Porsche 911 GT3 RS lap time at Area 27

Added A005 as tyres. Changing consumables does not make the car modified

I don't understand, is this a fastestlaps rule?
Adding non road legal tyres is cheating IMO. You can put any road legal semi slicks on it like Nankangs if you want, but slicks is just too much.
I mean otherwise it's not a road car, because it's not road legal.

Yes, it is a site rule. Swapping tyres/pads/fluids is not considered modifying cars. I dont know the exact reseaoning but I'm sure @FastestLaps can explain

I agree with SgtKanyo though. So somebody could put a production car on race slicks and per fastestlaps rules the car could break the Nürburgring record for production vehicles? Seems a bit absurd.

Gotta agree here. I think if the site's intent is to keep production cars clear cut from race cars, then staying definitive to the road-legal narrative is ultimately fair.

Full slicks isn't considered road-legal (I would hope everywhere), that should reason enough to be a track-only/modified vehicle at that point, if not a significant point of note to add to the time. Sure it's only one aspect, but it's one too many to refuse it being road-legal as well typically.

On the other hand, swapping new pads/fluids/rotors/semi-slicks/etc without drastically altering the systems outside consumables, could be considered unmodified yes, despite making at times a huge difference still.

I don't know this for sure but I'm pretty sure when you mark the car with slicks it will be removed from the production car laptime list on the circuit.