HELP - Solve my dilemma - SPEED WOBBLE
-
No new posts
Moderators: k9car363, alicefoeller | Reply |
2008-10-16 6:23 PM |
Member 15 Bancroft, Ontario | Subject: HELP - Solve my dilemma - SPEED WOBBLE I've been having a bit of problem. OK a big problem. Speed wobble. No problem right? Get a new bike. Done that. Twice. Here's whats happening. I live in a rural area with lots of hills. When going downhill I get a wobble so bad that I've lost all confidence when riding. That is not a good thing because I've not been enjoying my rides at all. It happens at approx. 45 + km/hr when I can't peddle anymore. My hands are down in the horn so I can brake and the front handlebar starts shaking. I get into a wobble so bad that I can hardly hold on and I use every muscle in my arms just to keep control. This first happened three years ago when I was on an old Norco bike that I used to get into the sport of triathlon. I upgraded to an OPUS and went a whole year before it happended again. This year I bought a new Specialized Tarmac full carbon bike. AND....it happened three times in my last century ride. I'm sweating right now just thinking about it. Anyway, the only thing in common with my last bike is the Tri bar. I am 6'5" tall but thin at 190 lbs. I was fitted professionally for both my last bikes in a semi aggressive position. I am very comfortable racing and on long rides. EXCEPT of course when I going downhill. I've spoken with local bike shops and no one can come up with an answer for me. I don't want to quit triathlon because of this but because of where I live I have to deal with numerous hills. I can't go anywhere because of the hilly terrain. There simply are no flats. Any solution or suggestions would be most welcome. |
|
2008-10-16 7:11 PM in reply to: #1748399 |
Cycling Guru 15134 Fulton, MD | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE Same hill every time, different hills, road surfaces??? How close is the Tarmac in geometry to the other bikes? Length of stem? Different wheels or same? Lots of vague info so can't really make any recommendations. |
2008-10-16 7:41 PM in reply to: #1748399 |
Member 15 Bancroft, Ontario | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE Happens on many different hills. The Tarmac is a 61 cm frame. Road surface is generally tar and chip so there is some vibration there. I don't have measurements for how the bike it set up as it is at home and I am at work. Because of my height the seat is quite high and with my hands down in the bars that would put a lot of weight on the front wheel. The tires and rims are brand new. Thanks for listening. |
2008-10-16 7:53 PM in reply to: #1748399 |
Cycling Guru 15134 Fulton, MD | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE The reason I ask is because the Tarmac is designed as an aggressive road bike and in the 61 you have a 74 degree steering angle. A lot of the American designed frames have aggressive steering geometires because of the types of racing we do predominately here (criterium and shorter circuit racing). Those types of races emphasize handling and cornering ability over high speed stability. Some other manufacturers are also known for that and high speed wobble has been reported on them. But since it is happening to you on all different frames I am at a loss of where to start to diagnose something. Each bike probably had different wheels/tires. But that is a place I would start. Look for either the wheel to be out of true side to side AND up and down. Then check the tire to make sure it is fully seated on the bead all the way around. |
2008-10-16 7:56 PM in reply to: #1748399 |
Veteran 185 Wilmington, NC | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE try this...its basically going more aero but will put the weight back in your normal CG...obviously don't pedal...keep the pedals parallel to the ground (on a clock left pedal at 9 and the right at 3 o'clock)or reverse this...whatever feels more comfortable...slide back in the seat and put your knees close together...the sliding back should cause you to have to reach farther forward and put a slight upward bow in your back and pointing your head down...look up only enough to see where your going...yes this will make you go faster...but at the same time I think your putting way too much weight forward of the CG and thats whats causing your speed wobble... I had the same problem when I first started and thats what fixed me...I run down one hill on crappy roads at 45 mph without even a hint of wobble... be sure to have the correct tire pressure...and check for any loose spokes also...you can always just sit up and go slower down the hill... |
2008-10-16 11:09 PM in reply to: #1748399 |
Champion 10668 Tacoma, Washington | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE Have you checked that the headset is at the correct tension? Is the front quick release tight enough? When this happens, does clamping your knees onto the top tube alleviate the problem? When I first got my TiCycles Softride, I had a problem TTing on it -- the front wheel would oscillate violently any time I got it over 32mph. Same wheel I'd used on my Barkley Softride, so I knew it wasn't that. And the bars would be steady. It's just the front wheel would shimmy a good 3" or more at the leading edge. I traded out the Trek carbon fork for a Kestrel, and the problem went away, never to return. So it could be that you're riding a fork that's just too soft. Usually not a problem with the current market, but you never know. |
|
2008-10-16 11:20 PM in reply to: #1748399 |
Gilbert, Arizona | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE I had this same problem and someone from this site told me to slide back on my seat when going down hills and it solved my problem. The hill was rough pavement and it happened after I hit 30 mph. I was also told to clamp my knees to my top bar which almost got rid of the wobble but the seat position took care of it. |
2008-10-17 2:21 AM in reply to: #1748399 |
