2014 Event #5

Got beat by Mike and Gary.

I do not think that the pavement got warmer in the afternoon. The sun peaked through a little during first and second heat, and then it got darker gray and felt almost like the rain drops were trying to form at ground level. I wasted a lot of time and effort carrying all my stuff from where I was pitted, to the covered seating area, thereby insuring that it would not rain so that my time and effort was a waste. A decent trade for driving on dry pavement.
But, the pavement temperature was around 97 degrees, 10-15 degrees cooler than it would be with sun shine.

I drove my first run with both feet, meaning left foot braking. The tail was jumping out.

I drove my second run with one foot. It was just about as fast with less tail slide. I decided to continue one foot driving, and adjust the car exactly the opposite of everything I had been doing this year, basically back to the setup from two years ago: minimum rear tire pressure, stiffened rear shocks.
The big drawback seems to be that the car is lifting the inside front tire just enough to spin coming out of turns. The left foot braking was holding the car a little flatter, and/or providing enough resistance to the slipping side to keep the differential working to limit slip (with a gear diff, free wheel acts like an open diff).
I was giving the cones a real pummeling, and my run that would have edged past Gary by a fraction of a second would have had six or more seconds of penalties.

Good advice on the Nitto NT01s and the aging Kumho V710s. The NT01 is available in a 205-50-15.
I am giving a lot of thought to the idea of slotting the rear brake pads. My concern is that the reduced surface area will then bite harder (performance clutch has fewer pucks and applies more force to a smaller area). Or that the rear pad will be more likely to glaze instead of lock.
I also talked to Sean, who is kicking all our butts. He is using the Toyo Proxes R1R in a 195-50-15 size, which is narrower, and should get up to operating temperature on my light weight and underpowered car (and resolve tire clearance issues). He runs those as a street tire, drives to and from the events on those tires, and said they show no excessive wear or sign of heat cycling or getting hard. He said they may work better than the Hoosier A6 on the Family Arena lot, which was something I have been suspecting. And they are about $30+ less than the NT01s. The question will be if they will be available in the future. The 100 tread wear makes them illegal next year for classes moving to the 200+ tread wear tire requirement.

Instant G Liar's Poker: My first run on the G-Tech meter shows "1 1.11". The second run I turned the ignition off before looking. The third run showed "1 1.81". I am not sure if that is an error code or maybe the second row in the digital display is broken or incapable of displaying any digit other than 1. I decided it was not worth messing with and gave up.
 
Sunday was a really good course! I enjoyed it and tried something new. I am wanting to learn to drive every second of the course on the limit like I did when driving the other 3 cars I have borrowed. I am trying to get on the throttle earlier and brake later while carrying more speed everywhere. Unfortunately I chose a cold track to start this endeavor, but that is ok as I still learned a few things. I ran run 1 using my normal conservative style to learn the track. That resulted in a 53.9. On run 2 I stepped it up to full tilt and it bit me with a spin. That was ok as I learned a new limit on what the car would take. On run 3 I backed it down only in the 2 spots where I made mistakes and made some other improvements. In the end I was .3 seconds slower than I was last event compared to a CP car (on bias hoosier slicks vs my NT-01 street tires) I am trying to catch on raw times. The CP car ran heat 3 which had a little warmer pavement so maybe my times were not really that bad.

Like Bill I continued to cone away good run times and ended up winning with my 1st very conservative run which was the only lap I had that was clean. Bill ignoring penalties my best run to your best run was a wider gap this event vs last event. My 52.1 vs your 55.7. That may confirm that your tires are starting to heat cycle out and are getting harder.

I only got 2 videos before the camera died:

Run 2 with the spin (59.3): https://www.youtube.com/watch?v=1gHff4IQ5Kg

Run 3 (52.9 - 1 cone): https://www.youtube.com/watch?v=S3Q5BlN2XIw
 
I got some video of Mike and Gary. Sort of hard to tell who is driving until the numbers become visible, and hard to get a good idea of the driving while aiming the camera, keeping the car in frame, and running the zoom in and out. Both looked to be doing well. The comments from the crowd are always about the sound of the engine and the 500+ HP. If anyone asks me I always throw in the amazing adjustability range and fine tuning to turn a Lemans car into a autocrosser.

