Very wobbly front end question

[GuyContinental]

It’s possible that your headset is worn out or (less likely) was loosened in the wreck. Pick up the front of your bike (rear wheel on the ground) and see if you can replicate the movement that you describe by holding the bar/stem and fork and moving fore/aft and side to side. If it has any noticeable play you can try and tighten the headset nut but it’s probably worn out. Replacement isn’t a big deal but it takes some special tools to re-seat the bearing races on the fork and depending on the headtube, to seat bearings. Price for a replacement depends on the bike set-up but I’d figure $40-$50 plus $25 for an install.

[jabberwocky]

I would check:

The headset (grab the front brake and rock the bike forward and backward, while feeling where the fork enters the frame. Is there any play?)
The front wheel (flip the bike over and give it a spin; does it spin true and even?)
Alignment of bars to wheel (just stand over the top and look down; are the bars perpendicular to the wheel?)
Alignment of front wheel to frame (stand the bike up and eyeball it from the front; is the fork twisted, or the wheel angled to either side?)

[Tim Kelley]

Some reading for you:

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

http://www.rivbike.com/kb_results.asp?ID=80

http://www.rivbike.com/kb_results.asp?ID=80

If you have this problem (especially if you’re going downhill at speed), the best way to overcome it is to touch your knee/inner thigh to the top tube which dampens the shimmy. Grabbing the handlebars even tighter (which is the natural reaction) can sometimes make the shake even worse!

[Certifried]

@Tim Kelley 33400 wrote:

Grabbing the handlebars even tighter (which is the natural reaction) can sometimes make the shake even worse!

I think that’s why she was trying to ride hands-free…. that’s a whole lotta shakin’ you got goin’ on

[thecyclingeconomist]

@KLizotte 33384 wrote:

So I used to be able to ride down the length of Hain’s Pt hands-free without any issues. I hadn’t done it in a while and decided to try it again just for kicks. I was rather shocked to find that within just a few revolutions the whole front end of the bike (wheel, handlebars) starts wobbling/shaking badly out of control. I tried it a number of times at different speeds while making sure to keep my body as motion free as possible but it happened every time. It is as if the front end is working independently of the rest of the bike.

It is very disturbing.

A couple of months ago the bike was in a bad crash that did squish the handlebars a lot (they were pried back into shape by the LBS) but no other damage was detected (my body broke the bike’s fall). Could that be the reason for the strange wobble? I don’t notice anything different handling wise when I have my hands on the handlebar.

Any ideas what may be causing this? It does seem like something that should be fixed.

Thanks!

It is very possible that your wreck actually bent the fork (are you riding steel?). The rake (horizontal distance from the center of the steer tube to where the drop outs are) could have been changed, which will very likely cause a wobble when you take your hands off the bars. It wouldn’t even cause the headset to be loosened (which is my first suspect: see below) If the fork is bent, a good mechanic/frame-builder can look at it, and if your fork is steel, it can be reset in a fork jig VERY easily. (or with simple grunt and a vice, while using a fork alignment tool to make sure you aren’t screwing it up worse in the process.)

To check the headset: take your bike, hold down the front brake, and then push and pull the front end by the handlebar. If you can feel a wobble/clicking at the top near the stem, then the headset needs to be tightened. It is a very simple adjustment; but you need to ensure you don’t over-tighten. You don’t want to crush the bearings or put dimples in the race. You want to make sure the handlebar can turn freely. The headset should be tightened just to the point where there is no play (wobble), but not too tight; where the handlebar won’t turn freely. You may just need to service the headset: clean/re-grease it and have it tightened properly. If the headset is messed up, it is a cheap fix for most bikes (but can also be stupid expensive in high-end road: a top end Chris King is a hundred bucks). You’ll most likely need a bike-shop to replace it, as most people don’t have the tools to remove the cups from the frame or set new-ones in.

Wobbles can certainly be very disturbing. My Mtn. bike has a crazy wobble if I take my hands off the bars (speed wobble as referenced above). It has done it since new, and has to do with the geometry/suspension fork/amount of crap I have mounted to it. (Have you mounted anything on the front of the bike: rack, fenders etc?…that can do it too.)

God bless and Good luck. I hope you figure it out!

[KLizotte]

Thanks for all the replies. The articles about shimmy developing while going downhill are scary!

The bike is quite new with less than 1K miles on it. I strongly suspect something is out of whack due to the bad fall I took. I’m going to try eyeballing it per instructions above but will end up taking it back to FreshBikes for a better looksie and hopefully a fix. I don’t want to have to worry about the death wobble while going downhill.

[thecyclingeconomist]

@Tim Kelley 33400 wrote:

Grabbing the handlebars even tighter can sometimes make the shake even worse!

True, often the BEST solution is to actually power up… pedal harder and accelerate out of the wobble while slowly taking control of the bars without trying to man-handle it all.

[thecyclingeconomist]

@KLizotte 33420 wrote:

Thanks for all the replies. The articles about shimmy developing while going downhill are scary!

