The lenders charge an interest rate on car loans as Marginal Cost of Funds based Lending Rate plus an additional spread. The investment loan rates charged is generally fixed. This makes repayment easier without having to worry about the increase in the EMIs in future.
However, if you think the interest rates will be coming down in future then you can opt for the floating interest rate. Presently (in 2017), the interest rate is in the 10.30-15.25% range.
Some lenders even offer .