Technology: big brake test

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Technology: big brake test

Technology: big brake test
Fear eats up the soul

Decreasing braking effect up to total failure – the nightmare on every pass descent. How stable are modern braking systems in extreme driving situations?

Jorg Schuller

07/31/1997

Brakes are for losers. This wisdom holds a lot of truth in an emergency – at the latest when the brakeman loses control of the vehicle. Seven motorcycles with different braking systems had to prove the stability of their stoppers on a demanding downhill stretch.
the Aprilia Pegaso 650, the Honda SLR 650 and the Kawasaki ER-5 are presented with the simplest form of modern front wheel brakes. They all decelerate with a fixed disk with a double-piston floating caliper. The Suzuki XF 650 Freewind has a floating brake disc at the front, which is also gripped by a double-piston floating caliper.
the Yamaha TDM 850 represents the all-rounder group. It is the representative of the frequently used combination of two large, floating discs with four-piston fixed calipers. The Suzuki GSX-R 750 represents the highest supersport standard with two floating discs with six-piston fixed calipers. Finally, the Honda ST 1100 combines all the features of modern brake technology. It not only offers ABS, but also Honda’s “Dual-CBS” integral braking system, in which both the foot and hand brakes act simultaneously on the front and rear brakes. Honda’s travel steamer is by far the heaviest candidate and decelerates with large brake discs and three-piston floating calipers.
The rear braking systems were of course also examined. However, since they are significantly less stressed than the front ones due to the dynamic shifting of the wheel load when braking (both in solo and in two-person operation), the rear brake is only mentioned in the individual assessment if the test results are conspicuous. But where is the critical area of ​​the stoppers??
Brakes are used to reduce the kinetic energy of a vehicle, and they are extremely powerful at the same time. With a braking deceleration of 8 m / s², braking from a speed of 200 to a standstill takes less than seven seconds. And each of the test candidates delays in this order of magnitude. Conversely, even the most powerful motor measured by MOTORRAD failed to accelerate a motorcycle from zero to 200 km / h in under seven seconds. Incidentally, the specified deceleration values ​​correspond to the achievable peak deceleration at the blocking limit under the given circumstances (steep downhill descent on undulating asphalt).
Braking from high speeds puts more stress on the brakes than braking from low speeds (the kinetic energy increases by the square of the driving speed). The kinetic energy is dissipated by the friction between the brake disc and brake lining. This creates frictional heat. This must be released into the environment as quickly as possible by the wind and thermal radiation. This degradation, in turn, works better at high speeds due to the airflow than at low speeds. If the heat is not dissipated sufficiently, heat will build up. And this is undesirable for the following reasons: As a rule, the coefficient of friction between the brake disc and the lining decreases at high temperatures. The result is reduced deceleration with greater hand strength and longer lever travel. This process is called “brake fading” and was noticed a few times during the test. If the saddle gets too hot, the brake fluid begins to boil, in extreme cases it forms gas bubbles – then the driver’s hand grabs nothing, nothing brakes anymore. And if the heat builds up too much, the brake disks or pads will be thermally destroyed. The temperature limit for this is around 700 degrees. But can it even come to a total failure of the brakes while driving?
During the examination, our seven test subjects had to endure countless emergency stops. It turned out that the standard offered is gratifyingly high. No brake failed, although the test conditions were anything but gentle. Furthermore, the fact that the dimensioning of the brakes is no guarantee for brute delays – the driver must also be able to implement the potential. All test persons were rushed down a pass road, first solo and then in two-person operation and packed up to the permissible limit. We drove within the framework of the StVO, but we always braked and accelerated as hard as possible (thanks again at this point to our trustworthy co-driver!). The tests were carried out on the Robfeld ring road near Berchtesgaden. The Robfeldstrabe with its up to 24 percent steep descents offers fast and slow passages with different braking loads: in the upper part several tight bends, further down long straights alternate with curves of narrow to medium radii.
The test specimens then had to endure the simulation of a descent with closely spaced turns in a braking and acceleration cycle. This should show how much reserve the brakes have beyond the harshest road conditions. Descending a bend is so dangerous because the cooling phase of the brakes from bend to bend is very short and the wind does not dissipate much heat because of the low speeds – the heat accumulates.
Measurement technician Rudi Tellert was on hand to provide MOTORRAD with advice and assistance in order to record all relevant test parameters via data recording. The temperatures of the discs and saddles were recorded as well as the hand force, the lever path on the hand brake lever, the braking deceleration and the driving speed. From the mountain of data determined in this way, not only extreme values ​​could be determined. The recorded curves made even the smallest changes in the interaction of the braking parameters visible.
And how did the test subjects fare in detail?

