Originally Posted by
ullearn
The gear weighed about 34lbs and I had it balanced left to right (was able to ride easily no handed) and 70% in the rear 30% in the front. The issue with flex in the frame that I had was when I stood to pedal the lateral flex in the frame was noticeable enough that I didn't want to tempt fate and bend the frame, so I stayed seated.
I was also able to reproduce the feeling in the frame when I wobbled the handle bars from side to side (not turn) while riding. Is this normal for loaded touring frames or should I worry about it?
The good news is otherwise the bike handles great even at 30mph+ downhills, no shimmy or shakes at speeds or turns and can't reproduce when not loaded. I also tested moving the weight distribution rear to front to what I guess to be about 60/40 or 50/50; moved the heavy blue bag to the front rack.
What you're describing is pretty much what I've experienced with several touring bikes - only I got the shimmy, sometimes at slow speeds (12-14 mph). This only happens with a load. I think this flex only sets up as an actual shimmy if you happen to hit the natural resonant frequency of the frame in some way (with your riding position, weight, load distribution, wheel size, speed - there are too many possible variables to even count here). If you're lucky then you get the flex but no shimmy, if you're unlucky then you get the shimmy as a special added bonus. Sounds like you're relatively lucky, so that's a good thing. However, I personally wouldn't want to have that type of flex on a touring bike, even if it didn't come with shimmy. Reason being, I want such a bike to feel nice and solid underneath me, I don't want to feel like I have to coddle it, or worry about 1 lb being positioned just right here or there. It's a work horse, it should be able to just take the load (in my opinion).
The way to increase the stiffness of the frame is to use oversized tubing - I think that's part of the reason why my Co-Motion Americano is so strong, and I don't see the same flex on this bike at all. It's rock solid, and funnily enough I don't seem to get the shimmy either - so I believe that even if I am close to some resonant frequency, the stiffness of the frame helps to damp it down so it can't get started. I think of the flex like a big pendulum - you might not be able to bend that frame with your hand normally, but if there is a natural flex with a load then that gets it started, and the resonance just reinforces it. So stiffness helps keep it from even starting.
I had a really bad flex and shimmy on my 1998 TransAm bike (a British Raleigh Randonneur) and in Yellowstone I took a day out to try all sorts of different combinations of load distribution. I found nothing seemed to make any difference. Who knows why that was happening... you may be luckier, if you can find a certain way of packing that stops the flex, but I think it's probably simple: You have a flexible frame. Short of building a new frame with oversized tubing, you can't really change that. In my view, touring bikes need to be built much more beefy than normal road bikes, but for some reason many "touring" bikes are made with standard diameter tubing, and they will flex. I guess for many people, they don't notice it or they happen to not get the shimmy, so it's not worth changing. Maybe I'm in a very small minority with my experience - I must be, otherwise they would have changed the standard designs before now.
A good, quick test is to load the bike up with front and rear panniers (and bar bag if you use that), then hold it by the saddle and try shaking it side to side. If it's just too flexy then you'll be able to feel it under your hand, it's just obvious that the frame is flexing side to side.
Neil