Monday, January 21, 2008

Q&A: Speed wobble, shimmy

Q: Just bought a new Colnago C50 and if I let go of the handlebars to make
adjustments, just sit up and take a break, or whatever, usually at speeds
15mph and greater, the handlebar/wheel starts to oscillate, if I don't put
my hands back on it quickly it will most certainly throw me off the bike.
Any ideas on what could be the problem?

A: Because it's a new bike I would strongly recommend returning to the
bicycle shop and asking the mechanic to test ride your bike so he can
experience the issue. Be sure to explain so he doesn't crash. That's the
best thing to do if it's new because it might be a bad frame or fork and as
long as it's new you should be fully covered under warranty. Usually, the
sooner you contact the shop and the newer the bike the more powerful the
warranty is and the easier it is for them to help you out. As you ride the
bike there is the issue of whether or not you caused the problem somehow.
But this bike is brand new so that's not likely.

Now, if you built the bike up from a frame, or something, it could
definitely be something mechanical causing the issue. The causes of wobble
are almost endless and all two-wheel vehicles (bikes or motorcycles) are
susceptible to this problem. If you want to do some research you can type
"high-speed wobble" or "speed shimmy" into Google and follow a lot of links
where people discuss this issue and what causes it.

Some things to check on your bicycle include:
-is the headset (steering bearings) adjusted perfectly?
-is the seat height correct? (too high and your weight will be too high,
which can cause wobbles if too much weight is way up high)
-are the tires bad (sometimes there are defective tires that have S bends in
them that can cause wobbles at speed)
-are the tires seated perfectly on the rims? (no hops or dips when you spin
the wheel and sight the tires)
-are the wheels true and round?
-are the spokes tight enough? (quality wheels, built well by a pro)
-are the wheels centered in the frame and fork and tightened securely?
-does the bicycle track straight at slow speed or does it pull to one side?
-do friends who test ride your bike feel this too (tell them to ride it
-are the hub bearings in the wheels adjusted correctly with no side-to-side
play when you wiggle the axles in your fingers or push/pull on the rim?

Those are just some of the checks you can do to try to find mechanical
problems. But, as I said, since this is a new bike I would let the shop
handle it and not accept it back until they fixed the problem. A bike of
this quality should ride perfectly at any speed. Ernesto Colnago would not
want it any other way. He's a class act.

A quick tip that every cyclist should keep in mind is that many bikes can
wobble at speed. Sometimes it's the road that causes it and it can happen
out of the blue on a bike that never wobbles in general. When this happens
keep in mind that you can almost always stop speed wobble immediately by
simply stopping pedaling and bringing your knees together and clamping them
against the top tube of the frame. This braces the top tube and should stop
the wobble right away. Remember this tip and it can save you if this ever
happens to you. I had to use this trick in the World's Toughest Triathlon
descending Monitor Pass at close to 60mph (I had just passed a Porsche!).
Had I not known it, I would not be typing this today.


Anonymous said...

Jim: I was informed of this blog spot by local shop from where I purchased my 2010 Specialized Tarmac. I have had some shimmy since purchasing this bike and have made the local bike shop aware since purchase last summer. I have played with stems, stem height, bars, saddles and post height as well. I did after nearly taking out a mass of about 25-30 riders in a local bike ride about two weeks after purchasing the bike, sell the OEM Mavic Aksium wheels and have since tried open pros with Dura Ace hubs, ksyrium Elites, and Hed Kermesse wheels to try and see if the problem is product but it has had no impact. I have had some luck using the knee press into the top tube as suggested and "feathering the brakes" which also has improved with replacing OEM with Dura Ace calipers. Local bike shop has tried to use tools to see if frame is out of line but that is not the case. Short of getting a "BG bike fit" which I feel will be the next thing from Specialized do you have any suggestions. As a side note, I have a second bike without these problems and have been suggested by Leonard Zinn that may need to sell the Specialized in my correspondence with him via e-mail. Do you have any suggestions? Any and all suggestion will be appreciated!

Jim Langley said...

Hi Bryan,
Do you know if the shop carefully checked your fork alignment? Here’s a nice article about this:

Also, have you tried checking your headset adjustment to make sure it’s on the tight side – not “just right” or “a little loose” Sometimes making it on the tight side will solve wobbles.

Also, are you certain that your seat is not too high? It’s pretty easy to make the mistake of setting your seat too high, and if that’s the case it puts your weight too high and that can make a bike wobble. So that’s worth checking carefully.

I hope something here is helpful, but I do know that some bikes are just wobblers so sometimes Lennard is right, that you just need to get a different bike. Just because it wobbles for you doesn’t mean it will wobble for someone else, so often you can sell it to someone else. Just be sure they test ride it and don’t have problems with it and you’ll be good.

In cycling,