32 replies to this topic

[meb58]

A recent alignment experience taught me that very few folks - professional alignment folks inlcuded - understand the geometric rationale behind the positive and negative values used to represent camber, caster and toe...I include myself in that group.

I understand negative camber tilts the top of the tire in, positive caster tilts the top of the steering axis aft and that negative toe is toe out up front and toe in rear.


205/45/17 = sin^ -1(0.128/24.26)...forgot to add, should = 1/16" toe out...

Edited by meb58, 15 September 2009 - 20:26.

[McGuire]

The service industry convention is "toe-in" or "toe-out," like this:

"+ 1/8 inch toe-in" means an eighth inch of toe-in.

"- 1/8 inch toe-in" means an eighth inch of toe-out.

Conversely,

"+ 1/8 inch toe-out" means an eighth inch of toe-out.

"- 1/8 inch toe-out" means an eighth inch of toe-in.

Here is a fairly straightforward explanation of the above: http://maxima.theowe...b/NTB91-049.pdf


The convention works the same front or rear, and if you do not specify toe-in or toe-out, only "toe" as in "postive" or "negative," you are not clearly specifying what you want. Personally, I have found over the years that in parts or services in general, from wheel alignments to heat treating, you can't be too specific. No such thing as too much information.

Side notes...Only in recent years has it become popular for toe-in/toe-out to be expressed in degrees -- the traditional specification is inches or mm. This was undoubtedly driven by the trend for four-wheel, centerline/thrustline-based alignment equipment and procedures. Obviously, the vehicle's centerline is at (we hope) 0'0". One interesting thing a lot of people don't know: Factory toe dimensions may refer to the OD of the wheels or the OD of the tires, while commerical alignment equipment may well take the measurement at the opposite points. Some equipment automatically compensates for this discrepancy; some doesn't. However, almost never does it cause a real problem.


Actually, there is no reason you can't do your own alignments... the equipment is not that expensive (you can often get by with a string, a square, and a protractor level or inclinometer) and pays for itself in only a few jobs. It's not the least bit difficult either, and the beauty is you know what you want. The fancy commercial alignment equipment is not significantly more accurate, just faster. However, it is quite useful when the car is tweaked somewhere.

[gruntguru]

McGuire, on Sep 16 2009, 07:55, said:

Only in recent years has it become popular for toe-in/toe-out to be expressed in degrees -- the traditional specification is inches or mm. This was undoubtedly driven by the trend for four-wheel, centerline/thrustline-based alignment equipment and procedures. Obviously, the vehicle's centerline is at (we hope) 0'0". One interesting thing a lot of people don't know: Factory toe dimensions may refer to the OD of the wheels or the OD of the tires, while commerical alignment equipment may well take the measurement at the opposite points. Some equipment automatically compensates for this discrepancy; some doesn't. However, almost never does it cause a real problem.

Toe angle is obviously more logical than the traditional units. You set the toe, lock up the tie rods, everything is perfect. Next day you fit wheels/tyres with a different OD - the toe setting is different! I don't think so.

[meb58]

McGurie,

Not exactly what I have thought all these years. So as you suggest, lets not try to be understood, but lets not be misunderstood... Your link provides a lot of insight...it's not as straightforward as I had hoped, in fact, there is plenty of room for 'error' given that a toe out specification can yield either toe in or toe out. The specs for my car are in postivie numbers so the tech toed both the front and rear tires out - very dangerous! The manufacturer, BMW, specs the tires to be toed in, however. But the manual nor the tech's alignment rig specs is clear...never enough information, agreed!

Gruntguru brings up an interesting point...in my little formula at the bottom of my first post is the number 24.26 and this refers to the 17" diameter wheels. Now, I can understand why a tire with a different circumference will alter an alignment, but why do the math if we have the same rolling circumference; if we have a 15" a 16" and a 17" wheel but all three have a tire whoes profile is adjusted to the same rolling circumference why does it matter?

I set the alignment for a .10 deg up front and -.15 deg rear...should be in the neighborhood of 3/64" toe in up front and 1/16" toe in rear. Quick, stable, good tire wear.

