Triple Eight Race Engineering's Shane van Gisbergen was deep into an 18-lap run (including in and out laps) when the shower began at around 10:35 local time/11:35 AEDT.
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It is unclear exactly what the provision for rain would be given today is officially a shakedown rather than a test day, but with unlimited mileage as opposed to the usual 60km cap.
However, the shower lasted only a handful of minutes and it is thought the rain is unlikely to set in.
Triple Eight Team Manager Mark Dutton told Speedcafe.com, “We've got some wets, so we can run in the rain.
“We don't want to run in the pouring-down [rain] because the cars are nice and clean and the water gets the grit through everything and things like that but, looking at the radar, it does look like it's just a passing shower so we'll go back out.”
As it stands, van Gisbergen's latest run is the longest by far, after the three-time champion started with a three-lap run (of which the full lap was not at speed all the way around the 3.12km circuit) and a six-lap run.
“The first thing is, you do a bit of an installation, get some temp into it, make sure that there is no finger trouble, that's really obvious ones,” explained Dutton.
“Then the next thing is, you go out and do a bit of a longer run, which really gets some good temperatures, some good heat good heat soak in there, so the cars are much closer to operating temperature.
“From there, you're doing more laps per run typically you would on a normal test day, because you really want that early mileage to try and flesh out if there is something there.
“There's thousands of parts that go into making a car so ‘something's got to be loose' is sort of the theory, so you've just got to keep running until you find it.
“You're super confident in your crew but you keep looking, and you try and shake it out with the drivers and get them comfortable.
“We still want to do some set-up tuning course on a day like today but it's not the primary focus.
“Because it's not the primary focus, you've got to make sure you nail your primary focus, which is reliability and the driver comfort and ergo[nomics] and seating.
“You don't want to be doing those changes in the next test day; then you haven't optimised today and the time in between.”
Feeney has just started his fourth run, minutes ago.