High Speed Wobble w/Aero Wheels

Triathlon Forum
1

Mavens,

I have a high speed wobble problem with BOTH sets of aero wheels I own. Anything over 35-38 MPH going downhill results in a bad case of wobble and shake on the bike. (Yes, I know to squeeze my knees on the top tube, doesnt help at all). Its scary as hell and I am barely holding on at these speeds.

Me: 5’8", 142 lbs, 9 % BF, built like an ant (strong and skinny). Cross winds always bother me as I am light.

My set up: Parlee TT Bike, Zipp 646 wheels (set 1) and Zipp 343 (set 2). Both sets have tubulars (vittoria) that are taped on. Both sets of wheels exhibit the exact same high speed behavior on fast descents. Both sets are about 5 years old, new tires.

My daily training wheels (Bontrager RaceXLite) with clinchers go over 40-48 MPH with out even a shimmy. They feel great!

I checked the Zipps on a wheel trueing stand and they spin true.

So what gives? Why the wobble on both sets of Zipps and nothing on the clinchers? Any advice help is appreciated.

TT

PS: I am doing IMMT in 2 weeks, and at this point I feel better and safer on the clinchers (though I am probably giving up just a bit of time with this choice)

2

Check the centering of the tires? Best is to put them on a grueling stand. Beyond that I’d check the mounting job itself ie is the tire contacting the rim uniformly. As I am sure you’ve heard tape sucks compared to glue but it should still “work”.

3

Hm, I’m slightly smaller than you (5’7", 130 lbs) and have the same problem. Easton Vista training wheels = no problem until 40+. HED Jet 60s with disc cover = death wobble at about 35 mph. No answers for you, sorry.

4

When you put the bike on a stand does the same spot always find the bottom? I have an old Campy (Shamal?) that has a heavy spot where the weld is. It was scary the first time I took it down a big hill. I balanced it by wrapping a few pieces of solder around two of the spokes. I have retired it but balancing took care of the problem.

5

Speed wobbles surely suck and they’re really hard to diagnose because overall they indicate resonance and instability mostly in the bike’s front end but there can be a lot of causes from loose or tight headsets or wheel bearings to weight distribution issues or other things. They’re a bit more common with deep wheels as small sidewind gusts can catch your deeper front wheel and normally that might not be an issue but if your bike is prone to resonance and wobble issues for other reasons the additional input of small sidewind gusts can be enough to start the oscillations. Everything else in the bike setup could be the same but if your training clinchers don’t also perturb the system with side gusts or if they’re not quite as stiff or pumped up as hard as your race day wheels then you’d be less likely to get the wobbles or the wobbles would happen at higher speeds with the clinchers vs. the race wheels.

One common reason is running too much tire pressure as excessively hard tires won’t dampen road vibrations and tend not to dampen the overall front end steering system. You’re pretty light so you shouldn’t be running too much pressure even though your tubulars can handle it. At 142 pounds you shouldn’t be running much over 95 psi or so up front, perhaps less. Maybe you’re already running realistic pressure in which case not much to add except to get your bike thoroughly checked out for things like headset and wheel bearing preload and make sure your fit ends up with reasonable weight distribution between the front and back of the bike.

Check your tire pressures and remember that harder tires are only faster on perfectly smooth conditions like a very smooth velodrome and that even though very hard tires feel faster, from an overall system standpoint they’re generally not when ridden on real world roads. Tom A. has a good piece explaining this here: http://www.slowtwitch.com/Tech/What_s_in_a_tube__1034.html

Good luck,
-Dave

6

Mavens,

I have a high speed wobble problem with BOTH sets of aero wheels I own. Anything over 35-38 MPH going downhill results in a bad case of wobble and shake on the bike. (Yes, I know to squeeze my knees on the top tube, doesnt help at all). Its scary as hell and I am barely holding on at these speeds.
…

PS: I am doing IMMT in 2 weeks, and at this point I feel better and safer on the clinchers (though I am probably giving up just a bit of time with this choice)

Bike stability is a complex thing, but has been studied quite a bit.

Generally, moving rearwards on the bike helps prevent “unicycling”, where most of the weight is over the front wheel. But it’s much more complex than that. below is the linear stability phase space of a Whipple bike, for example.
http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/JBike6_web_folder/index_files/bike_n_eig.jpg

I suspect that the added mass of the wheels shifts your overall centre-of-gravity down to the point where the lean-steer instability kicks in. If you feel adventurous, try riding with a weighted backpack (of 7kgs) and see if the wobble disappears. Not sure how this will help eliminate your wobble, but it may provide some clues.

