Tracking, Wossat then?
Discussion
Time again to expose my ignorance.
As far as i can gather, getting your car's tracking done involves making sure the front wheels are pointing in vaguely the same direction. In what way does this differ from "Laser Wheel Alignment", and a "Suspension Geometry Check" for that matter? Are they the same thing at different prices (pay per word), or is one better than the rest, or do they all do completley different things?
As far as i can gather, getting your car's tracking done involves making sure the front wheels are pointing in vaguely the same direction. In what way does this differ from "Laser Wheel Alignment", and a "Suspension Geometry Check" for that matter? Are they the same thing at different prices (pay per word), or is one better than the rest, or do they all do completley different things?
Depending on where you take it, tracking done by most of the high street tyre merchants(quackfit) etc usually only means the toe angles.
Laser alignment is the method used.
A setup would be where the entire range of adjustments possible for the model, camber ,castor, toe angle etc etc would be done. Costs more but does the job correctly.
Laser alignment is the method used.
A setup would be where the entire range of adjustments possible for the model, camber ,castor, toe angle etc etc would be done. Costs more but does the job correctly.
I've had my Integrale 4 wheel laser aligned and got it set up exactly how I wanted it. It does have fully adjustable suspension but this is the way to go for any IMHO. They checked all the stuff deltaf said and asked me what I wanted the handling characteristics to be like. Done a bloody good job too 
Deltaf's right - laser alignment is simply one method of 'doing' the tracking.
My dad used to have a Celica GT4 that would skip sideways on wet manhole covers. Toyota set the tracking up several (4?) times without curing it. Eventually, dad got the chap who looks after his vans & lorries to come and sort it out with his portable laser kit.
Apparently Toyota had it 'perfect', except for the fact that they chose one wheel as being correct & lined the others up from that starting point. Oddly enough, the 1st wheel wasn't right, so the 4WD system was trying to drive the car a few degrees off straight
My dad used to have a Celica GT4 that would skip sideways on wet manhole covers. Toyota set the tracking up several (4?) times without curing it. Eventually, dad got the chap who looks after his vans & lorries to come and sort it out with his portable laser kit.
Apparently Toyota had it 'perfect', except for the fact that they chose one wheel as being correct & lined the others up from that starting point. Oddly enough, the 1st wheel wasn't right, so the 4WD system was trying to drive the car a few degrees off straight
moleamol said: I've had my Integrale 4 wheel laser aligned and got it set up exactly how I wanted it. It does have fully adjustable suspension but this is the way to go for any IMHO. They checked all the stuff deltaf said and asked me what I wanted the handling characteristics to be like. Done a bloody good job too
Did that cost as much as it sounds like it did?
Not really, £200. But they did seem to like my car
agent006 said:Did that cost as much as it sounds like it did?
moleamol said: I've had my Integrale 4 wheel laser aligned and got it set up exactly how I wanted it. It does have fully adjustable suspension but this is the way to go for any IMHO. They checked all the stuff deltaf said and asked me what I wanted the handling characteristics to be like. Done a bloody good job too
There are many different angles that are crucial to control in the steering geometry. Tracking is the one which is most easilly affected (especially by driving up and down kerb edges and striking them when you park)
Tracking is another name for adjustment of toe in or toe out angles on the steering wheels. Rear wheel drive car are set to toe in (so the front inner edges of the tyres point towards each other such as in the sides of an arrow head) as when the power from the rear wheels pushes the car forwards, the front wheels through friction on the road are pushed outwards into a straight line.
The opposite, toe out is applied to front wheel drive vehicles so that when the car is being pulled along by the front drive wheels, the friction of the road surface pulls the wheels back into line from pointing away from each other.
Mechanical tracking devices and laser alignment are just ways of achieving the correct toe in toe out angle to make the wheels straight when they are under load, depending on the drive specificqation of the vehicle.
The other angles in relation to steering are
Ackerman,
King pin inclanation
Caster angle
Camber angle
and last of all tyre slip angle.
The above angles are only usually altered if you fcuk up in a big way and bend something badly in a crash.
Toe in and toe out are affected by lateral bumps to the sides of the wheels and need to be checked regularly if safe handling is desired and tyre wear is to be even across the tyre width.
