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 are you 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: the stopping distances from 100 km/h to 0 km/h, achieved with three full brake applications, 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.

The ABS (Anti-lock Braking System) was clearly and noticeably engaged during passes 2 and 3. In Test 1, I forgot to fully engage the clutch, but the 3.50 seconds still exactly matched the time from Pass 2 with ABS activation.
So, with the empty Ibiza and the nearly new 185/60R14 WR tires (Fulda Montero 2) on my test track, it's not possible to achieve braking distances shorter than 47 meters.
The rear drum brakes work, but the handbrake response, given the same amount of force applied, is less effective than the disc brakes found on the Polo. I have no idea if the Ibi-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 mentioned that I would install them, and 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 prone to wearing out quickly, especially in VW vehicles. For example, they work perfectly with Renault.
"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 parts from the store's own brand, 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. What the driver (of the company car) did with them is unknown." Anyway, it's been quiet for about a year now, while the same driver is still driving that route.
A friend of mine installed Ferodo brake pads on a Passat 35i. These had a maximum of about 60% braking power remaining when worn to 50%, and also produced 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. For example, they work perfectly with Renault. Bitte gib den Text an, den du übersetzt haben möchtest. A friend of mine installed Ferodo brake pads on a Passat 35i. These had a maximum of about 60% braking power at 50% wear, along with noises when braking at high temperatures.

That's strange... which brings us back to the friction pairing of SBB and BS.
What is the typical range of variation for the BS material used in everyday passenger cars? Could it be that Renault brake pads use such different alloys compared to VW that the Ferodos only work well in those specific applications?

Or where else could this discrepancy originate?
Do vehicle manufacturers likely prefer their own proprietary brake pad formulations, and does Ferodo supply VW brake pad formats with a Renault friction material?


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

Interestingly, our Ibiza 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 related to the manual stopping procedure). Should I really be randomly achieving 99% of the possible tire grip with my not-fully-depressed pedal?
If not, then that initial braking maneuver would have clearly taken much longer than the subsequent ones with ABS engaged?

Looking back, I'm also surprised that the ABS wasn't noticeably active during the entire Ibiza emergency braking maneuvers (with pedal pulsing and grinding noises), but only intermittently, roughly like this:
Scratch lightly – short pause (approx. 1 second) – scratch lightly – short pause (approx. 1 second) – scratch lightly – pause until it stops.

How can this be explained? Does the ABS only engage during the distinct screeching sound, and does it reduce the (average) braking pressure to the point where the wheel no longer locks up, and then "after a while" re-engage the system until it starts screeching again, etc.? The delay, however, was not noticeably periodic.
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 even notice it – and could I actually be triggering the ABS in my Polo, but simply not realizing 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 is so heavy in the front due to the 2:1 weight distribution that, during such braking, you can hardly transfer any force to the rear wheels because the rear axle is already unloaded. Therefore, she would have to block very quickly.

If the car is rolling slowly, you can definitely lock the rear wheels with the handbrake, right? At least, it works perfectly fine with my windows.

Interestingly, the Ibi likely has a 3-circuit ABS system that treats the two rear wheels equally. This led to a funny effect during my ADAC driving safety training: during the full-stop braking test, I drove perfectly straight, even with my hands off the wheel, with the "left wheels on a slippery surface, right wheels on a wet surface" scenario. In contrast, 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. By the way, my braking distances during the event were not longer than those of the others...

Best regards,

Jan.

Quote:

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

Have you ever thought about the increasing grip level of tires as their temperature rises? In addition to this, there is a shift in weight towards the front, and there may also be a decrease in the braking friction coefficient.

Quote:

Or where else could this discrepancy come from? Do manufacturers

often prefer their own SBB formulations, and does Ferodo supply VW brake pad formats with a Renault friction material?

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

Ferodo hasn't been a supplier to Volkswagen for very long. As far as I'm concerned, the Ferodo brake pads available on the open market don't seem to 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: "Squeaking – short scratching – about 1 second pause – short scratching – about 1 second pause – short scratching – pause until it stops . Have you ever thought about the increasing grip level of the tires as the temperature increases?" In addition to this, there's the shift in weight towards the front, and possibly a decrease in the braking friction coefficient.

Hmm, I can't quite understand right now how a change in these factors could cause a kind of oscillation (alternating between braking and not braking, 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 get the ABS to intervene multiple times, 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 just slammed on the brakes (except for the first time). Try to do it, and then just let the leg hang there.


