Fastrax review and alignment questions for the pros.

adriver said
The Longacre plates look like a good idea.
Yes.
I found out the Fastrax don't grip very hard.
I did buy two.
Mainly because when setting up a front end it seemed like it would be a PIT to swap from side to side and reset the thing for zero on each time.
And I'm doing it by myself so I'm laying the tape on the floor and using a level to find the position.
I hope I can get accurate enough.
The instructions say to turn the wheels 15 degrees, or make the pointer parallel to the car to measure castor.
I found that turning the wheels more will also make a different reading for castor
So, I'm thinking 15 degrees must be designed into the fixture some way because it is looking at the difference between straight and turned.
Any input on why recommendations are different for how much to turn the wheels for a castor measurement with different alignment tools?

Ive gotten pretty quick at attaching and zeroing the gauge. As long as I don’t kick it when I move around the car to make adjustments it stays on :D. I like the longacre toe plates, they make it pretty easy to measure the toe even by myself. Once you get your method figured out it’s easy to be repeatable.

As for how many degrees to turn the wheels to measure caster, it doesn’t matter that much. What really matters is that you turn them the same amount in each direction. Most gauges use 20*, the more you turn the wheels the more accurate the measurement will be. Not sure why fastrax uses 15* instead, but it’s not something built into the gauge. You’re actually measuring the change in the camber between the two wheel angles, which is telling you the caster.

Here’s a decent article on alignments and some of the definitions DIY Alignment Guide - How To Adjust Caster - Hot Rod

And here’s one that’s very technical. Like hard to read technical. It actually works through deriving the equations for how the process for measuring castor works.

https://disco3.co.uk/gallery/albums/userpics/24543/steering-geometry-and-caster-measurement[1].pdf

What all that math gobbledegook means though is that the turn angle doesn’t matter as long as it’s symmetric, but a wider turn angle spreads your measuring errors over a wider range, so, more accurate.