So endeth the lesson
>> Edited by madcop on Wednesday 2nd April 11:52
>> Edited by madcop on Wednesday 2nd April 15:35
Tracking is another name for adjustment of toe in or toe out angles on the steering wheels. Rear wheel drive car are set to toe in (so the front inner edges of the tyres point towards each other such as in the sides of an arrow head) as when the power from the rear wheels pushes the car forwards, the front wheels through friction on the road are pushed outwards into a straight line.
The opposite, toe out is applied to front wheel drive vehicles so that when the car is being pulled along by the front drive wheels, the friction of the road surface pulls the wheels back into line from pointing away from each other.
Mechanical tracking devices and laser alignment are just ways of achieving the correct toe in toe out angle to make the wheels straight when they are under load, depending on the drive specificqation of the vehicle.
The other angles in relation to steering are
Ackerman,
King pin inclanation
Caster angle
Camber angle
and last of all tyre slip angle.
The above angles are only usually altered if you fcuk up in a big way and bend something badly in a crash.
Toe in and toe out are affected by lateral bumps to the sides of the wheels and need to be checked regularly if safe handling is desired and tyre wear is to be even across the tyre width.
So endeth the lesson
>> Edited by madcop on Wednesday 2nd April 11:52
>> Edited by madcop on Wednesday 2nd April 15:35
madcop said:
Tracking is another name for adjustment of toe in or toe out angles on the steering wheels. Rear wheel drive car are set to toe in (so the front inner edges of the tyres point towards each other such as in the sides of an arrow head) as when the power from the rear wheels pushes the car forwards, the front wheels through friction on the road are pushed outwards into a straight line.
The opposite, toe out is applied to front wheel drive vehicles so that when the car is being pulled along by the front drive wheels, the friction of the road surface pulls the wheels back into line from pointing away from each other.
What about 4wd? Or is that a daft question - ie should be neutral.
mechsympathy said:
madcop said:
Tracking is another name for adjustment of toe in or toe out angles on the steering wheels. Rear wheel drive car are set to toe in (so the front inner edges of the tyres point towards each other such as in the sides of an arrow head) as when the power from the rear wheels pushes the car forwards, the front wheels through friction on the road are pushed outwards into a straight line.
The opposite, toe out is applied to front wheel drive vehicles so that when the car is being pulled along by the front drive wheels, the friction of the road surface pulls the wheels back into line from pointing away from each other.
What about 4wd? Or is that a daft question - ie should be neutral.
Haynes manual for the golf (Mk3) says it should be dead ahead anyway (though a small amount of toe-out would make sence in general for a FWD I suppose) -read the book (or find someone that has -a (friendly) local dealer is probably a good bet if no haynes (or similar) manual exists for it.
Saying that -its only a guide, and i might play with it sometime to see how much differance it makes to handling.
Also, my mates dad has got a little "tracking guage" which basically consists of 2 bits of plastic that can slide on top of one another in 1 direction (side to side), and you drive over it and if the plates move relavive to one another it tells you your tracking is out. -crude and probably not very accurate, but gives a good idea of how close of or otherwise it is. -he's had it "for ever" though, so i have no idea where you could get 1.
Pete
>> Edited by pistol pete on Wednesday 2nd April 15:05
mechsympathy said:
What about 4wd? Or is that a daft question - ie should be neutral.
Depends on the split of power from front to rear. I do not know about 4 wheel drive but I assume that there will have to be some toe adjustment somewhere. I only know about the principles involved and not the technical application.
pistol pete said:
Also, my mates dad has got a little "tracking guage" which basically consists of 2 bits of plastic that can slide on top of one another in 1 direction (side to side), and you drive over it and if the plates move relavive to one another it tells you your tracking is out. -crude and probably not very accurate, but gives a good idea of how close of or otherwise it is. -he's had it "for ever" though, so i have no idea where you could get 1.
www.toolsbypost.com it's called a Trakrite.
To elaborate further on previous posts (mostly nicked from my student days (in turn mostly nicked from Millikan : Racecar Vehicle Dynamics, good book)).
The axis about which the wheel steers on modern car with independent suspension is defined by the location of the ball joints where the suspension mounts to the upright. This axis is not necessarily vertical for a number of reasons, and is called the kingpin axis.
