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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! 

[maracus]

This may be relevant; I have done my wheel alignment before with a piece of string and a ruler...

In a nutshell, A flat level surface, rock the car back and forth a few times to settle the geometry, finishing on a "forward" roll, then pull taught a length of string from the back edge of the rear wheel (6 or 9 o clock respectively) to the front of the front wheel (opposite 9 or 6 position respectively) and measure the distance from the back of the front wheel to the straight edge line you've created by pulling the string tight, and adjusting so that the measurement is as specified..

When I've done this previously to one of my cars, I tell you what, it drove better then than ever before, dispite having it previously tracked professionally with Lazer equipment. But my thing is, am I mad and just got damn lucky, or is there actual method in that madness??

[05omegav6]

Damn lucky if that were an Omega

[maracus]

^ it was a cavalier. Funnily enough I did try on one of my migs but abandoned it as I wasn't happy with how it was working out. The rubbers stuck out too far for an accurate consistency.

[chrisgixer]

That implies there's a set measurement available from a position on the front wheel to a position on the rear. I'd be surprised if a manufacturer would give a figure other than the wheel base. And knowing how much play there is in the subframe positioning it would never be accurate enough.

However, if replicating a setting from a given point, then replicating that measurement after, say, a track rod change, then that would be a million times better than simply counting threads from the old track rod.

But remember the steering pivots around the steering ball joint on the wishbone. So movement for and aft through natural steering movement is minimal the nearer straight ahead the front wheels are.
 Where as the angle of the wheel is more pronounced. Which is why I used the method described in the guides for setting toe.
 But it's totally dependent on replicating the pre existing setting by lining up the outer edge of the front wheel with a point on the rear. Either by eye, or with a straight edge.

I would never ever present that/either as a replacement for proper set up though. Merely to save your tyres on the journey to Wim.

[Webby the Bear]

That's my understanding.... counting threads is simply a way of getting the toe angle close enough to be able to drive it to the alignment shop after say a rack replacement for example  its not there to call it done..... although I suspect some folk do.

a question on what you mentioned chris if you dnt mind.... and that's re the thrust angle. mine's 1 minute away from optimum (i.e. 0 degrees). is 1 minute big enough margin to cause the crabbing you mentioned? ive personally had none of that and my tyres have even wear so im thinking not. but obviously id like to get it as close to perfect as poss. 

[chrisgixer]

Correction.

This was in relation to off centre steering wheel. Not a pull.

The front was spot on, but the rear thrust angle/toe was off centre causing a slight crab, as the rear was steering out sideways. So had to be corrected by the driver at the steering wheel.

Sorry Webby, I steered you wrong there.

[Webby the Bear]

Correction.

This was in relation to off centre steering wheel. Not a pull.

The front was spot on, but the rear thrust angle/toe was off centre causing a slight crab, as the rear was steering out sideways. So had to be corrected by the driver at the steering wheel.

Sorry Webby, I steered you wrong there.

haha no worries mate. was this your car youre talking about or someone elses? out of interest

[chrisgixer]

Correction.

This was in relation to off centre steering wheel. Not a pull.

The front was spot on, but the rear thrust angle/toe was off centre causing a slight crab, as the rear was steering out sideways. So had to be corrected by the driver at the steering wheel.

Sorry Webby, I steered you wrong there.

haha no worries mate. was this your car youre talking about or someone elses? out of interest

Yep. Mine. Took several attempts to sort out. But we got there.

[Webby the Bear]

 

So with my thrust angle out of spec by one minute. . . Is this acceptable. As said I've had none of rear end crabbing. . . Just the front end feels loose where the wishbone bushes are destroyed

[chrisgixer]

So with my thrust angle out of spec by one minute. . . Is this acceptable. As said I've had none of rear end crabbing. . . Just the front end feels loose where the wishbone bushes are destroyed

Pointless conversation Webby. Fix the car, first.

But if the car drives straight... And the steering wheel is level, don't worry. If not obviously that's the first thing to adjust.

....with experience, you wouldn't let a car off the ramp with settings like that. Tbh.

