Is it permissible to take out a personal loan from a bank to buy a car, instead of buying a car in installments from the bank, so that the installments suit my financial capabilities?

It is impermissible to borrow with usury (riba), whether for car installments or anything else, unless there is a necessity that permits the forbidden. It is absolutely forbidden to deal with usurious banks, as this constitutes cooperation with them in sin. However, if the bank is Islamic and the transaction is a murabaha (cost-plus financing) that adheres to Sharia (definition) guidelines, such that the bank owns the car before selling it to you, then there is no harm in that. As for taking money from a bank to repay it with an usurious increase, this is forbidden whether it is with an Islamic or a usurious bank.