The angle of the kingpin axis in front view is called the kingpin inclination, and the offset of the kingpin axis from the tread’s centre of pressure at the ground is called the scrub radius. In side view, the angle of the kingpin axis is called castor/caster angle. The distance between the kingpin axis and tyre centre (at hald tyre height) is the kingpin offset (taking side view) or spindle length (front view). The distance between the kingpin axis and tyre centre at the ground in side view is called the mechanical trail.
The spindle length, kingpin inclination and the consequent scrub radius result from a compromise between packaging and performance requirements. The brakes and hub need to fit inside the wheel, outboard of the suspension mounting points. If the wheel bearings are to have little offset they must be mounted near (and ideally directly over) the tyre centre line, further reducing the amount of available space within the wheel. These considerations mean that spindle lengths are almost always positive.
A positive spindle length will cause the car to be raised up as the wheels are steered away from centre. Larger kingpin inclinations cause the car to be raised more, and for a given kingpin inclination, a longer positive spindle length will increase the amount of lift with steer. This effect aids centring of the steering at low speed.
With kingpin inclination inward at the top, when a wheel is steered in either direction, it will lean out towards positive camber. This effect is undesirable, but is usually small in normal driving due to relatively small steer angles.
Scrub radius acts as a moment arm which induces a torque about the steering axis under forward motion, and especially under braking. With positive scrub this torque promotes toe-out under braking, which tends to make the car less stable. Uneven braking forces at inboard and outboard front wheels will lead to a net torque being felt by the driver at the wheel. Since the dynamic centre of pressure of tyre moves under load and changes in tyre alignment, scrub radius is typically measured under static conditions, with zero camber.
Mechanical trail arises from castor angle and kingpin offset. The trail is the major source of self centring in the steering at moderate or high speeds. The wheel aligns itself with the direction of motion due to the moment arm between the tread’s centre of pressure, and the intersection of the steering axis with the ground. The greater the trail, the greater the self centring forces. The mechanical trail combines with the pneumatic trail to produce the total trail. For reasons of steering feel, the mechanical trail should not be much larger than the pneumatic trail.
Castor angle causes the wheel to rise and fall with steer. Unlike kingpin inclination, the effect is asymmetric. With symmetric geometry and positive castor, the effect of a left steer is to roll the car slightly to the right.
Castor angle affects steer camber in the opposite direction to kingpin inclination, and with positive castor angle, the outside wheel will camber in a negative direction, and the inside wheel will camber in the positive direction.
The static 'toe angle' is the angle in plan view that the tyre makes with the longitudinal axis. Toe is positive (‘toe-in’) when the leading edges of the tyres are closer than those trailing. Toe in produces a constant lateral force toward the centre of the vehicle centreline during forward motion. This force improves straight line stability.
Toe-out causes the loaded outboard tyres to tend to point toward the outside of a turn under cornering. Toe-out in the front tyres promotes understeer in the front, and oversteer at the rear of the car.
Ackermann:
When a car moves around a corner, the wheels describe arcs about an instantaneous centre. The inner wheels move about this centre on an arc with a smaller radius than the outside wheels. This necessitates a greater steer angle on the inside wheel for it to be tangential with the arc of motion. If the tires point in their direction of motion, the centre of the arc about which the car moves will be in line with the centre of the rear tires. 'Full Ackermann' steering causes the inside and outside wheel to point tangential to these arcs.
Both front and rear tires will assume slip angles under load, leading a change in the location of the centre of the arc described by the car.
In most racing situations, the steer angles at the front wheels are small (up to a maximum of about eight degrees), and the effect of slip angles is such that racing car designers employ much less Ackermann than ‘full’ and run parallel or even reverse-Ackermann steering. At low speeds and high steer angles, a considerable amount of Ackermann is required to prevent the inside wheel scrubbing.
The effect of Ackermann on the dynamic performance of a race car is lessened by the lateral load transfer which occurs during cornering. At high lateral loads the inside wheel has very little vertical load due to weight transfer, so it makes less difference what direction it points in.
The axis about which the wheel steers on modern car with independent suspension is defined by the location of the ball joints where the suspension mounts to the upright. This axis is not necessarily vertical for a number of reasons, and is called the kingpin axis.
