Evan Andreou Posted February 20, 2008 Posted February 20, 2008 Was going down klapperkop yesterday at about 50kphWhen my front wheel started going beserkNearly chidanga'd myself. Stopped to check but could see anything wrong with the wheel Any idea what caused it?
The_Break Posted February 20, 2008 Posted February 20, 2008 Hi Wolverine Had a bike that speed wobbled at above 60km/h about 2 years ago so I went through the long and hard route to fidn out what it was. Hope I can help. Fisrt some questions: How long have you had your bike?Have you changed anything like the wheels or the fork, stem, etc recently?Were you riding deep sections when it happened?Was there a strong side-wind blowing when it happened?How did you bring the bike under control? I would suggest you don't ride it until you get an understanding as to whether it was a freak thing or maybe equipment related.
scotty Posted February 20, 2008 Posted February 20, 2008 Happened to me once also going at about the same speed, tried everything including clinching the frame with my knees but still continued. Stopped and checked wheel and fork but found nothing wrong and has not happend again so its still very much a mystery.
Thug Posted February 20, 2008 Posted February 20, 2008 The only things I can think of are... 1. Headset could be loose 2. Bearings in front wheel could be in need of replacement.
Saddle Sore Posted February 20, 2008 Posted February 20, 2008 Well all bikes on the market will do this even motor cycle do this!!<?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> It has got to do with the geometry of the bike and your weight on it!Not all bikes do it on the same speed. All you need to do to stop this is to lift your bum from the saddle, but this is very scary because you natural reaction is to grab the handlebars!
The_Break Posted February 20, 2008 Posted February 20, 2008 Properly designed and maintained bikes ridden correctly should not do this unless you are going at such a speed that all the factors together cause the bike to go into its natural resonance. Correctly designed bikes take all road cournesses into account and are designed, yes, using correct geometry and stiffness, to allow a bike to be riden at all speeds so as to keep the resonance (speed wobble) frequency well above the frequency caused by the speed you can ride on the bike. Note I never asked him what bike he rode as nearly 100% of bikes in the world would not exhibit a resonance frequency at such a low speed. I believe it is another factor, either a freak occurrance such as a cross wind at the wrong time, incorrectly fitted parts or incorrect parts fitted as was my case. Let see what he comes back with.
Cois Posted February 20, 2008 Posted February 20, 2008 Wolfie I had the same happen down a pass near Loskop. Could not find the problem, but it was scary as hell. I took my MTB and went down there at 81 km/h without any problems.In the 94.7 (same bike and setup) I did a 78 km/h with no problems. Can it be the road and tyres used?
Mudsimus Posted February 20, 2008 Posted February 20, 2008 Relax. Most speed wobbles comes from tensioning up in the shoulders. Dont blame the bike.
controlc Posted February 20, 2008 Posted February 20, 2008 Have you tried adding a different coloured spoke opposite the valve?
Spinnekop Posted February 20, 2008 Posted February 20, 2008 Beste raad OOIT!!! Knyp.......daai........pyp vas tussen jou beneMaak o? toe soos plastic pop se speneSit jou tanne op die teer as wilEn gaan aan die gilSolank jy net bo bly... OK......rerig.....knyp net die top tube vas met jou bene en die wobble behoort op te hou.....
1hill@aTime Posted February 20, 2008 Posted February 20, 2008 wolfie you been drinking and riding again?
Man with no name Posted February 20, 2008 Posted February 20, 2008 Beste raad OOIT!!! Knyp.......daai........pyp vas tussen jou beneMaak o? toe soos plastic pop se speneSit jou tanne op die teer as wilEn gaan aan die gilSolank jy net bo bly... OK......rerig.....knyp net die top tube vas met jou bene en die wobble behoort op te hou..... Wat as die wobble agv selluliet is? Moet ek nog die top tube vasknyp?
The_Break Posted February 20, 2008 Posted February 20, 2008 Road courness and tyre rolling resistance can play a role if the bike is on the twitchy side. As you increase speed the frictional force pushing back on your bikes tyre, oposite to the direction of speed increases. An increase in road roughness will also increase this force. As the gradient increases the amount of mass on the front wheel also increases. The frictional force acting in the opposing direction to travel is also determined by the downward force on the wheel which has now increased. If you put all these factors together it means that there is a greater force actinig on the wheel and thus a greater force acting on the fork causing it to flex backward more than if these factors where not there. Depending on the amount of flex, which is dependent on fork and frame stiffness, the bikes wheelbase shortens making the bike more "unstable". If it is already on the twitchy side, a characteristic of a short wheelbase, then yes, speed wobbles can occurr. But like I say, a well designed bike should take all these factors into account.
Evan Andreou Posted February 20, 2008 Author Posted February 20, 2008 Spidy, sounded like you were ad libbing leeuloop
Evan Andreou Posted February 20, 2008 Author Posted February 20, 2008 wolfie you been drinking and riding again? Thought the water was off
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