Race car setup geometry / check my trig please!

[HustleRussell]

I’ve bought a racing car which appears to handle well with around;

• 10 minutes per side toe out front
• 7 minutes per side toe in rear

This is measured on a Hunter laser alignment system and these are around the settings my dad and I have been using on these cars for years

However the chap who set up the car which won one of last year’s championships has recommended the following settings;

• 3mm per side toe out front
• 1.7mm per side toe in rear

Assuming he uses the string method and is measuring from the 13” wheel rim (which has an outer rim diameter of ~358mm (1.)) I can use TAN rule to convert his measurements to degrees and then minutes;

• 29 minutes per side toe out front (-0.48 degrees)
• 16 minutes per side toe in rear (0.27 degrees)

Firstly, does my maths look correct?

Secondly, note how massive his angles are! Given that the proportions of front toe out to rear toe in are similar between the two setups, what would the effect be of me duplicating his much more extreme angles on my car? I would expect more rolling resistance so what is upside of increasing front toe out and rear toe in equally?

1. Googled figure, I have not yet measured a wheel

[E-bmw]

HustleRussell said:

Assuming he uses the string method and is measuring from the 13” wheel rim [/small]

Don't assume anything, ask him, if he uses rear rim to front rim instead they will be similar to yours if not the same.

[HustleRussell]

E-bmw said:

Don't assume anything, ask him, if he uses rear rim to front rim instead they will be similar to yours if not the same.

I will, just out of interest how does measuring rear rim to front rim work? I have assumed he has set up his strings and the given dimensions are the difference between the distance from the string and the trailing edge of the wheel and the string and the leading edge of the wheel.

[Mignon]

Most alignment systems give you a total toe in or toe out not just per side. I would suggest his 3mm and 1.7mm are probably measured like that and hence twice your own numbers.