This is based on my own experience ONLY.
Vibration at road speeds seems to have several factors.
1.
Three wheel vehicles , in general, have a resonant speed at which
they magnify any vibrations. My TriFun seems to have the most
magnification at about 42 mph.
2.
Out of round tires or wheels. Depending on how bad you may
want to swap your spare for the front tire to see which one is best.
3.
Unbalanced wheels/tires. ALL three wheels must be balanced.
Yes, the back wheels make a difference.
4.
NEW DISCOVERY! Front Forks. Odd but very noticeable on my
TriFun. Once in a while my wheel vibration gets worse. I
found out that the top of the front forks/shocks were sticking.
Also noticeable as the sudden settling or popping up of the front
forks when you get in and out of the vehicle. When I sprayed
the top of the forks where they slide in and out of the shafts, 70%
OF THE VIBRATION WAS GONE.
Parenting Guide