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MG MGA - Toe-In Question

Is the toe-in constant throughout the suspension excursion, or does the toe-in increase when the suspension is compressed or extended beyond the ambient static position?

I'm assembling my chassis on a rotisserie stand for convenience and it sure would be nice to set the toe-in with the suspension unloaded and fully extended.

Looking at the linkages, It would appear that the toe-in setting is correct only when the fully weighted vehicle is level and static due to the ball swivel joints at the steering rack ends. Otherwise it appears that the toe-in increases with bi-directional movement around nominal.

Is there a setting for a fully extended unloaded front end that will yield close to the right setting loaded?

Thanks,
Doug
D Sjostrom

Doug - I do't know all of the particulars to your question, However I would suspect that alignments change throughout the travel of the suspension in that everything I have heard is that adjustments should only be done with the car on the ground and at normal weight. Good luck - Dave
David DuBois

Doug

The reason everything must be done with the car on the ground is that the inner bushes on the A pans must only be tightened when you have the car on the ground, otherwise the bushes are compressed when they are not at the centre position, and have therefore a shorter life (because they are twisted beyond spec in the upward travel).

Setting the tracking / toe in can likewise only be done with weight on the wheels, because this is the position at which the car suspension spends most of its life, with +/- variations.

dominic clancy

Hi Doug

When you set your tracking try about 10 to 20 minutes toe out, this was recommended in a previous thread, I've set mine to this and the steering is less heavy when cornering, a vast improvement! The tyres dont seem to be suffering with this setting

Terry
Terry Drinkwater

Thanks All.
Doug
D Sjostrom

You should definitely do it in the ride position. There are two movements that translate into toe variation as the suspension travels. One is that the tie rod describes an arc and will be at full spread (toe out)when the rod is horizontal. The other is that the fulcrum point of the steering arm (halfway up the swivel, also describes a different arc (actually the average of the arcs described by the upper and lower arms) and it is not clear whether this compensates exactly for the tie rod arc. This would be part of the designer's task, but is probably not perfect.
Art

Doug; Yes toe in does change as a vehicle steers. This is called the Ackermann angle. If an MG is traveling in a circle the inside fromt tire is at radius X the outside tire must be at radius X plus 4 feet(the track width) If it is not the tire would be scuffing.Thought u would like to know. Bill.
w.g cook

With proper Ackerman steering geometry the centerlines of the front wheel spindles should intersect at a point on the centerline of the rear axle. This would make all of the tires circle around a common steering center, and none would have to skid sideways when you steer.

Well, it doesn't work. You may have noticed that if you turn the wheels one way to full lock it is difficult to hand push the car. This is because the front spindles do not intersect on line with the rear axle, and onr or the other of the front tires has to skid sidewise a bit to negotiate the turn.

With perticularly careful choice of geometry of the steering parts it is possible to get this common intersection point at one steering angle other than straight forward. The best setup might be to make this second 3-way intersection occurance at about half lock where it might do the most good for turning mildly at city travel speed.

In actual practice this is seldom done, because it is difficult to get the proper position for the tie rod end when the wheel and brake parts are located first in best chosen position. Things just get in the way. This is often blatently obvious when someone backs out of a parking space with front wheels turned to full lock, and the tires squeak on the pavement as the car moves.

It is for this reason that it is sometimes advantaguoes (especially for competition cars) so set the toe in to something other than original factory spec, so you can have the proper Ackerman angle for best tracking and best latteral grip when turning at speed, commonly around 1/4 rotation of the steering wheel either way from straight ahead.

Barney
Barney Gaylord

This thread was discussed between 10/06/2005 and 14/06/2005

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