For most forms of motorsport and for the more enthusiastic track driver a bucket seat with a composite shell will be the preferred choice. These seats tend to be both the strongest and lightest available.
The shells can be made from various different composite materials ranging from the cheapest fibreglass (or glass reinforced plastic) through to full carbon fibre, with a mixture of combinations in between. GRP is the weakest option purely because of the strength of the material used, and many of today’s entry seats from respected manufacturers feature a composite made from a blend of GRP weave and Kevlar strands.
This gives increased strength and allows seats made from these types of material to meet the stringent FIA tests, whereas some seats made from just GRP cannot meet the requirements of these tests and cannot be granted with FIA approval.
Other materials commonly used include Kevlar/carbon fibre, and a full carbon fibre. The GRP/Kevlar tend to be the cheapest, but heaviest of these three composites. Kevlar/carbon is lighter and stiffer, but more expensive. And the full carbon is the lightest and stiffest of the three, but also costs the most. All three types, though, meet the FIA requirements and are all designed to withstand impacts above and beyond the FIA testing.
In order to achieve this incredible strength particular attention needs to be taken when it comes to constructing the shell. The composite shells are all made using quality components and materials, although the exact details of the manufacturing process are closely guarded secrets.
You can see from the bare shells, though, that meticulous attention to detail has been taken to ensure the shells are as strong as possible, without increasing the weight unnecessarily. Strategic areas are highlighted after extensive testing and computer-based stress analysis, and are given extra material to increase the strength as required. Areas such as the spinal ribbon on the GRP/Kevlar seats often feature an extra ply to ensure the shell is as rigid as possible. This is not needed on the Kevlar/carbon, and carbon fibre shells because the increased strength of the materials used means it is not necessary.
Another area on all seats which has particular importance is the fixing points. Special steel plates with a captive nut are laminated into the shell during the manufacturing process. These areas receive extra material to give added strength, and the plates themselves are drilled to ensure they bond into the composite with maximum effect which prevents the nut from spinning free and detaching from the material when fitting the mounts.
As with the tubular seats, composite shells are designed to flex a little under impact. It helps dissipate the energy in the same was as a tubular seat deforming does, but as the composite is more flexible it will actually return to its original shape. This is why it is crucial to replace a seat after a big impact, as it may look alright but you won’t be able to see if the composite material has been damaged in any way. And when it comes to driver safety you simply don’t take risks.
Another benefit of using composites is the ability to feature more complex shapes and designs, such as those incorporating wraparound head restraints and being able to work in conjunction with additional safety devices such as the HANS device.
The type of material used is what gives the seat its inherent strength Three of the most common composites used include GRP/Kevlar, carbon/Kevlar, and full carbon fibre