Edited by meb58, 16 September 2009 - 14:08.

[Greg Locock]

It seems to me that these things are only ambiguous if you wish them to be so.

+ve toe in always means toe in.

-ve toe in always means toe out.

If anyone tries to present data in any other form, ask them to reconsider.

So far as using degrees, OK, we do beacuse all our rigs do, but mm at the rim is fine as well.

We used to have engineers who would talk about axle oversteer, so they would be talking about increasing vehicle understeer by increasing IRS oversteer. I think I've managed to kill that little meme off, all effects are spoken about at the vehicle level.

[meb58]

And that's about how my conversation went...I simply always use neg toe as out - front or rear and pos toe as in front or rear. Very simple!

When I was younger I used mm...now I'm older and machines are newer

I still have to throw out the question Gruntguru prompted...I understand a larger over-all circumference will alter alignment settings but I do not understand why folks are concerned with different wheel sizes if the tire's roll circumference is the same via different profile sizes...

Edited by meb58, 17 September 2009 - 16:59.

[McGuire]

meb58, on Sep 17 2009, 21:17, said:

And that's about how my conversation went...I simply always use neg toe as out - front or rear and pos toe as in front or rear. Very simple!

Seems to contradict your first post, where you wrote, "negative toe is toe out up front and toe in rear."

meb58, on Sep 17 2009, 21:17, said:

I still have to throw out the question Gruntguru prompted...I understand a larger over-all circumference will alter alignment settings but I do not understand why folks are concerned with different wheel sizes if the tire's roll circumference is the same via different profile sizes...

Don't know why folks would be. Are they?

[meb58]

[quote name='McGuire' date='Sep 17 2009, 13:42' post='3867134']
Seems to contradict your first post, where you wrote, "negative toe is toe out up front and toe in rear."

Yes it does...clarification; I gave myself a headache by asking as many people as possible about + and - and surprise...I got as many answers as possible. But "that" convention seemed to be more common than most. When I wrote I understand it was with this commonality in mind...like a new concept learned. Despite this, I use (d) + to mean toe in and - to mean toe out front and rear for the past 34 years with little trouble...well, until my last alignment experience.

Sorry if this was mis-leading.

Yes to your last question...very concerned that I have 17" wheels vs 16"...the circumference is nearly identical. My argument? When I install the snow tires with 16" wheels the car's steering inputs are virtually the same...the difference being the tires and profile. No dark surprises.

Still gathering codes for the other thread...

Edited by meb58, 17 September 2009 - 20:10.

[gordmac]

QUOTE (meb58 @ Sep 17 2009, 21:17)
I still have to throw out the question Gruntguru prompted...I understand a larger over-all circumference will alter alignment settings but I do not understand why folks are concerned with different wheel sizes if the tire's roll circumference is the same via different profile sizes...

The pointers go on the rim, they will have a different spacing for different rim sizes. For a given toe angle the size of in/out will be different for different pointer spacing.

[carlt]

General rule of thumb I've been told
Rear wheel drive - slight toe in on front wheels ,[ so your BMW should never have toe out ]
Front wheel drive - slight toe out on front wheels

I'm not quite following the reason why you are all getting confused over + and - numbers ?
toe-in is toe-in and toe-out is toe-out to my understanding
why confuse it with + and - ?


Ha Ha - of course your BMW is the FWD Mini ---- DOH

Edited by carlt, 18 September 2009 - 14:07.

[gordmac]

Letting your thumb rule can get you into a lot of trouble!
I believe modern road cars have designed in bump and maybe roll steer so presumably the specified toe setting will also have a specified ride height?

[meb58]

The mini has a very clean bump curve up front...the LCA is also located via a ball joint and an oil filled bushing - the bushing is at the rear. Even though this is precise, I replaced the oil filled bushings with a dual compund poly unit that also happens to have less bind or friction than the oil filled bushing. So in this case alignment precision is pretty important.

I am comfortable with 1/16 to 1/42 toe in up front - front driver - and about 3/32 to 1/8 toe in rear. This is a very good all round setting - daily driving and limited track time.

gordmac, I understand that but in this recent experience these guys were concerned about differnt tires sizes despite the fact the circumference is the same. They got the alighment right for the first four years of operation...suddenly everything is toe out and to spec?

