almost hospitalized, bicycle speed wobbles at 48 MPH

[Joe Bob]

Old frames like that simply aren't as good as new tech. If you are gonna do the bombardier route, get the proper equipment.

Or at least upgrade the head tube bearing.

I've exceeded 50 for brief periods on my CF/Ti bike with a Chris King threadless set up during an Angeles Crest Hwy downhill run.....of course EVERYTHING was checked out prior to doing the descent. Tires were at 130psi.

My camera got some great pics when I passed the Sunday drivers.....wasn't gonna look at them as I wasn't interested in turning into a pepperoni freaking pizza.

[Porsche-O-Phile]

Good info here:

http://en.wikipedia.org/wiki/Speed_wobble

In motorcycle parlance you had a tank slapper. Congrats!

[berettafan]

We don't have hills here so the fastest you go is up to your legs and a tailwind. Fastest I have seen yet is 28.8mph. To be honest it was scary. Every pebble had possible wipeout written all over it! That's twice my typical pace and I'm not anxious to see it again.

You guys doing 30+ on downhills have some steel ones, that is for sure!

[T77911S]

are you riding a time trial bike? frame geometry is what i was thinking. take the aero bar off. aero bar could also have something to do with it. aero bars are for time trials, never a fan of the guys that rode them in pack rides, especially in a pace line. dangerous. my thuoght was, learn to go faster without the aero bar, then when i did a time trial, i was that much better off. kinda like riding cheap, heavy wheels for training, light wheels for racing.

i have hit 55 on my trek OCLV, nevre had any problems.

[Kraftwerk]

I think there is great lassitude between a quality hand-built frame and factory production frame. The high quality tubed steel frames are much stiffer, but you are right, my wheels could have played a
part.

[herr_oberst]

Originally Posted by Joe Bob

.... Tires were at 130psi.

Whew! Bonecrusher wheels! I keep my tire pressure at about 100 these days, I don't see any advantage to rock hard tires, course I have never gone 50mph on my bike ever.

[Joe Bob]

I also run 100 on normal rides......high speed high pressure.

[LJ851]

Shoot, i've been 42+ mph downhill on my '80's bmx bike many times. Never had a problem. Sturmey Archer 3 speed hub laced in the rear wheel.

[scottmandue]

Glad you are OK...



48mph on a bicycle you must have humongous nads!

No way I would go over 30 with nothing between my fat white a$$ and the pavement but a wee bit of fabric.

[Porsche-O-Phile]

35 on a bicycle is fun, 45 is heart-pounding exhilarating!

[jyl]

Could be imbalance in a rotating part (wheels), looseness in a bearing (headset, hubs), too thin tubing/too much flex in frame or fork (unlikely unless frame is quite large - like >60 cm - or you are quite heavy - like 200 lb+ - or there is a crack or other damage to frame or if tubing is something exotic/super light. If you have aero bolt ons, they might be acting as a pendulum.

I'd have bike tuned up by a good mechanic, special attention to truing wheels, spoke tension, and adjusting bearings, maybe new tires, and check it for damage. Remove the aero bars. Try the hill again - I'd be a dork and wear my motorcycle stuff, have someone drive me to the top of the hill.

There isn't anything intrinsic about an older bike that should make it unable to descend at high speed. In the 1980s, you bet racers were descending at 60 mph on the bikes of the day.

[billybek]

When I had much younger legs, I passed an older lady driving in a 50 mph zone while I was on my road bike. My old Cateye indicated 83 kph but I suspect it was somewhat slower than that.
It was just out side Edgewater BC on Highway 95. Slight downhill and a stiff tailwind.
I scared the crap out of her, suddenly appearing in her peripheral vision on the inside. She almost ran me off the road, which in turn scared the crap out of me.
I guess we were even on that day and no one got hurt!

[einreb]

Originally Posted by motion

When they start, I just relax my grip on the bars and start moving my butt backwards, and increase pressure on the footpegs, by weighting them with my calf muscles. That usually calms things down. The idea is that I am moving the movement of the bike away from the ends, and towards the middle, by use of force. Same thing might work for bicycles?

The instinct is to tighten the grip... the same 'solution' Motion uses applies to the bike, but that's really tough to get your brain to tell your hands that when things are getting ugly.

The frame is not the problem.

[dave 911]

WOW! On my way to my favorite mountain biking trail in San Diego, there's a 1 mile + downhill road that I try to get my speed up as fast as possible because it's fun. After reading this, I don't think it will be fun anymore and I don't think I'm going to push it...

[mjohnson]

Never experienced it myself (thank god) but I understand that it's a resonance thing. Change the "system" to change/remove the resonance. Makes sense that on a bike (150-200# total package) you can press your leg against the top tube but on a motorcycle (600# package) you have to move your 150-200# of meat around.

Road biking is simultaneously boring (ugh, more pavement) and terrifying (scary drivers) for me. Have no heart for it - weak constitution, ADHD and all that... I can report that my Yeti ASR-5c on Schwalbe Fat Alberts at 32 psi is rock solid at 50 mph down a steep bit of asphalt 'round these parts.

[berettafan]

My GP4000S tires are 25mm and I run about 110/115 in them. I'm a fat ass and these are super comfy and faster than the 23mm tires that came with the bike.

[flipper35]

I don't think the steel frame is the problem. I have passed people on the highway on my old road bike. The speedometer indicated 65mph which may or may not have been accurate, but passing the cars I am sure we were in excess of 55mph. Coincidentally, the buddy I was riding with lost his father to a motorcycle accident that was the result of high speed wobble. I have never experienced it but I did see a friend whose front end bounced enough at speed that his chain came off. This was on a 20" bike with a Bendix coaster brake, no hand brakes. He swerved to miss a family walking their dog and went through the ditch and over the embankment and we didn't see him for a few minutes and we wondered if he was dead. When he did appear he had a few choice expletives at having no brakes.

[T77911S]

i always ran my tires very hi, 130+. i hate the feeling of a soft tire when standing up. body weight could effect the feel too i guess. i raced around 168lbs. a bit heavy. when i tried 90-100psi, the tires felt "swooshy". with the lower pressure i was more affraid of tires rolling and i felt i could take corners better with higher pressure. i won my first race because i held my corner speed up much higher than the guy i was chasing. i caught and came up beside him because of that. then it was a side by side sprint up a short steep hill. (crit race)

[Flieger]

After referring to Tire and Vehicle Dynamics by Hans B. Pacejka, I will make the following suggestions.

Lower tire pressures is better for wobble but worse for weaving instability
Stiffer frame- specifically torsionally stiffer
Heavier wheels (actually greater rotational inertia- it is a gyroscopic thing)
Shift weight rearward

[Jeff Higgins]

Wow - you are lucky to be alive. I know exactly how you feel - I had a similar experience years ago, albeit not on a bicycle. My own harrowing experience came at the wheel of my old '73 2.4 S Targa. I was checking top speed one day, and as soon as we hit 165 mph, it shuddered so hard it damn near ripped the wheel out of my hands. At first I thought it must have been because I had the Targa top off, but I realize now it was probably because it had loose suspension bushings or something.