Cheap corner weights

[olboy]

I have just installed BC coilovers and adjustable swaybars. I am getting into adjusting everything. It seems that I need to check the corner weights but I'm not going to pay the big dollars that proper car scales cost.
I live in the bush so know one around here has any I can get a lend of. Has anyone seen a cheap way of building scales using bathroom scales or something? I thought I could maybe come up with a see saw arangement using a plank and a pivot point in the middle. It wouldn't tell me the weight but it would tell me which wheel is heavy etc.
Any comments
olboy

[oztrackdays]

Mate they need to calibrated to be useful and each scale needs to be capable of measuring 500 Kg
and support the weight of a car.

I paid $2,000 for my set

Do you have a wheel alignment shop near where you live can't they weigh the car as part of doing alignment ?

[olboy]

I don't think I have ever seen an alighnment shop with scales, just basic stuff

[Smithy]

probably completly inaccurate, but if each tyre is inflated to same psi, would a trace of each tyres foot print give a rough estimate of which corner maybe bearing more weight than the others... ?

ie measurable larger front right over rear left? or such if front right corner is measuarably heavier!?

[manga_blue]

I've tried the footprint technique - parked the car on two heavy level planks and just measured length by width of each contact patch. Strangely enough it seemed to give consistent results, at least good enough to find and fix a bias.
You just need a good spirit level and a very good pressure gauge. Planks need only be level side to side. Front to rear doesn't matter.

[fattima]

I've not done it but you can use bathroom scales, some ideas in this thread
http://www.oz-clubbies.com/forums/index.php?showtopic=13689&hl=scales

[manga_blue]

I've not done it but you can use bathroom scales, some ideas in this thread
http://www.oz-clubbies.com/forums/index.php?showtopic=13689&hl=scales

OMG, do you have to assemble them all with an allen key?

[olboy]

The double scales idea looks good but why not just use one pair of scales and three equal height blocks of wood.
You could move the scales from wheel to wheel.

[manga_blue]

You might need to find bigger scales anyway. My NA8 weighed in at a rather porky 1033Kg on the Eastern Creek scales a few weeks ago, without the driver. That's more than 240Kg per corner.

[greenMachine]

You might need to find bigger scales anyway. My NA8 weighed in at a rather porky 1033Kg on the Eastern Creek scales a few weeks ago, without the driver. That's more than 240Kg per corner.

Remember the principle of the lever ... problem solved!!

[ricky-pinky]

You can corner weight a car without using scales. There are two ways. The first I read about in a magazine which I no longer have. The second I did to do my own car when I fitted adjustable schocks.

The first uses a see-saw beam that rocks on a pivot on the garage floor. The author of the magazine article developed this method for corner weighting his single seater with a space frame chassis. He made sure the two wheels sitting on the floor were horizontal using a spirit level, placing shims under the lower wheel as necessary. Similarly, the chassis was checked for level using the spirit level. Since you can't really use a spirit level on an MX5, you need a flat garage floor, although a small slope is okay. Before you start, you have to pump up the tyres to the same pressure at each end of the car; i.e. front tyres need to be the same pressure and rear tyres need to be the same pressure. And you also need tyres with the same amount of wear at each end of the car, after all, a new tyre will be up to 7mm bigger in radius than a tyre worn to the tread depth markers. This also applies if you use scales. You run one end of the car onto the beam. You have to centre the car accurately on the beam. For a single seater the centreline of the car needs to be directly over the pivot point of the beam. For a right hand drive car the pivot will need to be offset to the right of the car's centreline to compensate for the weight of the driver. The amount of offset is given by: x/d = m/(M+m) where x is the offset, d is the distance the driver is away from the centreline of the car, m is the weight of the driver, and M is the weight of the car. Units need to be consistent; eg. x and d in mm, and m and M in kg. Note that this assumes that the CG of the car without driver is on the car's centreline. When the car is on the beam, you first level the end sitting on the floor. You can measure from the floor to a datum on the car, say the inner lower wishbone bolts, adjusting one side or the other, depending which ride height you want, until the car sits level at that end. Don't forget to ballast the car with a weight representing the driver - get a family member to sit in it, for example. You then adjust the other end that is sitting on the beam in a similar way, except that when you measure the height of the selected datum, you measure from the beam. Obviously the beam needs to be strong enough to not bend measurably about the pivot under the weight of the car.

The second way is simply to jack the car up at each end in turn with the jack positioned accurately at the offset measurement described above, and on the axle line. I used a scissor jack with a short length of round bar as the pivot. I also placed a piece of 6mm plate between the car and the round bar to avoid damage to the chassis at the front and the diff at the rear.

The first method, using a spirit level, is very accurate. Measuring from the garage floor to a datum on the car is a little less so, but for my road car which is used for the occasional 'speed-off-the-streets' day, I figured it was good enough, especially since I haven't finished mucking around with the suspension yet.