Wednesday, June 4, 2008

Track Day #5 -- 2008/04/09

After I came home from the previous track day; I took a look at my rotors and pads and saw that they were pretty much shot. Running without the chicane meant that instead of braking from about 105 MPH into T1, I was now braking at about 125 MPH into T4. Physics tells us that energy of movement goes by the square of speed; so that extra 20 MPH increased the energy by 42% which the brakes had to deal with. Clearly they were not up to the task! The pads came out all crumbly and the rotors had deep grooves in them.

So, I went shopping for brakes. I didn't want to spend a tonne of money upgrading wheels, tires and brakes together; so that limited my choices quite a bit. None of the big brake kits would fit; I had to look for smaller upgrades. In the end, the decision came down to a 4 pot upgrade kit from Racing Brake and a Wilwood kit from TCE. I eventually selected the Wilwood kit; it had a really good selection of brake compounds with detailed information (Cf charts by temperature; etc.). If you're in the market for upgraded brakes, definitely checkout TCE's offerings of Wilwood kits.

The installation of the brake kit is all pretty straight forward. Just remove the old caliper, bolt on a new bracket, put together your rotors (they're two piece design that you need to bolt together and safety wire), and attach everything. The only "tricky" part is getting the shims right so the caliper is centered on the rotor and stands off the right distance from the rotor.

So for this track day, I was (again) evaluating some new equipment. The first session was all about feeling out the new brakes and making sure everything was OK. Being Portland, the first session was wet and rainy; so the lap times were pretty low (1:44.1), but the brakes tested out OK.

For the second session out, the track started to dry out a bit and as I was pushing more, I began to hear a buzzing noise coming from the front tire wheel area. It only happened in T7 where I was still fighting understeer problems; I just could not get the car to rotate properly towards the apex. Eventually, the buzzing noise got loud enough that the turnworkers started hearing it and I got meatballed. The meatball is a black flag with large orange dot in the middle (hence the name). It means that "something is wrong with your car, please come talk to us." So I went in to talk with the official, where he told me that they thought it was my brakes clicking under load and that I need to check it out.

I tried looking at it; and figured (wrongly) that it was expansion noises coming from the two-piece rotors (they snap, ping and pop a little bit as the hub portion is aluminum and the rotor is steel -- as they heat up they expand at different rates, causing noises). So they let me out again for the 3rd session, but (naturally) the noise came back and I got meatballed again. That pretty much ended my day -- I did manage a new PB of 1:39.3; but had some work to do to figure out what was causing the buzzing noise.

Fearing the worst, I did some tests to ensure that it wasn't the bearings or the CV joint (expensive items). I also took the brakes apart, and figured that I wasn't rubbing anywhere. While I was in there, I took out the backing plate to help cool things down. I also noticed that my race pads (Polymatrix-B) that I got with the Wilwood kit were about 60% used up! I was hoping to get a bit more than one track day out of a set of pads! And they had a pretty severe taper to the pads as well (thicker at the trailing edge of the pad than the leading edge). So now I had two things to worry about.

In the end, I got everything sorted out. With the help of YouTube and the nice folks at NASIOC; I was able to determine that the buzzing noise was nothing more than the tire rolling over itself. It would have gone away if I pumped up the tire pressure a little bit more.

The pad wear problem was solved by improving the rear brakes. I had so much forward bias by upgrading only the front; that it was doing nearly all the work. A quick couple of calculations convinced me that I needed to upgrade my brakes at the back to even things out and cool the front down a little bit. This will help with pad wear.

The solution was to order a Racing Brake OEM big brake kit for the rear. It is really little more than a bracket to relocate the caliper out from the axle just a little bit and replace the stock rotors with upgraded slotted rotors of the right size to match the increased diameter of the new brackets. My only complaint was that it took a long time for them to ship me the kit -- it was backordered for about 4 weeks. But it eventually came and I was able to put it on prior to the next track day. I also purchased some Hawk HP+ pads for the rears to help move the bias more to the rear.

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