[Webby the Bear]

Oh of course. . .i plan to get the car WiMd as soon as I've got the suspension work done. I was merely wondering out loud if this would create problems on the assumption all suspension was in good nick 

[chrisgixer]

Oh of course. . .i plan to get the car WiMd as soon as I've got the suspension work done. I was merely wondering out loud if this would create problems on the assumption all suspension was in good nick 

You'd have to drive it to tell. Obviously the idea is to get the setting correct first, and eliminate as many possible faults as you can.

My guess would be that the steering wheel would not be level with the rear thrust angle 1 degree off. But Tony would know a lot more with his experience, for sure.

[Webby the Bear]

Cheers Chris.as said just wondering. It's only one minute out, not a whole degree so thinking it shouldn't be too bad . ..but obviously it will be corrected at sim when I take it 

[TheBoy]

Obviously the idea is to get the setting correct first, and eliminate as many possible faults as you can.

Whilst correct, for clarity, Eliminate all related faults, then get the setting correct (before moving on to next setting.

If you come across an unknown fault related to steering suspension, start again from scratch.

But Tony would know a lot more with his experience, for sure.

Indeed. But we can work together to let WIM, or any other outfit, know in what areas our cars seem very sensitive to, such as rear toe and front camber...

...I'm sure wheels-inmotion would welcome any feedback we can give them in this regard, as our site covers a single model of a single marque. I see OOF and WIM as a two way thing for collaboration

[chrisgixer]

Keeping the road from feeding back through the steering is my main bug bear ATM.

Somehow, and I don't know how this happened, but fitting the front wheels on the opposite side has resulted in pulling and oddness due to uneven wear. Suspect costco cocked that up, when I took it back for a rebalance, after I praised them from being so careful fitting.
Ruined the profile of the front tyres going by the steering. I can't find any other faults, bushes are new. No play, bolts are tight only minor fault us about 0.25mm of play in a wheel baring.
It feels like something approaching your TT when they fell off a cliff/you said something was "broken". Which turned out to be tyres. Grip level is fine, it's just the pulling on imperfections. Doesn't show up on a motorway at all, which is the only blessing.

If it was possible, I get the urge to put the tyre in a lathe and re machine them back to standard profile so it behaves.

[Webby the Bear]

Chris, when you say 'feedback' what are we talking about? A vibration?

Obviously you've forgotten more than I have to learn but if it is... vibrations from what I've learned are something ''not being round''.... so that would indicate tyres, alloys and bearings.

like when I was looking for a dodgy tire could it simply be one if those 3....obviously if we're talking about a vibration if not then feel free to tell me to shut up 

[Andy H]

Wanderlust? (that's what he usually complains is happening)

[wheels-inmotion]

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.

Yes polly's or rose joints would be set to a static zero toe front and rear.

[wheels-inmotion]

+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! 

That's the tyre industry talking to you.... Reality is the toe displacement offers lateral scrub to the tyres. In the event to toe position is wildly out then you as a driver would definitely know with the car bolting on/ off bump and white lines.

The front toe is the only angle that's shared between the front wheels. Since it's shared it's also symmetrical so of an equal force... Can't pull.

[Webby the Bear]

so whilst youre on can I ask how much youd charge to correctly align my car based on the image of my current readings? pm me if you prefer

[wheels-inmotion]

Chris has raised some good, valuable points that members need to heed before spending a penny on wheel alignment.

Let's try this..... There you are in the tyre shop wanting the front wheel alignment checked/ adjusted would you dare to ask what they are aligning the front wheels to?

I bet my left nut they say each-other......"WRONG!"

The front wheels don't actually know where forward is, is it \ \ there or / / or | |? The front wheels point of reference is the middle of the rear, called the Thrust angle.

The Thrust angle is a geometric law despite the drive formate. The Thrust position is generated by each rear toe position. In an ideal world both rear wheels would have the exact toe position and within the tolerances permitted, but it's not an ideal world.

Globally a tolerance displacement of the thrust is 10', this has been downgraded from the 30' permitted some years back. The Thrust position establishes an imaginary centre line that's projected to the front wheels forward direction. From that data each front wheel can be adjusted to the forward direction born from that reference point.

It's from that i say to you "front wheel alignment" is a con, reason i say this is on it's own there's no reference point so.... What are they aligning the wheels to?

[wheels-inmotion]

so whilst youre on can I ask how much youd charge to correctly align my car based on the image of my current readings? pm me if you prefer

I need to be careful here because the forum has given me great leverage over the years but in this case i feel a real image of realistic pricing might help members know what to expect elsewhere.

