At 60+kph my bike’s perfectly stable as long as I’m down on my aerobars but if I move more upright or conversely lift my butt out of the saddle I get pretty severe wobble. Is this normal?
Peter
this is normal. It occurs alot when going down hill. The best thing to do out of your saddle is to shift your weight to the back. This will prevent that sensation from occurring.
Normal? After exeriencing the same thing on 3 different descents at about 40 mph, I did extensive research on it.
Basically, it is normal in that all 2 wheel vehicles will exhibit this trait at some speed. This speed differs due to a combination of things - wheelbase, fork rake, road surface, frame material/strength, wheels/tires, rider positioning and overall bike design. I was on a group ride last weekend and the guy right in front of me started having noticeable wobble at 27 mph.
In my case, I was able to minimize it by going to a shorter stem (positioning), fork with more rake (extending the wheelbase) and, most importantly, placing my knee against the top tube (changing the vibration harmonics). However, ultimately I sold the bike because it scared the hell out of me and I had become a very timid descender as a result.
“You know you are getting old when you see your father in the mirror.” Anon
konz,
High speed wobble is a harmonic vibration phenomenon that occurs at a different speed for many bikes.
Applying the brakes, even slightly, usually does not reduce the vibration, but generally makes it worse at least initially.
If this phenomenon begins to occur, the way to reduce or eliminate it is to disrupt this harmonic vibration.
Your comment about your being okay when on the aerobars but if you raise up, you begin to get this wobble illustrates how changing the dynamics of you and your bicycle affect this phenomenon. As you change the center of gravity on your “bicycle system” by raising up, you create conditions favorable to the development and progression of this harmonic vibration on your bike at that particular speed.
Things that can help reduce the likelihood that this will occur or modify and control the severity of it are the following:
Make sure your head set is properly adjusted. A loose headset will almost guarantee you experience this phenomenon also referred to as “death wobble.”
When descending at high speed clamp the top tube between your knees. This will dampen the vibration that causes high speed wobble and may enable you to avoid it entirely.
As others before have suggested, shift your weight more rearward, i.e., push your butt as far back on your saddle as it will go.
Lastly, this is open to debate, buy a really high end bicycle frame/bike from a company that has supported racing teams. Their flagship bicycle is a good choice. These frames generally have high speed wobble engineered out of them. But this solution comes at a price.
Now, some will wish to flame this previous suggestion, but consider that you don’t see pro racers fighting this phenomenon when on mountain descents at 100+ kph. Any pro who did would be changing his bike immediately, if he survived! You probably feel the same way, too.
I hope this helps you.
It is perfectly normal in poorly designed/maintained bikes…
It is perfectly normal in poorly designed/maintained bikes…
Yeah, like my Serotta Legend Ti. Try again.
Your Serotta wobbes at 37Mph? What a waste…
I think there might of been a bit of sarcasm in that last post ^^
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I stand up on the pedals and pinch the front of the seat between my legs. Seems to help.
wantstoridefast has it spot on. It’s also worth mentioning briefly that a badly set up bike in terms of geometry coupled with a lot of weight over the front end also causes it. The knee clamping thing helps. Last year i ended up in a ditch when i lost control of my old giant because I ran a forward post on it along with a hed 3. Bad idea…
Explained here:
For me this is usually caused by my knees knocking and my sphincter clinching shut as I realize my brakes are entirely inadequete for the speeds I’m going and grade I’m descending…I’m not sure it has anything to do with my bike.
As far as bike design and “quality” I suspect that it has more to do with “design” and positioning than it does “quality”. I did a ride this weekend hitting multiple 40+ mph downhills on various road surfaces from good to not so good. Never ran into any “wobble”…other than afore mentioned. This was on a very cheap, not so well maintained bike. Never hit anything over 50 although could have easily…if I had the balls.
Also a complete and utter PFA guess, I bet lighter, thinner tubed bikes are likely more susceptable to this than old heavy clunkers…which mine is.
~Matt