Bremsentuning? | Posts 96+

BM wrote:

The fact that you haven't ruined the brake discs yet, despite using Ferodo pads, is probably due to your otherwise cautious driving style... Build something new, everything else is just nitpicking.

And you're recommending Pagid-SBB again?
What specific (negative) qualities do Ferodos have, based on your experience?

Quote:

Tell me - does the brake make noises as soon as the pads get hot?

The only opportunity to experience that (heat) would probably have been during the full braking tests on the highway, but I don't recall anything like that. What kind of noises are you referring to?

I just took some measurements using Christel's ALH-Ibiza: specifically, the stopping distances from 100 km/h to 0 km/h, measured with a stopwatch, over three full braking maneuvers on a mostly dry country road.
The times ranged between 3.42 and 3.50 seconds (from initial speed to complete stop), which, assuming a constant deceleration according to the formula s = v*t/2, results in a calculated braking distance of 47.4 to 48.6 meters.

During passes 2 and 3, the ABS was clearly engaged. In test 1, I had forgotten to fully depress the pedal, but the 3.50 seconds still corresponded exactly to pass 2, which had ABS activation.
Therefore, with the empty Ibiza and the nearly new 185/60R14 WR tires (Fulda Montero 2) on my test track, it is not possible to achieve braking distances shorter than 47 meters.
The HA brake (drum) works, however, the handbrake delay with the same hand force is less effective than the Polo (disc brakes). I don't know if the Ibi's HA was already at the blocking limit during the tests .

After the Polo-SBB has been running for a few days and the wipers have adjusted to the windshield, I will perform the same test in the same location: let's see what the results will be.

Quote:

And you're recommending Pagid-SBB again?

No, I just wanted to say that I would install them, and that I have had very positive experiences with these parts over a very long period of time.

Quote:

What specific (negative) characteristics do Ferodos have, based on your experience?

In my opinion, these parts are disc brake wearers – at least, that's the case with VW. For example, with Renault, they work perfectly.
"I installed these in a Polo 6N once. After 3000 km (including a trip to Slovenia and back), I had to replace the entire set with a house brand product at my own expense because the brake discs were completely burnt out and made a rumbling noise when braking as soon as they got hot. It's unknown what the driver (of a company car) did with them. In any case, it's been quiet since then (about a year), while the same driver continues to drive that route."
A friend of mine installed Ferodo brake pads on a Passat 35i. He reported that when the pads were 50% worn, they only provided about 60% braking force, and they also made noise when braking heavily.

BM wrote:

Quote: What specific (negative) characteristics do Ferodos have, based on your experience? In my opinion, these parts are disc wearers - at least with VW. With Renault, for example, they work perfectly. Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. A friend of mine installed Ferodo brake pads on a Passat 35i. These pads only had about 60% braking power when worn by 50%, and they also made noise when braking heavily.

That's strange... which brings us back to the issue of friction material pairing (SBB - BS).
What is the typical range of variation in brake pad material that is possible for everyday passenger cars? Could it be that Renault brake pads have such different alloys compared to VW that the friction material (ferodo) only works well in those specific applications?

Or where else could this discrepancy come from?
It's likely that each vehicle manufacturer prefers its own specific brake pad formulations, and perhaps Ferodo supplies VW with brake pad formats using a friction material developed by Renault?


But one more question regarding the perceptible range of the ABS control:

Our Ibiza surprisingly delivered the exact same 100-0 km/h braking time during the initial braking test as it did during the subsequent ABS braking test (excluding any measurement errors from the hand-operated stopping method). Should I have, by chance, consistently achieved 99% of the maximum tire grip with my non-full pedal pressure?
If not, then that initial braking maneuver would have clearly taken much longer than the subsequent ones with ABS activation?

Looking back, I'm also surprised that the ABS wasn't noticeably active during the entire Ibiza emergency braking sequence (with pedal pulsing and grinding noises), but only intermittently, approximately like this:
Scrape – short scrape – approx. 1 sec pause – short scrape – approx. 1 sec pause – short scrape – pause until it stops.

How can this be explained? Does the ABS only engage during noticeable skidding, and does it reduce the (average) braking pressure to the point where the wheel no longer locks, and then "after a while" re-engages the system until it starts skidding again, etc.? However, the delay was not noticeably wave-like.
Or, to put it another way: Does the ABS perhaps have different levels of intervention, of which we only hear and feel the most intense ones (e.g., comparable to LD vibrations above 0.5 bar), while the normal ABS operation is so refined that we don't notice it – and could I actually be braking my Polo into the ABS range, but simply not realize it?

