Toe-in vs Toe-out Reg cornering
#1176858
02/12/12 08:16 AM
02/12/12 08:16 AM
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jcc
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SO I finally got a reasonable explanation on the science of this topic. And I remember I think it was Einstein who was quoted as saying one really knows a subject when you can explain it to your grandmother.  Hope Grandma is listening. Anyway, since I suspect a wide range of readers, let me first make sure we are all on the same page. I would define "yaw" (this is not a roundy redneck term  ) as the vertical axis looking straight down upon a car. A car exhibits yaw when it rotates about this axis clockwise, to the right, or counterclockwise to the left. This axis can be a geometric axis, say the two diagonal intersecting lines drawn catty corner from the four tire contact patches, the center of gravity, or the aero center of pressure. For this topic we can use the first. In the typical toe-in application, both front tires have toe-in the same amount. This toe in has two force components on each front tire, the left is pushing right, and the right tire is pushing left. These forces are thought to be in balance when driving in a straight line. Additionally, each front tire has a small slip angle because of this toe, and this scrubbing accounts for a small amount of drag, the drag for both front tires is accumulative. In a toe out configuration everything above applies, except the left tire is pushing left, and the right tire is pushing right, again while in a straight line. Now here is were it gets interesting. In a toe out set-up, when the driver initiates a turn say to the left, the left tire causes more slip angle, this also increases tire scrub and drag on the left tire. The right tire at the same time now becomes directly in line with the direction of the cars travel, all slip is gone, and no drag. At this point, because of drag on the left and and zero on the right, the cars likes to turn left. These forces help induce yaw. Same applies in a toe-out car when turning right. Going back to out common toe in set up, when turning left, the left tire goes straight, now has has zero slip, no scrub/drag, and right tire increases slip, increase drag, and car wants to yaw right, opposite of what our drivers intentions are. I suspect this effect is mainly upon "turn in", which is very important regarding driver's perception, and goes away upon entering a corner. I hope others will add/clarify what I have tried to explain, and the rest gain a smidgen of added insight 
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Toe-in vs Toe-out Reg cornering
[Re: Dcuda69]
#1176861
02/12/12 01:47 PM
02/12/12 01:47 PM
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Joined: Jan 2003
Posts: 27,468
So Cal
autoxcuda
Too Many Posts
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Quote:
When we set static toe-in, frictional forces tend to move the tires towards toe-out(zero toe) when we drive down the road(dynamic).Ackerman angles ( built into steering knuckles)create toe-out-on-turns or turning angle. Cars set with static toe-out tend to wander and be "twitchy"  
Yes, the ackermann kicks in after the car is in the turn and there is more tire angle. But like jcc mentioned the toe out really helps initial turn in. Most racing sedans (large cars) have a little toe out. The higher caster angle helps it not be so twitchy going straight.
Most road courses and autocross course dont have very long periods were the steering is completely dead on straight.
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Re: Toe-in vs Toe-out Reg cornering
[Re: jcc]
#1176862
02/13/12 03:13 PM
02/13/12 03:13 PM
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SoCal
68HemiB
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A car that has been aligned with the proper amount of static toe-in will be at ZERO TOE when driving down the road. Once moving, the forces at work make the tires want to toe-out, and the simple goal of static toe-in is to approximate the "give" in the components involved so that zero toe is achieved once in motion. Therefore, the inboard tire is NOT EVER traversing through straight ahead on the way to toeing out at the instant a turn is begun - the first movement is away from straight ahead into toe-out.
This new forum is for folks who think that "corners are best". I have steered clear (pun intended) from my soapbox about how the auto-crossing minority too often push their agenda of crazy-high negative camber into the faces of the vast majority of classic car folks here whose cars never see anything more strenuous than the occasional sweeping freeway onramp. It's your forum, so knock yourselves out with your negative camber.
That being said, I can think of no better way to ruin front tires in short order than by messing with toe-in. I think the O.P. is doing a disservice, even to avid auto-crossers, to suggest that significant benefit can be gained for anything other than a track-only car by messing with toe settings.
Down to just a blue car now.
