For 2014 the rule was:
For 2026 it's a factor of the min mass specified:4.2 Weight distribution :
For 2014 only, the weight applied on the front and rear wheels must not be less than 311kg and 366kg respectively at all times during the qualifying practice session. If, when required for checking, a car is not already fitted with dry-weather tires, it will be weighed on a set of dry-weather tires selected by the FIA technical delegate."
This is what I mean by lucking into the weight distro and how the rule seems to me to be there to mitigate against this...4.3 Mass distribution
With the car resting on a horizontal plane:
i. the mass measured at the front axle must not be less than the minimum mass specified
in Article 4.2 factored by 0.44.
ii. the mass measured at the rear axle must not be less than the minimum mass specified
in Article 4.2factored by 0.54.
If, when required for checking, a car is not already fitted with dry−weather tyres, its mass will
be determined using a set of dry−weather tyres selected by the FIA technical delegate.
If, when required for checking, a Heat Hazard has been declared, the increase in mass will not
be considered.
Anyway this is not really an MCL40 specific thing, but car in general, but I sure hope McLaren have still got the tyres under them and working for them like they did last year! Although that's also a function of McLaren's heat management of those tyres too... (so many moving parts to F1, which is why its so fascinating to me!!)
On an aside: I'm also certain I've heard commentary on the subject over the years (no chance I can remember specifics, I'm afraid) which leads me to believe there was an element of luck before some limits were set in the rules on weight distro to remove, or at least smooth out the benefit.
