Front OEM Brake Pads

[oldbmwfan]

@oldbmwfan Your post was helpful. I appreciate the extra perspective you provided.

Your chart you posted above shows how quickly the driver gets back on the gas. I noticed your comment about TC and how the driver still rolls into full throttle.

The question I have involves my remaining fear when lapping a track: throttle induced oversteer. I am still rolling the throttle on slower than I could be because I do not want to be "that Mustang guy" that gooses it too hard and ends up in the wall.

When you feel the rear beginning to break loose, do you correct with steering the same way that you would when it has already broken loose? By that I mean you can either begin your reaction before or after the rear is sliding. Is the reaction the same? Perhaps the initial reaction is the same, but returning to center is different?

I was watching a video of Randy Probst where he caught a slide by what appeared to be a deliberate (could have been described as violent even) turning of the wheel and then immediately returning the wheel to center. Does the act of returning to center precede the rear coming back into line and thus still sliding? Or do you return to center after the seat of your pants tells you the rear is in the process of coming back into line? Or do you wait to return to center until the rear is back in line?

I had the rear step out on me going through Bishop Bend and I successfully saved it, but I don't really know what I did. It happened so fast. I want to understand what is going on when trying to save losing the rear end.

First, you're doing the right thing - being cautious and progressive with throttle application is far safer and ultimately faster than matting it and hoping it sticks, or trying to save it when it doesn't. Safer for obvious reasons - no snap spins - and faster because a sliding rear is slower than a gripping rear in most cases.

The tires have a finite amount of grip to give. You can use 100% grip laterally (like at the apex of a corner), or 100% of the grip longitudinally (max power for the rear tires or max braking for the fronts), or you can use a mix (like 50% lateral and 50% braking, when trail braking into a corner). The key is you can't exceed total tire grip, so if you are applying throttle as you exit the corner, you HAVE to roll it in ... if you are cornering anywhere near the lateral limit, by definition you can't apply all the power or you'll spin the tires (and probably the car). On corner exit, you can increase throttle as you straighten the wheel, so you're always using up the full grip budget with an increasing portion shifting from cornering to acceleration as you approach the straight. On most corners, you can be at full throttle just a bit before the steering wheel is straight.

What you see Randy doing is exactly what you wrote - anticipate the slide, countersteer, and then immediately come back the other way to prevent a snap in the other direction (tank-slapper). Once you catch a power slide, the car will want to slide back the other way when it hooks up if you don't get the steering out.

My biggest on-track incident and the only one that resulted in a non-drivable car was one of those. At Watkins Glen, I had oversteer going into T5 (the Outer Loop after the Bus Stop, big, fast right-hand sweeper). The tail came around to my left as I entered the right-hander hot. I was a little slow to catch it and I overcorrected, causing the tail to snap back to the right, and that spun me all the way into the outside wall at 85 mph. Wasn't my best moment. My mistake was correcting with too much steering (turning wheel left into the slide - correct move, but I overdid it), and then holding that steering input too long and not anticipating the counterslide to the right. Once the momentum was going right at that speed, my hands were too slow to catch up.

Sponsored

 

[ChiefDork]

First, you're doing the right thing - being cautious and progressive with throttle application is far safer and ultimately faster than matting it and hoping it sticks, or trying to save it when it doesn't. Safer for obvious reasons - no snap spins - and faster because a sliding rear is slower than a gripping rear in most cases.

The tires have a finite amount of grip to give. You can use 100% grip laterally (like at the apex of a corner), or 100% of the grip longitudinally (max power for the rear tires or max braking for the fronts), or you can use a mix (like 50% lateral and 50% braking, when trail braking into a corner). The key is you can't exceed total tire grip, so if you are applying throttle as you exit the corner, you HAVE to roll it in ... if you are cornering anywhere near the lateral limit, by definition you can't apply all the power or you'll spin the tires (and probably the car). On corner exit, you can increase throttle as you straighten the wheel, so you're always using up the full grip budget with an increasing portion shifting from cornering to acceleration as you approach the straight. On most corners, you can be at full throttle just a bit before the steering wheel is straight.

