the 83 aspencade uses a electric signal for the speedo gage. its the little black box on the front axle on the left side with a wire running up the fork. most of the time the its the tangs on the plastic drive that wares out or gets broken off. that part from honda is no longer available . a used one is getting hard to find too.
the tack is run off the right cam from the fuel pump housing by cable. hope this helps some.
New tires on the front and the speedo stopped working? Could this be related?
Perhaps the sending unit was knocked out of adjustment?
I don't think that the tread pattern would cause a wobble. Perhaps it wasn't balanced
properly. Air pressure at the high 30's. Check the sidewalls of the tire and see if it
looks like it's centered on the rim.
The tire should also have an arrow on it to show the correct direction of rotation. Has
the fork oil been changed recently? You may want to put a jack under the motor - with
a block of wood in between - and jack up the front so that the wheel can spin freely. It
won't spin fast but you may be able to see if the assembly is out-of-round.