steelframeco

Bike: '77 Trek, steel frame, zombie parts. Wheels are modern, doublewalled, 700s.

I have experience with high speed wobbles, but this slow speed front wheel oscillation is new to me. I didn't see much about it online.

I just replaced my 700x35 tires with 700x23 Continental gators. In the process I obviously have a much narrower wheel with less road contact, and I lost the tread that was on the 35s. It was a struggle getting the Continentals on, but the wheel does not appear any less true. The only thing out of the ordinary is I reused the 35 tube on the 23 wheel. I don't know if the extra mass of the 700x35 tube, possibly bunched at certain points in the tire, would cause a noticeable rotational imbalance.

The symptom: going at really slow speeds, just coasting down a flat, concrete sidewalk, the front wheel will slowly curve left, then slowly curve right. The counter-curve might be due to my subconscious correction, but it doesn't feel like it. I'm afraid to ride hands free and end up eating pavement.

I'm new to such narrow, treadless tires and didn't know if this is a result of a somewhat common mistake in installation.

Fixes to be attempted: retrue wheel, change tube to a 700x23, change wheel bearings (not related to incident, but needs to happen)

Other ideas? Thanks!

HillRider

First guess is that it's the oversize tube bunched up and with the weight off-center. Changing to a suitably smaller tube would be the first thing I would try.

Andrew R Stewart 

I'm not sure if you're experiencing what's commonly called "shimmy" (speed man's wobble). Some of your description does match up but some not. There is a lot of words written about shimmy. A few google searches of various wording will bring up a lot. This forum has had some threads as an example.

But the first thing you should do is to base line the bike. Check for frame/fork alignment and any crass damage. Check for wheel trueness and dish. Check for headset condition and adjustment. Check for tire seating. Check for spoke tension.

I have found that for classic shimmy the rotating weight has a large effect. Also weight placement. Hopefully all is well and you're reactions aren't yet up to speed with the lighter rotating weight. Andy.

steelframeco

Thanks for the suggestions. I took another look at it this morning, and I found that a component of the mud guard I put on the front wheel was rubbing against the headset tube. It was causing the wheel to alternatingly be stuck against the headset tube, then want to veer to the side. Always something new!

Andrew R Stewart 

Glad that your problem was a simple mechanical one. Andy.