Hi,

Quote:

I have no idea if the Ibi-HA was already at the blocking limit during the tests.

Most likely. A TDI Ibiza has a front-heavy weight distribution of 2:1, which means the front is so heavy that during a braking maneuver like that, you can barely transfer any force to the rear wheels because the rear axle is already unloaded. Therefore, the rear wheels would likely lock up very quickly.

"When the car is rolling slowly, you can definitely lock the rear wheels with the handbrake, right? At least, it works perfectly with my brakes."

What's interesting about the Ibi is that it very likely has a 3-circuit ABS system that treats the two rear wheels equally. This led to a funny effect during the ADAC driving safety training: during the full-stop braking test, I drove perfectly straight, even with my hands off the steering wheel, with "left wheels on a slippery surface and right wheels on a wet surface," while all cars with more modern ABS systems that regulate the rear wheels separately drifted slightly to the side. Of course, the 3-circuit ABS doesn't utilize the braking force of the rear wheel on the more grippy surface, but it performs better overall. Incidentally, my braking distances during the exercise were not longer than those of the other cars...

Best regards,

Jan.

Quote:

Looking back, I'm also surprised that the ABS wasn't noticeably active during the entire Ibiza emergency braking sequence (with pedal pulsing and grinding noises), but only intermittently, approximately like this: "Scraping sound – short scrape – approximately 1 second pause – short scrape – approximately 1 second pause – short scrape – pause until it stops

"

Have you ever thought about the increasing grip level of the tires as the temperature rises? In addition to that, there's the weight transfer to the front, and possibly the decreasing friction coefficients of the brakes.

Quote:

Or where else could this discrepancy come from?

Perhaps every vehicle manufacturer prefers its own SBB (Synthetic Brake Board) formulations, and Ferodo supplies VW brake pad formats with Renault friction material?

It's not that simple. Ferodo has been a long-time supplier to Renault for original equipment, so there should be a reasonable synergy between Renault and Ferodo in the formulation of the brake pad compounds.

At VW, Ferodo hasn't been an original equipment (OE) supplier for very long. In any case, in my opinion, the Ferodo brake pads available on the aftermarket don't fit the older models.

BM wrote:

Quote: Looking back, I'm also surprised that the ABS wasn't noticeably active during the complete emergency braking maneuvers in Ibiza (with pedal pulsing and grinding noises), but only intermittently, approximately like this: "Squealing – short scratching – about 1 sec pause – short scratching – about 1 sec pause – short scratching – pause until stopping. Have you ever thought about the increasing grip level of the tires as the temperature increases? In addition to that, there's the weight transfer to the front, as well as possibly decreasing friction values of the brake.

Hmm, I can't quite understand right now how the change in these factors could create a kind of oscillation (regulating – not regulating, etc.)."

a) Weight transfer to the front -> remains (approximately) the same after braking is initiated.

b) Higher grip levels of the tires as temperature increases -> requires more pedal force to bring them back to their locking point and allow the ABS to re-engage.

c) Decreasing friction values of the brake -> also require more pedal force to bring the tires back to their locking limit.

To repeatedly activate the ABS, I would have had to increase the pedal force during braking to the point where the combined effects of b) and c) would be overcompensated – but I certainly didn't do that. I simply pressed the pedal fully (except for the first attempt) and then just kept my foot on the pedal.


EDIT
I just performed the ABS test twice with the Polo, after having disassembled, cleaned, and re-bedded the rear brakes.
Result from a test at 100 km/h with 195/55 R 15 Uniroyal WR tires: The ABS engages forcefully (for a longer duration than in the Ibiza), and the vehicle comes to a stop on the second attempt after 3.09 seconds (measured manually) -> calculated braking distance = 42.9 meters.
So, the question remains: why, about 2 years ago, did I never feel the ABS engage while driving over 150 km/h on several days on a dry Autobahn? Could this possibly be related to the well-known issue of salt buildup?


BTW, regarding the calculated braking distances:
Our speedometers are quite accurate, thanks to the twisted pointers (which compensate for the slight advance in the middle), and the error at 100 km/h is certainly less than 2 km/h.

