This is the second time I almost ate it at 30+ mph going downhill due to extreme shimmering. The whole bike and front wheel were shaking when hitting the brakes at 30 mph. I was going downhill and when it started to level out the bike became almost uncontrollable. This has happened several times, but this was the second time it was really bad. I had the same issues on my P2K. I changed fork on the P2K but that didn’t help. Now, with my soloist I have the same issues. I finally swapped the wheels (alps – also used them on my P2K) with a pair of 303 on my soloist and was pretty sure that was one of the problems, but no. I was going with a group of bikers and nobody else had this issue.
I have gotten various advices from Cervelo, Hed and others, but nothing seams to lead to anything that identifies the issue. So, anybody here at slowtwitch that know what causes this to happen on two different bikes, different wheels and different fork?
The last thing I am planning on shifting is the stem. Have to try everything but running out of options. Only thing that is the same are Cervelo and the rider?
If it is nothing mechanical (e.g. loose headset, wheel bearings, etc) then do the old school trick. clamp the top tube with your knees on the descent. that almost always works.
Do you ride the bike with the seat in the forward position with the seat forward? If so then you are experiencing the same handling problems than any poorly designed bike will have when ridden steeply. My P2 was downright terrifying on fast downhills, as was my Scott before it.
Regardless of their marketing, one bike cannot handle well in all positions from 74-79 degrees.
Sounds frightening !!! I haven’t had problems like that since the late 80’s when I rode my old all steel Gardin.
My educational background & original career was in Acoustics (Sound & vibration). Sounds like you bike’s natural resonance is being excited at specific speeds. The suggestion of clamping the top tube is a good one in that it moves the resonant frequency higher & outside of the forcing frequency. Clamping the top tube however, makes pedaling a challenge. Another way of moving the resonance around is by adding mass, have you considered adding lead shot to your down tube?
Seriously, have you checked your wheels to make sure that they are true? If they are off, it may be what gets the party shakin’
This happened with the first bike i ever owned, a Trek 2300 (carbon model from 1992). I took it back to the lbs and yelled at them. My bad!!! They told me to relax my grip on the bars!! Worked like a charm. I had that bike up to 55 mph without a problem after that. The secret is - RELAX!!
that happens to me when I’m going fast with no hands
doesn’t happen on my p2sl going down fast hills. that used to happen to me and other people in motorcycle racing, and like the other dude said, make sure you don’t have the death grip on your bars. try and stay somewhat loose.
Bike shimmy is the result of road surface or aero inputs forcing the bike/rider system at a harmonic near it’s natural frequency. Basically, some aero or road vibrations are causing the bike to begin oscillating laterally at the headtube (usually the pivot point is the seat tube/top tube junction). This is not due to the frame or wheels or any particular component, but a result of the harmonics and stiffnesses of the entire system.
Things we generally recommend are trying other wheels or lowering air pressure in the tires as changing wheel/tire mass will change the natural frequency of the front end, and changing tire pressure will change tire casing stiffness, thus affecting front end stiffness. You will probably also find that unweighting the saddle during this shimmy or squeezing your knees against the top tube will stop it as you are changing the fulcrum point about which the bike tends to shimmy. Relaxing your grip on the bars also seems to help, and I’ve seen numerous instances where changing the handlebar weight or even bar tape can affect this as it is mass sensitive.
Jobst Brandt has written on this quite extensively and can surely be found with google.
I posted info on this once before!! In a nut shell, it’s not the bike, it’s not the wheels, it’s YOU. I’ve been riding for a long time and had this same problem many times before AND it even goes ALL THE WAY BACK to when I was 12yr’s old riding my old 24" bike with the large basket for newspapers. I was going down a hill and the bike started acting radically with the result of me falling. I certainly didn’t have any of the new aero wheels or steep geometry or etc. of todays bikes when that happened. That was 1954!!! In the end what it turned out to be was me tensing up in a situation I was uncomfortable with. I tried to manage the situation by controlling the bike, RESULT over-mangement and radical bike response. WHAT YOU NEED TO DO IS RELAX WHEN THAT SITUATION HAPPENS. That goes against your normal response, but that is what you have to do. The last time it happened to me was in Hawaii IM with very strong sidewinds. I’t started and I literally stopped to check my front wheel Everything was OK, I started up again and it started happening again ONLY this time I forced myself to relax and it went away. You may need to do a lot of training rides with your race set-up to become accustomed to it. Once you feel comfortable, you won’t tense up under those conditions. I know everyone likes to think it’s not their fault, but it is, unless your have the RARE problem of frame alignment or wheel unbalance, etc. but not likely.
Sounds interesting, just hit 40mph, relax and hope it will not happen because I clamp too hard on the handlebars. Just don’t buy it since I ride a lot and it happens under certain conditions. I go fast many times so then it should happen more often. The first time it happened I didn’t expect it to happen so I doubt it was a result of clamping too hard.
You’re describing “death wobble” which is when an oscillation gets going betwen the rider and bike. My Giant TCR medium frame was bad at this. Very scarey.
The solution is to grip the top tube with your knees and unweight your butt on the saddle a bit. This will stop the vibration quickly. You are probably holding the handlebars in a death grip as you decend and not realize it. This is a contributing factor. Try to relax your grip.
I don’t buy your response!! I’ll give you one example and I have many very similar to it.
I rode my winter bike all winter. It’s a heavy bike with fenders, has a very relax rake on the front (more a touring bike) and got used to manhandling it. In the spring I was to go out with our club and I decided to ride my racing bike that day. That was the first day on it in around 4 months. I came down this steep hill close to home and developed a very severe wobble. My forearms nearly went numb by the time I got to the bottom. Now this is the same bike I ride all summer down that same hill and even steeper hills and NEVER have this problem Well I turned around and went home because I didn’t want to cause any accidents in our club. I instead rode another road on my own and after about an hour of riding and realizing I need to use finesse with this bike, I went down that same hill with NO PROBLEM. See what happened was the first time I was in an unfamiliar situation and subconsciously I tried to control it and of course speed wobble. The second time I went down, I was comfortable and now used to my lighter bike and no problem. Now this bike was the same bike I always race on, same wheels,everything the same, so what do you attribute the initial wobble too???
I like slowman’s site, lots of good info there. Will read it. and I do agree every bike is weaker in the horizontal position, but I still think everyone can control speed wobble by just relaxing when they ride. When I mentioned the problem I had in Hawaii, I did get out of the seat but it still wobbled on me. In fact I had that wobbling effect right down to 5km/hr because I was so tense and was just trying to control things. Now no one should have speed wobble at 5km/hr!!! So that pretty well tells you what your body can do to a bike’s performance at ANY speed. That also tells me IT’s NOT THE BIKE.
had the same problem at IMLP this year.I could only do 35-40 mph down hill and people flying by me at 60. It was frickin scary. One problem is my bike. Its a road bike retro’d to a tri bike with clip ons, seat forward, and its a compact so it already had twitchy steering to begin with.
I am now going with a tri-specific frame to see how that goes
i have also had some terrifying descents on my soloist with my reynolds dv wheels. did a road race where i’d put 1 minute+ into riders on hills and then they’d pass me on descents easy as.
When you get the “shimmering” on downhills are you hovering over the bike with not much weight on the saddle? Unweighting too much can cause the “shimmering”
