Wen I reach 90km per hour my front wheels vibrate

Run your hand around the tires and feel for any lumps or out of roundness. Check inside the rims for mud build up. Check the rims for any dings or dents and look for clues as to weather you may have lost a wheel weight. If the tires are balanced it could be a break rotor . If youve done a lot of heavy breaking you could overheat the break rotor and it gets warped and can cause a shimmy but you would really notice it when breaking. other things to check that can cause a vibration are bad shocks or strutts and bad ball joints as well as bad tie rod ends. Hope this helps and good luck