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.