hi,i have a karizma and i want change my rear tyre which is 100 number and i want to put 150 number,and i want to ask that when iam change my tyre the alloy also be changed or tyre will be put on the same alloy.............

You will also need to change your RIM as wider tyre will need wider RIM. Also, I am not sure if the tyre you want will work in your Karizma, however examining closely can show the better result.