I began this thread hoping I might learn that there is a fundamental convention used to determine what + and - are in relation to toe in or out...something every human can fall back on and not get lost. I have a bigger headache today, but I guess McGruire has it right; the information the better.

[Greg Locock]

gordmac, on Sep 18 2009, 21:48, said:

Letting your thumb rule can get you into a lot of trouble!
I believe modern road cars have designed in bump and maybe roll steer so presumably the specified toe setting will also have a specified ride height?

Indeed. If you take your car in to get its alignment done and he doesn't measure the fender gap (or something more complex) on each wheel before he starts then the result may be a waste of your money.

We used to spec the toe and camber at three heights, now we've gone insane and it is specced at all possible fender gaps from kerb up. It is a horrid job to prepare those tables -boring and error prone. Yes, I am involved, Virginia.

Incidentally we just measured a car that had 20 deg/m of bump steer, so if you get the fender gap wrong by 10 mm that is a 0.2 degree error per wheel, ie 0.4 total (that is a ludicrous example, some manufacturer must have been desperate). You can get quite a significant change in behaviour from just 0.2 deg total toe change. More typically bumpsteer varies from 2 deg/m to 8 deg/m, although many manufacturers don't use a linear bumpsteer curve.

[ddub]

I think the -ve or +ve, mm or degrees debate over toe settings largely depends on the equipment at your disposal. In single-seaters we typically work in mm because the toes are set using strings - so its far easier to measure distance rather than an angle. On GT's and touring cars we've used equipment such as BeissBarth which just spits out a toe angle on a laptop - in this case this is easier.

I would warn against "generic" toe angles as I've found that every car needs a different setting, depending on factors such as suspension geometry, compliance and above all the tyre construction. However, a good rule of thumb is toe-out on the front and toe-in on the rear for a rear wheel drive car, and in my experience front wheel drive tends to like toe-out on the front and also on the rear to help combat understeer.

I've never run a performance car (to date) with positive camber.

[McGuire]

In oval racing, postive camber on the left front is customary. On an Indy car at, say, Indy, 1.0 to 1.5 degrees, in NASCAR up to 7 degrees, maybe even more if allowed.

...getting back to the whole toe-in/toe-out aka positive/negative business, a good setup sheet will leave a blank space next to " toe" so in or out can be specified. A setup may well call for either and the can't really afford to assume it is one or the other. For instance, at Indy a setup might call for toe-out front and left rear, toe-in right rear, which will probably not be the case at other tracks. Meanwhile, engineers tend to have terrible handwriting (and often teeny, tiny handwriting, which is psychologically interesting) so plus and minus signs can be easily confused.

[meb58]

...the image rings one more point; I love it when I see a fellow begin to peform an alignment by checking tire psi and perhaps temps if the tires are hot...

[Fat Boy]

ddub, on Sep 28 2009, 13:39, said:

I've never run a performance car (to date) with positive camber.

Come over here and run on an oval. Like Mac said, positive on the LF and LR. I generally agree with what you've written, but there are caveats to everything.

I've never ran negative caster on anything. I can't really envision ever doing so.

[gruntguru]

McGuire, on Sep 29 2009, 01:27, said:

(and often teeny, tiny handwriting, which is psychologically interesting)

You never know when you might run out of paper - or ink.

[Tony Matthews]

gruntguru, on Sep 28 2009, 23:34, said:

You never know when you might run out of paper - or ink.

I think it runs deeper than that...

[cheapracer]

ddub, on Sep 28 2009, 21:39, said:

and in my experience front wheel drive tends to like toe-out on the front and also on the rear to help combat understeer.

I rallied a Civic for a year and ran the opposite (in/in). I started with out/out but the car just walked around all the time and I was always fighting it.

I've noticed the radius rod type and location (fore or aft) gives bearing to what toe you run on fwd.

[gruntguru]

cheapracer, on Sep 29 2009, 19:07, said:

I rallied a Civic for a year and ran the opposite (in/in). I started with out/out but the car just walked around all the time and I was always fighting it.