7

Does your bike have horizontal drop-outs on the rear wheel?

8

Yes, it has horizontal dropouts.

Regarding tire pressure, I run about 100lbs all the time in all sets of tires/wheels.

What I dont understand is why the aero wheels (which are supposed to be, well,… more aero and faster) wobble and the road wheels dont. I did check to assure unformity of the tire bead to the rim and it looks correct, and the wheels are true.

I wonder if the bearings on the Zipps have anything to do with this? Maybe too loose, or perhaps too tight. Too loose makes more sense.

The irony is that if I cant scream down the hills at 48 mph on aero wheels (and can only go say 33-44), and I can on clinchers, the aero wheels will actuall slow down my bike split on a hilly course like Tremblant! Strange but seemingly true.

TT

9

It could be a wimpy fork.

Years ago, I had just gotten my TiCycles Softride the year before, with a Trek composite fork (the lightest one, of course)… First TT of the season, with Specialized Tri-Spokes front and rear… Scary front-end oscillations at anything over about 32 mph. As in, the bars were steady, but the front wheel was oscillating side-to-side (pivoting about the steering axis) a good 2" at the leading edge of the wheel. Weight shifts did nothing. The only thing that corrected it was to slow down. Never had an issue with any spoked wheel.

Swapped to a Kestrel EMS fork, and the problem went away.

10

I had Zipp 404’s that would go into a “death wobble” a year or so ago at mph above 30 mph. I am 6’4", 200 lbs.

The problem was a small indentation in the side wall of my front rim. Very scary stuff, to be sure, especially when the wobble first occurred
on my first loop at IMLP descending into Keene.

I sent it into Zipp and they exchanged it at no cost as it was a clear defect. No problems riding the new Zipp 404 that was sent as a replacement.

I would check each wheel very carefully for construction inconsistencies.

11

I should also add that I tried both sets of wheels on my Parlee road bike, for an A-B comparison. SAME RESULT! Death Wobble!

12

With horizontal drop-outs, the pins you adjust every time you put a different wheel on, can come loose and cause the wheel to be all wonky. I just learned this myself—you should inspect the pins and how the rear wheel is set every time you ride. The pins coming loose can also lead to your brakes rubbing. Not sure if this is your issue, but I’ve been dealing with this and can tell you my next bike will NOT have horizontal drop outs!!!

13

Maybe it’s cuz you are so light, have you tried eating pizza? :slight_smile:

jaretj

14

Unfortunately there isn’t a universal fix or solution for the death wobbles. I get them (6’4, 210lbs) on almost every bike I’ve owned in the last 5 years—Parlee Z5, Z5SLi, Colnago CX-1, Time RXR VIP (by far the worst)----however, in EVERY instance, it isn’t the bike but the wheels. Running Zipp 303 Firecrest or Reynolds DV46 I get them at about 45mph. Running a 404 I get them at 35-38mph. I shudder to think what something deeper will do.

I do not get them, ever, with a standard Velocity V shaped aluminum rim or standard box rims (Mavic).

I’ve switched bikes/forks/position/stems etc…and the one constant is that the 303/DV46 & deeper simply create an oscillating effect that causes wobbles at a certain speeds. With the 303s, they were better on the Large Tall Parlee than the Time RXR, but still pretty annoying. I’m now back on a RXRS ULTeam & so far haven’t had any problems—but only have hit 40 so far.

15

That’s very strange as the weight distribution and front end characteristics of your road bike are likely quite different than your tri bike.

I’d start by checking the bearing pre load on both sets of deep wheels to make sure they don’t have slop and lateral play nor are tight and rough. That still seems like a less likely problem than other things but it’s worth checking. Then I’d probably take a divide and conquer approach and run the rear deep wheel with a spoked front and vice versa. It’s likely the front deep wheel has more direct connection to the wobbles and you’ll likely find you can run the rear without issues but it’s worth checking. If nothing else you can get some race day speed in your upcoming race if you haven’t worked out the issue yet by running a deep rear and spoked front, not ideal but better than running both wheels spoked.

You might also play with slightly less front tire pressure as an experiment to see if a softer front tire sufficiently dampens the vibrations, whether that’s a good race day option depends on how soft you have to run them to kill the wobbles. If you’ve got to go much below 90 psi it’s probably not a viable option but it might help you pinpoint the causes and potential solutions.

And of course a really objective look at bike fit and how your weight is distributed fore and aft would probably be in order but again you also see this on your road bike which presumably is more traditional in terms of weight distribution.