What you see Randy doing is exactly what you wrote - anticipate the slide, countersteer, and then immediately come back the other way to prevent a snap in the other direction (tank-slapper). Once you catch a power slide, the car will want to slide back the other way when it hooks up if you don't get the steering out.

My biggest on-track incident and the only one that resulted in a non-drivable car was one of those. At Watkins Glen, I had oversteer going into T5 (the Outer Loop after the Bus Stop, big, fast right-hand sweeper). The tail came around to my left as I entered the right-hander hot. I was a little slow to catch it and I overcorrected, causing the tail to snap back to the right, and that spun me all the way into the outside wall at 85 mph. Wasn't my best moment. My mistake was correcting with too much steering (turning wheel left into the slide - correct move, but I overdid it), and then holding that steering input too long and not anticipating the counterslide to the right. Once the momentum was going right at that speed, my hands were too slow to catch up.

That is exactly what I was hoping to read in your response. I suspected what you wrote is what I needed to do (especially returning to center at the right time) but I did not want to test my theory in real life. Maybe after I make the last payment on the car, I'll be more willing to let it hang out there, but I am just not there yet.

I appreciate your time and willingness to transfer some of your hard won experience.

 

[Michael_vroomvroom]

As for trail-braking, here’s a short clip of T12 at COTA in HB. Note, this was on lap 4 of the first session after my winter updates, so I was still playing around to find my ideal braking marker. On this lap, I braked too early, so I started releasing pressure really early so I didn’t scrub too much speed heading into the corner. It’s a fairly decent example of adjusting on the fly to keep things as smooth as possible. Notice how the brake indicator is on all the way until the apex.

Much educational info from you and oldbmwfan here. Definitely something I'll re-read a few times before my next (fifth) trackday.

Can I ask what program you used to record your video? I tried using a program called "Track Addict" last time, but it seems to only provide an on/off value for braking, unless I'm missing something. Your video shows (calculated or real?) brake application, which is of course much more interesting.

 

[honeybadger]

Much educational info from you and oldbmwfan here. Definitely something I'll re-read a few times before my next (fifth) trackday.

Can I ask what program you used to record your video? I tried using a program called "Track Addict" last time, but it seems to only provide an on/off value for braking, unless I'm missing something. Your video shows (calculated or real?) brake application, which is of course much more interesting.

I have a pretty pricey setup consisting of an AIM Solo II DL and Smartycam. The good part is that it's automatic. Starts when I head out on track and stops when I come back. I don't touch anything the entire day and all my data is overlayed on the video in real time. It's awesome.

 

[Michael_vroomvroom]

I have a pretty pricey setup consisting of an AIM Solo II DL and Smartycam. The good part is that it's automatic. Starts when I head out on track and stops when I come back. I don't touch anything the entire day and all my data is overlayed on the video in real time. It's awesome.

Hehe, ok, now you're talking. ;-) Thank you for the specific information.

Look and sounds really indeed. Concentrating on one thing at a time, it's really interesting to see how you apply your brakes when cornering, and it's well laid out in the video setup you use. Will be watching more of your videos. Thanks. :-)

 

[JAJ]

I have a pretty pricey setup consisting of an AIM Solo II DL and Smartycam. The good part is that it's automatic. Starts when I head out on track and stops when I come back. I don't touch anything the entire day and all my data is overlaid on the video in real time. It's awesome.

I was looking at the video and the brake application information, and I'm curious now. The brake indicator (red bar graph) shows you full into the brakes at 140, starting to ease out at 100 and more than half-way out at 80mph. That's what I'd expect. What's odd is that the longitudinal G meter beside the bar graph seems to lag a long way behind all this. It has you at 0.8 G's while the brakes are full-on, rising to 1.5 G's while you're easing out of the pedal, and at 1.4 G's when you're more than half-way out. Is this real?

