The seat and its supports are often underestimated by chassis tuners and drivers, but the seat is a fundamental part of the chassis and determines a lot of the handling characteristics of your kart.
Various seats and supports
The structure of the seat and its connections to the chassis generate a system which will change the chassis stiffness. The material of the seat: glass fibre, Kevlar, carbon or mixtures of these elements, with different thicknesses will generate variations in the torsional flexibility of the chassis, since the seat itself can vary in stiffness.
For example a carbon fibre seat is, with the same thickness, three times as stiff compared to a glass fibre one. A Kevlar seat is on the other hand much more elastic if compared to a glass fibre one. Costs are also to be considered and, as usual, carbon fibre seats cost at least double a glass fibre ones.
Seats vary in costs, depending on the materials used. The cheapest seats, start from £30 for a very basic OMP junior seat, up to around £200 for a seat like the Tillett T11. Seat fitting kits cost around £10 and additional padding can cost up to £30.
Seat fitting tool
Serious karters would be wise to invest in a Tillett T Board seat fitting tool which enables the user to log the sit fitting position, making it easy to return to successful setups when revisiting circuits. The Tillett seat fitting tool not only provides a consistent seating position but saves time in getting to that position. The tool ensures accuracy and can be used to position seats in relation to axles on other kart chassis. The tool isn’t cheap at £290, however your local club or kart shop may well have one you can use.
Three distances need to be addressed to fit a kart seat:
» Front to back in the chassis, » Angle or tilt of the seat
Most kart manufacturers tell you their recommended height – measure from top edge of the seat down to rear axle surface and the distance between the extreme edge of the seat to the front (often two measures are used starting from left and then right), and the front tubing of the chassis (where the heels usually hit)
Effects of supports on chassis behaviour
As the seat is part of the chassis, it determines the overall rigidity, especially of the rear of the kart. Generally speaking, so seats work better for low power karts, as these free up the chassis, stopping the inside rear wheel from dragging on the track and absorbing power (rear internal wheel lift earlier and at lower speeds). As the power of the engine increases the additional weight transfer of a slightly stiffer seat may prove advantageous (rear wheel not lifting too early and going back into position quickly for early acceleration).
However on some track surfaces or track conditions it may be better to achieve grip by putting as much of the tyre surface as possible in contact with the track, on others it may be that the only way to get grip is to increase the downward forces that act on the outside tyres. So there seems to be no absolute solution.