Serotta ride quality issue...

[sirroada]

Hey guys. I have a 2005 Serotta Legend Ti. It truly is a beautiful bike. I have about 18000 miles on it. I have slowly noticed (over the past 3 years) that once I hit 21 mph, all the way up to 30 that it has a vibration in the frame. The vibration started out as a high frequency, low intensity vibration. Truth be told, it has always had a subtle vibration since it was new. It has just been getting more noticeable.
A couple of weeks ago I happened upon a great deal on an S-works Tarmac that I couldn't pass up so I bought it and have been riding it for a couple weeks. Yesterday I thought I would take my trusty Serotta out for a ride and I immediately noticed how much it vibrated, very high frequency, very firm intensity. As soon as I go over 21 mph I notice it and it gets faster and stronger the faster I go. I was thinking, sheesh, have I been living with this for so long that I didn't realize it until I got on a new bike and rode without shaking for awhile?
A couple of points for reference...
1.) I put a different set of wheels on the bike, the results where the same. Shaking with both wheel sets and at the same speed. I currently have a set of 3 year old HED Ardennes on it.
2.) Everything seems tight...
3.) Shaking appears to emanate from rear triangle and terminate in the handlebars.
4.) I had one crash a few years ago where I hit a pedestrian that jumped out in front of me. It pushed my front shifter (left side) to the side. It was fixed quickly just by loosening the bolts and repositioning the shifter.
5.) It shakes even if I stop pedaling and coast.

I feel it is some kind of harmonic in the frame. Not sure, I am wondering what your thoughts are. I just know that it would be a shame to stop riding this thing for the shakes.
Thanks guys...

[Hilltopperny]

I've never dealt with a harmonic vibration like that before and would think that it would drive me a little crazy. I don't think I'd feel safe descending on a frame like that. Was the bike built for you?

[Black Dog]

There is a great thread on this topic and David Kirk gives some great insight.

http://forums.thepaceline.net/showthread.php?t=203949&highlight=frame+wobble

[93legendti]

The Ti man hit the nail on the head above - speed wobble is the frame winding up torsionally and then springing back and setting up a wobble.

Typically it starts when something small bumps the bike off line....a gust of wind, a bump in the road...etc. This causes the frame to twist ever so slightly and the frame becomes a spring that then returns to its unloaded position and of course overshoots it and goes past center. And here's the kicker - when it does return and the frame suddenly stops twisting one way and is heading back in the other direction the weight of the stem, bars, levers...etc (all far ahead of the center of rotation of the headset) will continue to swing just a bit....this in turn makes the bike steer slightly to the side....and then the frame whips back the other way and with it the bar/stem/levers and they then steer the other way. This is "speed wobble."

A few things about wobble -

- all bikes can speed wobble. Every single bike ever made can be made to do it. Zero exceptions. I'm sure there are a lot of folks reading this and thinking "BS - my bike won't"....but I'm here to tell you that I can get on it and make it wobble every time. Fly me to your house and I'll be happy to prove it :)

- big bikes are more likely to wobble. The longer main tubes will be softer in torsion than the same tubes in a shorter frame and therefore they are more prone to wobble.

- bikes with smaller main tubes are more likely to wobble because the tubes are not as stiff in torsion and it's easier for the cycle to set up.

- longer stems contribute to the likelihood of wobble. A long stem moves the weight of the bars and levers further away from the center of steering rotation and makes the bike more likely to steer to the side as the wobble cycles from one side to the other.

- heavy levers make a bike more likely to wobble. Back in the day, when STi was new we suddenly saw a rash of bikes of all brands wobble. It was the added weight of the levers so far from the center of rotation and make it more likely to steer.

- alignment is almost never the cause of wobble.....in fact the closer the alignment is to perfect the more likely it is to wobble. It sounds crazy until you think of it. If the bike is so out of line that it pulls hard to the left all the time it's very hard to get a cycle to set up where it will want to go right on its own. So rather than going right-left-right-left it just goes left. One can test this by purposely misaligning a bike by cocking the wheels in the frame or fork. Cock the wheels in there so it pulls hard to one side and it won't wobble. Not exactly a fix but certainly interesting.




So....if all bikes can wobble how can the rider prevent it from happening or deal with it on the very rare occasion when it does happen? The most surefire way to stop it NOW is to lift your weight out of the saddle. It can take some large balls to do this but it works every time. The reason is that the twisting of the main triangle needs something to twist against and the rider's weight in the saddle is just that. Unweight the saddle and it will stop in one cycle as there is nothing to work against.