 

[honeybadger]

I was looking at the video and the brake application information, and I'm curious now. The brake indicator (red bar graph) shows you full into the brakes at 140, starting to ease out at 100 and more than half-way out at 80mph. That's what I'd expect. What's odd is that the longitudinal G meter beside the bar graph seems to lag a long way behind all this. It has you at 0.8 G's while the brakes are full-on, rising to 1.5 G's while you're easing out of the pedal, and at 1.4 G's when you're more than half-way out. Is this real?

Hmmm good observation. I'd noticed that before, but never paid much attention. Your question had me curious, so I dove into my AIM file for my 2019 PB at COTA, my 2:24 lap, which illustrates the same behavior, but not as bad.



So max brake pressure on this lap for T12 was 715.1 PSI while G was still only -1.18g.

But when I reach max G, brake pressure is down to 687 psi. This is still early in the braking zone (map for reference).

Deeper into the braking zone where the other video was showing the -1.5g in the other lap, I am down quite a bit on both pressure and braking g's at 430.9 PSI and -0.93 respectively..

Must be a sync issue between the Solo and Smartycam. Interesting. I'll have to look into that.

 

[JAJ]

Hmmm good observation. I'd noticed that before, but never paid much attention. Your question had me curious, so I dove into my AIM file for my 2019 PB at COTA, my 2:24 lap, which illustrates the same behavior, but not as bad.



So max brake pressure on this lap for T12 was 715.1 PSI while G was still only -1.18g.

But when I reach max G, brake pressure is down to 687 psi. This is still early in the braking zone (map for reference).

Deeper into the braking zone where the other video was showing the -1.5g in the other lap, I am down quite a bit on both pressure and braking g's at 430.9 PSI and -0.93 respectively..

Must be a sync issue between the Solo and Smartycam. Interesting. I'll have to look into that.

It looks like there's some filtering going on in there somewhere, especially if you're getting different values at the same point along the braking track as measured by the Solo and the camera. I looked at the Smartycam specs and it has its own accelerometer, so it's possible that it's getting the G data from its own accelerometer and the brake pressure data from the CAN bus via the Solo.

 

[honeybadger]

It looks like there's some filtering going on in there somewhere, especially if you're getting different values at the same point along the braking track as measured by the Solo and the camera. I looked at the Smartycam specs and it has its own accelerometer, so it's possible that it's getting the G data from its own accelerometer and the brake pressure data from the CAN bus via the Solo.

Yeah, i'll bet that's the case. I'll have to open up the settings and see what channel it's using. Ideally I pull everything from the CAN bus since the Smartycam and Solo are mounted to arms that will mess with measurements

 

[honeybadger]

Interesting, looking at the SmartyCam stream in AIM's software, I don't think I can send the lateral/longitude data to the SmartyCam. Hmmm. Looks like I need to contact AIM.

 

[JAJ]

Interesting, looking at the SmartyCam stream in AIM's software, I don't think I can send the lateral/longitude data to the SmartyCam. Hmmm. Looks like I need to contact AIM.

Well, on the one hand, it doesn't really matter much, all things considered. You've probably looked at the video a bunch of times and not noticed it. I only noticed because I was stepping through the brake zone in tiny steps, and at the moment when I expected to see 1.5G's it wasn't there.

Question, though, does 1.5 G's show up in the AIM data? The second video shows the end of your 2:24.98 lap and all of the 2:24.88 lap, but at the same brake zone as the 1.5G section (around 1:32 into the slower lap and 1:03 in the 2:24.88 one), you did your braking rather more gently than in the lap with 1.5G's. Was that tires or was it just faster to use less pressure?

Back to the main point, though, it's odd for such a well-thought-out product like the AIM to get out the door with a weird glitch like that.

Sponsored