Speed wobble - Wrist Twisters
 
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post #1 of 11 Old 12-15-2006, 10:10 PM
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Speed wobble

I've been looking at some of the videos of crashes lately and one of the common things I'm seeing is bikes going down after violent front end wobble. Sometimes at high speed sometimes going slow. Is this instability something that is the result of modern steering geometry? I was wondering if having a bike setup for faster turn in results in a little instability as a result. I don't remember this being much of a problem on the older bikes.

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post #2 of 11 Old 12-16-2006, 07:07 AM
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Interesting topic, one of which I could go on and on about.

The vids. you have been looking at are more than likely of stunts gone bad.

The modern day bikes are light years ahead of the dinosaurs from the 60's and 70's. Frame design, tires, and components just to mention a few. IMO instability back then was worse then it is today for reasons mentioned.

Frame geometry plays a important part in overall stability. Trail is what gives a bike handling characteristics. Less trail improves turn in at the expense of becoming twitchy at high speeds.

One example was the original '99 Yamaha R6. It had radical trail numbers (81 mm) necessitating the need for a steering damper. To further reduce the twitchiness a '60' series front tire was fitted as original equipment. A Ohlins top mount damper cured the problem. Yamaha has since increased the trail (97 mm)on this model.

How to prevent or ride out speed wobbles and tank slappers is a topic unto themselves.

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post #3 of 11 Old 12-16-2006, 07:16 AM
 
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Older bikes were also heavier and with less HP so they were more stable I guess... today rockets are less the weight and double the HP.

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post #4 of 11 Old 12-16-2006, 07:43 AM
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Quote:
Originally Posted by RC90 View Post
Older bikes were also heavier and with less HP so they were more stable I guess... today rockets are less the weight and double the HP.
Older bikes had bicycle frames, ribbed front tires, and cheap a** steering head bearings to name a few. Push a early CB750 or Z1 kawi, the ol' pucker factor would get you real quick. By comparison, today's bikes are a pleasure and much safer to ride.

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post #5 of 11 Old 12-16-2006, 07:47 AM
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Originally Posted by MisterMike View Post
Older bikes had bicycle frames, ribbed front tires, and cheap a** steering head bearings to name a few. Push a early CB750 or Z1 kawi, the ol' pucker factor would get you real quick. By comparison, today's bikes are a pleasure and much safer to ride.


Amen, Brother!!!!!!

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post #6 of 11 Old 12-16-2006, 10:02 AM
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I know what you mean about the older bikes. The Kawi 500 triple I had was not a real pleasure to ride. Although I didn't really push it too hard. It was heavy feeling and much happier going in a straight line. As an aside, my first major crash was the result of speed wobble. I was about 5 or 6 on a 20 inch bicycle going down the biggest hill in the neighborhood. I've still got the scars from that one.

post #7 of 11 Old 12-16-2006, 08:17 PM
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A major cause of speed wobble is when the front end comes up (either intended or not) and doesn't come down straight. The result is a tank slapper which the rider is (usually) not able to recover from.

If you're concerned about it, buy a good steering damper.

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post #8 of 11 Old 12-20-2006, 02:33 AM
 
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Most wobbles are rider error. Modern chassis design is very advanced and one thing they don't factor in is that you might drop a sky high wheelie down on a less than straight wheel. Basically a steep drop of the wheel will weight it and with the wheel cocked you will generate a moment the chassis can't handle... enter chassis flex... and unflex... and flex and crash. You can even do this WITH a steering damper if your goofy enough.

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post #9 of 11 Old 12-20-2006, 03:13 AM
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Quote:
Originally Posted by hermit View Post
I know what you mean about the older bikes. The Kawi 500 triple I had was not a real pleasure to ride. Although I didn't really push it too hard. It was heavy feeling and much happier going in a straight line. As an aside, my first major crash was the result of speed wobble. I was about 5 or 6 on a 20 inch bicycle going down the biggest hill in the neighborhood. I've still got the scars from that one.
We must be twins. Been there done that on the bicycle. Asphalt surfing with shorts, sans shirt, wasn't exactly fun. I was winning the race against Tommy Lancaster when it happened though.

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post #10 of 11 Old 12-21-2006, 05:03 PM
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Yea, that one was not much fun. It shook so hard that it knocked my feet right off the pedals. I still can't convince my family that I wasn't just showing off for the neighbor girl who just happened to be there.

post #11 of 11 Old 01-23-2007, 07:13 PM
 
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If you have the time (and distance straight ahead) when a tank slapper is about to start, tell yourself your not releasing control of the bike. Then VERY GRADUALLY, apply the front brake, just a little bit, while doing NOTHING ELSE! The friction created between the pavement and your front tire, and directionally from the pavement going under your bike in a straight line tends to straighten up that front wheel.

Of course if you've got other circumstances to contend with simultaneously, then it's fast-forward speed of all that, while you deal with the other factors too!

Good luck.

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