SF Cyclotouring

Ride reports and other ramblings from a San Francisco cyclist.


More Low-Trail & Shimmy Findings

Yesterday I took my 700C P/R on its longest ride to date, a 90 mile journey from SF to Pt. Reyes Station and back. Prior to the ride, I swapped forks, replacing the 40mm trail fork with the 30mm version (actual trail is more like 42/33). I used a front rack + bag that weighs a bit under 10lbs.

I can report that the lower trail fork seems to make the weight of the front bag nearly disappear -- executing a quick turn to avoid a pothole, for example, while slow does not feel overly "heavy" or "floppy". You don't have to wrench the handlebars around to make the bike do what you want. The same was true of the 40mm trail fork, but the 30mm version makes the steering feel a bit lighter, which was nice.

Unfortunately, my bike still exhibits the shimmy whilst riding no-handed. The change in forks seemed to change the shimmy-speed, previously it was around 15-18mph, now it seems to occur at 18-25mph. More weight definitely makes the shimmy worse. Even touching a couple o fingers lightly against the top tube stops the shimmy. I freaked my riding companions out a bit by demonstrating this multiple times. I attempted to make a video of the shimmy, but it didn't really turn out well -- I couldn't hold my camera steady enough to reveal the bike's shimmy.

I also discovered that at around 40mph, this bike has an unnerving speed wobble (riding with hands on bars). Of course, touching a knee to the top tube stops it...but it makes me wonder what'd happen when I'm poorly focused during a long, tiring brevet?

I'm giving up on trying to ride this bike with a front load -- which really sucks because that's one of the main reasons I wanted this frame! Tonight I'm going to remove the front rack, swap back to the 40mm trail fork, and return to using a Banana Bag.

Summary: I'm quite liking the low-trail handling, but the frame's shimmy is a deal-breaker.


Blogger Boxer Bikes said...

Sorry to hear the alterations didn't help with your shimmy issue _and_ induced a speed wobble. Bummer!

Back to the drawing board?

8:35 PM  
Anonymous Anonymous said...

That's not the "rubber pencil" illusion. That's the "rolling shutter" phenomenon, common to ALL CMOS-based cameras, also known as "jellocam" (see also google). Different parts of the scene are recorded at different times and as a consequence each frame is distorted individually; it's not a motion illusion that happens in your brain during playback. As a further consequence it's not limited to the movie mode of this camera; still photos taken by the same camera will have the same problem. CCD cameras do not have this problem. But then, CMOS imagers don't "bloom" and produce vertical streaks around bright points in the image like CCDs do. So there's a trade-off to make. Which do you prefer, dear informed consumer? Unfortunately the manufacturers have all made the aesthetic decision for you (and they're all in agreement) and now CMOS cameras are the only kind of camera that they offer for sale--to the "consumer" market, anyway. For camcorders especially, seeing as how they're nominally dedicated to capturing moving pictures of changing scenes, the use of a CMOS imager is nothing short of design malpractice.

7:47 AM  

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