Aprilia Pegaso 650

The Aprilia Pegaso brakes at the front with a 300 millimeter fixed disc with a floating double-piston caliper. Even with the first braking, the relatively high hand strength and the soft pressure point are uncomfortable. Nevertheless, the deceleration level when driving solo is quite good with an average of 7.6 m / s². In two-person operation, it falls comparatively sharply to 6.1 m / s². The Aprilia brakes also get quite hot, although the temperature level hardly rises with the pillion passenger. In the extreme cycle, the brake reaches the highest temperature of all candidates at 619 degrees. Fortunately, this torture did not cause any consequential damage. The heavy fading of the Aprilia is more dramatic. The pressure point moves noticeably from braking to braking. This went so far that in two-person operation, at the end of the descent, the handbrake lever could be pulled up to the handlebars. An increase in the braking force is then of course no longer possible. Anyway – the delay achieved was still sufficient. Due to its strong tendency to fade, the Aprilia deserves the red brake light in the test field. The Honda SLR 650 proves that it can be done better with a comparable effort.

Honda SLR 650

Who would have thought that. The SLR achieved the lowest temperatures among the single-disc brakes in the test. It brakes with a fixed disc / floating caliper combination at the front, the simplest brake design in comparison. Although the disc measures only 276 millimeters, it is thick and can therefore absorb a lot of heat. The tendency to fade is correspondingly minimal. Neither in solo nor in two-person operation is a noticeable decrease in braking performance or a shifting pressure point noticeable. The Honda achieved the highest deceleration values ​​among the studded enduros in the test. Almost 8 m / s² when driving solo are remarkable. In the two-person operation there are still over seven. That can be seen. Even in the extreme cycle, the window temperature does not climb above 380 degrees. In two-person operation, the temperature even remains below that achieved when driving solo. Similar to the Aprilia Pegaso and the Kawasaki ER-5, this is due to the lower speeds that are achieved with a load from curve to curve. Despite the simplest design, the SLR brake is the best single-disc brake in the test. Whether the other manufacturers are saving at the wrong end?

Honda ST 1100 Pan European

A motorcycle with such a stately appearance naturally also needs a stately braking system. The Honda technicians install everything on the ST 1100 that the company has to offer in terms of brake technology: the »Dual-CBS« integral brake system, which always operates the front and rear brakes simultaneously, regardless of whether the hand or foot brake lever is operated, and the Honda -Anti-lock braking system that prevents wheels from locking with reassuring reliability. The test confirmed this once more. From a purely subjective point of view, it is always amazing how effortlessly the brakes decelerate the Honda steamer. This combination of 296 millimeter fixed disks with three-piston floating calipers is characterized by spontaneous grabbing as well as a brutal effect and an undeniable feeling of security. The measurement records confirm the positive impression. Delays of an average of 9.3 m / s² solo and still 8.3 m / s² in two-person operation are always possible, then the ABS regulates. The ST 1100 does not outperform the tested athletes in terms of top values, but on average. The temperature level is higher than with the other three-disc brake systems tested, in the extreme cycle it reaches 440 degrees. However, fading is only very minimally noticeable and verifiable. The ST 1100 justifies the constructive braking effort with the great result. And it once again confirms the performance of the ABS. Safety in every braking position – what more could you want?

