the week before the official three-day test session at the circuit, imsa altered the balance of performance in all three categories to create parity in the classes. of weight was added to the cadillac dpi-v.rs compared to 2017 but the decrease of handling abilities was countered by having the car's top speed raised by having its air restrictor increased by . the duo of nissan onroak dpis and the two acura arx-05s had their weight increased to to lower their performance, more than the lmp2 chassis and the pair of mazda rt24-ps. the nissan and mazda engines were not altered because imsa was satisfied with their performances, but the series changed the aerodynamic packages on some prototypes which affected their handing abilities. the debuting bmw m8 gte's weight was established at and its turbocharger boost curve was revised over its predecessor, the bmw m6 gtlm. the mercedes-amg gtd car had its top speed raised slightly with the enlargement of its air restrictor by .