Looking at BMW's fixed price servicing option the i4 is priced at £650 for five years whereas the i5 is £910 for the same period, so the increased size and complexity of the respective cars does mean an increase in servicing cost. However, we would always suggest shopping around to see if you can obtain a better price from another dealer or look at the pay monthly options. Having your new car serviced outside of the BMW network is a personal choice - it is inevitably cheaper to do so and a good specialist will offer a quality of service that is at least as good if not better than a dealer, but when selling on some buyers will consider a main dealer service history as worth more than an independent.