login
Help! New DEATH WOBBLE on downhills!!!
-
No new posts
 2009-06-22 1:04 PM |
Extreme Veteran  421  Central Connecticut |  Subject: Help! New DEATH WOBBLE on downhills!!!Hi all. I switched over to 66mm deep carbon wheels this year and I love them (almost always). If I'm in the aero position I never have a problem with stability, but we have a few hills here in New England that you can't ride in aero. At speeds over 35 or 40 my bike has been giving me the DEATH WOBBLE if I'm holding onto the base bar. What the heck!?? I was so close to falling yesterday. It goes away after slowing down to around 15mph. The problem does not happen if I'm in the aero tuck on other hills. I hit 49.9mph on a hill that same day (less steep, no stop signs) with no wobble at all. The wheel looks true. The tire looked a smidge off but almost insignificant. Could that be it? Just a minor adjustment of the tire? I was wondering if I should get a shorter stem and compensate (somewhat) by pulling my saddle back the same distance. PS: The old 35mm deep wheels never gave me a problem, same tires. Any thoughts? Thanks in advance! Edited by enduropro 2009-06-22 1:05 PM |
| 2009-06-22 1:09 PM in reply to: #2234347 |
Master 2218 Columbus, OhioCoaching member | Subject: RE: Help! New DEATH WOBBLE on downhills!!! If you are in aero, more of your weight is on the front wheel, right? So having more weight on the front wheel prevents the wobble. Could that mean that something is loose? Have you checked the quick release on your front tire? Sometimes they get loose for no good reason.... It's probably not that simple. I'm no bike mechanic, though, so this is all I could come up with. |
| 2009-06-22 1:32 PM in reply to: #2234347 |
| 8 | Subject: RE: Help! New DEATH WOBBLE on downhills!!! Google for front wheel shimmy. It's a "known issue" - and it has to do with weight distribution, your bike, etc. I've had it happen a few times and it's terrifying - but there's really nothing you can do do other than change bike parts. http://www.sheldonbrown.com/brandt/shimmy.html Read the article. |
| 2009-06-22 1:39 PM in reply to: #2234451 |
Cycling Guru 15134  Fulton, MD | Subject: RE: Help! New DEATH WOBBLE on downhills!!! It has to do with conditions and a bunch of other factors (frame design, parts, wheels, etc). In my race yesterday there was really strong constant winds and even stronger gusts and I was on my bike with my 999's. Same thing happened to me on the first long downhill where I was probably approaching 40. As soon as I relaxed my grip on the bars it lessened to the point where I wasn't crapping my tri shorts anymore. I'd never had that before on the bike, but I've also never descended with an 80+ mm front in wet conditions and 20+ mph cross winds for long periods. Needless to say I rode pretty conservatively the rest of the ride on the downhills. |
| 2009-06-22 2:44 PM in reply to: #2234347 |
Expert 2547 The Woodlands, TX | Subject: RE: Help! New DEATH WOBBLE on downhills!!! Someone with more knowledge on this needs to chime in, but in my experience it's been partially do to weight distribution on the bars. If you are grabbing the horns and you favor one arm over the other (we all do) and gripping the bars like it's your last down hill, then the wobble can start. Loosen your grip and squeeze your knees against the top tube of your bike. This usually does the trick. Of course it could also be a crosswind, uneven pavement, stem not lined up with the wheel, etc. Play with it a little at slower speeds, I bet you'll figure a solution of some sort. |
| 2009-06-22 3:19 PM in reply to: #2234347 |
Champion 7821 Brooklyn, NY | Subject: RE: Help! New DEATH WOBBLE on downhills!!! A guy in my tri club--a bike mechanic-- posted this response to another member's question about shimmies. It's long, but it's the best explanation I've ever heard about why it happens and what to do about it: "Speed wobbles are common as speeds pass 35mph on a bike. A short wheelbase, steep headset, skinny tires and an aggressive riding position are a perfect formula for the wobbles. They usually begin after some outside force upsets the ride such as hitting a bump, a blast of wind from the side, or tapping the front brakes at speed. Once the rhythm of the wobble sets in the only real cure is to get into a stable riding position (preferable sitting up in the wind) and slow down (no front brakes!). On motorcycles you can punch the throttle to break the rhythm, but you don't have that kind of power on a bike. A bike is an articulated vehicle and is upset when the rear overrides the front. So slow the rear first and the wobble will diminish. There is no reason a wobble should cause you to crash unless you are headed for a sharp corner. The wobble will effect the counter-steering nature of the bike and it will be hard to turn. Believe me I know. I hit a guardrail at 65 mph in a GPV race because of big wobble and a sharp corner. If you are going relatively straight you should be able to just ride it out. Now you can appreciate the decent skills of the lads in the Tour de France, no? To decrease the likelihood make sure: Your headset is properly adjusted The front brake is toed in. The tires are mounted on the rims evenly, without any hops. Your wheels are true, and mounted straight on the bike. If you are running a computer off your front wheel make sure the magnet is opposite the valve to offset the weight imbalance." |
| 2009-06-23 6:35 AM in reply to: #2234347 |
Extreme Veteran 421 Central Connecticut | Subject: RE: Help! New DEATH WOBBLE on downhills!!! Thanks everyone! |
|
|
|
View profile
Add to friends
Go to training log
Go to race log
Send a message
View album
CONNECT WITH FACEBOOK