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Re: Toe-in vs Toe-out Reg cornering
[Re: 68HemiB]
#1176863
02/13/12 05:21 PM
02/13/12 05:21 PM
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Pikes Peak Country
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I've been playing with cars that turn fast for a long time now and I can't really say I've seen a lot of people pushing "crazy high negative camber" on people that are just casual drivers. On moparts alone, I've seen many posts suggesting more negative camber should only be used by those who intended on pushing the envelope of driving through corners.
I will agree that occasionally the line between street and track applications does occasionally get blurred, but suspension and handling are not the only arenas where that happens.
For a street car, yes, I would stick with a toe in recommendation exclusively. Even on track cars, toe out can be minimilized. I noticed when I first started turning corners in my track cars that I tended to use more toe out than was necessary. The reason for this is because it does create a more stable transitional feeling and helps reduce some of the understeer. As my skills improved and my laps times dropped, I found myself using less toe out in the combination and instead playing with changes in ackerman. However, I also experienced a season when a track resurfacing left bumps on corner entry where I could actually utilize bump steer to initiate a toe out situation that allowed me to carry additional speed through the corner when others were still wrestling with the steering wheel. Since this was a car that only turned left under speed, this became a viable part of the set up. Otherwise, minmizing toe changes during bump and rebound are admirable efforts for a car that has to turn in both directions.
But, like so much other info, just because its on the web, even on moparts, doesn't mean its always correct. Each person needs to evaluate the info for themselves and apply as they feel it applies to their individual situations.If a casual street driver has never driven a car with a toe out situation, initial feel would probably freak them out to a point of dialing it back to a toe in situation right away. It does feel odd.
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Re: Toe-in vs Toe-out Reg cornering
[Re: 68HemiB]
#1176865
02/13/12 06:31 PM
02/13/12 06:31 PM
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Nebraska
72Swinger
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Toe out will make a street car a rut climbing pos.
Mopar to the bone!!!
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Re: Toe-in vs Toe-out Reg cornering
[Re: 68HemiB]
#1176867
02/14/12 12:02 AM
02/14/12 12:02 AM
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jcc
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Quote:
A car that has been aligned with the proper amount of static toe-in will be at ZERO TOE when driving down the road. Once moving, the forces at work make the tires want to toe-out, and the simple goal of static toe-in is to approximate the "give" in the components involved so that zero toe is achieved once in motion. Therefore, the inboard tire is NOT EVER traversing through straight ahead on the way to toeing out at the instant a turn is begun - the first movement is away from straight ahead into toe-out.
So back to "science". The above is what I have read/understood more or less to be the toe-in mantra for many years. However you mention "forces at work" What exactly are those forces? And are they speed dependent ( ie wind drag, tire slip, brake drag, etc) and if the main purpose is to allow suspension compliance until zero toe is achieved, what magic happens that stops all this compliance when zero toe is achieved, but the forces continue to rise as speed increases, or is it just zero toe at one set speed, and toe out above? Is this the basis for 11/16" TR? If tire slip was the main force, it would seem to me that as soon as zero toe was reached, the force would diminish, suspension compliance would return wheels to toe in and the process would start all over again, not an ideal situation.
Anyone? 
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Toe-in vs Toe-out Reg cornering
[Re: 68HemiB]
#1176868
02/14/12 12:26 AM
02/14/12 12:26 AM
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Joined: Nov 2005
Posts: 15,118
85086
moparpollack
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Quote:
Quote:
If a casual street driver has never driven a car with a toe out situation, initial feel would probably freak them out to a point of dialing it back to a toe in situation right away. It does feel odd.
...and will wear out front tires in no time at all.
So where does the magic crayon come into play when doing an alignment. 
56 Plaza 63 D100 step side 67 Coronet, 68 Roadrunner, 69 Super Bees, 69 Coronet 500 convertible, 70 Roadrunner Post, 79 D150 360, and a severe case of Mopar a,d,d
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Re: Toe-in vs Toe-out Reg cornering
[Re: jcc]
#1176870
02/14/12 02:58 PM
02/14/12 02:58 PM
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Quote:
So back to "science". The above is what I have read/understood more or less to be the toe-in mantra for many years. However you mention "forces at work" What exactly are those forces? And are they speed dependent ( ie wind drag, tire slip, brake drag, etc) and if the main purpose is to allow suspension compliance until zero toe is achieved, what magic happens that stops all this compliance when zero toe is achieved, but the forces continue to rise as speed increases, or is it just zero toe at one set speed, and toe out above? Is this the basis for 11/16" TR? If tire slip was the main force, it would seem to me that as soon as zero toe was reached, the force would diminish, suspension compliance would return wheels to toe in and the process would start all over again, not an ideal situation.
