Alignment - Degrees of Toe vs mm of Toe

[nsxtasy]

I just had my NSX aligned. I asked to use the original '91 alignment specs, which have total rear toe 6 mm +/- 1 mm, rather than the revised alignment specs, which have total rear toe 4 mm +/- 1 mm.

The printout shows that the actual total rear toe is now 0.33 degrees, and that the specified range is 0.24-0.39 degrees. I am concerned that the specified range might be for the revised specs, not the original specs which I wanted. Can anyone convert these settings from degrees to millimeters so that I can verify?

Incidentally, the specs are for "Acura NSX 1991-2001 Except Type S". Does anyone know whether the alignment specs are different for either (a) the '02-04 NSX, or (b) the Zanardi (Type S) NSX?

 

[ncdogdoc]

conversion table

 

[Briank]

Ken

Did some number crunching and it looks like you got what you requested. The only assumption I made was the denominator (the bottom # of the fraction the 1000)


.33 degrees = 20min

6mm/1000mm = .006

The Tan of 20min = (.00582) .006


3mm would have calculated out at .003

Tan of 10min or 1/6 degree or .16 degree = .0029 (.003)

 

[DonDavis]

Alignment questions

... and I think that in the three years I've owned my car, have been reading and posting to these forums, that's the very first time Ken has ASKED a question instead of ANSWERING one!



Don

 

[nsxtasy]

Thanks, guys!

 

[nsxtasy]

Each of us brings different strengths to the table, and our collective knowledge is more than any one of us has. I know that my technical knowledge is nowhere near that of the best experts here, like Larry Bastanza, DanO, and sjs, just to name three.

Oh, and that's not even the first time in the past few days that I've asked a question (let alone three years) - as you can see here. But I appreciate the compliment!

 

[DonDavis]

answers

Yeah, you're right, I'm continually amazed at how much some of these guys know about the cars... Given the time I could talk to them all day about details!

DanO was actually the kind gentleman that went out and did an inspection of my car before I bought it sight-unseen! He was very helpful and friendly about it all. I haven't been disappointed, either...

Hoping that with time I can do as much for others!

Don

 

[nsxtasy]

if you had used the "search" functionality you would have noticed that this was talked about quite extensively in the past.

http://www.nsxprime.com/forums/showthread.php?s=&threadid=31986
http://www.nsxprime.com/forums/showthread.php?s=&threadid=16478

I did try doing a search but didn't find anything relevant.

Incidentally, of the two links you posted, the first one is this topic (the one you're looking at now) - I think Lud folded in the separate topic that Don had started, about me asking a question, which could explain that. The second one is from the picture gallery... is this a joke from the "made you look" school of humor?

 

[nsxtasy]

DanO was actually the kind gentleman that went out and did an inspection of my car before I bought it sight-unseen! He was very helpful and friendly about it all.

He flew to Germany to look at a car for you?

 

[NSXBill2]

Ken,

I'm not done with this, but I believe your .33 degrees of toe in the rear is equivalent to 4 mm of toe, not 6 mm as you wanted.

 

[rrwildman]

It would be fair to say that my knowledge of suspension alignment is minimal, at best. There's a question I've ALWAYS had in my mind, and since we have the attention of some whose knowledge exceeds my own, and it's roughly on-topic, I think I'll ask it here:

Why would one specify camber and caster as an angular measurement (min/deg), while at the same time specifying toe as a linear measurement (mm/in)? This has never made sense in my feeble mind. If anyone has the answer, I'd love to hear it. I still won't know much, but at least I won't be totally confused by the specifications themselves.

Richard
'93 Blk/Blk

 

[Briank]

It would be fair to say that my knowledge of suspension alignment is minimal, at best. There's a question I've ALWAYS had in my mind, and since we have the attention of some whose knowledge exceeds my own, and it's roughly on-topic, I think I'll ask it here:

Why would one specify camber and caster as an angular measurement (min/deg), while at the same time specifying toe as a linear measurement (mm/in)? This has never made sense in my feeble mind. If anyone has the answer, I'd love to hear it. I still won't know much, but at least I won't be totally confused by the specifications themselves. What makes it even more fun is that there is more then one way to state fractions of a degree, Min,sec and decimal.

