I've a Hyundai Santro Xing eRLX car and currently it has 155/70 R13 tyres on four wheels and all tyres almost crossed 40000kms. I've recently replaced both front tyres with brand new tyres. I've two spare tyres which are of size 145/70 R13 (took from Daewoo Matiz car), which are pretty good condition (10000kms mileage). I wanted to use these two matiz tyres on Santro. I'm completely clueless about what are implications using two different tyre sizes for front and rear wheels. Also not sure what is the issue if I downgrade these tyres to 145/70 R13.
Can somebody explain me pros (if any) and cons and provide some details why this is a bad/good decision?
Wheel info of this car: Wheel Type - Pressed Steel Wheel Size - 13 Inch Tyres - 155/70 R 13