Interesting - we are seeing a number of steering settings (Ackerman is another) where dirt track goes counter-trend.

[McGuire]

Fat Boy, on Sep 29 2009, 06:14, said:

I've never ran negative caster on anything. I can't really envision ever doing so.

It's been awhile. Up to around '72-'74 as radial tires became standard equipment, U.S. passenger cars often ran from zero to 2.5 degrees negative caster to keep the steering effort down. There were lots of 3600 lb cars with manual steering; power steering was usually optional. Cross-caster aka caster bias left/right was also common to counteract road crown, generally around 3/4 degree to keep the farmers happy.

All this is not as bad as it sounds... in bias-ply tires the contact patch trails a bit, providing some natural caster. So when modern radial tires are first fitted to say, a '62 Pontiac or suchlike, it gets all floaty and wander-y. The caster must be flipped a degree or two to the positive to make 'em drive right.

[meb58]

I think Greg Locock described caster as a "convenient conceit" - on Eng tips a few years back...I've actually played with zero caster ona couple of modern cars and although the steering is lighter, I cannot say that feel is ruined...turn-in improved. About 3 deg change in all.

[cheapracer]

Oh caster is overated and usually the effect that people get excited about is a gain or loss in the more important but seldom mentioned trail. The car/s you zero'ed I guess had trail already designed in the upright itself.

I'm always surprised the amount of people who lower and stiffen their cars and of course end up with less roll, then throw in more caster cause it's the done thing for high performance handling - apparently.

[Dragonfly]

Now forgive a question from a lamer.
Toe-in or toe-out is relative to the direction of travel. Am I getting it right?

[meb58]

Dragonfly,

Yes...looking down on the car from above toe out points the forward portion of the tires out away from the car's center line and toe in points the forward portion of the tires in towards the car's center line.

Cheapracer,

I want to answer yes to your first question...but to be clear you refer to trail, the distance from the side view center line of the tire to the point ahead of the tire defined by the caster angle...then yes, sure...I starightened this out. Returnability seemed to improve a little as well.

I've heard and read the attributes in using more caster - a relative term to the cars I was driving - angle/trail but in each case steering response suffered, go figure. I know I probably lost a little "camber gain" but the car also felt more natural. If I remember too - in Milliken? - caster throws weight to the wrong rear wheel in an oppsite lock condition. Maybe that's a benefit in a rally on snow or mud???

Edited by meb58, 29 September 2009 - 19:02.

[Bruce302]

I have been doing wheel alignments on cars and trucks for a few years, including a couple of sedan race cars, and I think I have a little bit of a handle on the concepts. For me the proof was in how happy the driver is, and how the tires perform.
naturally different cars "like" different settings due to design factors like scrub radius, and load factors. I.e with BMW's we loaded them up to spec weight (a few of the boys) then make the adjustments to spec. Some cars we ignored the spec and winged it, and got better results.
I agree whole heartedly that an understanding of the relativity of each adjustment and each function is vital. The tire service industry has been badly serviced by alignment machines that flash a red or green light/graphic and or beep when the approximate setting is achieved. And all this on machines that need regular calibration, and seldom get it.
I used laser equipment and calibrated it regularly. In fact I had to rewrite the factory manual as it was not precise enough.
Of course different tire brands like different settings on the same car. Pirelli PZeros (on a 3 Series for example) seem to perform better if kept to under 1 degree of camber +/-, other brands will like more.

There are no absolutes. A friend of mine runs toe out on his road race '69 Camaro, it's what he likes, and it works for him. Most others run toe in, it's what they like and what works for them.

Bruce.

[McGuire]

Bruce302, on Oct 1 2009, 14:06, said:

The tire service industry has been badly serviced by alignment machines that flash a red or green light/graphic and or beep when the approximate setting is achieved. And all this on machines that need regular calibration, and seldom get it.

Amen, you nailed it. In another thread here recently, an alignment machine was directing the technician to move shims the wrong way because it (or the inputs) assumed they were on the opposite side of the control arm shaft. Automated machines are no substitute for simple, competent knowledge, but the industry keeps trying anyway. Their dream is to have untrained goons performing the work at minimum wage... which is in part because the industry has failed so badly in the formal training of real, competent mechanics.

