Alignment thoughts?

Increasing the caster to the factory spec 4 degrees should have a noticeable positive effect on straight line tracking. Probably will help centering as well, but I tend to look to toe-in for centering improvement. But as your toe settings look fine, it may just be the wider tires you are feeling. And I'm sure you know that if you get the caster to 4 degrees, you will have to reset camber as well.

Your picture of the camber/caster gauge on the bare hub is confusing. Are you trying to set things up without the suspension at actual or mocked up ride height?

 

Probably both, but it depends on the thickness of the shims you have. The 3mm camber shims give about a quarter degree of change, but I don't know the impact of one caster shim. Just swagging the dimensions it seems it will take about 3mm of caster shim change to move it a degree. I'm a big fan of getting the caster as equal as possible, side to side, and personally prefer to be on the high side of the spec for a street car. Increasing caster increases camber so there is an inevitable bit of chasing your tail getting them both where you want them.

Were you really checking camber with a jack under the suspension? I would say you can't get close that way doing one wheel with the spring mounted. You either need the car sitting on a fully 'settled' suspension (rolled some distance or driven after setting changes) which is the best way, OR by setting the control arms at target ride height angles with the body at it's ride height angle, and with the springs not mounted. Done well, that can get you close to an accurate measurement.

You must at least have the settings close to equal (side to side) though, for the car to drive well.

I would suggest you take the car to a track oriented shop for the final check and settings, especially for the rear toe. It can be very difficult in a home shop to ensure the toe is equal side to side so you don't end up with a thrust angle situation. The string method of toe alignment is valid, but getting the strings exactly parallel by referencing the body or even chassis of the "hand built" 308 probably is not accurate enough. I'm assuming that's how you set the strings as I don't see any marks on the floor indicating the use of bob weights or similar.

BTW, it occurs to me I should have first asked your experience with setting up suspensions. I don't mean to come off as if you don't know what you are doing or that I'm an expert. Your string setup and anti-friction bags under the front wheels indicates you have at least studied the process and probably have done this before. I'm just trying to help you get the car set up as well as possible. They really seem sensitive to correct set up when it comes to steering feel, especially on higher speed corners.

 

I do racecar alignments at home on scales. #1 get your floor flat. You need more caster. I was never a string fan. For me it’s toe plates, laser level, straight rule, L rule, scales, slip plates

 

I had similar difficulty getting the last degree right so to speak with the front after fitting a new rack ,.,using string .
In the end I took to Quickfit when they were quiet and had it put on a Hunter apparatus.
The machine had the specs , but I took a copy of the manual with them in .The kid seemed quite excited as he was a amateur tuner out side work .
It needed more toe in basically which on laser plates was easy to get right .
I understand when having a go myself the unsettling and having to roll it after every lift up , using home made skid plates and importantly with regards to toe in at the front the wider the wheels for more so with 17 s you in my view need to be at the top end of all measurements so increase the toe , camber and caster .You could start with 4 degree toe which if I remember is the max ? But that max is for 16 s I think 225s ? So with fatter 17 s 255 s I suspect you need to be at the top end or slightly over with ALL the measurements at the front .

They look nearer the lower ends If my memory serves me right ?
Bigger [ wider rubber ) = bigger numbers .


Feels tremendous now .Was good before but I think they are sensitive to even a few degrees out .

 

There should also be shims at the upper ball joint so you can do that in the other direction to get more of a caster change. How did you do a home-based caster measurement?

 

So is this using some sort of calibrated magnetic "level" bubble device placed on the brake disc surface with the wheel in place and the tire on the ground (while on the turn plates)? Since the amount of caster adjustment that you are needing to make seems to exceed what the Designers provided (and is off by about the same amount on both sides) = makes me worry that the measurement might have some sort of problem. You might want to try to make some confirming crude caster measurements (just using a ruler, square, etc.) as the amount of adjustment that you are making (6mm total) should be something that a ruler can detect, too. Just a thought, although, since your initial goal was to add a lot of caster and get more centering action, maxing the camber adjustment regardless might be OK.

 

You've lost me a little -- then, from those two vertical angle measurements (and knowing they were made at +/-20 deg), you do some mathematics gymnastics to calculate the caster angle?

 

That is not the definition of caster angle (although it explains why you are getting such a low value). To use that type of measurement directly you would have to zero the digital angle gauge at a 0 deg steering angle (and 0 deg camber angle) and then turn the wheel to a 90 deg steering angle (which, of course, is not possible) to read the caster angle directly. Your method is a practical method to make a measurement from which the caster angle can be calculated, but it is not the caster angle. Do you have a reference for this method, and how to use it?

 

More than most want to know, but a thoughtful read. Several pages in there is a more practical guide to caster setting.

 

The constant to use for the caster is 1.43 if you’re measuring difference in camber at 20 degrees turn in and out. So just multiply the measurement you got x1.43…


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Only other thing is according to that manual you’re supposed to do the alignment/stock settings are with a person in each seat and 20kg in the boot. Driving around for a bit will change the numbers a bit as well. One of the benefits of diy is that you can check again after a drive.


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Excellent...now watch tire wear and that will also tell you about your alignment.

 

Happy for you that you got it dialed in. You are fortunate to live somewhere you can take test drives in the gloom of December.