I've been trying to find some information about cutting the brake pad friction puck down to adjust brake bias. Not a whole lot of luck. There is some mention of doing this in circle track racing, where they have to use rear drums and prohibit biasing valves. The one article I found is at:
http://www.stockcarracing.com/techarticles/scrp_0412_race_car_brake_bias/viewall.html

He cuts 2/3rds of the pad material off and measures a 17% reduction in braking force.
I'm not seeing his math, he says it increased the pressure required for the same braking force from 450 PSI to 600 PSI. I'm reading that as a 33% shift in the point where the brakes lock up...
I measured the original pads used with the single piston calipers and the larger pads used with the four piston calipers. The front rear ratio goes from 85% to 78%, so the size difference is slightly increased. But, the original single piston calipers have the emergency brake mechanism built in, and are about as effective as holding your arm out the window as an air brake. I was thinking of reducing the pad face area by 20%, I just haven;t decided if I should try an end mill on the drill press with the slide vice, or a hack saw. I remember sanding the front pads that were too thick, the material doesn't cut easy.

On the liar's poker: I read the PDF instructions that Mike posted, it says the display for Instantaneous Gs is shown as "I#.##". So "I1.81" is Instantaneous G 1.81. Mike measured 2.11 Gs with bigger tires. Mine tires are narrower and not measuring favorably on the thumb nail test. I can live with 1.81 Gs.

I'm wondering about the extended ball joints to correct roll center, which might solve some inside front tire lift. And decreasing the rear brake force, which should make the brakes usable without spinning the car.
 
Ha...500hp. I wish! Only 400 in real life and only 350 at the wheel. The front is adjustable but the back is pretty set in stone which is the end I have problems with. It does sound good though.

Hurry up and get the video posted on YouTube, looking forward to it.

I would only use the chamfering of the pads as an experiment, but long term find some less grippy pads.
 
I'm researching brake bias, pads, calipers, etc.

Factors that will increase front bias
  • Increased front rotor diameter
  • Increased front brake pad coefficient of friction
  • Increased front caliper piston diameter(s)
  • Decreased rear rotor diameter
  • Decreased rear brake pad coefficient of friction
  • Decreased rear caliper piston diameter(s)
  • Lower center of gravity
  • More weight on rear axle
  • Less weight on front axle
  • Less sticky tires (lower deceleration limit)

Basic problem is that the car is ridiculously nose heavy with something like a 70/30 weight distribution. And half the rear weight shifts forward during braking. So the front brake has to be able to provide something like 6 times the braking force of the back.
I started out with the rotor that was available and would fit, and found the smallest four piston rear caliper that matched the fluid capacity of the OEM caliper that went with the rotor.

The easy/cheap solution is rear pad choice or area. The BP-10 is the lowest friction pad I have found. The other option is reducing pad area as discussed.
I should get the brackets made and put the larger front rotor on, which will help a small amount.

More expensive options:
Front brake calipers with larger diameter pistons. ($700!)
Four piston rear brake caliper with smaller diameter pistons are not available. Fewer pistons and smaller diameter pistons is only available as a Kart brake caliper.
Possible solution would be to sleeve the rear brake caliper to a .75 inch piston size. (Too much money, take too long).

Since the BP-10 pads are the lowest friction and only cheap pads ($50 vs. $150), the immediate solution looks like slotting the middle by 1/2 inch...
 
Many more hours spent/expended/consumed/wasted on brake bias research. Much of this is academic, but might be useful or interesting to any car builder...

As best I can tell, the car started out 2167 pounds, with a 65/35 weight distribution (1409/758). And FWD. Original brakes were 9.02 inch front rotor with 2.125 inch single piston front caliper, and 7.09 inch rear drums with 11/32 inch cylinders. My best ballpark guess on brake force is ~2570 in-b front and 500-600 in-lb rear.

