Gilera VX - wobble when grip is loosened

My biked failed its MOT for a dodgy front tyre, the guy in the shop said, it was bouncing all over, and out of shape.

I've had a new front tyre fitted, it's now passed the MOT but, when travelling at 30ish in a straight line on a decent road, if I loosen my grip on the handlebars they start to wobble from side to side so I grab the bars before the imminent tank slapper and Tarmac headbutt.

I'm not in the habit of riding no handed so I could live with it if this is normal for a bike with furniture castor sized wheels, but please tell me if this a sign of some mechanical malady and what might the cause be.

I hear the most common problem is the back end, even though the problem is at the front. I think my tyre on the back is a little squared off, even though it's got plenty of tread on it, it's also slimed!

Cheers,
Rob.

 

sounds like the wheel wasn't balanced when the tyre was changed and the wheel is out of balance.
take it back to wherever the tyre was changed if you didn't do it yourself and tell them to balance it.

 

Deffo was a wheel balance issue. New tyre sorted the problem.

 

My BMW has done this for 3 different tyres now.
Balanced the wheel,
Checked and changed bearing,
New brake disk.
Checked the spokes.
Still does it.
Normally its just a balance issue.