The Chassis

The Lotus Elise was very innovative in using a hydro-formed aluminium chassis 'tub', which was exposed on the inside. That was 1996 though and things have moved on. I was hoping to use a composite design to achieve the same purpose, one that is also exposed on the outside of the car. This could be done because I'm not planning to have any doors as such. The much higher sills mean that the structure would be much stiffer and the sills don't have to be as strong (and heavy).

The chassis is the one area where I can save some weight but not as much as you might think. The chassis on the Fisher Fury R1 is pretty light. The main advantage of going to a composite tub is in the rigidity and strength.

The plan was to use a three part chassis on this car but, realistically this is going to be too expensive:

  1. A front subframe and crash structure housing the front suspension and steering rack. There really isn't much to this part and the aim is to make it very rigid and very light. It also has to have some supports for the front bodywork.
  2. A central 'tub' that is exposed both inside and outside, thus also acting as the bodywork. The advantage of this approach is that the high sill makes the tub rigid and very strong.
  3. A rear subframe holding the engine and rear suspension. This also acts as the engine cradle, thus saving more weight.

I'm now looking again at a steel space frame chassis.

McLaren MP4-12C The closest thing to what I have in mind is the carbon fibre tub from the McLaren MP4-12C and I'd argue that this 400Kg sports car is better use of this technology too! Unfortunately, the technology and the mass production techniques behind it are not a realistic proposition for this 'one off' car and I'm going to have to think of some innovative alternative to realise the 'tub' at a reasonable price.

You see from this photo that a similar tub with higher sills (no doors) is going to be remarkably stiff and a solid platform on which to mount the front and rear sub-frames. You can also see how the windscreen surround might mount to this tub.

This Teewave AR1 design is also very close but it has doors and electric power.

Teewave AR1

The external dimensions of the car will be pretty close to those of my Fisher Fury R1. Despite being very compact, the Fury wastes a lot of space with wide side sills (to cover the exhaust) and a large transmission tunnel. I plan to free up a lot of this space with my design, making it feel much bigger inside despite being a similar size externally. A smaller central tunnel will free up more space and allow wider seats and a wider footwell. By being mid-engined and rear-wheel drive, the rear wheel arches will be further back, also providing more width at the rear of the cockpit. In the Fisher Fury R1 they intrude into you elbow space.

The following items will run though the transmission tunnel:

What ever material (aluminium, carbon fibre, etc.) I use, this 'tub' is going to be lighter and stiffer than the 'space frame' chassis used in my NOT DEFINED. A lot of the structural rigidity came when the aluminium panels were bonded and riveted in place.

Steel Space Frame

Realistically, a steel space frame is going to be the only cost effective way to go at this point in time. A one-off composite chassis tub will be extremely expensive. Advances in 3D printing may address this in a few years time though.

Roll Hoops

There will be no roll hoops as such but, something similar will be an integral and structural part of the chassis tub and will extend to the outside edge of the vehicle. The 'valley' between them will be grooved, to accept a slide-in rear polycarbonate window and a bar that runs across the top of window, between the roll hoops. This bar will be clipped down to hold the rear window in place.

The bar will have the same profile as the roof and is only required if the roof is not in place.

This looks like an interesting technology to build the chassis - inrekor.

Top • Last page update: 22 Oct 2015