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Track testing – First steps from seat positioning to running in

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The frame is prepared for the seat

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Measuring the distance between the rear axle and the top of the seat

The base setup of our Tony EVR was described last month. In general this is similar in all chassis, which means all chassis are set to work properly with neutral settings such as base caster and camber, 140cm rear width, neutral height front and rear, and with the front and rear bars mounted.

From these base settings it is then easier to fine tune the chassis with the possibility of decreasing or increasing angles, heights and widths. All this can only work though if weight on each tyre is well balanced. So at Tony we verified the mounting of the seat. From this point all setup changes will optimize the final balance for each track and asphalt condition/tyre compound and engine type. Only with the correct seat positioning we will be able to act correctly on the chassis setup.

Seat positioning

Four measurements are made to position the seat:

  • Distance between rear axle and top line of the seat back
  • Distance between the front line of the seat on both sides (under the legs, a sign is marked on both sides of the seat)
  • Distance from the front transversal tube of the chassis (just in front of our feet when we sit in the kart)
  • It will be positioned at height of a minimum of the thickness of three front sprockets on top of each other to a maximum of four.

Since I am not really the perfect kart driver physically speaking, as I am 183cm tall, my seat position was set so I could sit with my arms and my legs sufficiently comfortable so the seat was positioned some centimetres towards the rear of the chassis.

Measures for myself are the following with numbers in brackets as standard for shorter drivers:

  • Distance between rear axle and top line of seat back: 20.5cm (22cm)
  • Distance between front tube of chassis and front of the seat: right 63cm (66cm) and left 62.5cm (65.5cm)
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Measuring the distance to the front of the frame

For all drivers seat height should be set with the equivalent thickness of three to four rear sprockets. The aim is generally to have the lowest possible height of the seat for a lower centre of gravity, but limit is the seat finally touching the asphalt or the kerbs around corners. So a choice must be made based on the kind of track the kart has to run on – smooth or bumpy, and whether you need to ride the kerbs or not.

These measures were set with a Tillett seat. Changing the seat type can change its shape and so all measures would automatically deviate from the basic measures.

Finally, especially for tall drivers, such measures can also be varied, still trying to keep weight distribution on the four wheels as it is. Variation often is needed, especially on fast tracks where tall drivers generate a large front area of impact with the wind and air. This causes high resistance to the movement of the chassis since Cd (aerodynamic coefficient) will increase as well. We will work on this in future Track Testing articles though, also verifying the effects on high speed and lap times.

Running in

I finally got to the track for the first impressions of the Tony EVR and Rok engine. My choice was to go on a Friday just before a race at the track. This choice is sometimes avoided by shy karters who prefer to practice at tracks that are not busy. The best choice is to practice where the real competition is, with rubber covering more and more the asphalt. This is the best way to understand our limits, potential, and chassis and engine behaviour in really challenging conditions.

The first steps when preparing your kart to go out on track for the first laps of the day:

  • Prepare the fuel mixture (petrol with 3-4% lubricating oil) and fill the fuel tank about half full
  • Cover the kart chain with a good quantity of chain grease. Grease must be of the right type, dense and sticky so it really sticks to the chain and does not fall off at high revs.
  • Before greasing the chain verify its tension is correct, which means position the engine on the chassis so the central part of the chain between front and rear sprocket can move up and down around one or two centimetres.
  • Inflate tyres and measure the pressure and adjust to the correct value. If you have just mounted tyres on wheels you first have to “blow” them so they adhere well on the wheels and then regulate the correct pressure. Make sure you reduce pressure of the tyres before using your pressure gauge for measurement. Too high pressure could damage the gauge resulting in consequent incorrect measures.
  • Try both rear and front brakes and see if the force on the brake pads is enough or if the brake pedal and hand brake have too much excursion, which means they have to be checked and regulated and most probably the brake oil has to be changed.
  • We should then check the correct ratio between the rear and front sprocket. An indicative ratio can be got fromk other karters or someone at the track. They might not give you the perfect answer and value, but it will be near the correct ratio.
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The front brakes are checked

The first laps were to do the running in of the engine. Before starting the engine, check the fuel tube from tank to carburettor, it should be full of mixture. If not, when pressing the start button look to see the fuel moving along the tube to the carburettor. To help this, cover the air filter with your right hand and press the accelerator, to help the engine and carburettor “suck” the fuel from the tank. As soon as the fuel reaches the carburettor you will hear the engine start. Take your hand off the air filter and start accelerating and releasing accelerator until the engine is completely “on” and then go out on the track!

The first sensations driving the EVR and ROK are that there is a great balance of the chassis with great possibility to control the kart. The tyres used were quite worn and the track had medium grip. This led to a slow speed around the corners. The easy to use ROK engine has great torque but since it is limited to 13,800 max revs it is also used with long gear ratios which give it a good top speed, but difficulty in exiting corners. Better tyres and grip would have produced higher speed around corners and not problems in the exit.

In the next issue we will talk about tyres in testing and the effect of different types of tyres and the differences between using a worn out tyre and a new one. Also we will look at everything regarding pressures and the controls that can be done to understand if the tyre pressure is correct. Finally tyre compound, hardness, and tyre tread “reading” will give us good hints for the best performance of our kart.

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