Richard
'93 Blk/Blk

It's all up to the engineer/engineering standards that the car company uses. An angle can be defined in several ways,in degrees, rise over run, %grade or any of the trigonometric ratios. In the case of millimeter specs I believe that a 1 meter base is assumed or run so only the rise is given or if using trig Tan() = side opposite (the spec) over adjacent (the base).

 

[Briank]

Ken,

I'm not done with this, but I believe your .33 degrees of toe in the rear is equivalent to 4 mm of toe, not 6 mm as you wanted.

Bill

Why don't you believe?

 

[wilsonp]

The printout shows that the actual total rear toe is now 0.33 degrees, and that the specified range is 0.24-0.39 degrees.

According to a random Internet article I found, (inches toe) = (tire diameter) sin(angle).

Assuming you have stock 16 inch front tires, the FAQ states 24.9 inches for tire diameter.

This yields 3.6 mm of toe, which would be a little below the 4mm (new) standard spec.

I shot for 5mm as a compromise b/w the two myself.

BTW, Gerard says 6mm is about 0.8 degree on this thread:
http://www.nsxprime.com/forums/showthread.php?s=&threadid=36587

That would make your total toe way off, so I am not sure about that...

Considering the ranges on that alignment sheet as new standard, seems like 0.315 is 4mm, and you want 0.4725.

(That agrees pretty well with 0.39 == 4mm+1mm == 5mm.)

I'll check my alignment sheet when I get in my car.

 

[titaniumdave]

Why would one specify camber and caster as an angular measurement (min/deg), while at the same time specifying toe as a linear measurement (mm/in)? This has never made sense in my feeble mind. If anyone has the answer, I'd love to hear it. I still won't know much, but at least I won't be totally confused by the specifications themselves.

I believe the toe traditionally is given as a distance because it is easily measured.

 

[NSXBill2]

Bill

Why don't you believe?

Because I can't prove it, and I am actually trying to. Its just the way I am (an engineer).

 

[NSXBill2]

I believe the toe traditionally is given as a distance because it is easily measured.

I believe that this WAS true, but now toe alignment is commonly measured (on modern, commonly-used machines...not at the track) as an angle. This does make since, but gets confusing (to me, obviously) when trying to convert old linear measurments, because of the tire diameter variable (explained below).

 

[NSXBill2]

What was throwing me off so much on this is what tire diameter to use? Actual, 91-93 size, 94-2001 size, or some reference diameter.

If you were measuring with a tape, tire diameter doesn't come into play because you use the tires you have on the car.

When a machine measures the toe in degrees, it doesn't care what the diameter is because it doesn't matter in the measurement.

When the diameter DOES matter is when you try to convert toe in mm to degrees. The tire diameter is the adjacent side in the geometric relationship.

I got NSX readings from a Goodyear dealership using Hunter equipment, but could never figure in actual NSX tire diameters. I called Hunter and questioned them. As it turns out, they use a Reference Tire Diameter for all of their car toe-in-linear-mearurements to toe-in-degree-measurments conversions. They use 28.65 inches or 727.7 mm. Using this diameter, I was able to duplicate the NSX-Hunter readouts exactly for -3.5 mm front and 4 mm rear.

The formula using a total toe of 4 mm is:

arcsine(4/727.7) = 0.31 degrees THIS IS TOTAL TOE, divide by 2 for each side

This can be entered into an Excel spread sheet like this:

=DEGREES(ASIN(4/727.7))

Substitute the "4" for any toe you would like to convert to degrees for use on a Hunter machine. Example: 6 mm of total toe = 0.47 degrees.

Hope this explanation is helpful to someone.

Bill

 

[1BADNSX]

Ken, this is a very easy calculation and I am not sure why you are getting wrong answers, but .33 degrees is roughly equal to 3.66 mm. Yes, the calculation is slightly dependent on the tire diameter assumed, but not very much.

Yes, racers measure total toe with a tape measure and this is why it is quoted in units of distance.

Bob