BMW says the Z4 M40i now goes from zero to 60 mph in 3.9 seconds, a half-second improvement from the 4.4-second time it originally provided. (We originally reported that figure this morning in comparing the cars, but that post is now updated). It also bests the Supra's 4.1-second time, which makes sense since it has 47 extra horsepower and only weighs 46 extra pounds.
That curb weight, previously unpublished, is officially 3,443 pounds. The gross vehicle weight is 4,092.
So, what's the deal with the sudden change in 0-60 time? Logically, this seems like the result of the Z4 and Supra being developed together by two companies with differing 0-60 testing and reporting methodologies. Specifically, BMW has notoriously been conservative over the years when it comes to performance estimates. Toyota has not. When Toyota came up with its number, which was quicker despite the aforementioned power disadvantage, it's safe to assume BMW had to reconsider that conservatism — at least in this unique circumstance. Otherwise, it would be dealing with endless questions of why the Supra was quicker.
The Z4 sDrive30i does not get an updated time, with its 0-60 estimate holding firm at 5.2 seconds.
In the end, let this be yet another reminder to not take 0-60 times too seriously. Differing methodologies, be it between car companies or testing publications, mean that the exact same car producing the exact same acceleration can be reported differently.