DIY Geometry check
Discussion
Anyone got any good guides/linkys to setting up your own geometry checks at home with string, rulers, protractors that kind of thing? I want to have a quick go and see how far off my calculations are incomparison to a proper check when swapping my tires over in next two weeks. And from then on I can do the odd inspection myself if I think my measurement are close enough.
Ta
Ta
You can buy some simple tracking gauges online for less than £70, worthwhile if you mess around with geometry often.
There is the old method of 'boxin' where you make a perfect rectangle around the wheels but you need a perfectly level floor. See - http://www.pistonheads.com/gassing/topic.asp?t=273...
There is the old method of 'boxin' where you make a perfect rectangle around the wheels but you need a perfectly level floor. See - http://www.pistonheads.com/gassing/topic.asp?t=273...
The most important things are camber and toe-in, and you can measure those yourself very easily.
For camber you can use either a plumb line to get a vertical reference or a spirit level to get a horizontal reference, then measure the angle to the plane of the wheel. You could use an ordinary spirit level instead. You can even get special purpose devices which consist of a mini spirit level and a magnet to clamp it to the brake disk that makes it easier if you don't mind spending the money. But the plumb line I use cost about 50p and works fine.
For toe-in you need to establish a straight line parallel with each wheel and measure the angle between the two lines. I use a length of wood held against the wheel.
You can also measure caster by measuring the change in camber as the wheel goes from 30 degrees steering one side of straight ahead to 30 degrees the other way.
You wouldn't usually measure the angle directly but work it out by simple trigonometry. You can use the 'one in sixty' rule to estimate small angles from the dimensions of a right angle triangle. For example if your plumb line is 600mm long and the top is 10mm further away from the wheel than the bottom then you know that's approximately 1 degree of negative camber. To make the mental arithmetic easier make sure the triangle you're measuring is a multiple of 60 in whatever units you're measuring. 600mm is fine if you're working in metric, if you measure to +/- 1mm that gives you a resolution of +/- 0.1 degrees which is far better than you need.
For camber you can use either a plumb line to get a vertical reference or a spirit level to get a horizontal reference, then measure the angle to the plane of the wheel. You could use an ordinary spirit level instead. You can even get special purpose devices which consist of a mini spirit level and a magnet to clamp it to the brake disk that makes it easier if you don't mind spending the money. But the plumb line I use cost about 50p and works fine.
For toe-in you need to establish a straight line parallel with each wheel and measure the angle between the two lines. I use a length of wood held against the wheel.
You can also measure caster by measuring the change in camber as the wheel goes from 30 degrees steering one side of straight ahead to 30 degrees the other way.
You wouldn't usually measure the angle directly but work it out by simple trigonometry. You can use the 'one in sixty' rule to estimate small angles from the dimensions of a right angle triangle. For example if your plumb line is 600mm long and the top is 10mm further away from the wheel than the bottom then you know that's approximately 1 degree of negative camber. To make the mental arithmetic easier make sure the triangle you're measuring is a multiple of 60 in whatever units you're measuring. 600mm is fine if you're working in metric, if you measure to +/- 1mm that gives you a resolution of +/- 0.1 degrees which is far better than you need.
I've put some details up which are specific to the Libra.
But the principle can be applied to any car. It's just a matter of choosing the datum points to use.
It's worth making a set up plank, since once you have the reference points to push it up to, it is so much quicker than getting the 'string box' set up.
BUT....a level floor is a must.
http://www.drawmer.net/libra/librabuild.htm
and follow the 'set up' button.
But the principle can be applied to any car. It's just a matter of choosing the datum points to use.
It's worth making a set up plank, since once you have the reference points to push it up to, it is so much quicker than getting the 'string box' set up.
BUT....a level floor is a must.
http://www.drawmer.net/libra/librabuild.htm
and follow the 'set up' button.
Ill have re read through all the info given and try and work out what I need to do.A nice addition to the camber method is to get a straight piece of tube and tap one end M6 x 1.0 then screw a set srew into it. Have the length of the tube such that the bottom of the tube against the rim, and the screw is on the top of the rim. Put a spirit level against the tube and screw the screw a number of turns (and then fractions of a turn) until the spirit level bubble is level. Each turn of the screw will be exactly 1.0mm so you'll be able to work out the camber angle using that length and the length of the tube.
As for toe, I've used the "string box" method before but it takes ages - especially if the car has different track front and rear. I have two poles with holes exactly the same distance apart, both a bit wider than the car. I put one of them in front of the car transversely and the other behind the car. I then run threads of cotton between each pair of holes - one down each side of the car. At least then I only have to shuffle them sideways to get the two strings an even distance from the hub centres because I know the two strings will be always paralell.
As for toe, I've used the "string box" method before but it takes ages - especially if the car has different track front and rear. I have two poles with holes exactly the same distance apart, both a bit wider than the car. I put one of them in front of the car transversely and the other behind the car. I then run threads of cotton between each pair of holes - one down each side of the car. At least then I only have to shuffle them sideways to get the two strings an even distance from the hub centres because I know the two strings will be always paralell.
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