blunty 07

i got a mk3 escort and i lowered it by 30mm and ever since the rear tyres have been wearing down quickly.they look like i have been doing a track day with the tread worn uneven.it did not do this until i lowered it and changed all the bushes to polybushes.i have noticed the rear wheels toe in to the front of the car and was wondering if it has any thing to do with it or is it because i have no rear roll bar.if it is the promlem what would i need to do to put it right.