Thanks for the reply, but I'm not sure what you are proposing.

I swung the steering 20 degrees at the tire left and right for each side and measured the camber, did some math as described in Post #8 above, and calculated the caster.

What do you suggest I do differently?

I would like to make it a little more clear--"almost zero" is not quite accurate. She was slow to recenter from large inputs, and didn't completely recenter from those inputs, but there was some recentering.

I'm just wondering how accurate that method is. When I had 6 degrees caster before I got the car realigned after depowering steering it was very heavy especially at low speed.
It almost sounds like the caster is lower than what you're measuring if it doesn't self centre nicely. Going from the 6 to 4.5 was a big change. If I went down to 3.5 it would probably be too light and not enough centering just based on the change from 6 to 4.5.

This is messing with my cranium
 

I took the car to VIR this weekend. She was not happy. It was doing weird things I have never experienced before, such as darting around when upshifting from third to fourth, and acting strange in turns. The back end felt like it was wiggling halfway through a turn. I took her to Quantum Speed Works just outside the track and had the alignment checked. I believed I had -3.2* up front, -2.8* rear, 5.6* of caster, and no toe. The Hunter machine indicated I had -3.5* up front, -3.2* LR, -3.1* RR, and 5.6* of caster. I assumed my camber gauge was off 0.3 degrees. Unfortunately, I didn't have zero toe at any corner--the toe was small, but pointing in all directions. I needed to cross off the alignment as being good in order to troubleshoot the rest of the car's unhappiness, so I paid for an alignment. They got the numbers I wanted, with caster ending up at 5.5 on the left and 5.4 on the right.

When I go her back home and in the garage, I put my weight in the seat and got out my Smart Camber gauge. I measured -2.9 camber up front, and -2.5 in the rear. I recalibrated the gauge using the procedure in the owner's manual and checked the car again. I got the same numbers. I don't see how my gauge could be wrong. The calibration procedure is straightforward. I hold it against the window in the kitchen for 10 seconds, press and hold the Calibration button until the number flashes, then move to the outside of the window in the same place, hold for 10 seconds, then press and hold the calibration button again. The procedure could not calibrate the gauge with any errors as long as I'm measuring from opposite sides of the same plane, a pane of glass in my case. It can't be my garage floor, or the Hunter would have found different numbers for the left and right sides.

Could the Hunter machine be wrong?

Doubtful. Remember when I said pay for an alignment? Those camber gauges are a rough estimate at best.

This is what I have, minus the bag.

https://cimg0.ibsrv.net/gimg/www.mia...1836973a9b.jpg

It has served me well for years...

Yup, have one too. If it’s within half a degree of the John bean laser alignment system I use, im happy.

Curly, if you owned my particular unit, would you assume it reads an additional 0.3 degrees to the negative in future use?

We go to the track with our cars aligned with either the John Bean (snap-on) alignment machine, or lately we've started using the $40k Setup Wizzard on a car or two. We have that exact gauge in our track tool box really just to compare camber side to side in the event of a collision, as BMW knuckles like to bend, and their camber plates like to slip. Likewise, if I were using it on a Miata, I'd use it to compare side to side if I suspected slipped eccentrics or bent arms. We have SO much experience with our cars/tires/drivers that we know we're not going to be making a major change at the track just for a setup change.

I wouldn't focus too much on the exact number, instead pay attention to what it's getting you. Tire temperatures are more important than some camber angle you read on the internet. Start by getting it hot and have someone check your temps in the hot pits, do not do a cool down lap, and do not try to take your own temps, it takes too long to get out of the car. If you've got roughly a 20 degree spread, you're in the ball park.

Looks like the conversation may have passed the point where this information could be useful but I’d like to offer it anyways.

We’ve got a Hunter alignment rack that I use to align my car at work. It’s a really nice unit but I’ve come to find out that I have to do a rolling compensation check on the machine (rolling the car back and forward about a foot) and caster sweep after every major adjustment if I want to finish with accurate, repeatable numbers. Ex: set rear toe and camber, rolling compensation, readjust rear toe and/or camber again, rolling comp, adjust front camber/caster, caster sweep, adjust front camber/caster again, caster sweep, set front toe, etc etc.

If I don’t do this on our rack, I can drive the car home, put it back on the rack in the morning and get a different set of numbers at each corner, up to maybe .7-.8* difference on caster and camber, and up to a tenth or two of a degree off on the toe. Doing all those caster sweeps/rolling compensations between adjustments seems to yield more accurate measurements by the machine once the alignment is finished. I can drive the car after this, put it back on the rack, and the machine will give the same measurements as when it drove off. My Miata seems to be more sensitive to this than other vehicles I’ve compared it to (I don’t generally do alignments at work but have aligned a couple other cars on the rack). What’s funny is that to my knowledge, our Hunter rep never mentioned the possible need to do this to any of our technicians. I’m not gonna claim I’m smarter than anybody but again, this did seem to fix my issue.

