Printable View
bet me...
the end result of any works conducted by man and equipement is only ever as good as the skill level of the person using the equipment.
I dont care if you have the greatest gear on the planet. If you're a beltrame you're not even going to get close to what a master tradesmans going to do with just a bit of string and a bit of chalk.
where you're theory all falls over is (ok one of the many areas) you dont need to measure from the center of the tread.
Any method of measuring toe in that uses the edges of rims or sides of tyres will not be accurate unless these are running true. ie With no buckle in rim or bulge in side of tyre. A method of overcoming this, which may be easier with relatively smooth tyres than chunky treads common on Land Rovers is to first jack up the wheel and hold a piece of chalk, felt pen or anything that makes a clear visible mark to the middle of the tread while it is spinning. With line around tyre in middle of treads on both front tyres, lower and remove jack. Then measure distances between lines on tyres at axle height from front and back at hub height. Something more elaborate than a tape may be desirable if something obstructs direct line of measurement. eg on a level concrete floor, using something that functions as a square, mark the floor directly under the forward and rearward midline of each tyre, You can now measure these.
Chalk on the floor is somewhat lacking in precision. Toe in / out is measured, and specified, if memory serves after all these years, in millimeters at the perimeter of the wheel rim. If the wheel runout is too much to measure toe-in by, it's time for some new rims.
For those who may not necessarily be aware - an explanation of toe in: Front steering wheels when vehicle is going straight ahead should be parallel or very close to it, sometimes erring on pointing very slightly inwards to each other with a small recommended "toe in". It is important to note that the steering geometry is designed so the wheels "toe out" on turns when they pivot on separate king pins or whatever on the same axle.
Firstly consider what happens if a whole steering axle pivots from the middle, ie as with a turntable: The centre of the turning circle is where a line extending from the rear axle intersects with a line extending from the pivoting front axle. To avoid tyres scrubbing on turns, to achieve the same effect with front wheels pivoting separately, the inner wheel must turn sharper than the outer one so the right angles of the way each is pointing always line up with the same point on the line extending from the rear axle. That is the theory. In practice, with eg Defenders with 90. 110 or 127 inch wheelbases I am not aware of differences between setup of front axles to achieve this perfectly or the theoretical happy medium selected for the design purpose.
I recall the above is known as the "Ackerman principle" (Haven't yet tried googling it!) To achieve this result using a single piece steering axle with pivot points at each end, apparently when wheels are pointing straight ahead, where the tie rod ends should be are on lines between the king pin (or whatever) pivot points and the centre of the rear axle. Note that when the tie rod is behind the front axle, the distance between tie rod ends is less than the distance between the pivot points. When the tie rod is in front of the front axle this distance is longer. On vehicles with the latter setup tie rod ends are much closer to wheels than those with tie rod behind. Of course, design is more complicated to achieve this Ackerman principle effect with independent suspension for each front wheel.
Anyway, hope I have explained the above in a way that those not previously aware of the principle can follow it.
The point is transposing the points directly below the centre line of the tyre at hub height front and rear to the floor where it can be measured. How accurate it is depends on care involved. For " respectable" vehicles rims should give accurate measurement. However, remember some of those reading this forum own vehicles which may have wheels with a slight buckle and /or dings on the edges of them from wear and tear, including rough and problematic tyre changes but are still satisfactory for the uses required of them. Using a line put on the centre of the tread with the wheel spinning as the basis for measurements helps avoid errors caused by slightly imperfect wheels and /or tyres.Quote:
Originally Posted by POD
Quote:
Originally Posted by Blknight.aus
Spot on Dave.
I'd put one of my string jobs up against any 'laser' job.
On an open wheel race car you have toe in on the rear and toe out on the front and has to be accurate, let alone camber, castor and bump steer....
Static toe is generally set to compensate for tyre scrub inducing a thrust vector, in rear drive cars the front wheels tend to want to toe out when travelling forwards, hence often using an amount of static toe in adjustment, front wheel drive (and all wheel drive) tends to want to pull the leading edge of the tyres together as they drive, hence a static toe out adjustment.
Static toe out is usually used on race/rally cars regardless of which end drives as it induces a faster turn response, a more immediate effect of the Ackerman principle. (we're inducing our slip angle on the inside tyre immediately)
The Ackerman principle is nice in theory, in practise the car reacts somewhat differently depending on speed, tyre scrub and slip angles.
'Classic' Ackerman has the theoretical intersection point at the centre line of the rear axle, moving that intersection point forward along the wheel base usually increases the turn in response.
I've run classic, modified (various intersection points forward) zero and anti-ackerman.
The late, great Colin Chapman mounted an argument against Ackerman on race cars and generally in favour of anti-ackerman due to the slip angles involved.
In practise I wasn't convinced, and zero and anti-ackerman steering was a bitch to push around the pits, so at low speed without tyre scrub and slip Ackerman has something going for it.
Off topic Rick,
Bill runs reverse Ackerman on his hybrid
He doesn't mind it
(If you left that thing idling in first low (lowest) it would have backwards time travel capability, or it would be on someone's ceiling!!)
Dc
The tanks tent pole works for me
String all around can show how bad a 4 wheel alignment is
But that's another argument
Back to herding cats!!
Quote:
Originally Posted by modman
:lol:
I take mine to the local Bob Jane.
My cats do not travel well in the 110!:D
Dc