The bike is quite new with less than 1K miles on it. I strongly suspect something is out of whack due to the bad fall I took. I’m going to try eyeballing it per instructions above but will end up taking it back to FreshBikes for a better looksie and hopefully a fix. I don’t want to have to worry about the death wobble while going downhill.

What kinda bike is it anyway?

[thecyclingeconomist]

@jabberwocky 33399 wrote:

I would check:
Alignment of bars to wheel (just stand over the top and look down; are the bars perpendicular to the wheel?)
Alignment of front wheel to frame (stand the bike up and eyeball it from the front; is the fork twisted, or the wheel angled to either side?)

If you can see something is out of alignment, then that is almost assuredly part of the problem. However, a wobble can be caused by a bend that isn’t evident to our eyes at all. I highly recommend having someone that has tools that can measure alignment issues take a look at things.

Some of the big chain stores are NOT the place you want to go. I am new to the area, but going to a smaller shop that deals with vintage steel or does their own frame building would be better depending upon your bike.

[KLizotte]

@thecyclingeconomist 33423 wrote:

What kinda bike is it anyway?

The bike is not steel; it’s some sort of aluminum composite.

This is the bike: http://www.cannondale.com/2013/bikes/women-s/performance-road/synapse-alloy/synapse-women-s-5-105-compact-crankset

I’m so annoyed with myself since it is essentially a brand new bike. The crash was bad enough to cause a broken thumb so it’s possible something got slightly moved out of position. It’s been in the shop a couple of times for other reasons and no one spotted anything pertaining to this problem so it’s not real obvious.

Oh well, I need to learn more about bike mechanics anyway so this is a good learning opportunity.

[jabberwocky]

@thecyclingeconomist 33424 wrote:

If you can see something is out of alignment, then that is almost assuredly part of the problem. However, a wobble can be caused by a bend that isn’t evident to our eyes at all. I highly recommend having someone that has tools that can measure alignment issues take a look at things.

Agreed, totally. I was just listing some of the more obvious, easy checks. Running through my list should take a few minutes; if everything checks out I would definitely have a shop with the proper tools check the alignment more precisely. A bent frame/fork is an issue in more ways than just speed wobbles.

[thecyclingeconomist]

@KLizotte 33425 wrote:

The bike is not steel; it’s some sort of aluminum composite.

This is the bike: http://www.cannondale.com/2012/bikes/womens/performance-road/synapse-womens/2012-synapse-womens-alloy-5-105-21423

I’m so annoyed with myself since it is essentially a brand new bike. The crash was bad enough to cause a broken thumb so it’s possible something got slightly moved out of position. It’s been in the shop a couple of times for other reasons and no one spotted anything pertaining to this problem so it’s not real obvious.

Oh well, I need to learn more about bike mechanics anyway so this is a good learning opportunity.

The fork on that bike carbon (possibly full-carbon). Frame all aluminum (6061)…
That bike should NOT be wobbling at any speed; it’s a very nice mid-level road bike. You should be able to sit up and take your hands off the bars at 10, 20 or 40mph and have it just glide along smooth. You need to have it looked at very closely and explain clearly to the shop what’s going on.

[KLizotte]

@thecyclingeconomist 33428 wrote:

The fork on that bike carbon (possibly full-carbon). Frame all aluminum (6061)…
That bike should NOT be wobbling at any speed; it’s a very nice mid-level road bike. You should be able to sit up and take your hands off the bars at 10, 20 or 40mph and have it just glide along smooth. You need to have it looked at very closely and explain clearly to the shop what’s going on.

Oiy. Glad to hear that I’m not being hysterical that this is a real issue. I just hope it’s not a terminal diagnosis!

[GuyContinental]

@thecyclingeconomist 33428 wrote:

The fork on that bike carbon (possibly full-carbon). Frame all aluminum (6061)…
That bike should NOT be wobbling at any speed; it’s a very nice mid-level road bike. You should be able to sit up and take your hands off the bars at 10, 20 or 40mph and have it just glide along smooth. You need to have it looked at very closely and explain clearly to the shop what’s going on.

What he said. The Cannondales (like yours) don’t use a traditional headset, instead the bearing cups are built right into the headtube and tightened using a bolt to an expansion nut in the fork. Your stem clamps to the fork but the nut and bolt actually hold the whole assembly together. If you’ve messed with your stem and tightened the stem bolts before the headset bolt you can artificially build in some slack where the stem contacts the headtube, particularly if you (or someone else) messed with it on a bench. (After checking for play per earlier posts) With the bike on the ground release the two stem bolts, release the headset bolt. Now, with the stem loose, torque the headset bolt and then the stem bolts. Check play again. If still there, it’s time to go see TBSFKAC (FreshBikes)

[off2ride]

Hi K,

Check your fork rake. Perhaps it got bent from your crash. A loose headset will rattle plus play will be present when you brake the front caliper while pushing the bike slightly forward. Check your tires/wheel/spokes for anything that looks abnormal. Good luck. Lemme know if you need more help on your Cdale.

[Author]

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