# Braking, then the bike begins to wobble almost uncontrollable....Help



## spongebob (Mar 29, 2005)

I've been riding this bike as it is for 2 years. So now this has happened to me 3 times. Close to crashing. I'm going 25mph to 30. I put on the brakes. Then it feels like a flat tire, then the bike starts to wobble fast. I don't know if it starts from the front or rear. Then the front wheels goes back and forth, back and forth, uncontrolably. The bike slows and then it stops. Its a real panic situation. The wheels are generally true, and I have Dura Ace 7800 brakes, and Bonti RXL wheels, circa 2008, on a Tete de Course. I'm big @ 235lbs. XXX Bonti Fork. KCNC Ti QRs. 4 Axis Richey Stem. 
Its got me spooked. Any ideas? 
Thanks
SBob


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## heffergm (Jul 9, 2010)

You've checked the headset? If it's loose things get ugly.


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## ETWN Stu (Feb 15, 2007)

heffergm said:


> You've checked the headset? If it's loose things get ugly.


real ugly and fast! 

If you got some shunting or vibration up front than that could be it. If you cant fix it give it to some who can so you remain safe.


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## Erion929 (Jun 10, 2010)

Yeah, sounds like some kind of "tankslapper" (sorry, motorcycle term) in the front end....not safe, get it checked out.

**


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## spongebob (Mar 29, 2005)

Ok, let me check the Cane Creek S6 on there........Just so happens that I just bought a CKing which will be here next week.

Well, it feels fine, and its tight. Would I have to take it apart and inspect it, or would I feel it?

Could the Richey 4 axis WCS stem be too light for a big guy of 230 lbs? I have a Bonti XXX drop bar on the bike.....

thanks, and keep the ideas coming.


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## ETWN Stu (Feb 15, 2007)

Make sure you check the expander cap as well as the stem bolts.


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## ericm979 (Jun 26, 2005)

Check your bike, but chances are that it's not the bike, it's you. You need to be more relaxed, especially in the arms and upper body. Make sure your elbows are bent.


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## spongebob (Mar 29, 2005)

*nervous......*

that could be it too, being that I really don't like going fast, downhill, on these lousy pot holed roads here in NJ. I do tighten up.


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## AZ.MTNS (Jun 29, 2009)

When it wobbles squeeze the top tube between your knees .


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## frdfandc (Nov 27, 2007)

If you don't like going fast down hill - SLOW DOWN. That should be the very first thing you should do until you get confident, then slowly increase your speed when descending.


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## Kerry Irons (Feb 25, 2002)

*Clean rims?*



spongebob said:


> I've been riding this bike as it is for 2 years. So now this has happened to me 3 times. Close to crashing. I'm going 25mph to 30. I put on the brakes. Then it feels like a flat tire, then the bike starts to wobble fast. I don't know if it starts from the front or rear. Then the front wheels goes back and forth, back and forth, uncontrolably. The bike slows and then it stops. Its a real panic situation. The wheels are generally true, and I have Dura Ace 7800 brakes, and Bonti RXL wheels, circa 2008, on a Tete de Course. I'm big @ 235lbs. XXX Bonti Fork. KCNC Ti QRs. 4 Axis Richey Stem.
> Its got me spooked. Any ideas?


Along with all the other good advice given here, you might want to take a look at your brake pads and the brake tracks on your wheels. Give the pads a good going over with some sandpaper and an ice pick to remove any debris, and do the rims with a ScotchBrite pad to make sure you have a good braking surface.


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## testpilot (Aug 20, 2010)

A number of items can cause or induce "speed wobble". Speed wobble is a harmonic response to road and braking inputs to the fork and frame. Some items to check have already been mentioned but I'll make a comprehensive list. 

*Headset*
Loose - braking force causes the road end of the fork to shift rearward to the limit. Then the fork springs forward and the cycle repeats.
Tight - can cause you to slightly oversteer
Worn - because the ball bearings in the headset generally operate in a very small range, over time they can wear small indentations in the bearing races, especially on the lower bearing. This can cause loose and tight spots in the headset. See tight and loose above.
*Fork & Frame*
Bent/damaged fork - this can reduce fork rake and effective caster angle. The wheel can take on the characteristics of a wobbly shopping cart wheel.
Fork or frame cracks - the frame or fork becomes flexible and reacts to braking, steering and forward forces
Cracked steerer tube - the only way to check this is to pull it out of the frame, clean it and inspect under a bright light. Pay close attention to the bottom of the tube near the fork crown.
*Wheels*
Contaminated braking surfaces on the wheel - this can cause the thumping you mentioned that seems to preclude wobble. A grease spot or buildup of brake material in one spot can cause uneven braking forces to transmit into the steering
Bent, dented or out of true wheel - similar to above
*Brake caliper*
Mounting to the fork is loose or brake caliper pivots are loose.