My experiences with coated brake pads.
A woman drove a 1980 Volkswagen Golf. It was mostly used for short trips and the brakes were hardly ever used heavily.
After I drove her car once, I realized that the braking performance was terrible.
The brake pads were okay (the pad thickness was almost like new, even though the car had around 100,000 km on the odometer. I don't know if they were the original pads, as she bought the car when it had 50,000 km).
I braked hard several times, but there was no improvement in braking performance, so I replaced the brake pads.
These were heavily glazed.
New pads and a new rotor were installed, and everything worked again like it probably hadn't in years.
My friend really had to get used to it again.
Therefore, I conclude that brakes that are not used frequently are also prone to glazing.
Since then, she has been cooling it down drastically, about every 6 weeks, twice, to prevent crystallization.
Best regards, Jürgen.

Hi,

Brakes don't glaze because they are not used or are only lightly used, but because they are used incorrectly.

1.) You press down on the pedal for a long time, but only lightly.
2.) The rotor discs/pads are glazed.
3.) Minimal wear and braking effect.

The minimal wear you observed is therefore a result of the coated brake pads.

Regards,
Sure, here is the translation of the text from German to English:

"Micha"

So, the question remains, why I, about 2 years ago, never felt the ABS working on several days while driving over 150 km/h on a dry highway... could this possibly be related to the well-known issue of salt buildup?
...

Hi,

I haven't read the entire thread, but I still want to add the following:

If brake pads are used incorrectly for an extended period, they tend to glaze over. This obviously reduces friction and diminishes braking performance. The question then arises: how does one brake correctly? The goal is to ensure that the top layer of the pad is regularly worn away during braking, rather than simply being heated and glazed by prolonged, light braking. How to achieve this in practice is probably something that needs to be experimented with.

Furthermore, I once received advice from a mechanic at the ADAC to regularly apply full braking force to the system, so that all components are moved to their limits and kept in working order, which also ensures that they function properly in the event of an emergency braking situation. This regular 'full braking' can also be done with the vehicle stationary. So, simply with the engine running, press the brake pedal with maximum force once or twice each day before starting your journey.
I always engage the handbrake, even if the car wouldn't roll away without it, due to the gear and brake. As a result, the handbrake always performs very well during brake tests.

Furthermore, you should examine your brake marks to assess whether you are applying enough pressure to the tires. What's the point of having braking force if it's only being transferred to the tire sidewalls because the pressure is too low? That's why I always drive with the tire pressure recommended for a fully loaded vehicle, even when the car is empty. During a strong braking maneuver, the pressure will eventually reach the (front) wheels, equivalent to that of a fully loaded vehicle.
The risk of the tires wearing out more in the center than on the sides likely only arises when the tire pressure is significantly higher than what is specified for the maximum load.

Greetings.

Eike.

Okay, a side note:

How are car brakes actually sized?

The legally required minimum braking performance (§ 41, paragraph 4, of the German Road Traffic Regulations) is a deceleration of 5.0 m/s²: this results in a braking distance from 100 km/h to 0 km/h of approximately 77 meters.

§ 41, paragraph 12 of the German Road Traffic Regulations (StVZO) further states: The prescribed braking decelerations must be achieved on a level, dry road with normal effort when the vehicle is fully loaded, with warmed brake drums, and also at maximum speed, without the vehicle leaving its lane. The... prescribed decelerations must also be achieved when towing trailers.

What does "normal physical exertion" and "heated brake drums" mean?

The topic becomes particularly interesting for me when comparing my Polo with the next weaker model, the 74kW TDI:
The 74kW model weighs a minimum of 1115 kg without a driver, has a top speed of 188 km/h, and features 256mm brakes at the front.
The 96kW model weighs a minimum of 1155 kg without a driver, has a top speed of 206 km/h, and features 288mm brakes at the front.
The front and rear disc brakes are the same.
The gross vehicle weight of the 96kW model is 1700 kg. I don't have the exact figure for the 74kW model readily available, but the payload capacities are practically identical. Let's assume a gross vehicle weight of 1650 kg for the 74kW TDI.

Since I happen to have a small stock of new brake parts at home, I compared the weights of the rotors and pads (right and left) of a 256 mm and a 288 mm brake system: 9.7 kg versus 15.0 kg!
Regarding my car, Volkswagen uses 5.3 kg more brake material on the front axle alone (excluding brake calipers and mounting brackets) compared to the Polo with a 74 kW TDI engine.
(Okay, these small brake components are for the 66kW Ibiza, but for the 74kW Polo, the dimensions should be largely the same.)


