Warning, long post
 

Been suspecting something is off with my alignment methods, as the subjective feedback from driving did not match what was expected from the measurements, so I came up with a few tests.

First, the track test, made possible by my particularly deep garage. Center the steering wheel and move the car as far forward as possible. Use a straight edge/square to mark the ground at the outside edge of each rear tire. Then move it back until the front wheel is next to those marks and make another two marks. Move the car out of the way and measure the distance between marks on the left, then on the right, then subtract to get the difference. Inverse sine of that difference divided by wheelbase (2570 mm on the FRS) gets the angle. Mine showed it was off by 4.5mm, .09°.

Second, measure from the string to known points on the body. This assumes the string box is parallel to the centers of the wheels, but the wheels might not be centered on the body. Drop a vertical line off the string box at two points on the left, and again on the right, and measure the distance to 4 symmetrical points on the body. I measured to the crease in the rocker/quarter panel just behind the fender, and the edge of the rear wheel well. Subtract the front left from the rear left, ditto for the right, then subtract those results from each other to get the side to side difference. Measure the length between the measured points. Divide the difference by the length , and inverse sine the result. Behold, my result was 2mm, .05° in the same direction.

Ok, so something is clearly up. Bring it to a professional and have them measure it. Their toe numbers were precisely .09° off from mine, in the same direction as my tests indicated.

Now I'm trying to figure out what I'm doing wrong when building the string box. I'm not 2mm off each axel due to measurement inaccuracy. I'm measuring from the inside lip of the wheel mating surface (no center caps) so maybe that's inaccurate? Hard to believe that adds up to 4mm difference though...

Puzzling.

Also, my fuel trims went haywire and came back down again. My guess is that exhaust gasses from the double slip are getting caught in the O2 ambient air side and messing with it from time to time. Or my O2 sensor is broken. Maybe I need an O2 snorkel. It's definitely not having the wrong headers...

Ok quick update.

Did my 2nd autocross on the new setup. I made some changes between last and this one. Overall pretty pleased with the car, though it was damp, then wet during my runs.

New alignment figures (#30)
Front camber: -2.9°
Rear camber: -2.0°
Front toe: 0° to +0.03°
Rear toe: 0° to +0.02°

I was able to sort out the rightward pull a bit more by adjusting the rear thrust angle. Somehow my string box is off and after taking a bunch of measurements I still don't know why, but I just compensated for that while setting it up and it seems to have worked out. I think there's some minor adjustments I can make to camber, but for now it's fine.

Replaced the too-small front sway bar bushings with slightly larger diameter.

Set front bar (19mm Perrin) to stiff.

Fixed my undertray for real this time and forgot to take any pics to prove it...

I'm pretty convinced my theory regarding the o2 sensor is correct. I confirmed that at least one of the double slip fittings isn't sealing all the way when hot using a smoke stick. Also leaking on startup is bound to have some effect in there without the fans blowing. I'll deal with that eventually.

I haven't seen full results from the autocross yet but I was about 4-5 seconds off the competitive pace for STX judging by the few times I saw and my own on the timing board, which is to be expected considering I am not running competitive tires yet, and took a ride along, and left the spare in, and had a full fuel tank. I think I'll be looking for wheels and tires next if the budget allows. Might be regretting modding my house this spring...

Autocross impressions: Dry handling was well balanced I think, maybe a little sensitive at the rear but I kind of like it that way. Probably could use even more camber but I don't know how to figure that out yet. Was a bit of a handful when wet, as it rained on my last two runs. I am pretty sure I drifted the entire second to last run, though I think I somehow made all the gates without penalty. Good chance to figure out the wet limits in the new setup at least lol.

Lol that was a lot longer of an update than I anticipated.

Budget says yes. Wife says yes*. Wheels and tires are a go! :party0030::happyanim::thumbup::bow:

Now I need to figure out what to get...

*Ok she said "sure" when I wasn't able to answer her question on whether I would be more or less likely to die doing autocross with these. :iono:

The APEX racing ARC8s look great and where I plan to spend my money. I think I am just a sucker for the fact they are basically designed around our platform

The Arc-8 is the current frontrunner. Need to pick an offset though.

Please keep us posted :) I seems like 99% of people go ET42 over ET35. I was thinking ET35 myself until I saw so many people going ET42. Now I don't know haha

I sure hope I got those offsets right LOL

1st gen most people run +35. Second gen +42 for clearance issues.

Are you talking about wheel fitment in general or the Arc-8 ?

All the cars I saw were 1st gen and most ran the higher offset with the Arc-8

Both. +35 on the first gen is close to flush. The only situation you would run different is for brake fit, the RPF1 won't clear BBK in +35 due to spoke profile, or that is all the manufacturer offers. 57DR/CR +38, 949 +40, ect.

It would be the same for all wheels of that size unless one was concerned with brake clearance.

I haven't looked at wheels in a while (until now of course) but I think I recall +35 poking out/rubbing on fenders a bit unless you had a few degrees of camber, which I do have. I think you can also run a wider tire pinched on a +40 if you have coilovers with narrower springs.

I'll probably go with +35.

Just checking, you are talking about+35 on a 9" wide wheel with 245s right? Never looked at 9s until now so that's where some of my uncertainty is coming from.

Yes, that is what I figured you would be looking to run.

Here is how that looks on my car.

Well, +35 it is then.

Lol is that a transponder zip tied to your splitter support?

Yeah lol. It wasn't always picking up when on my grille.