is 75kph... plenty fast for me.
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Postby McPete » Thu Oct 23, 2008 9:20 pm

Other things to check would be if your wheels are not egged, buckled or tacoed to any degree. Check spoke tension as well, come to think of it. I've had all those issues causing wobbles on mountain bikes.
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Postby James Quinton » Thu Oct 23, 2008 10:06 pm

Thanks for the responces.

I just went to the bike shop and had the front wheel trued a bit.

Will go down and try to reach 70km - the speed I'd be happy with - and report back. Hopefully they'll have the net in hospital.

One question though: how do you decelerate without braking when you're going down hill?
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Postby toolonglegs » Thu Oct 23, 2008 10:15 pm

James Quinton wrote:One question though: how do you decelerate without braking when you're going down hill?



:lol: ...the painful way.When you get a tank slapper on a motorbike the best way to get out of it is too accelerate hard...so better pedal faster!.
Never had a bike get a speed wobble...hope the shop didn't tell you that!.
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Postby bowie » Thu Oct 23, 2008 11:00 pm

when it doubt, power out ;)

hope you had your wheetbix ;)
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Postby Mulger bill » Thu Oct 23, 2008 11:31 pm

Didn't put that well did I... :roll:

Sit or stand up, make a big 'chute of your body.

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Postby senator52 » Fri Oct 24, 2008 8:36 am

sogood wrote:Have you checked if your headset bearing and other major bearings are in good order?


+1 First thing I thought was check your headset is not loose.
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Postby toolonglegs » Fri Oct 24, 2008 2:55 pm

senator52 wrote:
sogood wrote:Have you checked if your headset bearing and other major bearings are in good order?


+1 First thing I thought was check your headset is not loose.


...or too tight.
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Postby il padrone » Fri Oct 24, 2008 6:33 pm

Were you pressing on your bars a bit? Weight on the front end above the headset will generally precipitate a speed wobble. It began to happen to me on a local descent when I got to about 55kmh. I was mildy concerned about what was going on. Later on another descent I got into my standard descending stance (which I had been slack about earlier) - weight towards the rear of the saddle, cranks level, knees clamped on the top tube and arms relaxed with no weight on them. All of a sudden 65kmh+ was quite comfortable.

Any half decent road bike should track quite straight, given half a chance. The caster on the steering geometry will ensure this.
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Postby il padrone » Fri Oct 24, 2008 6:36 pm

James Quinton wrote:One question though: how do you decelerate without braking when you're going down hill?

Stop pedalling and sit up straighter - air braking :wink:
Riding bikes in traffic - what seems dangerous is usually safe; what seems safe is often more dangerous.
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Postby muggah » Fri Oct 24, 2008 6:50 pm

il padrone wrote:Were you pressing on your bars a bit? Weight on the front end above the headset will generally precipitate a speed wobble. It began to happen to me on a local descent when I got to about 55kmh. I was mildy concerned about what was going on. Later on another descent I got into my standard descending stance (which I had been slack about earlier) - weight towards the rear of the saddle, cranks level, knees clamped on the top tube and arms relaxed with no weight on them. All of a sudden 65kmh+ was quite comfortable.


I had something similar happen to me the other week, I hit 70 and it started to buck, at which point I was glad my knicks weren't white!! :wink: . I'm putting it down to the fact that I was rooted from the climb up the hill and was too lazy to shift my bum back on the saddle for the descent. I hope it dosen't happen again though cos it scared the **** outta me!!!
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Postby 318ute » Fri Oct 24, 2008 6:53 pm

Wobbles.....
How fast is too fast (road legal of course) and what should I consider a maximum speed for a Trek 3900 mtb.
I have skinny road tyres and so far have topped out (before squeezing the brakes lightly) at 71kph! No Wobbles 8)

Do bikes come with a manufacturer top speed??


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Postby il padrone » Fri Oct 24, 2008 7:07 pm

My highest speed (twice) was 83kmh, on the road.

The day I did 69kmh on a fire-trail near Healesville on my rigid MTB, some of the guys on DH bikes with suspension had done 89kmh!! On a steep, rocky track with off camber corners - going a full 20kmh faster than I did. Yikes :shock:
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