It is (apparently) caused by what the track owner charges for the day, alledgedly around £13k for Brands Hatch full track, clearly they charge less in winter as no one would pay £200+ for a trackday in December and some money coming in is better than no money at all coming in even if it doesn't fully cover all the track costs.
As long as it pays more than the extra staff the day requires, i.e. marshalls, emergency vehicles etc. cost it's worth it as the other costs, rates, general staff wages, any outstanding finance etc. still have to be paid anyway.

As anyone who has tried to run a business knows cash flow can be far more important than outright profit especially in the shorter term.

Obviously all staff will need paying more for Saturday and even more for a Sunday.

And depending on how cynical you are they'll either charge more just because they can and people will pay it in summer or charge less in winter because they have to just to pursuade people to go.

As 100%bikes and a couple of others went broke last year no one is getting very rich from us anyway.
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