I can't quote for the entire country but i would like to offer a smattering of knowledge....

If you are told a "free alignment/ geometry check" then that's hook so ask what is any adjustment fee in advance?

MD will offer a total fee. This is regardless of the corrections made so top dollar.

We offer members a worst-case fee of £60+ vat including adjustments assuming the front subframe doesn't need moving, if it does then it's £95+ vat ( worst case )

Now in my tiny little mind the adjustability of the Omega doesn't command more than the normal discounted £60+ vat. Data positions are established so to me the calibration is fire-and-forget type of thing.

Thank TheBoy for this because he is the one who's helped me maintain the price structure without change for the last five years.... Think i might need to send him a letter bomb for Xmas 

[05omegav6]

Some bricks would suffice

Joking aside, finding someone prepared to offer an actual solution rather than a mere 'Green is fine' approach is a rare thing, and much appreciated 

[chrisgixer]

Chris, when you say 'feedback' what are we talking about? A vibration?

Obviously you've forgotten more than I have to learn but if it is... vibrations from what I've learned are something ''not being round''.... so that would indicate tyres, alloys and bearings.

like when I was looking for a dodgy tire could it simply be one if those 3....obviously if we're talking about a vibration if not then feel free to tell me to shut up 

Feedback is unwanted sensations from the road surface "feeding back" to the driver through the steering. Ime the most common starting point for this degrading of handling towards "wonderlust" is, pulling up to a set of traffic lights with wheel depressions in the road surface from heavy traffic, busses trucks and cars etc, commonly known as tramlines.
 You slow down to the line to stop, the slower you go the more the pull on the steering increases, the more you have to turn into the pull to keep the car on line. Similarly having stopped, creep up a few feet with no hands on the steering wheel, and you can observe the steering wheel turning on its own, due to ruts in the road. As if there was a mechanic or a little gremlin working on the road wheel pulling on a spanner. The driver feels that leverage on the steering wheel.
 In effect, the road is steering the car, not the driver. As the road is causing an uneven contact patch, or, an uneven contact patch in relation to the steering axis centre line of the front wheel.
 This is the same as a worn tyre as far as the steering feedback to the driver goes. Except its only present during contact with poor road surface. Tyre wear if present, is active all the time so the car becomes twitchy to the driver, rather than that one piece of bad road surface at the lights.
 The tyre wear in conjunction with poor road surface conspire to pull the steering, and feedback to the driver.

Poor road surface alone should not pull so much as give mild sensation mostly through the suspension.
Poor road surface and tyre wear however, and your into correcting the steering due to feedback, and the worse it gets as the tyres wear more.
Poor road surface, tyre wear, AND braking increases the feedback again. To the point that an emergency stop/severe inside shoulder wear/badly rutted road from a poor road repair, can see the car violently dart off line into the face of oncoming traffic. As I had with those Audi rated sc3. Luckily I was able to keep the car from crossing the white line, but the other driver coming the other way wasn't so convinced.

[05omegav6]

How likely is the thrust angle to change if the rear subframe bushes are poly?

[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.

Yes polly's or rose joints would be set to a static zero toe front and rear.

We hear talk of tyre slip angles... Presumably aiding tyre grip by generating heat. I presume that's not desirable in a road car? Or with road tyres?

Personally I find it difficult to see how slip angle in tyres can be helpful.

[chrisgixer]

How likely is the thrust angle to change if the rear subframe bushes are poly?

Do you mean a before and after change in angle due to fitting? Or during use of poly?

Both seem to be zero chance going by TB's before and after settings when poly where fitted. Poly have no voids like oe, so there's little chance for the rear subframe to articulate with poly.

[chrisgixer]

Although the rear trailing arm bushes are still rubber, so a level of deflection is still possible there.

[05omegav6]

If the car is set up after the polys are fitted, will the thrust angle setting degrade over time?

[chrisgixer]

If the car is set up after the polys are fitted, will the thrust angle setting degrade over time?

Due to poly bush in the subframe to body, no.

Due to to track rod wear(extremely rare), spring sag, trailing arm bush wear, all effecting the combined toe/camber setting... Yes

[05omegav6]

Thinking out loud as I need to replace the front track rods due to a knackered ball joint or two

Beginning to show on the inside edges of the front tyres