Geometry measurements and how do they relate?

[alnug]

ok all you specialists :graduated: ...here is my question. how does the mm translate into geometry measurement? I mean where do they relate this mm reading from? E.g. The accord has a Toe in spec for the rear of 2mm+/-2mm...now where is this specified from?...so say we take it as 1mm toe in either side....how is this measured in terms of the actual wheel? is it from the front edge and back edge of the tyre??

 

It is very easy to understand if it's in degrees and minutes since then it's just an angular measurement so tyre size etc don't come into it.

 

Also if the spec is given in mm what info does the operator have to enter into the aligner? Does this also mean that if you change the rolling diameter this spec would also have to be changed? (would be far easier if it was spec'd in degrees and minutes!).

[Tony]

ok all you specialists :graduated: ...here is my question. how does the mm translate into geometry measurement? I mean where do they relate this mm reading from? E.g. The accord has a Toe in spec for the rear of 2mm+/-2mm...now where is this specified from?...so say we take it as 1mm toe in either side....how is this measured in terms of the actual wheel? is it from the front edge and back edge of the tyre??

 

It is very easy to understand if it's in degrees and minutes since then it's just an angular measurement so tyre size etc don't come into it.

 

Also if the spec is given in mm what info does the operator have to enter into the aligner? Does this also mean that if you change the rolling diameter this spec would also have to be changed? (would be far easier if it was spec'd in degrees and minutes!).

 

Hmmmm this won't be easy to explain.... Lets start with

 

X= left/ right

Y= forward/ backward

Z= up/ down

 

MM can measure linear angles like toe/ set back and axle alignment since it's line of sight is X/ Y.

 

To acquire Z the increment can only be degrees since the position is perpendicular to Y.

 

Longidutinal X/ Y angles can be converted to degrees @ 1mm= .9'

 

All Geometry machines can have the increments changed... Decimal degrees and minutes or degrees and minutes for Y+Z and mm or minutes for X

 

Other than machines like TDi's and wim's most need to know the wheel size if the X is in MM, reason being is the cameras don't know where they are in space so to acquire this they need to now the wheel base (Y) the wheel track (X) and the wheels size (Z)

 

I found that most students were happy if the increments are... Y/ Z degrees and minutes and X MM, it's just an easy format i suppose?

[alnug]

Longidutinal X/ Y angles can be converted to degrees @ 1mm= .9'

 

All Geometry machines can have the increments changed... Decimal degrees and minutes or degrees and minutes for Y+Z and mm or minutes for X

 

Other than machines like TDi's and wim's most need to know the wheel size if the X is in MM, reason being is the cameras don't know where they are in space so to acquire this they need to now the wheel base (Y) the wheel track (X) and the wheels size (Z)

 

I found that most students were happy if the increments are... Y/ Z degrees and minutes and X MM, it's just an easy format i suppose?

 

Thanks for the reply Tony..I knew you'd get back

ok the highlighted bit is the bit i can't get my head round (oh and is that 0.9 minutes or 9 minutes?). now you say 1mm=9' .......but where is the reference point for the 1mm measurement? doesn't this depend on how big the tyre is (if this is used as the reference point?)? since if you use pythagoras..if the angle stays the same but the y distance increases then the x distance would also increase (wish it's easy to draw diagrams here!). :graduated:

[Tony]

Longidutinal X/ Y angles can be converted to degrees @ 1mm= .9'

 

All Geometry machines can have the increments changed... Decimal degrees and minutes or degrees and minutes for Y+Z and mm or minutes for X

 

Other than machines like TDi's and wim's most need to know the wheel size if the X is in MM, reason being is the cameras don't know where they are in space so to acquire this they need to now the wheel base (Y) the wheel track (X) and the wheels size (Z)

 

I found that most students were happy if the increments are... Y/ Z degrees and minutes and X MM, it's just an easy format i suppose?

 

Thanks for the reply Tony..I knew you'd get back

ok the highlighted bit is the bit i can't get my head round (oh and is that 0.9 minutes or 9 minutes?). now you say 1mm=9' .......but where is the reference point for the 1mm measurement? doesn't this depend on how big the tyre is (if this is used as the reference point?)? since if you use pythagoras..if the angle stays the same but the y distance increases then the x distance would also increase (wish it's easy to draw diagrams here!). :graduated:

 

Look at this image...

 

 

The reference point is the thrust angle, generated from the rear wheels forward direction.... If this is the only type of information needed then the wheel size is irrelevant as is the increment of measurement.

 

Oh it's 0.9' decimal = 1mm