it goes like 50mph or higher
Your front tires are defective. Its time to replaced them.
50mph to 75mph it depends on the condition of bike.
Most likely your alignment is out of whack or bad struts. Could also be the wheels need balancing.
u need to balance your front wheels at a local tire shop.
Probably a wheel balance problem or possibly a bent rim.
50mph = 80.47kmh
I can't find any mentions for a Suzuki DR-Z 125 2-stroke. The Suzuki DR-Z 125 4-stroke bike has a top speed of 50mph
Get you front end aligned, that should take care of the shakes.
50mph = 80.4672 km per hour.
50mph A mile is longer than a kilometre
The speed is still 50mph, no matter the distance measured...