About 18 months ago I changed my mountain type Powabyke for a Shopper. The handle bars are much better for me than straight bars. I have two problems: one - I hit a pothole in the road and the bars momentarily came out of my hands. I have cured this one by fitting a suspension handle bar stem, two -if I go fast downhill I get quite a severe speed wobble. Any suggestions why this is?
I presume you've checked that everything is solid and secure? It sounds as if you're hitting the natural resonance frequency of the frame. It's a problem that can occur with heavily-laden touring bikes as well - basically, you've got a heavy weight (the battery) on a spring (the frame), and it's oscillating. There are several ways it can be solved: Move the weight - easy with luggage, probably harder with a Powabyke battery. Reduce the weight - ditto. Stiffen the frame - if the battery was on a rear carrier, then this is doable, but for a Powabyke probably not - though you could try wedging it more firmly if it's moving about. Reduce the source of vibration - this might help - by fitting suspension forks. Change the tyres. Fit some kind of steering damper. With touring bikes, unfortunately it seems that some designs and geometries are more prone to it than others, and there's very little that can be done.
I was doing about 17MPH and yes it did it prior to fitting the stem.
It sounds like a loose wheel bearing or headset. Have you have tested/tightened these areas? Also the bolts holding the rear rack, if you have one with any weight. This solves most problems on heavily loaded touring bikes. Hope this helps
