Choke!

I realised last night that the last time I drove the car was on Christmas Eve when I drove a mate to work. I normally cycle to work and was fed up of being battered by wind and frozen to death so I decided to go to work in the Cobra today. I realise that "being battered by wind and frozen to death" also applies to a car with no roof and no heater to speak of but still, a change is as good as a rest, so they say.

I've left it stood for more than a month before and its started immediately with the normal procedure, one long pump of the throttle, then hold the throttle halfway and turn it over. This morning though, it absolutely refused to start. I could get it to splutter holding the throttle fully open but nothing could coax it into life. Eventually I had to admit defeat and use the choke.

There is no choke cable fitted and I've never had to use it before but it was -4°C in the garage and I've never tried to start it from as cold as that. I think the coldest I've used it is probably +3 or +4°C. The choke is wired fully open with some reasonably stiff garden wire so I got some pliers and bent it so the choke was closed. The car then started immediately, and I mean I had barely touched the key and it was alive. I left it for 20 seconds or so and it was idling on its own so opened the choke again, locked it off and jumped in quickly before it died (no fast idle). The car was then happy, used it at lunch time to take a colleague out for a quick spin, and it also started first time coming home even thought it was -1°C.

I don't know why I'm constantly amazed that it works, hundreds of millions of other cars around the world start every day but it still surprises me that a car we built ourselves works in everything the British weather can throw at it.

Driving was a different matter. I've driven in rain, damp and fairly cold but never below zero before. Man alive! It's twitchy round the corners! even pulling away at a T-junction, lift the clutch with no throttle and it slides sideways. I knew it would be a bit sketchy but it was absolutely ridiculous. At lunch with my colleague in the car I picked the driest, straightest piece of road I could find and gently squeezed the throttle in 3rd gear from 1500 rpm. It was fairly controllable until the cam really comes on at about 3000rpm and the back end lit up.. Luckily my passenger is a veteran of Ariel Atoms and similar so he wasn't too worried. Eventually I got the hang of it, if you know its going to step out then you can be ready for it and to be honest, the car pretty much sorts itself out and makes you appear a much better driver than you are.

At junctions and roundabouts, there's something about the De Dion rear end that's very forgiving and breaks away nice and gentle at low speeds (i.e. below 25mph or so). Not unsurprisingly I don't tend to stab the throttle like a madman in the middle of a corner on a public road going at any reasonable pace so I can't describe what its like at higher speeds.

On the way home I slipped into my familiar paranoid mode and thought the steering felt a bit vague so tomorrow morning I might just jack it up and have a poke underneath but I expect its just the bumpy road surface and the fact I haven't driven it for a while so I'm not used to it.

Formula Student 2006

Now that there's less cobra stuff going on I thought I would keep the blog going with some other car related things so here's a few pictures from Formula Student UK in 2006.

Formula student is a competition entered by universities around the world who design, build and compete on track in single seater formula-style cars.

Naomi and I were team members for the class 1-200 car at the University of Hertfordshire. Class 1-200 is for previous Class 1 cars that have been modified and improved, normally by first year students. This car was called UH08B and was powered by a 600cc Triumph Daytona bike engine through the bike gearbox and chain drive to the rear. The track that we raced on was based more on handling than speed so 6th gear was removed from the box to save weight.

The engines are restricted by a 20mm intake. If I recall correctly, the engine put out somewhere around 110bhp and the cars wet weight was well under 300kg. 0-60mph was sub 3 seconds.

This is another of the University's previous Formula Student cars:

More Rally Cars - Goodwood 2011

Rally Cars - Goodwood 2011

A few rally cars from Goodwood Festival of Speed 2011

String Box

I thought I should post the method I used for setting up the suspension. At the rolling chassis stage I posted some stuff on setting the toe using laser alignment made from a steel ruler, a builders laser level and an assortment of straight metal edges but now the car is complete that is a bit redundant. There was another post here: Correct Ride Height where I just simply state "we string boxed the car" but didn't explain it, so here is how I did it - and continue to use it to make small adjustments.

I first learned this method at university where we had a Formula Student car. We had some fancy corner weight scales and also set the alignment using the string box method. By alignment I mean toe - how much each wheel is pointing "in" (towards the centre of the car) or "out" (away from the centre of the car) compared to the direction of travel, and the relation between each wheel.

All you need is a long bit of string, fishing wire or I use brightly coloured sewing thread, 4 axles stands and a steel rule. This guide will focus on taking the measurements rather than how to adjust it - as that will be specific to this car (although I will write that up too).

1. Camber

Before I get stuck in to measuring the alignment, with a bit of string and a ruler its unbelievably easy to measure the camber. I tied a small washer to the end of the string and taped it to the wing so it falls down the centre line of one of the wheels. This method assumes the body work covers the wheels when viewed from above. Make sure the car is settled. If I've just had it jacked up I sit on the corners then roll it back then forwards to a stop and wedge a wheel with a block of wood. Make sure the steering is centred as even a small amount of steering could pile on camber depending on the geometry.

It's pretty easy really - you take three measurements. Firstly measure the diameter of the wheel rim which in my case is 498mm. Note that the diameter of the edge of the rim will not be the diameter quoted for your wheels (i.e. 18" in this case). 498mm is 19.6 inches. 

Measure the distance from the string to the wheel rim at the top and bottom of the rim. For this wheel in the example this was 12mm at the top and 8mm at the bottom. If the top of the wheel is further away from the string than the bottom of the wheel, then this means that the wheel is leaning (cambered) inwards i.e. negative camber.

With an easy bit of trig you can then say the camber angle = inverse tan(8/498) = -0.46°. Note that the result of the calculation was positive but the top of the wheel tips in towards the centre of the car so this is negative camber. Luckily I have a digital inclinometer to check and this read -0.5°. I did this for all 4 wheels and got the following results:

FL = -0.46°         FR = -0.58°

RL = -0.23°        RR = -0.3°

For the Dax De Dion, the manual says the rear should be zero and the front should be -0.25°. The rear is set by shims which is easy to adjust and when you're done, that's it really. When I first set this up before the first drive to the IVA test, I spent a long time trying to get it perfect but the adjustment required was less than the thickness of a shim , so -0.23° and -0.3° on a target of 0° was about as close as I was going to get. Interestingly I have just referred back to some old posts at the rolling chassis stage here: Alignment and the camber was -0.1° and -0.2° rear left and rear right respectively. It seems that as everything has bedded in and a few spanner checks progressively tightening everything up has increased the camber slightly.

The front is a little harder to set up precisely on the Dax and is more like most road cars. The top of the upright is secured by two bolts in a long slot. To adjust the camber, you loosen the bolts, give the upright a tap so it slides in the slot then tighten up the bolts again. Needless to say, this is a little hit-and-miss and took ABSOLUTELY CHUFFIN AGES to get right and it seems  by the results above that over the last year and 2500 miles this has wandered out a little bit. Looking at my notes I had this at -0.3° front left and -0.35° front right but in normal driving a normal person can't possibly tell the difference between -0.3° and -0.5° camber so I probably wont bother adjusting it right now.

Next - toe measurement.