Hmmmm…know lots of folks who ride down steep hills pretty well on both P2K’s and P3’s.
Are you a heavy drinker perhaps? Maybe that is causing the “extreme shimmer/wobble” 
From reading the articles it sounds like I should not have any weight on the saddle, losen the grip, clamp the top tube with my knees. Sounds simple, sometimes it is. We will see.
Thanks for helping out trying to resolve this issue.
How about posting a picture of both bikes? My guess would be a bunch of spacers and a short stem on both bikes…
had the same problem with my p2k in edmonton last summer. nearly went down several times, while everyone else was flying by me. sold the p2k
Interesting point, the stem is 90mm (same on both bikes) and the spacers are about 50/50 (the same difference above and under the stem). This is pretty much the same set up on both bikes. I can’t imagine this is the issue though since I don’t think that is an uncommon configuration.
Interesting about the P2K as well. Is it possible that crosswind effects the shimmering? I did read in one of the Cervelo Carbon soloist reviews that they considered the frame to catch some crosswind. I do ride with a lot of crosswind when going downhill and since both frames are aero frames maybe they are being effected more then a normal frame?
How about trying a different rider 
.
First of all, 90 is on the short side. 50/50 tells us nothing. If the fork was 10 meters long, that would be 5 meters on each side. How much stack do you have on there?
Ok, now picture taking a Formula 1 car’s steering and nimbleness…and STACKING it up into an 18-wheeler. The result… unstable at best!!! You are doing the same thing with your bikes.
THEY DON’T FIT YOU! Lesson learned (I learned this myself with a P3)…don’t buy a bike because it is cool. Buy a bike because it fits… I now ride a custom Yaqui.
maybe the prismatic paint is causing half the problem, switch to the new anodized flat black and the shimmering should fade…wobbling too difficult to diagnose over the web, high altitude or excess alcohol is my guess.
Maybe I missed it. Did you check your headset?
check for what on the headset? I do have most of the spacers below the stem if that is the question?
Thanks
Pick up the front of the frame bike. do the stem and/or fork wiggle when you move them or the handlebars? If so, your headset might be loose.
I don’t know. I’m not a wrench. Anyone else know about headsets?
there are really 3 things that can go wrong with a headset (and diagnostic tests).
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too loose (does the fork move back and forth when you rock the bike back and forth with the front brake applied?)
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too tight. (pick the bike up by the seat, so the front is pointed downward and can freely rotate. when you push the bar to the side, does it return back to centre? Any resistance when you turn the bars?
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damaged bearing surface. (aka indexed steering) does there seem to be a detent in the steering, typically when the bar is pointed straight ahead.
#3 will cause more handling problems than the first 2.
<Wheel bearings - headset bearings> combo + sitting up & back , with 80% of the weight on the rear wheel. Bingo most any bike will wobble.
How many spacers below the headset??? I doubt it is a loose headset. My guess 3 or 4 1cm spacers below the headset. Short stem with a positive rise…am I right???
Are your brakes “off-center” so that when braking it is pushing the wheel out of center? That would essential make your wheel out of true while braking.
Since it is 2 wheels, it doesn’t seem like it can be spoke tension etc.
I really doubt that the answer is “relax.” I am sure that might be true to some extent, but I can’t imagine that TdF guys fly downhill at 60mph “relaxed” while the bike wobbles below them so badly nearly causing them to fall off. Seriously. Some simple engineering would have ended that long ago.
Had a similar problem with a softride rocket tt. Came down the hill at 40 and it shook like Janet Reno. I got off the bike, changed my shorts and checked for a flat. Took it to my bike shop and he checked the rake and trail. He told me it couldnt handle high speeds with the rake and trail it had. This made sense because I used to have Harley choppers with a ton of rake and would handle great at high speed but wouldnt handle at low speed. The same works in reverse. Less rake=better handling at low speed but poor high speed handling.
just a thought
Henry
I really doubt that the answer is “relax.” I am sure that might be true to some extent, but I can’t imagine that TdF guys fly downhill at 60mph “relaxed” while the bike wobbles below them so badly nearly causing them to fall off.
If you are relaxed (meaning a relaxed grip on the bars, not “hey mon, nah worrie” relaxed) then the bike won’t start wobbling to begin with, unless it is a harmonic thing. The harmonic thing is easily controlled by clamping the top tube with your knees, and really isn’t that much of a problem with modern frames. Older, lightweight frames were much more flexible than current lightweight ones, so were more prone to this phenomenon.
Andy, that is pretty much right. About 4 spacers at 1cm each with a 90mm stem. While I can probably relax more it don’t think that is the only issue. I am going to get the bike checked out. However, my butt was off the seat while it happened. One of the other riders confirmed that.
Thanks!
Having your butt OFF the seat is a bad thing. the bike can move back and forth a lot more easily. I disagree with folks who say to unweight the saddle without doing something else.
What I do sometimes on fast descents is to raise my butt off the saddle (just a bit), but actually clamp the saddle with my thighs. that allows my legs to absorb road shock easily, but prevents the bike from moving laterally.