Wednesday, May 6, 2009


So, up to now I've been basically living with the knowledge that my alignment at the track is not what you might call "spot on." I have a static alignment of approximately -1.0 degree camber at the front and -2.0 degree camber at the rear with zero toe all the way around. This is OK for street use, but not nearly aggressive enough for the track.

So, with my adjustable camber plates I can jack the weight off the front and swing the strut tops in towards the car centre and generate an additional 2-3 degrees of negative camber. I don't have a camber gauge, so I'm really just going off numbers I've read in the forums. In reality it doesn't really matter that much, I do have a infrared pyrometer so I'm able to get a rough estimate of the tire temperature across the tread, so I generally just use that to tune in my camber.

A few months ago I posted a note to one of the message boards about some mid-corner understeer that I'm experiencing in Turn 4. Essentially a long sweeper where I just can't stay on-throttle all the way through it, I need to breathe just a tad around mid-corner to bring the front in line; otherwise I'll push out (just like my oops video from earlier). I got an answer back that excessive toe out can cause this behaviour which got me thinking...

So I went home and ran a very rough experiment, with the car parked in my garage facing straight ahead I ran a plumb bob down the outer groove of my tire both front and back and put a dot on the floor and repeated it for both tires. Then I backed the car out of the garage and measured the distance between the two front dots and the two rear dots.

With the car setup for "street" driving (meaning the top-camber plate is reset to the zero mark) I measured 1/32" of toe in. Very much within specifications for WRX cars. I repeated the measurements for when the camber plate is pushed all the way in towards negative camber and found it to be 15/32" of toe out; which is a massive amount of toe out! I was really surprised by this finding; I expected a bit of toe out -- maybe 5/32 or so, but nearly half an inch was way beyond my expectations.

So as a consequence, I've invested in some toe plates from HRPworld which just came in this week. They're essentially two flat metal panels that you lean up against the tire with slots to put a tape measure in. With this you can measure the toe much easier than putting marks on the garage floor. I'll take the toe plates with me to the next track day and I'll see what changes it brings when I zero out the toe while I'm running the negative camber.

Speaking of track days, the next one should be a fun one for me. It's an AR Auto track day run more like a test/tune day than a track day. Basically there won't be any run groups, just 8am to 4pm (with a break for lunch) and you go out when you want to and come in when you want to. This is perfect for this kind of tuning because I'll be able to make a change and test it right away throughout the day. While I'm there, I'll be collecting data on tire pressure, camber changes, sway bar settings; along with collecting some ECU data (boost, RPM, timing, MAF, etc) using my access port in a data logger mode. It will be a lot of fun, and of course; I'll do a writeup afterward.


I spent a bit of time on the weekend to figure out how to adjust the toe so I wouldn't waste time at the track learning this stuff. I came away from the experience with a few lessons:

First, you really need to mark the tie rod in some way to know when you've done a full revolution -- it's too easy to get out of sync without something marked on it. Unfortunately, I learned this lesson a bit late (after I messed up) but I did come away with a quick solution. My tie rods have fairly wide flats on them to accept a 13 mm wrench, so I wrapped a cable tie around the flats to hold it in place and I can just watch the position of the ratchet part to know when I've come fully around.

Second, to re-centre the wheel you want to toe out on the side the wheel points and toe in the opposite side. For example, if you're driving down the road straight but the wheel is cocked over to the right, you'll want to toe out the right tie rod and toe in the left (by equal amounts) to re-centre it.

Third, if you get the tie rods of of sync it takes a lot of finicky work to get it aligned straight again. :-) It's the typical cycle of adjust, drive around the block, adjust again, drive again, etc, etc until you get it straightened up.

Fourth, one full revolution of both left and right tie rods will change the toe by approximately 1/2". So in my case, at the track I will end up putting in one full turn of toe in for both left and right sides when I slam in the camber.

In the end of the day after about 2 hours of fiddling around, I was able to successfully adjust the toe with the camber set at full negative and recover back when I put the camber back (zero toe and centred steering). Due to the experiences I went through, I think it will be much easier at the track now so it was definitely time well spent.

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