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Discussion Starter · #1 ·
I have been drueling over a Cervalo Carbon Soloist for a while now and had decided , "Yep" thats the frame I want.... I have two nice bikes and the newest one I have was built buy myself, purchasing components and putting them all together....

My bike is wonderful and light , but is prone to "speed whobble" ... I am use to it now and can control it , or actually keep it oput of speed whobble...

So looking at the Cervalo Carbon Soloist I thought this frame is super strong (although) I have not physically sseen one.... But I read a thread at one of the online stores, and a "Ed" wrote in that he was disapointed with the frame. What he dsecribed was "speed whobble" and I was crushed.... Say it ain't so Ed....

Does any one have a Cervalo CS , and how is the - Latteral - stiffness of the head tube.
Has any one experienced speed whobble with this frame.
 

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I think that any road bike can be made to shimmy, although some are more prone to it than others. The rider is the cause. The Cervelo, being fairly stiff and having a reasonable steering angle, should be ok. Here's an article that explains shimmy:
http://www.sheldonbrown.com/brandt/shimmy.html

If you ride descents loose, with your elbows bent, and put your weight on your feet, you are unlikely to get shimmy on any bike. If you grip the bars in a death grip and have your butt planted on the saddle, you can probably make most bikes shimmy.
 

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Discussion Starter · #3 ·
ericm979 said:
I think that any road bike can be made to shimmy, although some are more prone to it than others. The rider is the cause. The Cervelo, being fairly stiff and having a reasonable steering angle, should be ok. Here's an article that explains shimmy:
http://www.sheldonbrown.com/brandt/shimmy.html

If you ride descents loose, with your elbows bent, and put your weight on your feet, you are unlikely to get shimmy on any bike. If you grip the bars in a death grip and have your butt planted on the saddle, you can probably make most bikes shimmy.

Yes I agree one hundred percent with you... YOU are the initiator of the whobble... If oyu relax your grip and do not spaz on a decent the bike will NOT whobble... I also clamp my knees against the top tube... No way to get speed whobble with this method....

But let talk about my two bikes.... One is a Fuji Newest 2004, and an Airborne Blackbird.... The Fuji is more stiff than the Airborne and never gets speed whobble even if I spaz. I can actually make the Airborne whobble on purpose at 5 mi hr by shifting my weight left and right on the handle bars... On the FUJI - can't do it.... More stiff , Laterally , at the head tube....

I believe its because the down tube on the airborne is very flat (time trial like ) and the FULI is diamond shape, and has more lateral stiffness.... The Cervalo CS has a down tube that is also flat, and that is what I fear....
 

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merckxman
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I thought geometry could also influence shimmy

I also agree that how you ride can influence but here is a straighforward read from the pages of dave moulton (at: http://www.prodigalchild.net/Bicycle6.htm#Shimmy)

High Speed Shimmy

You are out for a spin on your new lightweight road bike. On a steep descent you reach a speed of maybe 45 even 50mph when all of a sudden your front wheel begins to flutter back and forth and the whole bike shakes uncontrollably. You manage to bring the bike to a stop but you have just been scared out of your wits; you have experienced “shimmy.”



Shimmy is usually caused by not having enough trail. To explain trail for those who don’t know: If you draw a line through the center of your head tube and therefore the steering column, that straight line will reach the ground at a point (Point B.) ahead of the point where the wheel contacts the ground (Point A.)I always built my bikes with at least 2 ½ inches of trail. Trail is common to all wheeled vehicles, cars and even a shopping cart will have it.

If you make the head angle steeper it means less trail because you move point B closer to point A. Also if you increase the fork rake (Fork offset.) you make for less trail; in this case point A moves closer to point B. The worst scenario is a bike with a steep head angle and a long fork rake; trail can be reduced to almost zero. Trail keeps the bike going in a straight line, and also assists a two wheeled vehicle in its self steering abilities.

As you lean to the left, point B moves to the left and the wheel Pivoting on point A will turn to the left. The gyroscopic action of the spinning wheel also plays a big role in self steering, but this is another subject and I only mention it because the heavier the spinning wheel, the more it keeps straight. Road bikes with ultra light wheels and tires are more sensitive to small changes in the amount of trail.

What happens in a high speed downhill shimmy the wheel is turned one way or the other by a bump in the road or a gust of wind. (Like when swinging out of a pace line.) The caster action of the trail corrects this, but if there is not enough trail it will over correct and then correct again starting the wheel fluttering back and forth. You can see exactly the same thing on a shopping cart if you run with it across the parking lot the caster wheels will flutter back and forth in the same way.

Large frames are more prone to shimmy for two reasons. Large frames are taller and also should be proportionately longer, but there is a school of thought that believes a race bike should have a short wheelbase, so the builder makes the head angle steeper to shorten the wheelbase, but in doing so lessens the amount of trail. Large frames are more flexible because the tubes are longer, also they tend to have shallower seat angles to accommodate the rider’s longer legs therefore the riders weight is more over the rear wheel.

Any vehicle that has its weight towards the rear is less stable; ask anyone who has driven an old VW bus in a cross wind. So if you are a tall person with a large bike frame, try to keep your weight forward when descending. Also keep your body in a low aerodynamic tuck; if you sit up wind pressure on you chest will push more weight towards the back wheel. Finally if you should get into a high speed shimmy; try not to panic, grip the top tube between your knees, and apply the rear brake first very gently and only apply the front brake after you have come out of the shimmy.

A bike with a shimmy problem usually has a design flaw in the frame and there is little you can do to correct it short of changing the frame. However do check that the head bearings are not loose. Also fitting a slightly heavier tire to the front wheel may increase the gyroscopic action of the spinning wheel enough to correct or lessen the problem. The design flaw will still be there but you have added and element to maybe alleviate the tendency to shimmy.
 

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It's in the game!
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Nope

Speed wobble is not a "stiffness" issue:

1. Either your headset is not installed correctly or too tight, or wore out.

or

2. The rake of the fork is too small for the frame.

The two articles above are correct.
 

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While I won't even pretend to know as much technically as the above posts, I do own a Carbon Soloist. I had an R2.5 before this and had an issue and it was replaced with the CS. The ride is Awesome, but as with any bike ride it and make sure its what you like.

As for the ride and I will say control and on descending, its as good or better then any bike I have ever had. I have always used my own benchmarq as my 99 Colnago C-40, still have it and the CS descends as well or better. Each unique but like riding on rails. I had a Trek 5900 before my R2.5 and CS and that for me was the worst of all, my own $0.02.

I also just did the deathride this weekend in the CS and I have never had so much fun descending, and as a bigger guy (205lbs) I do feel a lack of control in bikes while descending. But ride it and see if its what your looking for and please don't take my word for it.

cheers
 
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