How to corner weight your car… for under a tenner!

We did this a couple of summers ago. I just found the pictures we took on an old PC and thought they might make a useful how to guide for fellow Turbosporters.

Step 1

Get down to Tesco and buy yourself 2 x value bathroom scales. They were £4 each at the time and I doubt they are much more now.

Each scale weighed up to 150 kg giving us a max measurable weight of 300 kg per corner or 1200kg total. The car we were measuring is a stripped out track / fast road toy so we were confident it was under a ton.

If you think your car is going to be more than 300kg per corner you will need to buy three. Remember to allow for the drivers weight.

If you are planning on doing a lot of corner weighting and adjustments I recommend you buy eight (still only £32). You will see why in a bit.

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Step 2

Because we are tight and only wanted to buy two scales we had to search around for some wood.

From memory I think the scales are 2” high and we used a 3” x 2” bit of timber to spread the load over them both. This meant we could use three bits of 4” x 4” to bring the car up to level while we measure one corner at a time. If you bought scales for all corners you would not need the wood and the whole process would be much quicker.

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Step 3

After a bit of rolling around on the drive and jacking up and down we had a measurement for each corner with the driver in place.

To check the accuracy of our method we weighed all the corners again with an empty car. We then weighed Colin the driver (feather weight 64kg). I then added empty car weight and driver weight up and it was the same as the car plus driver when they measured together!!

We then made the appropriate adjustments to the coil overs to balance the car.

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Step 4

While you have your jacks out you can also use the scales to measure the unsprung weight on each corner.

We simply undid the top shock mount and then rested the wheel on one of the scales. I know technically a bit of the coil over is sprung weight but it is accurate enough for us.

Measure the front and back wheels as they will be different.

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Why would you want to measure un sprung weight I hear you ask? At the time this car was stupidly over sprung. The coil overs were supplied with springs for a road car with full leather interior and possibly five passengers (1270- 1500kg). This car only weighed 937kg so was a real struggle to drive on anything but a billiard smooth road and would bash and crash over the smallest bumps. Traction was also poor off the line.

Using the un-sprung weight you can use Staniforth’s calculations to work out wheel frequency and from there select appropriate spring rates.

With the new reduced spring rates the car handled much better and was far more drivable.

top info there mate

I would add that care should be taken to ensure the measuring surface is flat. I'd use a spirit level or a plank of wood with a known weight in the middle to allow you to adjust the readings between each pair of scales, then between front and back. Adjusting the zero setting of scales will not work, adjustment should be made to the heights of the scales until they're dead flat.

Also a spirit level will help.

Great post by the way!

"We then made the appropriate adjustments to the coil overs to balance the car"

can you elaborate on this? :thinking:

Quote:

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Originally Posted by duncan

"We then made the appropriate adjustments to the coil overs to balance the car"

can you elaborate on this? :thinking:

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Don't you wind the bottom platform up or down to take more or less weight on the strut till they are all the same ?

as you imagin, the 4 corners weigh different amounts, so when the car is sitting on its own wheels, it would sit crooked as each spring would compress by a different amount.

you adjust the spring platforms to keep the ride hight the same on all 4 corners.

---- DONT READ IF EASILY CONFUSED -----

if it sounds odd its because it is.
you can compress a spring, and it will always compress by a measurable amount for a given force.
so from 0-1 inch of travel might take 100kg, and 1-2 inches of travel will take another 100kg, and 2-3 another 100kg.

This is known as the spring rate and in this case would be 100kg/inch

The other measurment is known as spring load, this is the load on a spring at any one time, so where as the spring rate is constant, spring load varies,

so when released, the above spring would have a rate of 100kg/inch, and a load of 0kg.
when you compress the spring 1 inch, it would still have a rate of 100kg/inch, but a load of 100kg as its taken 100kg to compress it 1 inch.
after another inch it would have a rate of 100kg/inch, and a load of 200kg and so on.

how does this affect coilovers when corner weighting a car?

well it shows that you can adjust a spring up and down to make the car level while the rate stays the same, so in practice it dosent affect the way the car drives at all,

hope this explains it somewhat,

P.S. if someone wants to put this post in tech guides as a thread then that would be a help

JOSH

you could go to a scrappy, say i'd light to weight in my car then change your mind once weighed :D

What engine it that running, looks nice bit of kit

will they tell you COG aswell:D

There is a "weighty" arguement for ingenuity...

Well done...

Russ.

You could buy 4 of these scales and weigh the whole car at once, you dont need 8 or 12 if you use leverage principles. Take 4 peices of timber 1m long, 6x2's would be fine, mark 500mm along the 2" edge, put something say 3" thick to one end, add something 1" thick to the centre of the scales (assuming the scales are 2" high) Do this to all 4 corners, the planks of timber should be at right angles to the car, scales on outside, 3" block to inside, and the wheels should be positioned exactly centre on top of the 500mm mark. Whatever the scales read per wheel, just double for the actual weight per corner. if your car is heavier than 300kg per side, just increase the length of the lever, mark say 333mm from the 3" block end, reposition car so most of the weight is now sitting 666mm off the scales,333mm from the 3" block end, then whatever your scales read, times it by 3 for your actual weight per wheel. Make sense :dunno:
I once lifted the back end of a hilux off the groud by myself when I got stuck in a bog with a 4m pole, same principle.