This guide is intended to be kept simple and easy to carry out for anyone with a kart trolley although any large flat surface on which to put the chassis on would suffice. There is a slightly more complicated and time consuming way of fitting a seat which involves weigh scales being placed under each wheel of the kart to help find the ideal front-rear and side-side weight distribution. This service is offered by several kart preparation specialists such as Kartune Motorsport who are based at PF International Kart Circuit but for the purposes of keeping it simple I am going to give you the seat placement measurements derived from the corner weighting method having being carried out on a number of different drivers and karts and found to produce a well balanced kart that responds to adjustment in a linear way.
For the Maranello RS9 LS I recommend the Tillett T11 or Iztech IZ3 of the soft or medium stiffness. This seat is more laid back than most others and has a perfectly flat bottom lending itself to a lower centre of gravity. The flat bottom also makes it the easiest seat to fit.
Step one is to place the chassis on your kart trolley or flat surface making sure that nothing that sticks out underneath the chassis such as brake/sprocket protectors are not allowing the chassis to sit level. The engine should not be attached to the chassis at this time to help get access to the seat support. Your aim is to have the bottom of the seat level with the bottom of the chassis rails. Placing seats any lower than this is guaranteed to shorten the life of the seat to days due to the odd off track excursion or contact with curbs damaging the seat. I place a flat piece of board approximately 5 inches wide by 1 inch thick and about 7 foot long between the kart frame and the trolley on the longitudinal axis. This piece of wood is perfect for placing the seat in the kart and is also narrow enough to allow access for the drill to the lower seat mounts. Tillett also make a very nice T shaped jig that attaches to the underside of the kart frame but I find my piece of board does the job just as well.
Step two is to put the seat on the board and place a heavy object in the seat such as a lump of lead or a Max battery. The aim is to have the seat sit flat on its bottom without any help to be stable and not be too easy to move.
I then use the following measurements:
Measuring from the back of the transverse 30mm frame rail on which the pedal mounts are attached to the front most point of the seat should be 61-62 cm. Measure both the left hand and right hand sides and get seat in roughly this position.
Measuring perpendicular to the spine on the back of the seat to the middle of the rear axle should be 17 cm. The seat should sit in the middle of the seat supports.
Step three: Once the seat is at this position it is time to start drilling holes. Holding the seat steady, begin by drilling through the sides of the seat from the outside using the seat support as a guide for your drill bit. Place a few bolts in your new holes and go down below the chassis and drill from beneath the seat. This way, if you have held the seat in the right position when drilling, your seat holes will line up perfectly with the seat mounts. Some people make the mistake of guesstimating where the hole should be, marking it on the inside of the seat and drilling from the inside out usually ending up with a hole that is 10mm or more out of line with the seat support necessitating some bodging with the drill to make it all fit. The lower seat supports on the Maranello RS9 always need to be bent down slightly using mole grips to fit flush with the T11. Leaving them out of line with the seat is a quick way of cracking the seat once the kart is in use. For bigger drivers the upper seat supports sometimes need to be bent out to fit the large and extra large seats. This can be done using an axle placed over the seat support and with someone else bracing the chassis, the supports can be bent out between 5mm-10mm each side.
Step four: Start using nylon or plastic spacers, (not metal washers unless you need the weight!) to fill the spaces between the seat mounts and the holes in the seat. I aim to have the seat sitting neutrally on the seat supports once it is bolted up so that the seat is not preloaded in any way while the kart chassis is static.
Thats it your seat is fitted in the optimum place given the tools available. The last step is to adjust the pedals and heel rest to a position which is most comfortable for the driver.
