Friday, May 22, 2009

Track Day #10 -- 2009/05/21

Yes, I had another track day. This time I went to an open track day event put on by AR Auto Service for experienced drivers. There were about twenty folks so plenty of open laps without much traffic. The mix of cars was mostly high performance sports cars and race cars; lots of GT3s, a few Miatas, BMWs, Ford GT, etc. In terms of raw performance, my poor little WRX was way outmatched here. I think there was maybe one Audi out there running slower lap times than me, but most folks quite simply blew my doors off.

The day was an open track even, meaning that they didn't divide us out into run groups. They basically just had 30 minute sessions where you were welcome to get right back in line to pre-grid on the next session if you wanted to. Track went hot for quiet/street cars at 8:30AM (or 9:00AM for race cars) and went cold at 4:00PM; with 30 mins off for lunch (Yummy lasagna catered in).

All this meant is that I had WAY too much track time. My first realization was that anything more than 30 mins at a stretch is really a bad idea. I ran half a session and stayed in line for a full next session and it was way too much; I need more breaks in between sessions. The other thing is that I got my full about mid-afternoon (2pm) so didn't really use up anything close to my full potential.

My plan for the day was to experiment with different things (both driving and car setup):
  • Zero out the toe when changing camber and evaluate.
  • Evaluate the Hawk Blue rear brake pad upgrade.
  • Experiment with tire pressures.
  • Play with lines and weight transfer, etc.
So, my results... well, I'd say they're kind of mixed. First observation is that I can't tell all that much from zeroing out the toe. It grips a bit better in T4 and doesn't wander so much on the straights, but the lap time didn't improve dramatically.

The second observation is that the Hawk Blues are a nice pad, and I can definitely feel the grip there (once it's bedded in) but it's probably not worth the extra money. I was able to get better trail braking into T7, and T1 was pretty consistent; but the pad was wearing pretty quickly and my data logger tells me that my overall braking performance wasn't really that much better. I'll probably stick with HP+ in the future.

Now on to tire pressures... that's an interesting one. I originally tried to shoot for 40 PSI front and 45 PSI rear (hot) and get pretty good feel out of it; however, I get quite a bit more tire noise in T12 when set up this way which goes away when using higher front pressures. I took a look at the tire temperature with my infrared pyrometer and I'm seeing about 160 on the outer edge, 162 in the middle, and 157 on the inner edge. This implies that I'm slightly overinflated and not running enough camber (even though I'm maxed out on camber). One observation I did have is that I had my fasted lap during session 2 where I had the tires set too high (48 PSI on the front left); so that argues (perhaps) that I need higher pressures? Clearly I still have some work to do here. One observation I did have is that track temperature has a huge impact on whether I can get a good lap time or not. The second session of the day was cool and dry (maybe 60F) and I was never able to reach even close to that time for the rest of the day as it warmed up. My best laps were always within the first 5 laps and then things settled out. I don't know if it's simply tire heat or if it's pressure related.

Now on to my driving experiments. First thing to note is that I stopped shifting down to 2nd gear for T7; I just left it in 3rd. According to my data logger this is definitely the right thing! By doing this, I'm able to hit another 1-2 MPH by the end of the back straight, so it's going to be my normal approach here. I also played around with braking early and accelerating into T7 apex vs braking later and trying to get it to rotate down to the apex. In general, I think braking early and accelerate through works better. With the Hawk Blues I am able to rotate the car under brakes, but I've got to be more careful about it -- it's very easy to overdo it and end up missing the apex.

The other experiment I was running was to try to carry more speed through T5 and that worked out really well; a slight lift/touch of the brakes and then accelerate out. My problem then shifted down the track a bit to the transition of T6 where I was having a really tough time getting set up. The problem with T6 is that I'm carrying so much understeer through T5 that I have a bit of a "moment" as I transition from the right hander (T5) to left hander (T6). It's probably a matter of smoothness, which I'm working on; but also dealing with the understeer.

I didn't really play that much with T10-T11; just doing what I did last time, but not as aggressively. I know I can hit that better than I am, but it's also one of those things that requires some commitment from me and I had enough to work on. :-) I did try a few things in the chicane though (nice safe place to have some fun) -- mostly trying to get the car to rotate better for the left hander coming out of T2. Sometimes I got it, sometimes not. Occasionally, the car would rotate so well that I'd run up on the curb more than I'd like; so clearly I need more work here too (or just play it safe and not try to "drift" it around here...).

My fast lap for the day was 1:34.3 which is 0.6 seconds faster than my previous best. Here's my fast lap comparison from my previous best. As you can see, staying in 3rd gear for T7 really helps me get a good pull onto the back straight and propels me to almost 120 MPH. The interesting thing is that with all the better here but worse here parts in the lap, I'm actually at a dead heat for the entry of T12. This means that my pull onto the front straight was where I found my time. All the rest is just lost opportunities. :-)

And here's the video of the lap:

Here's some pictures of the other cars at the event. It was a lot of fun running with these guys, even if it meant they were blowing my doors off -- all except for the black Lamborghini who was going at a nice controlled pace; probably didn't want to risk the nice car. The Subaru guys came over and we chatted for a bit; he was running about 1:25-1:26 lap times, so clearly out of my league. He seemed to like my lines, so maybe I don't suck as much as I thought.

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.