Is Cervelo R5 a noodle?

[Permon]

I wonder if it accidentally came with a fork with much more rake, as specced on the 48/51 frames?

Good point! But I guess mine is OK, it means 43mm (the smaller sizes has 53mm)
Am I right? See the picture, there is written 43.
What is wheelbase of size 56 with correct fork?

[sedluk]

You have the correct fork

[js]

The performance improvement versus other frames is enough that I took almost 1min out of what was a 7.5min Strava KOM decent versus last year's S-Works SL4 - sure other factors likely contributed too, but 1min??

How often did you do that descent?
Just wondering, because I allegedly broke the 400m WR the other day when I was out running, and tracking with Strava. The GPS was just very inaccurate that evening.

I probably rode that descent six times last year and another four this year (plus a few more in 2011). Last year's top run (at the time a KOM) was done with one other rider in my wake, as was this years - so we have four Garmins recording those measurements. All in all, it's enough that I definitely believe the bike made a significant contribution, and therefore, that the OP should be getting a MUCH better sensation out of his R5.

[Permon]

Guys, I recorded a short video of the "HT stiffness". I am not sure if it is easy to see what is happening....whatever...check it and let me know, if this movement is OK.

http://www.youtube.com/watch?v=Y4EFKwPvQr4&feature=youtu.be

Thank You.

[NGMN]

Can we agree once and for all that you seem to be talking about stability and not stiffness??

[djconnel]

That's shimmy! Scary stuff.

Good article by Jim Langley.

Here's Jobst Brandt's FAQ on the subject (not as useful, perhaps).

Here's a video by Jan Heine demonstrating shimmy.

Headset bearing adjustment seems the most likely culprit.

[btompkins0112]

Can we agree once and for all that you seem to be talking about stability and not stiffness??

Yes.

[Permon]

Can we agree once and for all that you seem to be talking about stability and not stiffness??

Yes.

Whatever we call it, is this a standard R5 behaviour?

[duodiscus]

Never felt or seen any instability with my R5. Also, doubt the Garmin team would be riding the R5 if it were a problem like you show.

There has to be something misaligned/misadjusted.

[refthimos]

...the R5 as a design and execution is most certainly not a noodle... in fact, it might be the best descending frame made.

I couldn't agree more with this statement. I actually went out and bought an R5 after I experienced some shaky descending on my S5... granted this was on >45mph gusty descents with Enve 6.7s (which are amazing in crosswinds for their size but are still deep-section wheels). The R5 was a revelation in handling/descending. Rode it to a KOM on the Haleakala desent in Maui: http://app.strava.com/segments/661686... Until of course it got taken back from me few months later! Haha. But the point is, I have ridden the R5 in some pretty challenging situations and its handling is an A+. To give further context, I have gradually lowered my front end over the past several months to the point where my stem is "slammed' on the S5 (and the R5 as well, since they share the same geometry) and for me, getting rid of the 2cm of spacers really tightened up the handling of the S5 (and I suppose the R5 as well, though it never had any handling issues to begin with). S5 handling improved to the point where I recently touched >56mph on the S5 coming down from Mt Baldy. I mention this only because even with that said, the R5 remains a much stabler descender IMHO and I could easily see hitting well >60mph on the R5 if the grade and road allowed.

The R5 is a sublime descender - something is not right with yours.

[djconnel]

No. I'd check headset adjustment.

Another discussion on the topic (suggests headsets may be "too good" and contribute to problem).

[refthimos]

Can we agree once and for all that you seem to be talking about stability and not stiffness??

Yes.

Whatever we call it, is this a standard R5 behaviour?

Your video shows shimmy, or "speed wobble." It doesn't look like you are even going fast in that video, though hard to tell - which is surprising because IME speed wobble usually presents itself at speeds over 30mph, even more commonly at speeds over 40mph.

Everyone points to the headset first, and that can definitely be the culprit, but speed wobbles are notoriously difficult to diagnose, because they can be caused by any one or more combination of things, including frame, fork, headset, wheels, stem/bar, rider position... it's something you really have to diagnose by changing one variable at a time. And even then, it can be difficult, as some speed wobbles seem to present at certain speeds, while others seem to be induced by crosswinds...

It's not a permanent solution, but for safety, next time you get a speed wobble, try to avoid a death grip on the bars, and grab the top tube with your legs. Your legs will absorb the wobble and absorb the vibrations that are harmonically resonating and allowing the wobble to occur and worsen.

[goodboyr]

I know you've said that you've checked your headset and its fine, but I've found that the common approach to checking headset preload usually ends up with a loose headset. In other words, if you check by squeezing the front brakes and checking for knocking, the absence of knocking does not indicate proper preload. I suggest you tighten the preload down until you get no steering movement, then back off 1/4 of a turn. That should give you steering movement and a proper preload on the bearings.

[NGMN]

One other thing. Are you "shaking the bars" with your hand? Because to me that's not "speed wobble."

[5 8 5]

I was wondering the same thing.