Anyone?
Really? I'm suprised you would ask this question after posting the initial write up. But, I'll bite.
The force is friction. The motion of the tire rolling over the road creates friction that pushes the toe in to zero toe, if it has been set properly. It is simply to take up tolerances in the myriad assortment of components in the steering system. If you wanted to get precise in it all, you should probably measure how much deflection a system has and use that to determine exactly how much toe is required. In a competition car this may be worthwhile, but in a street car a general range should be sufficient.
This friction is always present and it is not elastic in such a manner that the tires are constantly changing back and forth once in motion. If your sitting still and sawing the wheel back and forth then you may remove the force to a degree, but friction is always there to sufficient degree need the effect. Yes, the force does increase with speed, but once all the slack is absorbed, additional speed does not create additional toe, unless components are worn or failing. It is a hard stop that keeps toe in spec so long as the components are in good working order. That is why analysis of tire wear is the best tool an alignment tech has to get a car dialed in. Wear is a better indicator of what a suspension wants than actual specs can be. On my competition cars, wear, via temperature measurements, is what we used to dial in these specs to create an alignment that allowed maximum tread contact with the road surface for the intended application.
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Re: Toe-in vs Toe-out Reg cornering
[Re: TC@HP2]
#1176871
02/15/12 12:21 AM
02/15/12 12:21 AM
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Joined: Dec 2003
Posts: 22,696
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jcc
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Quote:
Quote:
So back to "science". The above is what I have read/understood more or less to be the toe-in mantra for many years. However you mention "forces at work" What exactly are those forces? And are they speed dependent ( ie wind drag, tire slip, brake drag, etc) and if the main purpose is to allow suspension compliance until zero toe is achieved, what magic happens that stops all this compliance when zero toe is achieved, but the forces continue to rise as speed increases, or is it just zero toe at one set speed, and toe out above? Is this the basis for 11/16" TR? If tire slip was the main force, it would seem to me that as soon as zero toe was reached, the force would diminish, suspension compliance would return wheels to toe in and the process would start all over again, not an ideal situation.
Anyone?
Really? I'm suprised you would ask this question after posting the initial write up. But, I'll bite.
The force is friction. The motion of the tire rolling over the road creates friction that pushes the toe in to zero toe, if it has been set properly. It is simply to take up tolerances in the myriad assortment of components in the steering system. If you wanted to get precise in it all, you should probably measure how much deflection a system has and use that to determine exactly how much toe is required. In a competition car this may be worthwhile, but in a street car a general range should be sufficient.
This friction is always present and it is not elastic in such a manner that the tires are constantly changing back and forth once in motion. If your sitting still and sawing the wheel back and forth then you may remove the force to a degree, but friction is always there to sufficient degree need the effect. Yes, the force does increase with speed, but once all the slack is absorbed, additional speed does not create additional toe, unless components are worn or failing. It is a hard stop that keeps toe in spec so long as the components are in good working order. That is why analysis of tire wear is the best tool an alignment tech has to get a car dialed in. Wear is a better indicator of what a suspension wants than actual specs can be. On my competition cars, wear, via temperature measurements, is what we used to dial in these specs to create an alignment that allowed maximum tread contact with the road surface for the intended application.
Suprised? That seems to happen when I shoot from the hip 
I think what you are saying is there is enough rolling resistance (friction?) alone to take up all the "slack" in a toe in configuration to result in zero toe. Does that then mean for all intents and purposes static toe in use causes no additional tire wear?
Anyway a previous poster mentioned "give", I then used "compliance", and you used "slack", which probably is the most descriptive in this case. So the slack is considered the only variable that toe needs to correct, and that slack is from only the wheel bearings, the 2 outside tie rods, and the 2 inner tie rods, on a typical mopar? Wouldn't a simple robust bungie achieve the same result? 
So does Strut bushing compliance play any part in toe setting as the LCA moves front to rear, or do the tie rods keep the toe consistent?
