Exige Diary June 2008

June 2008

Removing the Aero Devices

I mentioned removing the wing and splitter to my family and was surprised at the response. The youngest was most upset, suggesting the car looked much better with the aero devices attached. The older son was less adamant and my wife even suggested the car looked better. I wanted to clean up the lines on the car and remove a bit of the "bling".

I remember talking with a person from Lotus about the wheel sizes. Marketing wanted the push-to-start button and the 16 - 17 inch wheel combination. The engineers wanted the 15 - 16 inch wheels because the car handled better with them. I wondered if the rear wing contributed significantly to the downforce and so I did some research.

From the Lotus press release on the Exige Sport:

Key to this phenomenal performance and handling is the total aerodynamic package (which gives 41.2
kg of downforce at 160 km/h - 19.3 kg: front and 21.9 kg: rear) and light weight, the latter made possible
through innovative engineering and clever design.

From Evo:

To keep the Exige glued to the Tarmac, Lotus has gone to great lengths with the car's aerodynamic make-up. According to the company's own figures, at 100 mph the Exige creates 41.2kg of downforce, split 47 per cent (19.3kg) front and 53 per cent (21.9kg) rear. These figures are achieved with a completely flat underside, a rear diffuser, a deep front sptitter (mounted just 108mm from the ground) and a fixed rear wing at an 11.5 degree angle. Extra cooling ducts for the brakes and optional oil coolers have been designed in.

From an Richard Hill at Lotus:

Removal of the rear wing and front splitter would result in an overall aerodynamic lift condition. Front downforce would be reduced to a very minimal degree and rear lift would be in excess of 50 Kg's. This would induce a very significant high speed aerodynamic oversteer effect as opposed to the mild aerodynamic understeer condition induced by the design intent balance. The result would be a very tail happy car which would be unstable under heavy braking and step out of line when accelerating out of a corner. Lap times would consequentially be reduced. If you want to know how much real difference it makes and are a competent enough driver to deal with / catch a sudden oversteer condition - you can always experiment for yourself - on a track, in non race conditions, with plenty of room to manoeuvre! - as aerodynamically it will be no worse than most road going saloon cars on the road today. However bear in mind the chassis / suspension has been tuned for the design intent aero balance and being rear wheel drive you will be able to break traction at the rear far more easily than a front wheel drive saloon!

I will take Richard's advice and try the car without the wing and splitter. I was impressed that the aeor downforce was portional to the weight distribution of the stationary car. This helps keep the handling the same, no matter the speed.

Unfortunately there is a side effect of the aero downforce. The springs of the car must be capable of handling the extra apparent weight. I noticed the increased spring rate when I tried to lower the car according the the track package specification. The ride height did not come close to the 120mm specified because the springs were stiffer. A friend with contacts at the factory was able to confirm the increased spring rate and hopefully will be able to supply the specifications for a better solution. Because I do not corner at the limit at over 100 mph, I do not think I need the springs. The feel of the car is heavier and less nimble than the original Elise. It may even be possible to put the LSS springs in to regain the original feeling.

Modifications

I returned my Elise to stock configuration before selling it, assuming the car might be more attractive. I will be the first to admit that I have unusual, read quirky, taste when it comes to setting up the car. I retained the components and was able to install them as before on the Elise. Several of the modifications were retained by the new owner and the components needed to be repurchased. You can see instructions for these modifications on the Elise portion of the website.

raise the seat one inch
install a loud horn (Steibel)
remove the visors and the interior rear view mirror
install the steering wheel from the 111R
install Lotus Cup wheels and Toyo R888 tires
install a Halon fire extinguisher in front of the passenger seat
remove the wing and splitter
remove the "EXIGE" decals and the "S" letters above the turn indicators
turn off the day time running lights
make a clear panel to mount the traction control knob and status button

Information on all these modifications will be provided in September 2008.