To get to my point, there’s a chance the measured angles from the Hunter machine could have been a little off depending on the operator’s procedure. Obviously, there’s a lot of other factors at play, just thought I’d throw this out there.

I agree 100% with this, but I was working a new alignment.
I had been running with a Dual Duty alignment, even though I was now trailering the car. Since I was replacing so many of the front suspension parts, I decided to go with a more race focused alignment. I needed to start somewhere. I hadn't paid for an alignment in almost a decade, and she was pretty fast, despite my best efforts. I did learn that the caster calculations I included above work, and I need to be more precise with setting toe.
-------------------------------------------
Different issue...
With the new alignment and ELBJs, I'm getting wheel spin on the right rear powering out of right hand turns. I assume my fat ass in the driver's seat is preventing that from happening on left handers. I plan to put the full size battery back in. Will it be enough?

Thanks,

He did not do that during my alignment. That said, you'd think there would be inconsistencies with the numbers if his procedures were off, but there wasn't when I remeasured after getting home. My gauge just read it as 0.3 degrees less camber all around. I didn't look at toe, and probably won't put myself through the pain.

i have this same one plus the bars to do the string toe alignment.
this stuff is expensive.

Sooooooooooooooooo, I couldn't find anything visibly broken or bent underneath, so I decided to go back to OEM-style ball joints. It seemed to be the only way to tell if there was something else wrong. If the wheelspin went away with the OEM ball joints, then I'd know it was the ELBJs. I don't have as much camber as before, but caster is down to 4.35 degrees. Unfortunately, the wheelspin (or whatever) is still there. I came out of Turn 1 at VIR and jumped on the gas and the rpms shot up. That doesn't happen with someone in the right seat. I thought it might be the clutch, but wouldn't that be worse with more weight in the car? It didn't feel like the clutch...I have to admit, I can't swear to there being actual wheelspin, only that the rpms shoot up without acceleration, it only happens powering out of right handers, and it doesn't happen with someone in the right seat.

It has to be the diff. I'm going to assume the car shouldn't be driven to prevent something worse from happening to the differential, unless someone can convince me otherwise.

Any words of wit would be greatly appreciated.

If the inside wheel is lifting a torsen will act like an open diff, giving free spin and a corresponding jump in rpm. Did you fiddle with the rear sway at all? Are you still using a torsen?

It did not do this before the crash. The diff doesn't make any weird noises when I'm pushing her around in the garage. Everything is smooth.

If I broke something inside the diff, how would I test it?

From what I've read, if the inside wheel is lifting, the Torsen and the open diffs act the same. Is that correct?

I do believe she's a little bent, although she will take an alignment. I need to take pics of all the shocks to show where the spring perches are set.

Thanks,

It sounds like your wreck introduced some “wedge” to the chassis. IE it grip’s differently left vs right cause it’s got more/less weight on alternate corners. I’d be curious to see what the corner weights are. But clearly seems your rear right is light as it sits.

If the differential doesn’t make abnormal noises or pops and grinds when driving and making slow turns I highly doubt anything is wrong internally

She's not corner weighted. Seemed like a lot of effort and expanse for an HPDE-only car.

I just took a lap at VIR. I really laid into the gas coming out of Oak Tree and spun the right rear with a glorious display of smoke.

Does that mean the diff is probably okay and I now have a corner-weight issue?

Yes, but also likely a chassis issue if the shocks are all set to the same height, as the right rear is clearly getting very light relative to the left when cornering

The spring perches were adjusted with my weight in the driver's seat, 4 3/8" front ride height, 4 1/2" rear at the pinch welds. The spring perches look odd. I took pics. Will upload them when I'm in for the evening.

This.

Corner weight it. Go back to that (track) corner and check for difference, set it up consistent with last time. See if it is back to 'normal' for you/that corner.

If the chassis is pushed up in one corner, the cornerweights will probably show it in the initial readings, but if you have never done a corner weight there is no baseline to properly compare, so just get them as close to balanced as you can.

OTOH the chassis may have been pushed laterally, with or without some 'up' component. This will show up in your wheel alignment at the rear where both will 'off' in the same direction on initial measurement. That condition may not be only caused by chassis distortion though, but it is a pointer. If this is the case, I don't know if it would be contributing to your wheel lifting, but it would affect the feel of the car in its handling of LH and RH corners.