How do you weigh a car - affordably?

[Chartman]

Every book I read stresses the importance of good weight distribution but all the scales I've seen seem to cost in the region of £1000, which is way outside my budget. Also its obviously very important to be able to weigh the car accurately in order to comply with championship regulations. I've seen cheaper devices for measuring corner weight (sold by people like Demon Tweaks for about £200) but are they any good.

Like many people I race on a very tight budget so would appreciate any helpful advice.

[spook]

If you are handy with tools and have a little skill you can make your own corner weight gauge using a clutch slave cylinder mounted on the end of a lever that is connected by hydrulic line to a pressure gauge. Simplpy lift each wheel with the lever - note the pressure - and adjust until all four wheels/each axle show the same pressure - who cares what the actual weights are - you are looking for balance - not the numbers. Good Luck.

[imull]

Have you tried Sheffield Uni? They are bound to have a set of scales I would guess...

[JR Ewing]

I'm assuming you have a single-seater?

[Chartman]

I'm actually racing a mini at the moment but am in the process of preparing a 1979 MGB GT for the track. The MGB will be the first race car I've prepared from scratch.

[MA2]

You can do surprisingly well with some inexpensive stuff.

Get 2 electronic bathroom scales & reinforce the tops & bottoms by gluing down 1/2" - 3/4" plywood. Mark them for left and right. Soem electronic scales shut off the display after 30 seconds or so, which is a royal pain, so look for those that don't do that. Mechanical scales will also work, but aren't quite as accurate due to the extra deflection.

Get a bar of alu - 1" x 2" - long enough to go past the outside of the tires. Or a 6 ft carpenters level.

Get a machinists precision level - the Chinese ones are about $150 from the right industrial suppliers. A machinists level is incremented usually at .0001" per foot per line, or .0002"/ft/line (this means that if the bubble is off 1 line from being centered, you will be off-level by .0005 or .001 " at 5 feet of length)

Mark the bar and level so that you orient them exactly the same way each time you use them.

Gather up alu, plywood, and paper shims of various thicknesses to use to shim both ends flat. Make sure that the scales are not only level side to side, but that the tops are in the same plane. If you want to get fancy, you can make up some boxes with adjuster screws out of 3/4" plywood, glue, & screws. The levelers can be bought thru various industrial suppliers for anywhere from $10 to $20 each - you'll need 8 total, or four per box.

You will also want to make up some ramps from wood that will allow you to easily push the car onto the scales.

Find as level a spot of concrete as you can, chalk mark were the centers and sides of the tires are, move the car & set the scales in place. Shim both ends so that each end is level - don't worry about front to rear, just side to side.

Push the car back into place, and double-check the levelness of the scales while loaded. Excessive uneven deflection from side to side will screw the weights - every .010" difference from side to side ( or unevenness between front and rear)with 100 pound springs (actually - 100# wheel rate. ) will put the balance off by 1 pound.

You are now ready to go.

[Mark Benson]

I have one of the cheaper versions (£150 or so from Raceparts) and although it takes longer than having the car on 4 pads, it works fine.
Just remember to do diagonally opposite corners together as a change in one, tends to upset the other, if that makes sense.

[Kid Prozac]

there was an article in racetech a while back by Mike McDermott on an inexpensive way of doing cornerweights, i'll edit tommorrow with the mag number

[sunbeam73]

Sometime ago I had an idea for weighing and setting up my car (about 850kg) - and it proved quite accurate when compared with proper corner weight scales.

Looked through the Argos catalogue and found some cheap bathroom scales that weighed upto 120kg - I bought ten of these and placed thre in a row under each front wheel and two in a row under each rear. Along the top of each row placed a length of 3" x 5" timber to spread the load over each group of scales. Zero the reading then drop the car onto the top and measure each corner by adding up each scales reading.

You can reduce any error by swapping scales around and rechecking.

It may sound like a crummy idea but it worked and only cost about 20 quid.

Sean

[Chartman]

Sunbeam, that was the sort of cheap idea I had considered myself but I wondered if anyone had actually tried it. With my budget I have to consider all the crummy ideas as they are usually the most affordable.
That said one of the cheapest corner weight gauges at Demon Tweaks is 'only' about £120 - trouble is I don't know how they work or how accurate they are.

[sunbeam73]

I've tried quite a few cheap, crummy ideas!!

[Werewolf]

CCC Magazine did a report on weighing/measurement equipment in one of their monthlies.Unfortunately I cannot remember which month.They may be able to send a back copy.They tested expensive to home made items

[ozracer]

Havent tried it but often thought about it. Put four peices of paper around each of you tyres. Carefully butt them up to each side so that they sit hard up against the tyre.

Measure the contact patch of the tyre, in mm^2.

measure the tyre pressures in MPa.

MPa is N/mm^2, so the number of newtons acting on the ground under each wheel is equal to the tyre pressure multiplied by the contact patch area.

To get kilograms divide newtons by 9.81.

Or maybe jack the car up, mark the ground with chalk or something, then let it down again.

Anyone think this would work. If you know how much your car weighs you can verify how close you are.

