Leading on from my post the other day about Hed 3 death wobble I went out to test again yesterday. I rechecked my headset and front QR and bearing cones and hit a few 30-40mph descents.
Any decent with speeds above 35mph gives a shimmy that is nearly unrecoverable. This is reagrdless of speed change and top tube touching. The wheels trueness seems ok. I nearly ended up in hitting the traffic at 40mph and god only knows where my drinks bottle launched to. The torque caused by the wheel nearly pulled it clean out the fork dropouts.
Bear in mind here that I was using a Hed 3 in a carbon Giant TCR fork and that feel for you will vary from bike to bike. The TCR fork is a road bike type was reputably a bit ‘twitchy’. It probably wasn’t designed to handle that kind of loading.
Anyone recommend a suitable replacement fork with a similar rake and trail ?
I think you are right about that although they used the slightly older larger more aero version ('99-03). I’m wondering if perhaps the cobb airstream or the Ouzo aero may be a sounder bet…
It’s ALL in your head… next week try to descend at 50mph, I’m sure the shimmy will go away
Seriously, that’s a very interesting phenomenon and I don’t have a clue why it’s happening. But I think this can originate from the way the frame loads the wheel, so having a fork with the same rake and trail might not do the trick.
Try taking off your aero bars and see if there is a difference (unless you have a TT front end). It has worked for me in the past. You are on a road bike that was not designed to have all that mass on the front, and that could exacerbate the shimmy.
I would probably just swap the front wheel out for an Alps or something similar - it will be lighter and nearly as aero. If you sell the Hed3 on ebay, this would be a cheaper option than replacing the fork. Alps - Hed3 < Reynolds Ouzo Pro Aero
I have experienced “death wobble” on both my tri and road bike and the thing to remember is that it is not just the equipment but the rider as well. As I understand it, when riding the resonante freq. of the entire system (bike+rider) is at a certain point, when the wobble starts all you need to do is un-weight your saddle or pick your ass up and the wobble will stop immediately, becuase the effective dynamics of the system have been broken and there is a new resonant freq.
There might be nothing wrong with your wheel, it just might not be good for you.
I know this is kind of cryptic and I apologize, but if you still want the wheel, just learn to unweight your saddle when it starts. Also try to relax your upper body as the rider ususally has some blame as well.
Did you try the age old trick of clamping your top tube with both your knees until you get through the resonanant frequency (in essence changing the natural resonant frequency of the bike+wheel+rider system) and then accelerating through to 50 mph. I used to do this with an old touring bike riding through the alpes and pyranees, totally loaded down with gear on both the front and rear rack.
I have tried this and it does work but I find it hard to continue to accelerate. Lifitng off the saddle is instantaneous and makes me feel much better.
I have a wheel which is true but has a heavy spot where it is welded. It created a bad wobble which got worse as speed increased. I balanced it with a piece of an old inner tube between the tire and tube opposite the weld. It took some trial and error to figure out just how big a piece I needed. It works fine now. Could your wheel have a similar problem?
Are you a tall rider, using a tall stack of spacers between your stem and headset? The death wobble often shows in this configuration, especially as you move weight fore and aft. If you are running high like this, and your stem is level, or nearly so, try flipping the stem over, moving some of the spacers above the stem.
Check your weight distribution on the bike. Mount the bike in a trainer and put a scale under the front wheel. Make sure that the axle height both front and rear is exactly the same by putting boards under the scale. We have found a lot of speed wobbles are directly related to weight distribution. If you are riding a road bike with a tall stem set-up you have too much weight on the rear of the bike. There are a number of different scenarios for what causes this. Also, Giant had a big fork recall a year or so ago. All of these light aero bladed forks are not known for stability. The hed 3 wheel is not going to absorb shock like a spoked wheel either. It is the fastest thing out there though and we have had no problems similar to this. Also check the roundness of the tire as well as making sure it is seated properly.