The typical results of popular braking tests, with stopping distances from 100 km/h (approximately 62 mph) around 40 meters (approximately 131 feet), correspond to an average deceleration of 9.6 m/s², which is almost double the legal requirement.
If the 74kW Polo can handle it, then its smaller brakes should also be sufficient for the 96kW Polo, without the deceleration falling below 5.0 m/sec²?
The difference in weight between a car with a trailer and a car without a trailer (e.g., 2300 kg for a 96kW Polo, likely 2250 kg for a 74kW TDI) doesn't, in my opinion, explain why the 265mm brake system is suddenly overwhelmed due to only a 2.2% increase in mass.

So, will the stress during maximum-speed full-stop braking become so extreme that the 256mm system fails at 206 km/h instead of 188 km/h?

Or, do vehicle manufacturers, for prestige reasons, unnecessarily add excessive braking power to sporty models, which is often unusable under normal circumstances because the tires lock up well below the brakes' maximum capacity?

ulf wrote:

So, will the stress during maximum-speed emergency braking become so extreme that the 256mm system fails at 206 km/h instead of 188 km/h? Or, do vehicle manufacturers unnecessarily add a large amount of braking power to sporty models for prestige reasons, which is not actually usable under normal circumstances because the tires lock up well below the brakes' maximum capacity?

Hi Ulf,

Is this law still from the early days of automobiles, or am I mistaken? These delay values are completely outdated nowadays.

"However, the reserves in the braking system are depleted through sporty driving, driving in traffic, etc. For example, if you brake from 206 km/h due to a truck, and then immediately accelerate to full speed again, encountering another truck, the brakes will be heavily stressed. Various brake cooling measures are intended to cool the brakes in the medium term, but they are less effective with a "gas-brake-gas" driving style."

Here's another example: In the Frankenwald region, I know of a 15% gradient. It's almost 3 kilometers downhill. Without using the engine to some extent, especially in older vehicles (e.g., weighing 1135 kg with 247mm ventilated rear brakes), you can really feel how the braking system reaches its limits. Larger braking systems simply have more reserves and, due to their larger surface area, dissipate energy more effectively to the surroundings.

"In my opinion, with a slight delay, the braking systems of all vehicles within a specific model range are almost equivalent. The maximum deceleration depends on the tire grip, the suspension, the body stiffness, and other factors."

It's good that people voluntarily exceed the legal requirements. Those regulations still date back to a time when cars were built with cable-operated brakes.

Brake sizing is determined by power and weight. The more power, the faster you'll be between two tight corners, which, as mentioned, leads to a "throttle-brake" driving style. Larger discs can (in some cases) absorb more heat, dissipate it better, and require less pressure due to the more favorable leverage. The main drawbacks are essentially the costs, both for the brakes themselves and for the tires if you want to install a large system.

It's worth noting that if the ABS system immediately brings the braking force within its normal operating range during emergency braking, the frictional loss (thermal load) will be distributed more towards the tires and less towards the brake system, depending on the quality of the ABS control.
Extreme case: Without ABS, the wheel locks up, and after coming to a stop, only the contact surface of the tire tread heats up.
Perforations or slots can further enhance the cooling of the friction surfaces.
However, the increased braking demand will cause the larger, better brake to be thermally overloaded just as much as the smaller disc brake that was previously installed, even in the hands of an inexperienced driver! The advantage is that he can now brake later.

teileklaus wrote:

I would like to add that, if the ABS system immediately brings the vehicle back into the normal operating range during emergency braking, the frictional loss (thermal load) is more likely to affect the tires and less the brakes. This depends on the quality of the ABS system. Extreme case: Without ABS, the wheel locks up, and after coming to a stop, only the ground contact area of the tread heats up.

I'm not quite following your reasoning. Redirecting heat is much more effective in a braking system than on the tire. Overheated rubber actually has better grip. Depending on how you look at it, a braking system is the best way to dissipate energy, as there should normally be enough braking pressure reserves to create more frictional force by simply increasing the pressure on a heated braking system.

During a full stop, you should apply approximately 800N of force to the pedal. This force, along with the corresponding disc and pad temperature, usually provides sufficient reserve.

If it's truly the case that some vehicles experience problems with the ABS operating within its normal range even with a load of 80kg and a slightly pre-warmed brake system, then that's a serious design flaw.

@aron: Please see Ulf's first post.
I agree with your assessment: the brake dissipates energy through frictional heat.
Reverse inference: If the wheels are "immediately" locked, there is no friction between the tires and the road surface, and therefore no (further) heating.
It was not a request for tire-skidding anti-lock brakes.

Perhaps this is too scientific and only marginally helpful.

I consider the matter of new brake shoes and pads to be resolved.