Master 1325 Lake Oswego, OR | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE I'm not an expert on cycling but given your size and the bike geometry, I go with the suggestion that you should slide back on your saddle. I think your center of gravity is too far forward. Reminds me of the first time I descended in the mountains trying to put my chest on the handlebars of my road bike years ago. I saw a pro do it and I thought what a great idea. Scared the sh*t out of me. There just wasn't enough weight on the rear tire to maintain stability. But that is just my personal experience. It may not have any relationship to the problem you are having. |
2008-10-17 9:21 AM in reply to: #1748399 |
Champion 6962 Atlanta, Ga | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE You are reaching a harmonic. Do as others have said to stabalize the bike (knees, slide back a bit). BUT...do not put a death grip on the bars. Relax and the wobble will go away. One of two ways, you can slow down or as speed increases past the harmonic, the bike will settle down. It's scary, but you wont' die. |
2008-10-17 10:05 AM in reply to: #1748399 |
Elite 5316 Alturas, California | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE Shrug, my bike goes 45 mph down a hill no wobble... |
2008-10-17 12:01 PM in reply to: #1748399 |
Pro 4828 The Land of Ice and Snow | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE I know from experience how terrifying the death wobble is!! It happened to me when I was just learning to descend properly ...at a speed of about 60kph. I second the advice of gripping the frame with your knees and trying to keep everything else as relaxed as possible.After a summer spent training in the hills I now fly down at 70kph and have bruises on my knees from gripping the frame. Hope you can get this sorted out...its fun to fly down the hills!! |
|
2008-10-17 12:21 PM in reply to: #1748399 |
Member 297 | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE |
2008-10-17 12:29 PM in reply to: #1748399 |
Elite 4344 | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE I have a bike that does the same thing. It really helps to lift your weight off the seat but grip the nose of the seat with your thighs. You can press your knees into the top tube a bit too. Another sure fire cure for wobble is to put on the brakes. Be gentle though, when you are nervous about the wobble you can clamp down too hard and go over the handlebars. I have heard a lot of theories about what causes wobble, forks, frames etc. I don't really know what is right. I think in my case that the wheels have a lot of lateral flex and that is a main component in the wobble dynamcs. Getting some stiffer wheels would move the harmonic frequency higher and out of my speed league. I haven't had the money to get some really stiff wheels to try the theory out. I have an idea for a really cool home science project to measure the resonant frequencies of various part of the bike. I will do it when I have some free time. It will make great geeky reading for all my super techno BT friends. It involves rubber mallets, microphones, a computer and Matlab. Way cool stuff you can do at home.
TW |
2008-10-17 12:45 PM in reply to: #1748570 |
Master 2638 | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE tiggere - 2008-10-16 7:56 PM try this...its basically going more aero but will put the weight back in your normal CG...obviously don't pedal...keep the pedals parallel to the ground (on a clock left pedal at 9 and the right at 3 o'clock)or reverse this...whatever feels more comfortable...slide back in the seat and put your knees close together...the sliding back should cause you to have to reach farther forward and put a slight upward bow in your back and pointing your head down...look up only enough to see where your going...yes this will make you go faster...but at the same time I think your putting way too much weight forward of the CG and thats whats causing your speed wobble... I had the same problem when I first started and thats what fixed me...I run down one hill on crappy roads at 45 mph without even a hint of wobble... be sure to have the correct tire pressure...and check for any loose spokes also...you can always just sit up and go slower down the hill... This was my suggestion also. When going downhill, I get up to speed and stop pedaling. Get in a good tuck and clamp my top tube with my knees. I don't know why, but the more aggresive stance (weight on the front tire) and knee clamp really seem to help. |
2008-10-17 1:42 PM in reply to: #1749361 |
Expert 2547 The Woodlands, TX | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE Marvarnett - 2008-10-17 9:21 AM You are reaching a harmonic. Do as others have said to stabalize the bike (knees, slide back a bit). BUT...do not put a death grip on the bars. Relax and the wobble will go away. One of two ways, you can slow down or as speed increases past the harmonic, the bike will settle down. It's scary, but you wont' die. Bingo. It's not the bike. Chances are you are putting too much weight on the front wheel and the weight is not even( more weight on your right hand than your left). Shift the weight to the back wheel and squeeze the frame with your knees. And no death grips allowed. Hopefully that will cure the sweaty hands!!! |
2008-10-17 5:13 PM in reply to: #1748399 |
Member 15 Bancroft, Ontario | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE Thanks for all the advise. I will try all of it. For those of you who have experienced the wobble....you know. For those of you who haven't. I pray that you never will. For me. Baby steps. THANKS ALL. |
|
2008-10-18 5:50 AM in reply to: #1749533 |
Extreme Veteran 694 | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE Baowolf - 2008-10-17 8:05 AM Shrug, my bike goes 45 mph down a hill no wobble... Same here, no wobble on my Trek 1500SLR going as fast as 45MPH downhill. However, I do think about the relative danger and potential bodily damage if something went wrong while going this fast.
|
2008-10-18 6:46 AM in reply to: #1750863 |
Expert 1603 Westchester, NY | Subject: RE: HELP - Solve my dilemma - SPEED WOBBLE I don't think anyone has asked this yet. You said you've gotten a new bike and it still happens. Are you using the same wheels? If so, what is on the front? |