I just bought a new Trek Emonda SL (about a month old) and everything has been going well. I've done about 250km on it just doing short loops around my house. However, on the weekend I had some time to venture a bit further away where there are larger hills. On this ride I noticed that once I reached approximately 60 km/h on the descents, the bike would vibrate as if I had ridden over the ripple strip on the side of the highway (that makes the tires really noise to wake you up). At first I thought I had ridden over a bad patch of road, but by the fifth time it happened I was certain it was not related to the road surface. The funny thing is, the vibration would only last for about one second at a time. However, it did happen about 5 times on two different descents.

I thought maybe it was related to be half holding the brakes, but I'm almost certain I wasn't braking at some of the occurrences. It may have occurred more when leaning in on turns, but I can't be certain because it hasn't happened enough and I'm a bit scared to go and try again at 60km/h down hill.

Does anyone have any ideas on what it could be?

I checked the quick releases on the wheels were secure, which they were.
I visually checked the wheels were aligned as they pass through the brake pads, which they were.
I have slick tyres on, so it shouldn't be the thread on the tyres.
I've ridden down this road on my old bike which did not vibrate.
On my normal rides (speeds up to about 50km/h) it hasn't happened.

Any help is appreciated!

Have you noticed if the vibration goes away or lessons about 5 to 10 mph above and below the speed of the vibration? If so then it's a harmonic vibration which means you have a wheel out of balance which could be a rim issue or a tire issue. Did you locate your computer magnet opposite side of the rim of the valve stem? Spin the tires while off the ground and look to see if the tire has any up and down motion, or side to side motion, even a minor movement will be exaggerated when riding at speed.

Check to make sure the headset is properly adjusted and tightened. Make sure the hubs are adjusted properly and the quick releases are tightened.

Make sure the fork doesn't have any cracks, first visual check it then strike with coin all over the fork to see if the tone changes from one blade to the other.

I'm out of time, have to get to work, others may chime in with ideas that I don't have time to list.

Shimmy, or Speed Wobble

If the bike is from an LBS, take it back for a mechanic check. However the vast majority of side to side shimmy in the front wheel
are due to a loose headset. You can check this at rest by standing by the bike, locking the front brake and pushing the bike forward
and back a bit. A loose headset will be obvious. Fixing it takes only a few minutes with allen wrenches.
eg Threadless Headset Service | Park Tool

This is the most likely cause on a new bike, with the wheel hub problems less likely. A loose wheel hub is detected by grasping the tire in front
of the brakes and pushing side to side. There should be no play at all.

An off balance wheel will produce an up-down hop at speed. I put some reflectors on my spokes a few years ago and the hop was really noticeable
at 20 mph or so. Rims tend to be heavy at the rim joint which is opposite the tire valve. Hop is surprising and annoying but side to side shimmy
is alarming and very hazardous and needs to be fixed.

We don't yet know if the OP's problem is a shimmy or some other event not well described. So before we all assume we should get more/better description from the OP as to what he's talking about.


The recent Phily Bike Expo had a seminar consisting of 6 frame builders talking about what makes a good rando bike. The topic of shimmy came up but too late in the session to fully delve into. What was said is much of what I've read/heard before. If we (the collective bike industry) knew what shimmy really was we would not have any bikes that did it as we would design said bikes to not allow shimmy to happen. To not do so but still understand it is opening one up to a liability suit and isn't the reputation any company or builder can survive.


Now we should go back to the OP and get his follow up. Andy.

I've found that front wheel shimmy is brought on more easily by an overtightened headset than by a loose one. A trip to the mechanic is not a bad idea.

That said, some bikes will shimmy at a certain speed no matter what. I doubt that is the case here, but it happens.

Depends on the shimmy, if you can clamp the top tube with your leg and the shimmy stops then it's a poorly designed frame! This can be due to several reasons, either the top tube is underbuilt, or the frame is out of alignment and the front wheel is not tracking in line with the rear, or trail is too large.