*What to do if speed wobble happens*
Force yourself to relax. Everything inside you says "Grab tight and hold on!" That's probably the worse thing you can do. Stiff arms and shoulders act like springs and they will react and overreact to the frequency of the wobble, making it worse. RELAX!
Release the front brake. This allows the frame and fork to stretch out and relax a bit.
Clamp the top tube with your knees. This changes the harmonic frequency of the frame and gives the frequency waves a new and shorter path where they can be absorbed by your legs.
Pray until it stops.
Pray again after it stops.


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## gr8blues (Nov 20, 2009)

If you can't find anything wrong and a more relaxed stance does not help consider a different bike. With a lighter person this high speed wobble might not ever happen. I had a bike that did this a few times, got rid of it and none of my bikes since ever had the problem. You may be incompatible.


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## dgasper (Sep 1, 2007)

I'm going to suggest a lower center of gravity. Keep pedaling or at least keep the weight on the pedals and not just on the saddle. Riding in the drops while riding fast downhill might also do the trick. 

My old bike used to do this, and yes, it is very scary.


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## ericm979 (Jun 26, 2005)

dgasper said:


> I'm going to suggest a lower center of gravity. Keep pedaling or at least keep the weight on the pedals and not just on the saddle.



That works to prevent wobbles, but it doesn't lower the center of gravity (and lowering the CG wouldn't do anything about wobbles anyhow). Getting your weight off the saddle decouples you from the bike. Speed wobbles are caused by the feedback loop from the bike to the rider. The bars wiggle a bit and you try to correct, but you're out of phase so you make the wobble worse, not better.

If you can 'hover' your butt just off the saddle (so the nose is between your thighs for control) and bend your elbows, you'll be incredibly stable. I can wiggle the bars on purpose when I am positioned like that and it will stop immediately. Not having your butt firmly planted on the saddle also helps stability on bumps, since you're not bounced around. I don't sit often on descents, unless I know the pavement's smooth (or if I am cornering hard).


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## Mr. Versatile (Nov 24, 2005)

Almost all bikes can do this occasionally. Like AZ.MTNS said, press a knee, or squeeze the top tube with both knees. IME that stops it immediately. One caveat - I just bought a new bike for the first time in 14 years. It's a compact frame. I went into a wobble on a fast downhill with a tight right hander at the bottom. When I tried to clamp the top tube I couldn't find it because it's much lower on the compact frame. Just sayin'.


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## normanzo (Jun 23, 2013)

*Braking-induced wobble - I experienced this too and resolved it.*



spongebob said:


> I've been riding this bike as it is for 2 years. So now this has happened to me 3 times. Close to crashing. I'm going 25mph to 30. I put on the brakes. Then it feels like a flat tire, then the bike starts to wobble fast. I don't know if it starts from the front or rear. Then the front wheels goes back and forth, back and forth, uncontrolably. The bike slows and then it stops. Its a real panic situation. The wheels are generally true, and I have Dura Ace 7800 brakes, and Bonti RXL wheels, circa 2008, on a Tete de Course. I'm big @ 235lbs. XXX Bonti Fork. KCNC Ti QRs. 4 Axis Richey Stem.
> Its got me spooked. Any ideas?
> Thanks
> SBob


Hey spongebob, I know this is an old post, but I just stumbled onto it and thought I would comment. I experienced this same non-standard wobble a few years ago on my IF 953. I was just starting out with more intense riding and racing. There's a lot of detail, but basically the wobble you describe isn't the classic speed wobble. It happened to me several times --the wobble is a near-tank slapper almost instantaneously when you apply brakes at certain speeds on some gradients when descending. There's no time to press knee(s) to the top tube... impossible to get your knees on it and still stay on the bike. I tried all the standard recommendations with knees, and relaxing, and shifting weight here and there. But, still death seemed out to get me in the hills.

My bike was checked out by several very reputable mechanics in SF and NYC and everything was shipshape. Some folks recommended that I replace the flimsy steel fork with a carbon fork, so I got an Enve 2.0. That reduced the likelihood of this instant, braking induced wobble, but it was still a problem. Like you, I was "spooked" and my mediocre descending got much, much slower.

Then I tried riding some different bikes. I rented a Trek Madone in Scottsdale, AZ on vacation once... and went into the hills there to test the handling... no handling problems. Zoom to a year later, I buy a Spooky Skeletor and start descending beautifully (after slowly coming to trust that the wobble wasn't going to happen). I still had the IF and when riding it, I still had the problem. I have ridden a number of other bikes now (carbon, steel and aluminum), and so I've determined that it was the bike. What about the bike? Not sure. Everyone has their guess. No one really knows --not any of the experienced cyclists, engineers, or even my physics pals. But the frame is probably too flexy in places that affect steering in the described situations --braking loads the front-end and the front-end squirms like a stuck marlin.

Hopefully, you've found all of this out on your own... and are enjoying your bike --and descending on it-- much more.


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