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[wheels-inmotion]

Born from another post i thought i could add a little understanding on this topic which is actually under the realm of chassis geometry....It's not a grey art so don't run away.... 

If we just concentrate on the front wheels for now and the toe position AKA
1: Alignment
2: Tracking
3: Four wheel Alignment

Historically the manufacture offers a static toe in or toe out position with a given tolerance.... Question to you is why?

[TheBoy]

Is the Q why is there a little toe in/out (this various if the steering wheels are driven or not), or tolerance (I guess not viable to get it bang on every time (given cost/time constraints, plus tiny play even in new components), so a tolerance has to be specified what is acceptable?)

[wheels-inmotion]

Q is why is there a toe in/out position and why does this vary between marques.

Remember team this is not designed to be a test nor is it designed to belittle any answers.... It's simply designed to help understand what your £30 or £40 quid is paying for.

[Webby the Bear]

Q is why is there a toe in/out position and why does this vary between marques.

Remember team this is not designed to be a test nor is it designed to belittle any answers.... It's simply designed to help understand what your £30 or £40 quid is paying for.

toe in is to compensate for rear wheel drive cars natural tendancy to ''push'' the wheels outwards whilst driving.... FWD cars naturally drive where their wheels come inwards hence the ''toe out'' to compensate to keep the wheels straight when driving

[Andy H]

The way I visualise it is this:
- The steering wheels have pneumatic tyres with soft sidewalls.
- When driving straight ahead there are no sideways forces on the tyres (if there is zero toe).
- When a sideways force is exerted (say a change in camber or a gust of wind) the tyres will deflect slightly and the vehicle change path. The driver then has to turn the steering far enough to load up the tyres to provide enough force to correct the vehicles path.

If a RWD car is set up with zero toe it feels "loose" with no feel through the steering and a tendency to zigzag down the road as the driver reacts to the car drifting off line.

Setting the steering to toe-in allows the sidewalls to be "pre-loaded". The value is chosen to be enough to give some feel but not enough to cause the tyres to scrub.

The tyre on the outside of a corner is the one that does most work. The toe-in means that the tyre is already pushing in the right direction as the steering input increases.

[Andy H]

With wrong wheel drive the steering is in a constant battle with the driving forces. Go round a corner with a trailing throttle and you have toe-out and the resulting 'loose' steering.

Accelerate round a corner and the steering geometry sorts itself out. Whether you have enough grip to get round the corner depends on your entry speed................

[05omegav6]

...and nerve

[chrisgixer]

A setting selected to give the best average given all conditions. All of which compromise each other in differing ways. If only there was a real time hawk eye, to see all parameters live, and understand the dynamics fully. Play station style.

Toe specifically ? Depends on the chosen suspension set up and wheel drive of the manufacturer, due to budget probably. Fwd being more dead ahead on an average of acceleration and braking forces within those blasted sloppy bush things. if you've got knackered front bushes on your omega there's not much point worrying about toe. As there will easily be 1" of for and aft movement in the wheel position under braking.
 Turn in feel, tyre slip angle, bush play, braking dynamics.

Clues all in the tyre wear. ...I wonder how many tyres manufacturers go through to arrive at their settings?

Anyway, that's how I see it.

[AndyRoid]

If only there was a real time hawk eye, to see all parameters live, and understand the dynamics fully. Play station style.

We certainly have the technology to do it but I suspect the cost would make it unfeasible.

[chrisgixer]

If only there was a real time hawk eye, to see all parameters live, and understand the dynamics fully. Play station style.

We certainly have the technology to do it but I suspect the cost would make it unfeasible.

I envisage some of those chav me wheels with spinners and a pair of wim wheel targets attached.

[wheels-inmotion]

Well you all seem very clued up on the topic so well done team....

As said the toe is a compliance angle.... Compliance as in the expected movement in the bushings under thrust/ tyre rolling resistance and braking force. The globule desire for the collective forces is a dynamic 0 toe.... This is the geometric law no matter what form of drive the car has albeit rear/ front or all four.

The suggested differences in the toe position over the marques is due to the bushing size and configuration. The downside is the variables? These suggested settings are all well and good for a newish car with lovely fit bushings but our cars live most their lives in the realm of worn........ Not new and not knackered but worn.

As an instructor i know operators/ calibrators in the field cannot work in an ideal world where the suspension and bushings are lovely and new so there has to be a realistic compromise..... How?

An initial visual check of the suspension, bushings and running gear like steering box and so on. Measure the chassis ( before the car is jacked up ) so that a "rested reading" is taken before the suspension/ bushing positions are violated.

Once proved the car sits happily in the realm of worn they can then simulate the tyres dynamic rolling resistance by installing a spreader rod? This is a sprung loaded bar that fits under the car and pushes the front tyres apart ( rolling resistance )

Once done and with live readings on the screen the toe tendency needs to be found?

Toe tendency what's that?
Remember we are in the realm of worn! Well every cars actual toe setting with differ depending on the level of worn. So with the spreader rod fitted a bounce on the suspension ( bump ) and a lift on the suspension ( droop ) within the expected range of travel they should be able to calculate the toe tendency.... Once read the static adjustment should be made at the centre of that tendency.

Example
Lets say the manufacturers suggested toe setting is +2mm total for the front wheels. I use mm because most tyre centres measure in mm although this is not really the correct way to measure the toe position! Anyway 2mm toe total, meaning a collective measurement between both front wheels.

If the cars bushings are tired and the steering linkage a bit "energetic" lets say, then with the spreader rod fitted and the tendency calculated the actual static toe position might need to be +6mm, giving that car a dynamic 0 toe.

Sad thing is after reading this you will know more about the toe angle than most tyre shops, and it's for this reason i post in great forums like this so that you get a heads up in the industry i work in and embarrasses me constantly.

Final note..... The toe angle is the least damaging, least influential regarding tyre wear and it CANNOT make the car pull!

[chrisgixer]

But an out of line thrust centre(combined rear toe) can. (Make the car crab)

So given the desired rolling toe setting is zero, that's alot of rolling resistance to give +0.10 mins static. Would poly give less deflection from rolling resistance? Given the comparatively soft oe bushes.

[chrisgixer]

Should add, for those not aware, poly are only available for the front bush.

[TheBoy]

Thanks, wheels-inmotion, that was a good description, hopefully useful to all our members

[Webby the Bear]

+1.

Very informative.... especially regarding the toe as I was led to believe it's this that is the most aggressive tyre wearing angle! And also that it can't create pull!