shoota 

Hey dudes, I'm trying to figure out why the front end got the shakes at the end of a sprint yesterday. I've done this sprint lots of times and never experienced this before. Pan flat, smooth road, nothing in the environment that I can think of. The best I can describe it is that it felt 'wobbly' and I had to ease up slightly to let the bike stabilize again. Anyone have any ideas?

I doubt it matters but here's the data just in case. Again, I don't see anything out of the ordinary:

Fiery

It might be a good idea to check fork and frame around the head tube for cracks, and then make sure the headset is correctly preloaded. Doesn't have to be anything, but it's free to check and better safe than sorry.

PepeM

Is your fork, or any part of your bike, crabon?

silversx80

Could have been wind, precipitation, tire pressure, exhaustion, etc. Too little info to determine the cause. Do it again and try to get the results to repeat.

rpenmanparker 

I would think about your weight distribution. If you put your weight too far forward perhaps, that could have caused a speed wobble. Since we are talking about a harmonic resonance, it depends upon both speed and weight distribution as well as the harmonic frequency of the bike. Maybe you just reached the right speed and weight distribution combination for your bike to start to wobble, but had never been at that exact place before.

shoota 

This had crossed my mind but I've been this exhausted at the end of a sprint before so I don't know..

I hadn't thought about weight, that may have something to do with it I suppose.

Clipped_in

bmthom.gis

It's clearly time for a new bike.

Dan333SP

Were you seated or out of the saddle? Was your front skewer loose? Check your headset to be sure it has proper preload and isn't loose. Those are the obvious causes of a front end wobble. Of course, a new bike would take care of the issue too. Unless the new bike is crabon.

rpenmanparker 

They are the obvious causes, but they are not the causes. The more tightened up a front end is, the more likely it is to wobble.

Dan333SP

Depends on the type of wobbling he's talking about. Over-tight headset could lead to a speed wobble, an overly loose headset could lead to a clunky feeling with each pedal stroke which could be described as a wobble (same for loose skewer), hard to say without a better description.

Like grandpappy used to say, One man's wobble is another man's speed shimmy.

02Giant 

200+ heart rate, I think it was you not the bike.

Dan333SP

No kidding, I saw that too. OP is a jackrabbit.

shoota 

Out of saddle. Front skewer tight, and no reason to think the headset isn't correctly adjusted.

shoota 

It very well could have been me. Maybe a combination of being tired and having too much weight forward or just all over the place. Hard to say, because like I said this is a first for me.

Dan333SP

Did it feel like the front wheel was oscillating back and forth very quickly? Like a speed wobble on a descent? Are you in the drops pushing down on the opposite side of the pedal stroke with your arms?

shoota 

I just thought of something. Right when it happened I had someone come around me on my left. Could their presence have thrown off the aerodynamics? Seems unlikely but worth a thought I suppose.

rpenmanparker 

Well, a gust of wind can definitely do it. The situation you describe, I dunno. Maybe. You didn't inadvertently grab the front brake, did you? That could have done it for sure.

shoota 

It felt similar to a speed wobble. The best way I can describe it when you are going a decent pace and you do short turns with your handlebars while going in a straight line to feel how much flex there is in the front end. Does that makes sense?

Dan333SP

It does. No way to know what caused it for sure, but I do know when I've had people come around me in a sprint and then move over on me (races, so anything goes to a certain extent). I've gotten unsettled and my rythm has been thrown off. Not sure I've had a wobble like that but I can see how a quick and slight shift in the way you're moving your body on the bike could induce something of the sort, you may have unconsciously reacted to the sudden appearance of the other rider by torquing one of your handlebars more or shifting your weight forward/back.

shoota 

Yeah it's very possible. I'll be conscious of it in the future so if happens again I'll try remember the factors and see if I can pinpoint it. But you're right, it's probably something I did.

popeye

Were you in the drops? If so move your hands further forward. This happens to me at the track.

Homebrew01

But cadence was only 102. Up your cadence if you're sprinting.

shoota 

Roger that, thanks.

Yeah I was surprised at that too, it's usually a little higher.

Edit: That just reminded me. I remember trying to shift again but couldn't because I was already in the 52/11. At 100rpm I should have been fine there, so I guess I was just tired.

Looigi

It's already been mentioned, but low tire pressure could cause it.