However the easiest and cheapest thing to try is to move your body weight and change your grip. The next time that wobble happens, and you should try to get the wobble to happen repeatedly till you find out what stops it, is to slide forward on your seat with your elbows bent and loosen your grip on the bar, if that does nothing then try sliding back on your seat with elbows bent and a loose grip. If one of those positions removes the wobble then you may need a longer or shorter stem depending on which position corrected the situation. Personally if weight distribution is the issue than more than likely your weight is too far rearward which is unweighting the front wheel. If you test your bike and move and lean forward when the shimmy happens and it goes away then you need either or a longer stem with a shorter height. You might be able to reduce the height of the stem so that it's about an inch lower than the saddle and that may do the trick without having to get a longer reach stem by removing a spacer or two.

However all of what any of is saying is theoretical, there are some that believe that loose, or tight headsets, loose hubs etc have nothing to do with shimmy. The only time I've ever had a shimmy was when I put my computer magnet next to the valve stem, but this was a harmonic shimmy that came on at a certain speed and went away as I went faster, so I relocated the magnet and repeated the speeds where the shimmy was and no more shimmy. Anyway to read another theory on shimmy see this: Shimmy, or Speed Wobble

I read that article myself and not sure if I agree with all of it. I've ridden steel bikes mostly for the last 40 years including racing and including speeds in excess of 60 mph and never had shimmy other then the one with the magnet. Maybe if I rode a very large frame then maybe? I do know that I test rode several Peugeot PX10's over a several year period and they flexed the most of any bike I've ever tested, those I could believe when Sheldon Brown said they shimmy, but why did these shimmy, that's the question, was due to inferior metallurgy? or not stiff enough top tube? maybe the stays were underbuilt? I don't know since I never got one up to high enough speed to experience it, but I know they flexed a great deal because when I hammered on them I could get the BB to flex enough so that both sides of the chain would rub on both sides of the front derailleur, and that's why I never bought any French bike.

Lately it has come out that some CF forks that are not made significantly stiff enough, or may be defective could be causing the problems. After reading about that possibility I'm glad I got the stiffer and stronger Enve 2.0 instead of the 1.0.

If the bike is new and all the home testing fails then you need to take the bike back to the shop and have them figure it out because if you have a faulty fork or frame then obviously you need a replacement, so you need to get this figured out before the warranty runs out.

Put 20k miles or so on a PX10 back in the '70s and never had a shimmy. Put together a Lightspeed Vortex in 2001 and had a shimmy at
35-40mph on Cherohala century. Stopped and tightened the headset, shimmy went away, never to return. New Trek Emonda is not likely
to be an intrinsically shimmy prone bike. Shimmy in unloaded bike is one thing, put bags on the front and back as in randoing, and
shimmy can occur due to frame/pack interactions, which is quite another. Doubt the OP is riding a loaded bike, but until he responds....

Given that it only happened for less than a second at a time, it is quite possible it only occurs at a particular speed. Though it is hard to say the exact speed because I just basing my speed estimate looking at Strava after the ride.

When I spin the wheels and look for any sideways or up/down motion I don't see any. However, this is just by eye so I could be wrong.

I don't have a computer magnet on the wheels.

Fork doesn't seem cracked or damaged.

The headset is nice and tight, I can't see/feel any movement when I lock the front brake and rock back and forward. Quick releases are nice and snug.

Try this simple thing, swap the tires from front to rear then try to duplicate the speed where the event occurred and see if it happens again.

The vibration was not like a really wobbly type feeling. I didn't feel like I would crash immediately. It was more like a high frequency vibration with really small amplitude if that makes sense. It really was as if I was driving on the ripple strip on the highway - unpleasant but I didn't feel like my body weight was shifting left/right because of it. It felt like the whole bike was vibrating. I couldn't tell if it was from the front or back or both.

Bike doesn't have reflectors on the spokes nor was it loaded up (just two water bottles and a small saddle bag).