Kawasaki ER-5

When you look at the Kawasaki ER-5, it looks like it is equipped with a halved GPZ 500 S brake system with a slightly larger disc – unfortunately the brake feels accordingly. Similar to the Aprilia Pegaso and the Honda SLR 650, a double-piston floating caliper grips a fixed disk. The measurement record confirms the subjectively weak response. Decelerating solo is still okay at 7.6 m / s². In two-person operation, however, the achievable braking deceleration is only 6.1 m / s². Strong fading is already noticeable when driving solo. This is no wonder, because at the end of our descent the front brake disc is at least 507 degrees. In the extreme cycle, it can even exceed 540 degrees, a value that is only exceeded by the Pegaso brake. Although the ER-5 brake never reaches temperature ranges where there is a risk of thermal failure. Nevertheless, the peak temperatures and the heavy fading do not leave a good feeling. Like Aprilia, Kawasaki, otherwise known for good brakes, has to put up with the accusation of saving at the wrong end. The ER-5’s brake is sufficient, but it is not good. It shares the red lantern with the Pegaso brake.

Suzuki XF 650 Freewind

The Suzuki XF 650 Freewind decelerates at the front with a floating single-disc brake with a diameter of 300 millimeters. Here, too, a double-piston floating caliper presses the linings onto the disc. Obviously, the friction pairing is chosen sharply. The Suzuki brake grabs snappy and very progressive even with low hand force, which does not necessarily simplify the dosage in the limit area. Perhaps that is why the deceleration level at the blocking limit is not particularly high at an average of 7.5 m / s². In two-person operation it even falls to just 5.8 m / s², the worst value of all measurements. The Suzuki struggles when braking with its soft fork that quickly locks up. The bike starts to punch even with moderate decelerations, the transferable braking power drops, and the Freewind brakes get quite hot. In pillion operation, the window reaches a temperature of 478 degrees. Noteworthy fading does not occur in any situation. The Suzuki cannot convert the structural advantage over the Honda SLR 650 into better deceleration values. The brake is too toxic for the chassis tuning. In return, it is completely free from fading despite the high temperatures.

Suzuki GSX-R 750

The braking system of the Suzuki GSX-R 750 presents the state of the art among modern super athletes. Floating, lush 320-millimeter discs and six-piston pliers that grip even with little hand strength, plus sticky sports tires and a low center of gravity – that has to brake. Normally one should be able to expect above-average deceleration values ​​with such a braking power plant. But under the test conditions mentioned at the beginning, reality contradicts expectations. On the solo descent the GSX-R achieves peak decelerations of 9.5 m / s², but mostly it only decelerates with about 8 m / s², and that in solo or two-person operation. Not bad, but not great either. How can that be? Similar to the Freewind, the GSX-R brake also bites mercilessly with little manual force. The feeling of deceleration is enormous because the GSX-R driver has to support himself strongly with his arms. So it is of course more difficult to dose the leverage – especially since the degree to the blocking limit is narrow. However, higher delays can easily be achieved on smooth surfaces. What is certain is that GSX-R drivers do not have to worry about brake failure. From a thermal point of view, the GSX-R brake is completely insensitive and absolutely fading-free – regardless of whether it is occupied by one or two people. Delays at the blocking limit are easier to realize with the less well-equipped competitors.

Yamaha TDM 850

the TDM 850 is equipped with a long-serving Yamaha braking system. The combination of floating 298 discs and four-piston calipers has never been a blast, but always worked satisfactorily. This proves itself again at Robfeld. With fairly high manual forces, the TDM consistently achieves 8.5 m / s², sometimes a little more. In two-person operation, the braking performance changes only slightly, and the temperature level is very low overall. Unfortunately, there is a slight but noticeable fading. All in all a good result.

Conclusion

We can breathe easy. Serious safety deficiencies did not occur in the brake test. However, the Aprilia Pegaso and the Kawasaki ER-5 showed severe fading. The Suzuki XF 650 Freewind was average. The Honda SLR 650 performed well. the Yamaha The TDM 850 and the Suzuki GSX-R 750 proved that good brakes simply brake well. And the Honda ST 1100 shone thanks to its sophisticated brake technology.

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