Lightening Production Seats

Many enthusiasts would take out the seats to reduce weight.  Some would want to do it for the sheer pull factor of a branded race car seat.  In the Malaysian market, Recaro and Sparco tops the list of preferred seats.  Bride from Japan and local outfit SSCUS provides a cheaper alternative.  I have nothing against them.  With the exception of them being expensive.  Writing this on New Year day of 2013.  The start of the US Financial Cliff.  So the idea of reducing cost, without paying more money is very apt.

If you really look into the construction of them, the top brands seem to layer on the whole value adder schmooze on the unsuspecting public.  Hiwever, those who do indulge in it, will manage to reduce its weight in kilograms.  My preference is for something that is as light as possible without the need to go Carbon Fiber.  Aluminium seems a favourite material at the moment.

The standard production seats for the driver and front passenger is modified form of the Satria Neo CPS seats.  The differences are:

  • Vinyl covers instead of upholstery
  • Some alcantara bits and pieces with red stitching
  • Shoring of the shoulder area
  • Shoring of the outside leg area

That’s pretty much it.  It’s probably adds a bit of weight.  If you ever tried to remove the seats, it feels like 15kgs.  I have never really weighed it.  But it fell it was the single most heavy part the car could have other than the engine and transmission.  It has four anchor points, removed with an M12 socket driver.  But you would need to be careful on removing the plastic cover of the mounting bolts.  I broke off mine and decided to remove it.  It spans the length of the rails.  I could possibly just removed about 250gms just by removing these plastic bits.  From the perspective of a roadie cyclist, that in itself is huge!

There are two parts which I have done weight reduction.  The lower seat cushions and the rails themselves.

Seat idx

Indications of varous parts of the driver seat, with plastics shroud taken off including the adjustment wheel.

Lower Cushions

Once you have taken out the seat which we will refer to as the Assembly.  You remove four numbers of M8 bolts to get access to this part of the seat.  Yes, for a second, my immediate thought was for replacing it with aluminium bolts.  However, one had a very tight tolerance and therefore negate the possibility of replacing it with a more ductile and lower shear strength material.  The lower cushion has a base steel plate, formed to match the profile of the cushion.  On the front, another piece is welded for the seat cover to be fastened and hold the polyurethane foam.  When drilling or grinding, I covered the exposed polyurethane with a non flammable cloth.  In this case, it was my fire retardant coverall.  During these kind of hot work where sparks are generated, the Polyurethane can melt due to the heat of the chipped material.

Lower Cushion Idx

Details of location of holes which I made. Drawn holes are found to be feeble attempts to make it lighter but also increase strength to support the driver’s weight.

When observing the base plate against the rail assembly, the mounting of the four bolts were seen over-sized and does not always come into contact with the base plate.  There is an access on the mounting tabs.  This perhaps is accomodate the tabs as levers.  Under the tabs are pivot mounts.  The driver seat has a wheel to turn to adjust the fore-aft position of the base plate.  What it actually does is by turning the wheel, you turn a set of gears and link to the aft tab.  The other tabs pivot to the side plates.  The tabs themselves are made with a thicker material than the rest of the seat assembly.  I assume that the thckness and the drawn lines were to provide strength to support the weight of the driver.  That is why I focused on drilling these points, both on the tabs and on the base plate.  I do not see these two spots will ever be in contact.   If they are not in contact, they will never have direct forces acting on them.

There is also raised ridges in between the mounting points.  These provide additional bracing for rigidity of the front of the seat.  The land on which is quite spacious and does not provide any additional benefit.  The shape of the rise  itself increase the strength of this part of the seat.  The bent part and its close proximity increases the rigidity.

Seat Rails

The rails provide fore-aft adjustment of the seat and need bracing to absorb lateral or longitudinal forces acting on it.  There is a standard load on the vertical. The brace that holds the rails in actuality are two parts.  The seen structural brace made out of bare galvanized steel is the foremost seen.  The base plate of the lower cushion provide additional bracing.  So if you see both the raised land and the steel seat brace is actually, very close together.  It is quite possible that if there ware additional drawn holes on the seat, then the seat brace itself is not required.  In my observation, the tabs hit the brace and limit its ability to be moved lower and rearwards.

Seat rail brace

Taken after the two M18 holes were done

Seat Brace Mod

Finalised brace with more holes

The material itself is rather thick approximately 2.5mm.  It is definitely Stainless Steel as proven by the many cheapo HSS drill bits I’ve made dull.  The brace itself weighs 380g.  It lends support lateral loads of the seat frames and not the actual lower cushion.  The brace is mounted to the rail frame by 4 x M6x25mm bolts.  There is possibility to change this bolts with Aluminium ones.  I did not have any more and resort to maintain them until I get some.  The brace in its totality just provides support against the seat frame from collapsing inwards.  Therefore it is subjected to more of a compression acting towards the center of the brace than a deflection over the top.  It is easy to make a decision on making more holes to reduce the weight.  From originally 380g, I have managed to reduce it to 290g.  A reduction of 90g or 23%.

Next is the mounting tabs.  This is for all 4 tabs having M18 holes on them.  As I mentioned, the area where I drilled does not have any other function other than provide rigidity of the mounting points.  These tabs are also quite thick at 2.5mm.  Again it is Stainless Steel.  I would like to think that it is 304.  Picture below is of the two front holes.

Mounting tab mod

More holes to reduce weight of a thick material. Note the holes for the screws. One is of a fixed diameter while the other is an elongated slot. This provides some measure of adjustment to align the lower cushion to the rails.

Plastic moldings for the coverage was an easy decision.  It weighed 144g.  There was no significant use for it other than trying to make the whole seat nice.

Summary

If we look at both driver and passenger side, we could see the weight reduction as per below:-

  1. Plastic Moulding Removal   144g x 2  =  -288g
  2. Brace rework    90 x 2 =  -180g

Total Reduction  = 468g.  If I take into account the other holes I have made around the bottom shell and the bottom cushion, it should be close to 500g.

 

 

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