Plank or skid block
Ralf Schumacher showing his 10mm thick wooden plank (Toyota 2006)
A wooden or any other homogeneous material strip that was fitted front-to-back down the middle of the underside of all cars in the mid-1990s to check that cars were not being run too close to the track surface, something that was indicated if the wood was worn away. It must be made out of a material with a specific gravity of between 1.3 and 1.45 (to prevent excessively heavy or hard planks producing a performance benefits and lowering the car center of gravity). Typically the plank is wood based, eiterh jabroc a laminate of beechwood, although more exotic blends of woods and resins not unlike MDF have been used. Plank must measure 300mm in width, with a tolerance of 2mm. It must run from the frontmost point of the reference plane at 330mm behind the front wheels centerline to the rear wheels centerline. Skid block may comprise of no more than three pieces, the forward one of which may not be any less than 1000mm in length. Plank must be fixed symmetrically on the car centre line in such a way that no air may pass between it and the surface formed by the parts lying on the reference plane. The lower edge (facing ground) of the front end of the skid block may be chamfered at an angle of 30° to a depth of 8mm, and trailing, rear edge may be chamfered over a distance of 200mm to a depth of 8mm.
When measured through six pre-cut 5cm diameter holes, plank has to have a tolerance of just 1mm on its 10mm thickness. Seven precisely placed holes in the plank allow the cars reference plane to sit directly and exactly on right place on the FIA scrutineering platform, for legality checks over the course of a GP weekend. Any holes made into it must conform to a FIA template (see picture below). Four further 10mm diameter holes are permitted provided their sole purpose is to allow access to the bolts which secure the Accident Data Recorder to the survival cell.
If plank is consumed too much, car can be disqualified. Skid block or 'plank' must run along the reference plane. It is not considered part of the floor for measurement purposes, and is there only to enforce a minimum ride height.
Plank was introduced with intention of FIA to reduce aerodynamic capabilities and bottoming of the cars, following Austrian Roland Ratzenberger death in qualifying for the San Marino Grand Prix in 1994 driving his Simtec, and Ayrton Senna in a Williams car at the San Marino Grand Prix same year during the race.