One of the things that are really not usable for doing (pre-defined) tours with the Elise is the tripcounter. You have to press the button for quite some time to reset the counter. When standing still, no problem, when driving (at speed ;) you could miss hunderds of meters (or yards) by this delay..

What to do? Buy an expensive tripmaster? ... there are much cheaper options! Read all about the TripSlave here...

What? This looks like a bike computer!!! ahm... yeah.. it is! :)

The only disadvantage to using a bike computer would be that a bike normally doesn't do 220km/h.... ?? ....
Well.. Sigma Sport deliveres each and every bike computer with a maximum speed readout of ... 299 km/h !!! (Ever thought of such a speed on a bike????.)

So, went to the local Halfords, bought the 'top of the bill' model and started thinking about some practical problems.
1st. Where to put the display?
2nd Where to put the sensor?

The display was pretty easy.. As you can see in below picture, the display can be glued on the small dash insert just between the radio and the heater control..
In this way, the trip computer can be controlled either by the driver or the navigator..

To do so, you'd need to make some 'adjustments' to the bracket of the computer... As it is designed to be strapped to a bike steering wheel, the

 internal radius at the backside of the bracket is a bit overdone compared to the radius of the dash insert.

Not a real problem, if you just put the bracket on a sanding machine.
It will probably not be possible to create the same radius as the dash insert, but then again, if you use good double sided sticky tape, it doesn't have to match that good..

Don't stick the bracket to high on the insert. The reading angle would be to far off.. To get the wires behind the insert just cut out a small bit of the insert..

Now it's time for the most painfull job of this installation... drilling a hole in the alloy behind the insert.
Using a small connector would be preffered to be able to remove the bracket from the dash if needed.

As the wire from the bracket to the speed sensor is not long enough, you'll have to connect a longer wire. For this project you'd need about 3 meters of thin two wire cable (like cheap speaker cable). Polarity isn't an issue.

Now you'll have to open up the dash (see flying dash springs section to find out how) and lead the wire through

the dash, to the rear of the dash (just poke it through the little hole which is at the rear next to the big rubber cable entry) and bring it to the alloy center console.
The complete center console also have to be removed to get the wire through..

Now it's time to get the wheels of the Elise in the air... Remove the engine tray and diffusor (keep it in one piece so you don't have to adjust it when you want to bolt it to the car again) and push the little wire through the hole which is also occupied by the gearbox control cables.
Run the wire parallel to the gearbox control cables all the way to the actual mechanics of the gearbox control.

Now it's time to connect the wire of the bracket (which you've just brought all the way to the gearbox) to the actual sensor.(which is in below picture)

Coming back to the initial question.. where to put the sensor? you could think of some different strategies.

You could try to put the little magnet on a rear rim, make some sort of a construction to hold the sensor. This will not help the balance of your rim and the sensor would be out in the open, meaning it could catch quite some dirt and could eventually be destroyed...

The other way is to put the magnet on an inboard C.V. joint on one of the Drive Shafts.. Would not get so dirty, but will get pretty hot....

We opted for option 2.. the C.V. joint... If you have a good look at the right hand area, you'll find a very convinient hole in the gearbox, straight under the Drive Shaft. Take an M6x20 bolt out of the box, produce some sort of a bracket and ready! (the hole is marked by an arrow in below picture)

To get things going, you should first dig up the dremel tool and clean the surface of the C.V. Joint. Then disassemble the magnet from the plastic package and stick it on the C.V. Joint. Please notice the position, not to close to the gearbox as it would probably run into the gearbox control mechanism!!

As the rotation speed of the wheel can get pretty high, just sticking on the magnet won't work.. You should fix the magnet to the C.V. Joint in any way.
Don't get misleaded from the above picture! The tierap desappeared as soon as the two component glue was hardened.. It was only placed there to hold the magnet in place while putting on the glue...

After putting on the glue, let it harden for a short while and remove the tierap. Turn the wheel in a position so that the magnet will be on top of the C.V. Joint and let it harden.

Time to start working on the bracket...

I took a small piece of 90 degree angled alluminium and created a bracket out of it.
What you see here is an non-adjusted and certainly not final version as the bracket has to be VERY close to the magnet to keep the computer counting.
So, the 90 degree angle of the bracket should really be 90 degree and the best you can do is to cut out, like two holes above eachother where the bracket should be fixed.
(To be able to adjust heigth..)

To prevent any sensors falling off the bracket and turning round the C.V. joint (where did that computer go so fast? :) you'd also better glue it with the same two component glue.
First produce the bracket, check if it's fitting and if it's adjustable and then glue the sensor to the aluminium. You can use a small tierap to keep the sensor on it's place while the glue is getting hard.. (sensor should be at the heart of the magent on the C.V. Joint!!)

After a cup of coffee or two .. and a lunch, you can start fitting bracket with the sensor.

Besides waiting untill the glue is really hard (like 24 hours) I couldn't wait testing the computer and decided to put a piece of tape on the C.V. Joint, just to prevent any flying magnets.. When removing the downtray a few days later, the magnet was there, the tape was disappeared..  ;)

As mentioned before, it's mandatory to put the sensor in the exact center of the magnet and to move it as close

as possible to the magnet without hitting it in it's rotation....
At the fist attempt, the system seemed to work just fine and just quit after 25km... (my theory: engine getting hot, C.V. Joint getting hot, magnet getting hot, loosing it's magnetic power and finally not able to pull the little piece of metal in the reedrelais anymore..)
After re-adjusting the sensor (like bending it to a true 90 degree angle and adjusting the bracket even closer to the magnet) the system works fine now and is not showing any malfunctions ever since....
Adjusted the system with a GPS receiver and have a ultra precise (even better then the Stack!) tripmaster for just a few guilders...