WashWizards727

I have a 25 inch steel Trek 400 bike from 1989. I think it is a sport-touring bike. I used it on a fully loaded three day trip, and I noticed that whenever I got up to about 14mph, the frame would start to wobble side to side. On the downhills, while going about 30mph, it would wobble considerably. On the second day, I packed my panniers very carefully making sure that the weight was evenly distributed. That helped a little, but there was still wobbling. I think that part of the problem was also that one of the screws on the front rack had popped out, so the front bag on that side might have been shaking the bike a little bit. I didn't even realize that it had popped out until I got home, so it might have happened while loading the bike on the car to go home. I really don't want to buy a new bike, so what do you think I should do. Would getting new wheels help. My wheels are 700 X 25.

Bacciagalupe

That may be possible, but that wouldn't explain any wobble when unloaded.

I would thoroughly check the wheels and the hubs, to make sure they are on firmly enough and do not have any play. Then I'd check the frame for any cracks. If you can't figure it out for yourself, take it to an LBS.

WashWizards727

It doesn't wobble at all when unloaded.

gerv 

Headset? When unloaded can you grab the brakes and shakes the bike. (Make sure you are off it when attempting this...)
If you feel any play, you might need to adjust or fix the headset.

Also check that the wheels bearings are adjusted properly. Is the front and rear wheel solid in the fork?

ReelExterminato

If your headset turns out to be fine, you might also want to check your spoke tension. After putting aero bars on my bike (I assume this changed the weight distribution over the front wheel), I started getting wobble in the handlebars, but it turned out that the spoke tension in my front wheel was really low (~60kgf). I bumped it up to 100 and the problem disappeared.

Medosu

I am not an expert but I will give this a try. You are tall, you ride a large frame, and the frame is made with small diameter tubing. The problem you have is shimmy. The load on the front of your bike has a major impact on this problem, but when riding loaded, the best you can hope for is to adjust things so that the shimmy starts at 20 mph rather than 17 mph. Smaller frames or frames made with larger diameter or ovalized tubing are unlikely to shimmy as your bike does. My guess is that shimmy can become quite dangerous and cause loss of control or your front wheel to collapse if the stresses are strong enough. I have suffered this for many years, but am now shopping for a new bike. Perhaps there is another solution, but I am not aware of any. I look forward to better materials and better engineering.

While I am here I want to add this caution about your mention of the bolt falling out of your front rack. My friend had a front rack, the style with the hoop that goes over the wheel (as opposed to the style where the right rack and the left rack are independent and attached to only their side of the fork), and did a bolt fell out of his rack. The rack fell on top of the wheel, instantly wrapped around the backside of the fork, which in turn instantly stopped the front wheel from turning. I was right next to my friend, in mid conversation when this happened. He went down so hard and fast that all I knew was that he simply disappeared from next to me and there were some horrible sounds of a bike and a man hitting the asphalt.
His face hit the pavement quicker than he could get his hands in front of him. It was not pretty and he required a number of surgeries to repair broken bones in his face and an injured shoulder. DO NOT neglect to check the security of the bolts that attach you rack to your bike. I would not one anyone else to suffer such an accident.

RobertH

I suspect the mysterious 'speed wobble'. The cause would be some combination of frame geometry, tube size, materials and possibly age. One thing that I could suggest is to try 'low rider' front racks, which put the panniers down by the front axles). Barring that, try moving weight fore and aft to see whether that helps.