[A. C. E. motors]

We have used the scales after scrutineering has finished, at Cadwell, Castle Combe and Snetterton. Just be polite, don’t get in anyone’s way and most scrutineers are happy for you to use the scales.

[sarrcford]

MA2,

I would like to know which bathroom scales you recommend and ask you some more questions. I live in the Atlanta, GA area and race a 97 VD FF2000. Thank you.

Rob Poma
sarcford@bellsouth.net

[JimW]

Would this not be a good thing for series organisers to provide?

Jim

[Red Dog]

Chartman,

I have used the following very cheap method with my clubmans car with some success.

I bought 4 bathroom scales with flat tops from my local Homebase at £4.99 each. (My car is 365kgs, a mini would need 2 scales per wheel at the front) and I put 1/2" mdf on each scale to spread the load. I prepared the flat area and made some plywood/mdf/hardboard shims to get it as level as I could, which was about 1.5mm. I used an ordinary builders level and a long bit of ally angle. If you swap a level end to end on the same spot you can do an immediate check on its accuracy - the bubble should come to rest in the same place - and if you use small card shims at one end you can easily see how much the bubble moves with a 20 thou packer at one end. I made some small wooden ramps to run the car up. The scales need to be zeroed and checked against each other. Use your own body weight on each one and note the difference. I just add on the diffence to each measurement each time. You could try setting the adjuster wheel to make them all read the same at the weight they will be 'seeing' when the car is on them.

With the car race ready, anti roll bars disconnected, tyre pressures correct, car at correct ride height, etc, etc. and half fuel and me in the drivers seat I got an assistant to read the scales.

Side to side balance is what you are looking for. I then adjusted the spring platforms to bring the weight roughly even. You need to roll and bounce the car a bit after each adjustment - it helps to have a ramp with a flat section after it leading on to the scales - and when the weight was almost equal at the front (1-2 kgs diff) and only a bit more at the rear I rechecked the camber, castor, toe-in. Then I weighed and adjusted again (very little).

Car was transformed from a wicked nasty evil thing into a pleasure. That was two seasons ago. This year I finished third in the championship and got pole and fastest lap at Lydden. I still have heaps to learn about driving but it was only my second full season.

I see that other posts have suggested a greater accuracy is needed. I'm sure they are right and I will follow their advice.

I have used the £120.00 long pole with pressure gauge and I do not think it is as accurate and you still need the flat patch, but the chief drawback is that you need lots of space to use it. My garage and drive are way too narrow.

[MikeM]

Quite a few do now, but most scrutineers are helpful in my area (we get weighed most practices and races anyway)

If it's for handling you only need corner weights really.
If it's for eligibility then best to use the scales you will be checked on but know how much petrol you have in so you can check the real nett weight

[ianselva]

For weighing the car overall , just go to the Local public weighbridge ( address in yellow pages) or scrapyard or Gravel pit . They all have weighbridges , which have to be calibrated regularly.. Probably more acurate than the ones at circuits . I have never seen an up to date calibration certificate at a circuit.

[tzei]

Hi!
I have been working with four bathroom scales and four 1 m levers. Idea is to make a pivoy point (?) to same plane as the scale and then lower car onto them with tyres between pivots and scales. Then with a little math calculate from the two distances (pivot to tyre and pivot to scale) and one scale reading (per corner) the weight of the corner. In theory it should work but so far system needs fine-tuning with the distances to calculate. It seems that in pivot to tyre, measurement to center on the tyre gives a bit too high result. Stil I think that in balance-vice good as it is now?!

[BugEyed]

Strangely enough, this discussion was going on "somewhere else" before the VSCC contingent arrived here.

The idea of the weighbridge (grain/scrap/sand) merchant is effective but means you have to transport the car there. Alternatively, the bathroom scales idea works for light cars (circa 500 kg max) so covers racing Austin 7's. Don't forget that all of the wheels need to be at the same height to avoid any roll stiffness affecting the result, so support the other wheels on blocks of 2"x4" to get them level.

As a Physics Teacher the idea of levers to increase the maximum force appeals - this is basically how the commecially produced corner weight gauges work. However, it requires a greater knowledge of moments to calculate it than most school leavers now possess. Also, you actually need the car to be between the pivot and the scales, and nearer to the pivot, for it to reduce the measured force. Hope that helps.

Duncan

[tzei]

Hi Duncan!
Sorry but your inpunt had nothing helpfull. Have been talking about this idea with my workmate (a physics teacher).
Regards Tzei

[reddy]

Why don't you try to hire some off a richer team in your area, It works for me

[tzei]

Well there aren't any near. There are scales nearby and this quest for homemade scales is merely academic - just out of curiosity to see if I can produse a working method

[GolddustMini]

Originally posted by spook
who cares what the actual weights are - you are looking for balance - not the numbers. Good Luck.

i would if i wanted to get the distribution right, and the diagonal split etc, also by lifting one wheel, even slightly above the rest you alter the distribution on each tyre, and thus the method will not be reliable.... hence why you check all suspension settings/cornerweights etc on level ground