Hand brake, Yes or No

Sometimes even trying new karts can be quite frustrating, even if it’s always fun. The thing is, looking at things professionally, all in all the vehicles are more or less the same – like anyone can see even without using particular measuring instruments - and what is often decisive is set up for that particular track or on that particular day. Then, if we want to be nostalgic to the core, we do miss a track like the one in Parma, where you could immediately see how a kart”worked” in the different circumstances. So, making the most of the karts given to us, the lads from Officine in Progress, together with their sensors and data acquisition instruments decided to expand the range of our tests a bit. One of the first things that came to mind to “test” from a more technical point rather than to see the sensation you get is a very current topic: manually controlled front brakes on direct drive karts.
Everyone knows that on the KF and also on some direct drive karts you can have a double and distinct braking system; the single rear braked controlled by a pedal, and front discs controlled by a lever on the steering wheel. And we also know that in the new OK classes, either because they wanted to save on weight or because they wanted to go back to a concept that is closet to the origins of karting, you are not allowed to have front brakes. Well, why not try to see what actually happens on a track when a kart uses or doesn’t use a front braking? On the contrary, even more: what actually happens to the brakes of a kart? A question, the last one, which we have been able to come up with an answer thanks to the use of numerous sensors that OiP mounted on the kart we used for our test.

In Viterbo with Tredicine e Pulcini

We had an Vortex powered FA kart for the test, one that Stefano Tredicine’s KGT team kindly let us have for the test. But this isn’t all, he asked test driver Leonardo Pulcini to come along too. Leonardo has been working with motor sport for a while now, first in Formula 4 and more recently in Formula 3. «I hadn’t been on a kart for about two and a half years», the driver from Rome said, but in any case he showed us what runs in his DNA, he only needed a few laps to get back into the swing of things and be at home in a kart and on the track in Viterbo.
In fact, our test has been hosted at the 1300 meter long track in Viterbo: it’s ideal for this sort of test because apart from braking which is relatively “soft” at the first turn (this is because you brake on corner entry and with wheels turned) and then immediately after there are other braking points that are much more decisive. They are the one at the first turn and more so the one at the end of the fast internal transversal straight that ends in quite a narrow turn even if it’s less than 180°. Well, two braking points that enable you to register the peak values with the two braking systems. Two more braking situations have been added to this where you have to be able to manage corner entry well: in a few words, in Viterbo you must know how to use the brakes well…

Experience from years ago

Obviously after Pulcini’s first laps the first thing that came to mind was to ask him what it was like to try the two types of braking system. And we only found balanced by absolute tranquillity on behalf of the driver… «I didn’t have any particular problems – said Leonardo – I just got to get the hang of karting and using this circuit, find a few reference points». We can assure you that he soon found them… «However I am used to using both systems, especially with the one with just rear brakes, when I used top race with the KF Junior», a class with which he has taken some great satisfactions. «Then I also did some races with the KF2 – he continues – But I really wasn’t very lucky there». In any case, he gave us some important support for our test; he also gave us some answers to our deductions “on the pc” regarding how you should tackle the various turns.

THE TRACK IN VITERBO HAS TWO IMPORTANT BRAKING POINTS:
THE ONE BEFORE THE FIRST HAIRPIN AND THE ONE AT THE END OF THE INTERNAL STRAIGHT

UNDER PRESSURE

1 and 2 are the ones that gather the most significant data during a fast lap carried out with the two types of braking systems. In the first case, you use both the front brakes and the rear brakes. Studying the measurements starting from low down, and therefore, testing pressure on the rear hydraulic circuit (PfrenoPost) and the front one (PfrenoAnt) you can see how in several turns you tent to let go of the front brakes that the rear ones, a manoeuvre that allow for improved corner entry. However, in a very strong braking manoeuvre, a long one like the one at the internal turn, when you are close to 800 metres, you tend to use really from start to finish all the available braking power.
A strange thing, which is underlined also in the graph of the diagram of the derivative regarding rear power (Deriv_Pfrenopost), a parameter that tells you how much aggressiveness goes onto the brake, it shows us how a tester continuous to correct rear braking to put it right, it looks as though after a first “strong” braking he has to release continuously to prevent the engine from blocking too much, and this happens repeatedly during the course of the same braking. It really looks as thought the driver concentrates more on the front brake and therefore it is not as accurate compared to the rear brake. Then it acts almost like a physical and instinctive ABS, and we checked how this occurs with intervals of 4 tenths of a second: puts Bosch to shame!
In the second picture that shows just rear braking (you can see that front pressure is always equal to zero) braking is more homogeneous and net, even if it’s always decisive: This can also be seen in the “Engine” graph. Obviously, it is the engines speed, but being a direct drive kart, it is obvious that it’d the engine speed, but being a direct drive kart, it’s obvious that the engine and wheels turn in direct harmony. So, you can see the wheels block early on, but it is less accentuated and more constant than with the other system. The rear disc (infrared) temperature measurement allows us to see how this oscillates between 139 and 172 degrees centigrade when it rests only on the rear brake; if not the front brakes makes the work of the rear brake lighter, so the temperature of the latter varies from 109 to 130 degrees. These values are quite contained compared to what happens in other motoring specialities. We must also underline that temperature peak is not at the end of the strongest braking point, but of the following one (at the so-called “chiocciola”) because besides it too being quite long, you reach it without having completely disposed of the heat accumulated previously.

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VARIABLE SPEED

In picture 3 we take an even closer look at the braking manoeuvre in question, the one of the small internal turn, directly matching what happens with the two different braking modalities: the black line with just the rear brake, the blue line with both systems. It’s interesting to see how just with the rear brake you have to brake earlier and it blocks slightly more; then with both systems speed is lowered faster – which in simple words means “it brakes more”, this is obvious – in fact, more than half the final phase of the braking speed is definitely less. The same applies also for corner entry it’s faster having used just the rear brake, in any case, also in terms of time something is gained, as you can see in the “reference” graph below. However, immediately after you can also see that this faster corner entry speed doesn’t allow you to accelerate again so soon as when you have braked more, so you again lose something on corner exit and along the following straight.
As for this “hard braking” we can give you some more information that probably we’d all like to know, for example, how long braking lasts in both cases. Well, with both brakes, the braking starts at the 781st meter of the lap and ends at 815th, it’s 32.8 metres long. Instead, with just the rear brake it lasted from the al length of 39.1 metres. Well, the second braking did start earlier, but it also ends later and more “within the turn”.
You can see a comparison of both types of braking throughout the lap in picture 4, with speeds, longitudinal accelerations and total pressure put on brakes (here the black line is for both, and the blue line is just for the rear brake). Another couple of parameters to tell you are for example that deceleration reaches 1.2 g with both brakes and 1.0 g with just the rear brake. Both are remarkable values seeing that they have been obtained on track which wasn’t optimum and especially with tyres that weren’t particularly soft (Bridgestone used for the Rok Cup). To conclude, the strength of the braking is confirmed by the hydraulic pressure values in the two systems: to conclude, the braking strength is confirmed by the hydraulic pressure values of the two systems: 33 bar with just the rear brake and a total of 47 bar (front + rear) braking with both. While maximum and minimum speed is similar, both at about 106 km/h before the braking point and 46 km/h round the turn.

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COLDER AND MORE LOADED 

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TESTER

LEONARDO PULCINI

BORN IN 1998 - ROMA