EDIT
I just performed the ABS test twice with the Polo, after also disassembling, cleaning, and re-bedding the rear brakes.
Result at 100 km/h with 195/55 R 15 Uniroyal WR tires: The ABS engages forcefully (for a longer time than on the Ibiza), and the car comes to a complete stop on the second attempt. Manually timed at 3.09 seconds -> 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 highway? 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 ceramic brake pads.
A woman was driving a 1980 Volkswagen Golf. Mostly used for short distances and the brakes are rarely 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 it. I don't know if they were the original pads, as the previous owner had 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 acquaintance 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's been lowering the temperature significantly, about every 6 weeks, twice, to prevent blooming.
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.) Apply a coating to the discs/pads.
3.) Minimal wear and braking effect.

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

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

"Micha"

So, the question remains, why did I never feel the ABS engage above 150 km/h on several days, over a period of about 2 years, on a dry Autobahn...? 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 their friction and diminishes the braking effect. 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 over by prolonged, light braking. The best way to see how this works in practice is probably to try it out.

Furthermore, I once received advice from an ADAC engineer 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 are ready to function in the event of an emergency full stop. This regular 'full braking' can also be performed with the vehicle stationary. So, simply every day before starting your journey, with the engine running, press the brake pedal with maximum force two times.
I generally always engage the handbrake, even if the car wouldn't roll away on its own without it being in gear and with the brakes applied. The result is always very good handbrake performance during the braking test.

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 use the tire pressure recommended for a fully loaded vehicle, even when the car is empty. At the very least, during strong braking, the pressure on the (front) wheels will be equivalent to that of a full load.
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, here's a side note:

How are car brakes actually sized?

The legally required minimum deceleration rate (§ 41, paragraph 4, of the German Road Traffic Regulations) is 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 delays must also be achieved when towing trailers.

What does "gewöhnlicher Kraftaufwand" (ordinary physical exertion) and "erwärmte Bremstrommeln" (heated brake drums) mean?

The topic becomes particularly interesting for me when I compare 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 the 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 the same. Let's assume a curb weight of 1650 kg for the 74kW TDI engine.

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 the brake caliper and mounting bracket) 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 common results of popular braking tests, with stopping distances from 100 km/h to 0 km/h being around 40 meters, 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 pulling capacity with a trailer (for the 96kW Polo: 2300 kg, presumably 2250 kg for the 74kW TDI) doesn't, in my opinion, explain why the 265mm brake system is suddenly overwhelmed due to only 2.2% more mass.

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

Or does the vehicle manufacturer, for prestige reasons, unnecessarily add a large amount of braking power to sporty models, which is not actually usable under normal circumstances because the tires lock up well below the brakes' maximum capacity?

ulf wrote:

So, will the stress during maximum-speed full-brake stops 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 constructive 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 these days.

But indeed, the reserves in the braking system are depleted by sporty driving, tailgating, etc. For example, you might brake from 206 km/h because of a truck, then immediately accelerate to full speed again, only to encounter another truck. Various brake cooling measures are intended to cool the brakes in the medium term, but they offer little benefit with a "gas-brake-gas" driving style.

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

With a slight delay, I believe that the braking systems of all vehicles within a specific model type are almost equivalent. The maximum deceleration depends primarily on the grip of the tires, as well as factors like the suspension and the rigidity of the car's body.

It's good that people voluntarily exceed legal requirements. They are from a time when cars were built with cable-operated brakes.

Brake sizing is determined by power and weight. The more power, the faster one needs to be between two tight corners, as previously mentioned, requiring a gas-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 and the tires, especially if you want to install a large system.

I would also like to point out that if, during emergency braking, the ABS system immediately engages and brings the vehicle back within its normal operating range, the frictional loss (thermal load) will be distributed more towards the tires and less towards the braking system. Depending on the quality of the rules.
Extreme case: Without ABS, the wheel locks up, and after coming to a stop, only the contact area 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 in the same way as the smaller disc brake that was previously installed, even in the hands of an inexperienced driver! He can brake now, but he can brake later.

teileklaus wrote:

I would also like to point out that if, during an emergency braking situation, the ABS immediately brings the vehicle back into the normal operating range, the frictional loss (thermal load) is more likely to affect the tires and less likely to affect the brakes. Depending on the quality of the rules. 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. Direct heat dissipation is much better suited for the braking system than for the tire. Warmer rubber actually has better grip. Depending on the perspective, a braking system can be considered the best energy dissipator, as there are usually sufficient braking pressure reserves available to create more friction by simply increasing the pressure in a heated braking system.

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

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

@aron: Please see Ulf's first post.
I agree with your assessment: the brake dissipates energy through friction heat.
Contraindication: 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-killing anti-lock brakes.

Perhaps this is too scientific and only marginally helpful.

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