The angle of the kingpin axis in front view is called the kingpin inclination, and the offset of the kingpin axis from the tread’s centre of pressure at the ground is called the scrub radius. In side view, the angle of the kingpin axis is called castor/caster angle. The distance between the kingpin axis and tyre centre (at hald tyre height) is the kingpin offset (taking side view) or spindle length (front view). The distance between the kingpin axis and tyre centre at the ground in side view is called the mechanical trail.
The spindle length, kingpin inclination and the consequent scrub radius result from a compromise between packaging and performance requirements. The brakes and hub need to fit inside the wheel, outboard of the suspension mounting points. If the wheel bearings are to have little offset they must be mounted near (and ideally directly over) the tyre centre line, further reducing the amount of available space within the wheel. These considerations mean that spindle lengths are almost always positive.
A positive spindle length will cause the car to be raised up as the wheels are steered away from centre. Larger kingpin inclinations cause the car to be raised more, and for a given kingpin inclination, a longer positive spindle length will increase the amount of lift with steer. This effect aids centring of the steering at low speed.
With kingpin inclination inward at the top, when a wheel is steered in either direction, it will lean out towards positive camber. This effect is undesirable, but is usually small in normal driving due to relatively small steer angles.
Scrub radius acts as a moment arm which induces a torque about the steering axis under forward motion, and especially under braking. With positive scrub this torque promotes toe-out under braking, which tends to make the car less stable. Uneven braking forces at inboard and outboard front wheels will lead to a net torque being felt by the driver at the wheel. Since the dynamic centre of pressure of tyre moves under load and changes in tyre alignment, scrub radius is typically measured under static conditions, with zero camber.
Mechanical trail arises from castor angle and kingpin offset. The trail is the major source of self centring in the steering at moderate or high speeds. The wheel aligns itself with the direction of motion due to the moment arm between the tread’s centre of pressure, and the intersection of the steering axis with the ground. The greater the trail, the greater the self centring forces. The mechanical trail combines with the pneumatic trail to produce the total trail. For reasons of steering feel, the mechanical trail should not be much larger than the pneumatic trail.
Castor angle causes the wheel to rise and fall with steer. Unlike kingpin inclination, the effect is asymmetric. With symmetric geometry and positive castor, the effect of a left steer is to roll the car slightly to the right.
Castor angle affects steer camber in the opposite direction to kingpin inclination, and with positive castor angle, the outside wheel will camber in a negative direction, and the inside wheel will camber in the positive direction.
The static 'toe angle' is the angle in plan view that the tyre makes with the longitudinal axis. Toe is positive (‘toe-in’) when the leading edges of the tyres are closer than those trailing. Toe in produces a constant lateral force toward the centre of the vehicle centreline during forward motion. This force improves straight line stability.
Toe-out causes the loaded outboard tyres to tend to point toward the outside of a turn under cornering. Toe-out in the front tyres promotes understeer in the front, and oversteer at the rear of the car.
Ackermann:
When a car moves around a corner, the wheels describe arcs about an instantaneous centre. The inner wheels move about this centre on an arc with a smaller radius than the outside wheels. This necessitates a greater steer angle on the inside wheel for it to be tangential with the arc of motion. If the tires point in their direction of motion, the centre of the arc about which the car moves will be in line with the centre of the rear tires. 'Full Ackermann' steering causes the inside and outside wheel to point tangential to these arcs.
Both front and rear tires will assume slip angles under load, leading a change in the location of the centre of the arc described by the car.
In most racing situations, the steer angles at the front wheels are small (up to a maximum of about eight degrees), and the effect of slip angles is such that racing car designers employ much less Ackermann than ‘full’ and run parallel or even reverse-Ackermann steering. At low speeds and high steer angles, a considerable amount of Ackermann is required to prevent the inside wheel scrubbing.
The effect of Ackermann on the dynamic performance of a race car is lessened by the lateral load transfer which occurs during cornering. At high lateral loads the inside wheel has very little vertical load due to weight transfer, so it makes less difference what direction it points in.
Be very selective where you take your car to have the tracking checked. I once took one of my disreputable old heaps (cars that is) to get a couple of new tyres fitted. The oiks in the tyre depot asked me if I wanted the tracking checked. Foolishly I said yes, as I knew the front tyres were wearing perfectly evenly. Amazingly they said the tracking was way out and did I want it fixed. Since I didn't believe them I said no, but on driving the car away the steering had clearly been interfered with.
Be warned.
Be warned.
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