The car has been lightened to 1969 pounds, and probably has a weight distribution more like 70/30 (1400/600).
I have upgraded to the 90-93 brakes from the next generation of chassis, which are 9.7 inch front rotor with a 2 inch single piston caliper, and a 10.1 inch rear rotor with a 1.25 inch single piston caliper. That car would have been 2411 pounds, with a 63/37 weight distribution (1519/892). Braking force something like 2529 in-lb front and 1065 in-lb rear. Big issue with the single piston rear calipers: The emergency brake is built in, it self adjusts when the rear wheels move backwards, and the caliper would not clear the chassis without being switched from the original front side of the axle to the back side of the axle (left to right and right to left, rotating backwards, and inevitably self locking!).

I installed the four piston calipers. 4x 1.38 inch diameter on the front on the 9.7 inch rotor, and 4x1.00 inch diameter on the rear on the 10.1 inch rotor. Braking force something like 3582 in-lb front and 1745 in-lb rear, with the bias valves turned full down and 60% reduction in rear pressure (~1047 in-lb). Th rear brakes seem to have bedded really well and lock up too easy, spinning the car. The rear caliper is not available in a smaller size, and they do not make anything with pistons smaller than 1 inch, so there are no pistons and seals to rob from another piston for a sleeve down rebuild.

I got out the spare 11 inch front rotors. Shipped them off to be cryo treated. Took the mounting bracket drawing over to the machine shop. Thought that Event 6 was July 27. I was wrong, it is July 20, so the rotors will not be back in time.
The 11 inch rotor with the four 1.38 inch piston caliper should be 4164 in-lb (16% increase).
Front calipers are available in larger piston sizes. Oddly, not all priced the same. One step larger is $275 per caliper, two steps larger is $202 per caliper...
11 inch rotor with four 1.5 inch piston caliper should be 4920 in-lb.
11 inch rotor with four 1.63 inch piston caliper should be 5809 in-lb.
11 inch rotor with four 1.75 inch piston caliper should be 6696 in-lb.

The rear four piston caliper is not available in a smaller piston size. But I did manage to find a single piston caliper that might be promising. It would require a totally different bracket and possibly spindle backing plate (bolt on). But they are $100 each! $250 for a pair and brake pads from Summit.
The 10.1 inch rotor with two 1.38 inch piston caliper should be 1662 in-lb.
Not a big jump, but more of an option than nothing.
The 1 inch, 1.125 inch, and 1.25 inch pistons and seals are available for other calipers. So a sleeve down rebuild would be possible with off-the-shelf pieces. That rotor and caliper with a pair of 1.25 inch pistons would be 1363 in-lb. Step down to 1.125 inch and that goes to 1104 in-lb.
 
Speedway and Summit are close on price. But since Summit stopped the $12 minimum handling charge per order, and started in with free shipping on orders over $100, their price is a little better overall. Not sure what kind of price I could come up with from the wholesale distributor, but then I pay shipping, and anything not in stock gets tagged with an inbound freight charge.

Also, Speedway is carrying only the larger piston calipers, not much of the smaller piston stuff. I'm trying to find the smallest pistons that also fit a .81 and .28 inch thick rotor.

I like the Dynapro calipers a little more. The pad retaining clip is a lot better. All of the Dynalite stuff is lug mount, and the lugs overlap the spindle mounting ears on the front. The Dynapro radial mount works a lot better and does not require notching the caliper back to fit the spindle.

I had a disagreement with Hawk a long time ago. I tried to arrange a wholesale purchase, and someone local sabotaged the whole deal to keep me out of their selling area. (Odd thing about the whole deal, after the minimum purchase to get an account, I would have been doing exclusively mailorder sales of off-the-wall Japanese pads and no local sales at all...) Might have been Dave, but he never let on. The Hawk company president made some big asinine statement to me, claimed I revealed his wholesale price list to the public (big mystery, wholesale is 60% below retail!), and I told him where he could stick his pads. I'm pretty sure I can do a better job on the brakes and never use a Hawk product...
 
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