Really confusing one, lot’s of things to check out but since it’s always a system problem and that system includes the rider it’s really hard to offer simple answers. Definitely carefully check the wheels but it’s likely as not other things that set you up for the wobbles and the wheels are just the final straw that sets the oscillations into motion but still check them out and check out everything else related to weight distribution, headset adjustments, wheel tracking and alignment (e.g. front dropout alignment, wheel dish when installed, front vs. rear wheel tracking, horizontal dropout pins, etc.) and do some fast rolldown tests to try to see what combinations are the most reliable and wobble free.

This kind of stuff really sucks as it’s usually hard to pin down so good luck,
-Dave

17

Read this - from Slowman:

http://www.slowtwitch.com/Bike_Fit/Geometry_and_Handling/Bike_geometry_225.html
.

18

I found the issue occurs when I take my weight off the saddle, even partially. I had a habit of standing on my pedals during fast descents. I also have Jet 6 C2’s which were over inflated.

Between those two I have reduced wobble, I get it very occasionally but manage to keep it under control. Scared the shit out of me at Grand Coulee Half a couple of years ago. During the final descent I had a huge wobble on and veered across the road in front of a semi truck. Ended up on the opposite hard shoulder. It just went straight into tank slap mode, hardly gave me any warning. I managed to stay on but never go hard down hills now in training and still not 100% in races. Just not worth it.

19

I just bought a HED Jet6 front wheel from the classifieds, put it on for the first time this weekend and experienced this wobble at about 35-38 mph. I had no idea that this can happen and it scared the shit out of me. Luckily it was towards the bottom of a descent and I was able to slow down shortly after it started. It was so bad I had to stop on the side of the road afterwards because I could have sworn the wheel skewer was loose or the wheel was coming off.

There is a lot of helpful advice in this thread about what may be the cause of the wobbles, but what is the best method of handling them when they start? Figuratively speaking is it similar to hydroplaning in a car? …i.e. just hold the wheel (in this case the bars) straight, foot off the gas and small corrections? Every training ride/race I do has lots of climbs and descents, and I would think that having to hold back on the descents for fear of the wobbles would actually result in much slower split times than if I were to go back to my old aluminum clinchers where I can just freewheel the whole way down.

20

SPEED WOBBLE

When a customer brings his bike into his LBS and complains of speed wobble (death wobble, front-end shimmy) often the typical bike shop mechanic immediately starts farting around with the headset adjustment. There is no adjustment problem, nor are the wheel bearings loose, and in fact it is most likely that nothing is wrong at all.

Speed wobble is just an inherent “flaw” of bicycles. Bicycle frames are amazingly stiff and strong in a vertical plane, but horizontally they are not. They are like ladders, and when you stand on a ladder it is strong, but when you and a friend stand a distance apart, each of you grasping one end of the ladder, and you twist, the weakness of the ladder is apparent.

In that same way, when a bicycle is moving in a line straight ahead, and gyroscopic effects of the wheels weigh on a unit as elastic as a bicycle frame—with its fork and wheels—you might get shimmy.

Shimmy occurs at a certain speed, depending on the bike and the rider. I have heard it said that every bicycle is prone, depending on its geometry, materials, and rider position, a particular resonant frequency, at which the bicycle oscillates. All that occurs when a given speed is reached on a descent.

The shimmy will stop if the rider unloads the saddle, because the mass of the rider is the anchor about which the oscillation operates. It may also be helpful to place the inside of your leg against the top tube on a descent when you experience a shimmy.

Certain elements will make the bicycle more prone to oscillation. All other things equal, those elements that render the bike more elastic will aid in its ability to shimmy. Therefore, a longer head tube will make the bike more likely to shimmy. Lighter, thinner tubes will make the bike more prone to shimmy. I suspect that shimmy might be more prominent now than in days past because bikes are so light, and their components somewhat more susceptible to lateral flex.

Shimmy is more likely in cold conditions, or when a rider is nervous and grips hard on the bars, because the vibration of a shivering rider is roughly similar to that of a frame’s shimmy frequency, and this can help bring on the shimmy.

Therefore, while speed wobble is disconcerting, if you can adopt the habit of unweighting the saddle during a long, straight descent any shimmy problem should be largely abated.- Dan Empfield, here quoted.

I’ve lowered my aerobars, thus shortening the effective head tube height. Seems to help a bit. I may go lower at MT because I’ll be spending quite a bit of time climbing anyway. At least I hope I’m climbing and not stopped!

-Robert

21

how many spacers/stem setup on that tt bike?

everything tightened down well on the front end?