And to others, I am only discussing the mechanics of this, not sure how that was mis-interpreted, I'm not suggesting anyone make any changes for any intended result.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Toe-in vs Toe-out Reg cornering
[Re: jcc]
#1176873
02/16/12 01:46 AM
02/16/12 01:46 AM
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Quote:
I think what you are saying is there is enough rolling resistance (friction?) alone to take up all the "slack" in a toe in configuration to result in zero toe. Does that then mean for all intents and purposes static toe in use causes no additional tire wear?
Yes, if your suspension components are all in good working order, move freely, and have no issues, there is more than enough friction in the road surface/tire contact patch to push the tires to zero toe. I wouldn't say it causes no additional wear as ther eare slip angles to consider in all of this as well, but it does minimize it. Also keep in mind that I'm referencing this all from a RWD configuration. FWD is different.
Quote:
Anyway a previous poster mentioned "give", I then used "compliance", and you used "slack", which probably is the most descriptive in this case. So the slack is considered the only variable that toe needs to correct, and that slack is from only the wheel bearings, the 2 outside tie rods, and the 2 inner tie rods, on a typical mopar? Wouldn't a simple robust bungie achieve the same result?
In simpliest terms, yeah, a robust bungie could do it. But that bungie would need to be weather resistant, heat reistance, abrasion resistant, etc. plus be capable ot snaking through all the fancy engine components that hang down from the k frame.
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So does Strut bushing compliance play any part in toe setting as the LCA moves front to rear, or do the tie rods keep the toe consistent?
It depends. Strut bushings compliance doesn't signficantly impact the toe situation during driving on a relatively smooth road and normal suspension motion within a limited range of motion, lets say 1-2 inches. Out beyond that it may have an impact. With significant suspension motion, 2-4 inches, it may have an impact and during heavy braking it may have an impact.
One drawback to a strut rod suspension is that it forces the spindle to move in an arc fore and aft during travel. This motion will pull the tie rod position forward with it since it is attached to the lower ball joint. Since the tie rod is changing position in an arc that moves in and out from the vehicle centerline you are shortening its effective length the further it moves in its arc. This shortening action will inrease toe. If the strut bushing is allowing excessive compliance, it is allowing the spindle to move further forward in its motion, which pull the tie rod end further out, which pushes the toe out.
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Re: Toe-in vs Toe-out Reg cornering
[Re: ThermoQuad]
#1176877
02/16/12 01:11 PM
02/16/12 01:11 PM
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Quote:
Wouldnt bump steer correction make up for the toe changes during suspension travel?
Yes, it does help a great deal to correct bumpsteer in a classic mopar. However, eventually all strut rod suspensions will run in to a problem as travel increases because of the conflicting arcs of motion. Also keep in mind that for the purpose of this conversation, we're talking about very minor changes at rather large arcs of motion. If a change of a degree takes place, how much are we talking about? Well, one degree is 1/360 of a circle. So depending on how far out from the origin that measurement is taken, it could be very, very, tiny or simply a small unit of measure. Also, most street suspensions are not going to be moving 3-4 inches of jounce travel at the shock absorber. Travel can be viewed from the perspective of the wheel, shock, or bump stop and because of the arc, all three will be different numbers.
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Great discussion but let me ask the $500.00 question.
What will toe out do for my lap times if I set the toe out instead of in, as it would mean 2 trips to the alignment rack and $200.00. Will I be 5 feet ahead of the miata instead of it up my tail pipes?? Remember the focus here in the forum should be street cars driven on the track.
Just wondering...
Ah yes, whats it worth. Like EV2Demon said, it is kind of a driver preference. If your corner entry has a slight amount of understeer, additional toe out may help. If you have a slight amount of oversteer, toe in may help loosen up the nose. In general though, toe in will typically be the faster lap around the track than toe out. However, toe out does create a more stable seat of the pants sensation which may help the driver push the car harder through the corner. So again we're back to preference and maybe skill level.
The ability to read tire wear patterns and look at grain structure as the tire wears can do a lot for helping you understand what you need to set teh suspension at. Heck, tire temps are a quicker way to do this. For $40 you can get an infared thermometer from Harbor Freight and learn very quickly what your car wants for alignment specs.
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