Geometry Alignment

[Lotus Roy]

Hi,

I am about to get new rear tyres for my '91 manual. Having alignment done on their Hunter system. Problem is toe in setting is in degrees not mm. Does anyone know what 3mm equates to in degrees and minutes? Or how to convert one to the other

[goldnsx]

y (in deg) = invtan (x (in mm) / 1000)
3mm = 0.17 deg
if you have minutes instead of degrees: 0.17 * 60 = 10.3 minutes

[Lotus Roy]

Brilliant, thanks.
Roy

[Kaz-kzukNA1]

No longer posting on the forum like I used to and mainly focusing on the blog but this one caught my eye so hope I can share my experience.

You really want using the unit in deg and not in length (mm/inch) to remove the tyre size effect.

Not sure it's still the same with the latest software version but when using Hunter machine at the alignment platform I use, if you set the display unit in length (mm/inch) rather than the default setting of degree, the software is going to use virtual external tyre diameter of about 726mm unless you set it up to use OEM tyre size spec.
Not ideal for much smaller tyre diameter on our NSX and thus, should use deg.


Toe [deg] = ArcSin (toe[mm] / tyre external diameter [mm])
1deg = 60min

Although the equation includes the external tyre diameter, it has very minor effect so you can use pretty much the following for all OEM rear tyre spec or similar.

225/50/16, 245/40/17, 255/40/17 or similar; Toe 3mm = 0.27deg = 0* 16' (0deg 16min)


By the way, this 3mm toe, are you referring to one side or total toe?
Please double check the rear toe data stored on the machine.

By default, for 91 model, it would be using the original setting of 3mm toe per side that is 6mm total toe.
While you can still use this (and I was using it when I used to drive my NSX in Japan), for UK road surface and weather condition, I normally set all NSX including mine with Rear toe per side at +0* 11' +/- 03' (equivalent of toe-in of 2.0mm) that will result in total toe of +0* 22' +/- 06' (equivalent of toe-in of 4.0mm). Then, you need to customise this to one's taste depending on the chassis setup but good starting point.
This is the same as the modified spec released by Honda/Acura.

Kaz