Speed wobble! What's the cause?

[Johan Bornman]

Johan' date=' bikes are designed with specific angles, if youu deviate from the original design it will not function as designed and hence may do things you do not want it to do. Such as give a speed wobble.

 

[/quote']

 

If a bike is designed with certain angles and then presumably manufacturered according to the blueprint, then how on earth can you deviate from those angles? The user has no control over those angles and thus cannot deviate.

 

 

I hate to be a pedant on this one' date=' but the word is BRAKING or BRAKE. Nothing is breaking until he falls.

 

Are you German?

 

[/quote']

 

No. Nor do I harp on about every single bit of spelling and typo. Netiquette calls for a certain leniancy towards typos and the like, but on the technical forum it is neccessary to distinguish between stopping and breaking.  Considering your nickname, you should know better.

 

 

 

 

Have you ever ridden a set of deep section at high speed and hit a cross wind? This is exactly what will happen. Your bike can give a speed wobble. Try it' date=' it fun!

 

[/quote']

 

Yes I have and I've never found it to induce a shimmy. I specifically use the word shimmy instead of speed wobble in case there is an argument on ambiguity. 

 

This doesn't mean it won't induce a shimmy. A shimmy needs a catalist and this can be shivering in the cold, road surface, a death grip on the bars etc. Likewise, I imagine it could be an effect of a sidewind.

 

 

Johan' date=' if you say rake has nothing to do with a bike being stable then you will argue with nearly all bicycle designers. Getting the correct wheel base, steerer tube angle, rake, etc is what makes good bikes handle well and bad bikes handle poorly. Making sure you are using the correct fork for your frame is like making sure you put the correct fuel or oil in your car.

 

[/quote']

 

I don't think that's what I said. I said rake has nothing to do with shimmy.

 

We have not defined stability but I'll assume it is the bike's ability to track straight riding no-hands.

 

Stability is not the opposite of shimmy and they are not mutually exclusive.

 

  

 

I still think bottom line is that whether I got the spelling incorrect or the terms incorrect' date=' the bloke needs to check those points on his bike. All you did was rip the text apart, you never helped the guy solve his problem.

 

[/quote'] 

 

I don't think I ripped the text apart. The two literary lessons were done in good faith and to aid clarity on the issue. They were not issued with malice. Lets keep the discussion technical.

 

Also, I do think I gave good advice and some suggestions how to overcome a) the shimmy and b) the fear thereof.

 

I still argue that things like brake centering is not the cause. This is very, very easy to demonstrate. As for deep section wheels. I ride only box sections and I get shimmy on all my bikes.

 

Shimmy is interesting and elusive.

[kosmonooit]

 

 

 

 

 

 

Okay okay stop ur b!tching, and tell me who wasnt paying atttention in Physics IA ?

The phenomenon is caused by harmonic nodes or natural frequencies of the structure being excited by any or a number of means. On a pedal bike I think vibrations from slightly out of balance wheel or those transmitted from contact with the road surface are the biggest culprits. Wind? Well its its a howling 50 Knot South Easter side-on causing vibrations through turblence over your ?less aerodynamic parts maybe but I think thats unlikely.

I know in rockets this has been a problem, and they build dampers in the structure to stop the destruction of ?the craft: resonance/wobbles at the natural frequencies or harmonic nodes building up from the constructive interference from various sources of vibrations like the rocket engine. Its all entirely understood and easily modelled with software, so cant see why that can be done with bikes. Perhaps we should get hold of our home boy Elon Musk (SpaceX) and see if he can help.

Other thing that comes to mind: is it more pronounced with carbon frames??

?

 

 

 

 

 

kosmonooit2010-02-07 15:29:26

[The_Break]

Johan' date=' bikes are designed with specific angles, if youu deviate from the original design it will not function as designed and hence may do things you do not want it to do. Such as give a speed wobble.

 

[/quote']

 

If a bike is designed with certain angles and then presumably manufacturered according to the blueprint, then how on earth can you deviate from those angles? The user has no control over those angles and thus cannot deviate.

 

 

I hate to be a pedant on this one' date=' but the word is BRAKING or BRAKE. Nothing is breaking until he falls.

 

Are you German?

 

[/quote']

 

No. Nor do I harp on about every single bit of spelling and typo. Netiquette calls for a certain leniancy towards typos and the like, but on the technical forum it is neccessary to distinguish between stopping and breaking.  Considering your nickname, you should know better.

 

 

 

 

Have you ever ridden a set of deep section at high speed and hit a cross wind? This is exactly what will happen. Your bike can give a speed wobble. Try it' date=' it fun!

 

[/quote']

 

Yes I have and I've never found it to induce a shimmy. I specifically use the word shimmy instead of speed wobble in case there is an argument on ambiguity. 

 

This doesn't mean it won't induce a shimmy. A shimmy needs a catalist and this can be shivering in the cold, road surface, a death grip on the bars etc. Likewise, I imagine it could be an effect of a sidewind.

 

 

Johan' date=' if you say rake has nothing to do with a bike being stable then you will argue with nearly all bicycle designers. Getting the correct wheel base, steerer tube angle, rake, etc is what makes good bikes handle well and bad bikes handle poorly. Making sure you are using the correct fork for your frame is like making sure you put the correct fuel or oil in your car.

 

[/quote']

 

I don't think that's what I said. I said rake has nothing to do with shimmy.

 

We have not defined stability but I'll assume it is the bike's ability to track straight riding no-hands.

 

Stability is not the opposite of shimmy and they are not mutually exclusive.

 

  

 

I still think bottom line is that whether I got the spelling incorrect or the terms incorrect' date=' the bloke needs to check those points on his bike. All you did was rip the text apart, you never helped the guy solve his problem.

 

[/quote'] 

 

I don't think I ripped the text apart. The two literary lessons were done in good faith and to aid clarity on the issue. They were not issued with malice. Lets keep the discussion technical.

 

Also, I do think I gave good advice and some suggestions how to overcome a) the shimmy and b) the fear thereof.

 

I still argue that things like brake centering is not the cause. This is very, very easy to demonstrate. As for deep section wheels. I ride only box sections and I get shimmy on all my bikes.

 

Shimmy is interesting and elusive.

 

well, it seems we agree on more than most then. Put it down to language and term usage.

 

Since I bought my new bikes I have never had it again. Decend like I bomb luckily.