There is nothing to worry about changing to 18" except that in a long run, your wheel bearing might give way as its too heavy. changing the coil over springs to sports would make it lowered but mind you riding on 18" with sports suspension would break your back. if you are planning to sell ur standard 16" rims & tyre, please do PM me. I'm interested to "downgrade" mine from 18". hehehe coz i've been riding on 18" with GAB sports suspension for the past 6 years & getting pretty tired with it.