Living Car Free - Odd instability with passenger

First, the bike. For my general utility bike I ride an old Schwinn c.1984. This a lugged steel bike with 27” road tires. It has a Wald rack and two folding Wald baskets.

I had an odd condition today. I rode down to the bus stop to get my daughter (20) and she hopped on the rack, sidesaddle, and we rode off. However, it was extremely wobbly. Almost to the point of being unworkable (but it was that or walk a mile and a half in flip-flops).

Any ideas what may have been wrong? This is the first time we ever did this in the US. However, we rode this way often in P.R. China. This bike seems a bit more flexy (older steel v. a newer bike) that the ones I had in China. We considered that the tires on this bike are narrower.

The Wald, steel, rack is as good, if not better, than the ones we had in China. There was the issue that I am a bit out of practice, having not ridden with a passenger in over six months. It did get smoother, but it never felt as stable as I remember.

Any thoughts? Has any one else had something similar and what did you think the difference was?

How is the bike in hands-off riding? The extra weight could affect things if the bikes frame is out of true. Could the extra weight have knocked the rear wheel out of alignment?

I can't ride this one no hands. But then, I couldn't ride my "giant Tourer 2.0" no hands either. I will check the rear wheel. It has a weird spacer in the rear dropout on one side that I have never figured out what it is for.

It could just be geometry differences. I have two bikes. One becomes wobbly and twitchy when I carry more than 20 pounds or so in the panniers. The other makes loads up to 60 pounds seem to disappear. Haven't had occasion to carry more.

I would guess that your old bike in China had a longer chainstay so that when someone sat on the rear rack then their weight would be mostly over the rear wheel or possibly even a little bit between the front and rear wheels. The Schwin may put the passengers weight behind the rear wheel causing the bike to wag its back end like a dog with a little steering input. This was my problem when I was touring with a short chainstay bike with good racks and a true frame.

However, I could be wrong...

I vote for short chain stay putting the weight out back too far. Next time try putting the passenger side saddle on the top tube and see if that helps. That would tell you something. Around here I see more people carrying passengers on the top tube than on the rear, except on extra cycles of course. Of course, most people have flimsy rear racks if any.

check for loose or broken spokes that will not support the load on a rack.

It could just be geometry differences. I have two bikes. One becomes wobbly and twitchy when I carry more than 20 pounds or so in the panniers. The other makes loads up to 60 pounds seem to disappear. Haven't had occasion to carry more.

I think this is probably it.

I went out and looked . The axle had not slipped in the dropout, the spokes all made an even sound, no nuts or bolts missing.

This is the bike in question and I can see that the rack is a ways back. The baskets extend further back than the end of the rack; but, I suspect that she was putting weight on that part as well.
http://lh5.ggpht.com/_AS68O8wctBQ/SkkZUtqZXQI/AAAAAAAADMg/qtloafLHBgg/s720/DSCF0004.JPG

Uh, what's the rated load capacity on your rack? I'm just worried that it might buckle if you hit a pothole or something. I think the PRC bikes are pretty bombproof and are more or less designed to take an astounding amount of abuse.

FWIW, I wouldn't feel comfortable doubling anyone.

That bike is just not made for it. Your bike in China was probably made for carrying cargo, with much thicker tubing, a lower center of gravity, longer chainstays, etc. This bike is made for racing, and definitely not for carrying the weight of two people. They're vastly different in geometry, that's all. (And I wouldn't really think it'd be a good idea to try that again...probably not safe...)

The extra weight in the back probably made the front steering kinda "light" too.