To this day I have yet to see a technical school that can actually produce a working journeyman mechanic. The good mechanics you encounter, whether formally schooled or not, have for the most part trained themselves on the job with some mentoring from coworkers. Cheapracer, I bet you have some interesting things to say about it.

[cheapracer]

McGuire, on Oct 1 2009, 19:45, said:

Cheapracer, I bet you have some interesting things to say about it.

2 days fishing first, National Holiday starts in China today.

I don't like fishing but I do like sitting on my ass in the mountains for 2 days pretending I like it, terrible when one of the bastards actually gets stuck on the hook and you got to wake up and take the slimy smelly bastard off - stupid concept, for $10 I can buy all the fish I can eat at the supermarket not that I actually eat them and this is China's water we are talking about too..... I prefer my food cadmium, lead and mercury free and only 2 eyes thanks.




Look after the place while I'm gone.

[Tony Matthews]

McGuire, on Oct 1 2009, 12:45, said:

To this day I have yet to see a technical school that can actually produce a working journeyman mechanic. The good mechanics you encounter, whether formally schooled or not, have for the most part trained themselves on the job with some mentoring from coworkers. Cheapracer, I bet you have some interesting things to say about it.

Small off-thread rant, inspired by the quote:-

On UK TV at the moment, a programme about British design students competing for the honour of a stint working for Philippe Starck - the students so embarrassingly rubbish that Starck threatens (and I don't believe for dramatic effect) to cancel the show, and 'Master Chef - The Professionals', working chefs with between five and ten years experience... Never have I seen so much hand-trembling incompetence, fundamental errors and tear-stained faces. But judged on the standard of tuition that my daughter recieved at University, on photography, it is not realy surprising. Worrying, though...

Sorry about that...

[Bruce302]

Their dream is to have untrained goons performing the work at minimum wage... which is in part because the industry has failed so badly in the formal training of real, competent mechanics.

I had those goons working for me.
We re-aligned repaired crashed cars. The certifier wanted a computer print out to "prove" that everything was back in spec.
One of my goons at another shop so called aligned a car. It was rubbish, pulled left, steering wheel way off centre, but the print out said it was perfect. I took it back to my shop, lined it with the lasers (no computer link or print out), and presented it back to the cerifiers, driving straight and true.
Needless to say I moved the goon on, though he had 20 years experience.

[gordmac]

Sadly, in this part of the world at least, despite what they say education isn't really valued by people or governments. Governments don't manage provision properly and children are not encouraged to do well in areas that will add value to the country. We have lost the reasons for a lot of things we used to do because we no longer understand why we did them.
Things are a bit better now but a few years ago an engineering graduate could start in a teaching career on a salary about half of that of industry, where are the "more able" going to go? If your teachers are not towards the "better" end of ability this will "dumb down" the education system and we are on the downward spiral. Remember when money is tight government paid salaries are driven down, you can't have something good on the cheap.
As far as mechanics go, unless things have improved recently the industry isn't prepared to pay well enough to attract more able/intelligent apprentices (does industry take on apprentices any more?) or invest enough in proper training. How much of the £100 or so per hour charged by dealers does the mechanic see? Looks to me that the markup is a lot more than most companies can get on the stuff they sell. Meanwhile the government is trying to get the people who would do well as apprentices to go into full time higher education, often on courses that don't do much for their job prospects when they graduate.

[meb58]

And I'll add my aecdotal story as well...I draw for a living. Everyone who works for me uses a computer to draw. When the power goes out they go home...they cannot draw by hand...no sense or feel for perspective or the tactile sensation derived from doodling with a pencil. While deisnging anything I think it paramount this language - drawing - be more than just a persuasive gesture to our clients...be able to draw with a pencil can reveal so many problems at a pace that make a computer turn red. Oh, my pencil has not crashed in over 35 years...

Back on track...alignment folks should begin study by perform alignments with a string...I doubt any perform rudimentary tasks such as checking tire pressure or verifying that the chassis is square before an alignment...