The rider can also fight instinct and keep a loose hold on the bars. The stiffer the arms and the harder one holds on the more the cycle can work against the rider's body weight. A loose hold damps the cycling and tight one helps it. This is one of the reasons that riders see more wobble when it's really cold...their bodies are stiff in the cold and the bike more prone to wobble. I once read a thing online by a "top builder" that said bike are more prone to wobble in the cold not because the rider is stiff but because it changes the stiffness of the metal tubing. Uhmm....no.

Run lower front tire pressure. A lower pressure give s larger foot print and more twisting friction when steering and this can help damp the system.

I spent countless hours studying this issue during my Serotta days and it was my job to take bikes to the top of the hill near the factory and see if i could get them to wobble and figure out how to change the design so that they would't. it was during this time that I found I could make every bike wobble....especially if the bike was dead straight. It's interesting stuff and when one can set up a safe low speed wobble and just sit and observe it it becomes fairly obvious what is happening mechanically.

One last thing (finally I know)....you don't need to dig too far online to find people that will say that they had a bike wobble once and they made a change and it never did it again. This is a red herring at best. If the guy rode the bike for years and thousands of miles and it only wobbled the one time how does he know if he fixed it? He doesn't. He could have let it alone and it would have gone years before it did it again. It's just takes the right circumstances and every single bike ever made will wobble. So throwing salt over your shoulder of putting pins a doll won't fix it.

Back to sanding stainless for me.

dave

Here you go...what size is your legend?

[Ken Robb]

Does this model have the rear end with pivots? If so, could you have a worn/loose bushing?
I have had bikes with speed wobbles but I wouldn't have described the vibrations as high frequency.

[sirroada]

Speed wobble... first that I've heard of that word but to be honest with you it fits with exactly how I feel the bike is behaving. It is a standard 54 size frame that was built specifically for me. It has definitely gotten worse with age which makes me wonder if I'm just worn the frame out. I have a hard time believing this though as titanium is an aerospace grade material and I'm only 180 pounds BUT, I do ride really hard. I will also say this is less of a wobble then it is a high frequency vibration and it feels the factor of the vibration is vertical, up-and-down, not side to side.

[Ken Robb]

Headset worn or loose? You have checked the frame/fork for cracks, right? Loose fork dropout?

[donevwil]

Speed wobble... first that I've heard of that word but to be honest with you it fits with exactly how I feel the bike is behaving. It is a standard 54 size frame that was built specifically for me. It has definitely gotten worse with age which makes me wonder if I'm just worn the frame out. I have a hard time believing this though as titanium is an aerospace grade material and I'm only 180 pounds BUT, I do ride really hard. I will also say this is less of a wobble then it is a high frequency vibration and it feels the factor of the vibration is vertical, up-and-down, not side to side.

Although it sounds like you may be experiencing something other than true speed wobble I'll just throw this out there regarding it getting worse, have you adjusted your fit during this timeframe? Many riders decrease reach (shorter stem) and drop (raise bars/stem) as they get older, if these changes are major they can alter a bike's balance and exacerbate any pre-existing issues.

[eddief]

it is hard to believe anything about the frame is different...unless it is cracked somewhere. in other words, what could have changed to have the vibrating get worse?

my guess is you are missing a variable and maybe need a second objective opinion. find another 180 person and see if it vibrates for them.

what could possibly be vibrating? inquiring minds want to know.

[Peter P.]

Headset worn or loose? You have checked the frame/fork for cracks, right? Loose fork dropout?

Since you've already swapped wheels, then Keb Robb's suggestions above are your next two suspects.

When you first called it "vibration" I took it to mean you're merely getting feedback from the road surface. If in fact it's wheel shimmy, then I've never heard of it feeling like it's coming from the rear of the bike. It's usually the front end that's shaking.

If it's the rear end that's vibrating, then something unusual is going on.

If it's the front end, it's front end shimmy and you need to check the usual suspects, starting with Ken's suggestions.

[sirroada]

Since you've already swapped wheels, then Keb Robb's suggestions above are your next two suspects.

When you first called it "vibration" I took it to mean you're merely getting feedback from the road surface. If in fact it's wheel shimmy, then I've never heard of it feeling like it's coming from the rear of the bike. It's usually the front end that's shaking.

If it's the rear end that's vibrating, then something unusual is going on.

If it's the front end, it's front end shimmy and you need to check the usual suspects, starting with Ken's suggestions.

I'll check the headset and forks and report back.

[ultraman6970]

This is so weird, never had the problem and never heard of the problem coming from the back of the bike and I had my quote of weird wheels that were never straight back in the day.

In a matter of fact I do have a wheelset with a rear tubbie that is not super duper and evethought I can feel the thumb thumb at low speeds once I reach like 12 mph the thing is gone.

Do you have a picture of the bike in question? Just curiosity of the fit.

[bigreen505]

To me it sounds like a small crack that has been growing over time.