SF Cyclotouring

Ride reports and other ramblings from a San Francisco cyclist.

8/31/2009

An End to Shimmy? Almost!

I think most people are sick of my harping on shimmy issues...if so, please skip this entry now.

The latest major change I've made to my "Sister Kate" bike was a tire swap: I replaced the 700x32 Panaracer Pasela TourGuard tires (Kevlar belt & folding bead) with their less-sophisticated non-Tourguard, steel-bead, non-folding, supposedly-slightly-lighter siblings.

It's been conjectured that the non-TG version of the Paselas are more supple and roll more smoothly than the heavy-duty version, and I think I can now attest to that, although we're definitely venturing into Princess-and-the-Pea territory here. At roughly the same inflation pressures, the non-TGs seem a little more spring-y, a little more grippy, and a little bit more stable during hard cornering.

The other noteworthy thing is that my shimmy problem has been further reduced. On this past weekend's ride, I found myself pedaling along for several minutes, almost effortlessly hands-free. During coasting moments, I discovered that if I plant my butt firmly on the saddle, shimmy ensues, but if I unweight the seat just slightly, it all but goes away. This phenomenon was readily repeatable, as well.

I'm curious to see how the bike rides once I mount some lowrider panniers on the fork...

4 Comments:

Blogger Lee said...

Congrats on the shimmy reduction! I find that I can usually smooth things out by leaning my upper-body backwards (G2 53cm P/R).

Lee

2:30 PM  
Anonymous Anonymous said...

Jim -- my RB-T shimmied with a big rear bag. This year I got a new fork with extra rake per Alex W.'s specs and mounted a front rack and a h-bar bag. Still shimmies, just as bad.

Took off the bag and rode with no bags. Very little shimmy. Still there but very subtle and not alarming like it was with a load.

My conclusion is some bikes just don't like weight up high. I may try panniers some day but for now I'm just gonna go bagless.

Dan S., WI

6:47 AM  
Blogger Jim G said...

Dan, what size is your RB-T?

12:57 PM  
Anonymous Anonymous said...

Hi Jim -- my RB-T is the 61-62cm size, the biggest one. Easy conclusion is that I'm too big for standard-size tubing. I wish I were a framebuilder and could do stuff like build this frame with all tubes the same but a larger diameter top tube, stuff like that. My other thought is to just save my money and get a Riv Sam H. or something, but for now the only real option is to ride it unloaded, which is no great hardship. Dan

11:56 AM  

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