Text: m. Voltini - pics: d. Paolicelli
Text: m. Voltini - pics: d. Paolicelli
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
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
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
For information found that are necessary for our “exploration” on what happens to kart brakes, Andrea Saccucci and Daniele Parravano from OiP mounted a nice chain of sensors, on the kart given to Pulcini. Besides what is now normal (for them) regarding the usual working and motoring parameters, amongst which we underline the tri-axial GPS and a lambda probe on the exhaust, with a, and a small simonised camera with the data picked up, other more specific probes were mounted for what we were testing. For example, the infrared sensor “pointed” to the rear disc that allowed us to pick up the working temperature whilst moving. Then there are those that tested the pressure present in the front and rear hydraulic systems on braking. Also the sensor on the axle that measured the rotation speed of the wheels, together with the engine speed: in this case, more than the kart speed (moreover already picked up by the GPS) it helped to register brakes blocking on braking. Obviously, the combination of all this do put things right data gathered is what enables you to read, on graphs on the computer, and see what really happens on braking, something that no mechanic had been able to “measure” yet. Also because – for some reasons, those concerned are more careful watching out on making sure that their driver doesn’t brake before the others instead of keeping track of other amenities.
UNDER PRESSURE1 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.
VARIABLE SPEEDIn 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.
FROM 33 TO 39 METRES
COLDER AND MORE LOADED
If you want to know more on graphs like this one, you could do one of the courses held by the lads from Officine in Progress, which among other things, with their experience also in other motor sports fields they have given us the chance of “summing up” the kart’s braking performance. For example, deceleration is good, but what surprised us is the high hydraulic pressure generated in the circuit, nearly 50 bar. With racing cars, similar pressure is only registered with some GT, but in that case we also have about a thousand kilos more to slow down… Moreover the material used is quite different, and this also makes you see why there are so many problems concerning sealing with our normal “rubber washers”. This when with racing motorbikes a front braking system (the rear one is practically never used) reaches about 20 bar.
Among other things with motorbikes we talk about “hard braking” when you drop from 330 to 80 km per hour, not from 106 to 46 as in our case. The same applies for motorbikes you reach temperatures of about 300-350°C. This is talking about steel brake discs, when on cars you usually have carbon or carbon-ceramic discs, for these the normal working temperature is quite different and closer to a thousand degrees. Well, the rear disc of a kart hasn’t gone over 180°C even when used alone, therefore an incredibly low temperature range in comparison. Who knows, maybe this could be another field to explore, also using different brake pads. We’ll see…
LEONARDO PULCINIBORN IN 1998 - ROMA
|TRACK FRONT/REAR||2.5 SHIMS / 139.5 CM|
|SUPPLEMENTARY BARS||FRONT ROUND|
|TOE-IN||OPEN 2 MM|
|AXLE||Ø50X1030 TYPE N|
|THIRD BEARING||NOT FIXED, NO GRAINS|
|CARBURETTOR||IBEA Ø24 MM|
|FUEL||4% ROK LUBE|
KGT RACING TEAM
VIA MORBEGNO 59 - 00166 ROMA (I)