Very cool! I remember seeing the Exposé on the web, back when it first came out, and of course in William Taylor's book.
I'd love to see more photos and video. And more details about how they got the weight so low. I'd love to know the comparison of the polycarbonate body to the 2-Eleven Coremat® body.
Getting the car down to such a low weight required a philosophy of removing absolutely everything that wasn't strictly necessary for Hill Climbing. For circuit racing you need a few things like sustainable cooling and lights but for Hill Climbing this was not needed. That means taking a 340R and removing oil coolers, wiring harnesses, lights and adding lightweight catch tanks, single person rollcage etc etc. On top of this the bodywork saw a large weight saving (IIRC 30kg) from the 340R, this was partly due to the production 340R panels being handmade fibreglass and therefore thick. The biggest weight saving of the body was seen in the reduction of body panel count, down to 4 (front clamshell, sides and rear engine cover). There really isn't much bodywork covering the car. Also helping was the fact that the car is based on the S1 elise, it has the VHPD Rover K-series engine. This is a fair bit lighter than the 2ZZ. The car also has the original MMC (metal matrix composite) aluminium rotors which are not suitable for track use, however can stand up to the short duty cycle of Hill Climbing.
Comparing the body technologies of the 2-11 and Exposé is quite in depth. I don’t know a lot about the Coremat technology but I will do my best to cover it in basic principles.
Composite body panel material requirements are usually dictated by stiffness of the panel rather than strength. A 1 ply (single layer) panel would have more than enough strength to cope with the tensile loads put into the panel but in the real world you never see this type of loading. The panel would most likely flap around in the wind and have a failure in bending. To add stiffness you need to increase the section modulus which basically means thickening the panel. Traditionally this was done by adding more plies to make the part stiffer; however this is actually an expensive and heavy way of increasing the part’s stiffness. For a composite sheet in bending the two outer skins are taking the majority of the stress, the composite in between is simply holding the two outer skins together via a shear mechanism. This is where the coremat comes in; it is a lightweight core material that links the two composite skins together at a better stiffness to weight ratio than multiple laminates alone.
The polycarbonate panels on Exposé use a slightly different method to save weight. Polycarbonate has a lower density than both GFRP (Glass fibre reinforced plastic) or CFRP (Carbon fibre reinforced plastic). The lower density allows for a thicker panel with an increased section modulus giving it inherent stiffness. Even so the material has a much lower stiffness material properties than GFRP so overall the polycarbonate panels are a fair bit more flexible than what you see on the 211. It’s a really good material for race cars as it can take a lot of abuse without cracking unlike GFRP.