The wheel doesn't have any side to side play when I hold the wheel near the brake and try to move it.


I'll definitely take it back to where I bought it. Just wanted to get some ideas first as it is a bit of a hassle to get back to the shop.

I could try and learn more about when it occurs on my next ride, but not sure if it will happen on the smaller hills near my place. Also, if it is something dangerous I don't really want to be testing it at 60km/hr.

Thanks for the ideas and posts so far everyone!

The vibration was not like a really wobbly type feeling. I didn't feel like I would crash immediately. It was more like a high frequency vibration with really small amplitude if that makes sense. It really was as if I was driving on the ripple strip on the highway - unpleasant but I didn't feel like my body weight was shifting left/right because of it. It felt like the whole bike was vibrating. I couldn't tell if it was from the front or back or both.

Bike doesn't have reflectors on the spokes nor was it loaded up (just two water bottles and a small saddle bag).

The wheel doesn't have any side to side play when I hold the wheel near the brake and try to move it.


I'll definitely take it back to where I bought it. Just wanted to get some ideas first as it is a bit of a hassle to get back to the shop.

I could try and learn more about when it occurs on my next ride, but not sure if it will happen on the smaller hills near my place. Also, if it is something dangerous I don't really want to be testing it at 60km/hr.

Thanks for the ideas and posts so far everyone!

Worth a try! I'll try and replicate it again on some hills closer to home first then swap them over. I might try the front wheel from my old bike if I can consistently replicate it too.

Thanks!

If you can't get the front end to vibrate when you do the wheel swap then you have isolate the issue, is it the tire or the rim, thus if you put the front tire on the rear and the rear on the front that will isolate it. If after you do the rim swap and the vibration is still there try moving your body weight more towards the front and see what happens. If after moving your body weight, and the rim, and the tire swap then there is either something wrong with the frame or more than likely the fork. According to what I've read on Sheldon Browns site, the headset won't cause that? Not sure if I agree but I do recall once while riding my commuter bike the headset became loose and I could hear it knocking, I first checked the quick release and it was tight, so I applied the front brake and rocked it back and forth and that's when I discovered the headset was loose, the bike never vibrated the whole time, so maybe Sheldon is correct, but you checked your headset so it almost would have to be the fork primarily and frame secondary by off chance if the vibration continues no matter what you do to try to correct it.

Swapping out a wheel/tire and having the problem go away is not the same as saying the problem is the old wheel. This is a mistake that many make. Thinking there's something "unique" to the old wheel that was bad/wrong. As some understand (Jim Papadpooulos comes to mind) shimmy it's a harmonic issue. So the old wheel on another bike might not ever show the problem and another wheel on the bike in question might not also show the problem. The wheel isn't at fault, the system is.


This is why I find these threads so frustrating. Knowing the amount I do (which is that no one can predict or design reliably the chance of shimmy out of the riding experience since those who have actual academic credentials and international peer review can't even explain it fully) has me see through the simple claims of cause. The interesting thing is that any of the suggestions might or might not change the system enough to change the on set of shimmy to a situation we riders won't ever experience.


But do understand that what might change the harmonic enough for one rider (and the rider is a major factor, major) won't transfer over to another with any degree of certainty.


Case in point is that I have ridden hundreds of miles with a low speed shimmy om some loaded touring bikes that used roller bearing headsets (Stronglite A9s). Yet this "solution" is one recommended by some pretty well recognized people. On a couple of the bikes I removed said roller bearing headsets and installed high end balled ones with no difference in the experience of shimmy.


I won't make the false claim that the type of headset is a factor that isn't at play. Yet some will do the opposite.


So what have I done to change my touring bike's potential to shimmy? Stiffer frame, fork steerer and smaller/stiffer wheels. I changed a lot of the basic aspects of the system. Not just one. So far version 4 shows no shimmy. Check out this thread in the frame building forum. https://www.bikeforums.net/framebuild...ng-frames.html Andy.