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Having two different purposes, wheels have different dimensions too. The back ones have surface and diameter bigger than the front ones. The diameter, even if bigger, is not too big and can assure a reasonable speed and not to loose acceleration; in fact a bigger diameter (with a same rpm) can assure higher speed, and at the same time a bigger dimension (and the mass) negatively affects the acceleration since these wheels have a too big inertia. The back wheels have to assure, thanks to the tyres, a good lateral road holding and a good road holding during acceleration and braking, but at the same time they have to slip a bit at the end of a bend; on the other hand they would be too sticky to the ground and for the engine would be too difficult increasing the rpm. The front wheels, no matter if big
or small, do not let the speed vary, but they are a kind of obstacle
to the acceleration, in the same way the back wheels are; in order
of reducing this lost, they are smaller and narrow.
Pressure The first thing you could do in order of really changing the kart “behaviour”, is the tyres pressure. Even if every kind of tyres requires a different pressure, we are going to say something about Cont, since these are the enthusiasts’ tyres, with a standard (hard) mixture and a unique type which can be used on dry grounds. Later, we are going to say something about rainy tyres. Cont tyres are tubular and they have a hard mixture. The basic pressure is variable between 0,8 bar and 1 bar; despite this point, the maximum pressure for these tyres is 4 bar, but this value is completely useless since so hard tyres would slip a lot. In addition to this, you have to consider that with warmth, the pressure increases and inflating the tyres a lot, they risk of exploding. Considering this fact, when tyres are “cold” a basic value has to be done, but you need to set it keeping into consideration the air temperature: in very hot days the pressure will raise a lot, in cold days just a while. Finally, if the track is wet (also without puddles) tyres will have some troubles in reaching the right temperature. Generally it’s advisable deflating tyres in order of getting a better grip and inflating them in order of having a smaller resistance and a better “glide” capability. For example if you have a lot of oversteering, you can deflate a bit your back tyres or inflate the front tyres. If at the end of a bend, your kart has problems in increasing the rpm, before operating on the tidy up, you should try to inflate a bit the back tyres. If your kart slips a lot, do the opposite. Actually more inflated tyres have sometimes a better grip on the ground: that’s because deflated tyres are inclined to grip only on their lateral parts and not on the central part, and so the grip worsens. In addition to this, a wrong pressure regulation can cause an irregular tyres wearing. ”Rainy” tyres In case of wet track (or when it’s said it’s wet), it’s compulsory using specific “rainy” tyres (at least during races, when you are running “just for fun” you can enjoy with slick tyres,… as Jean Alesi did). These tyres are very damaged, in order of improving the grip on a track with a lot of water on it, but you cannot use them on a track slightly wet or completely dry: they could be deteriorated very fast and in an irregular way, and they would perform very bad. Rainy tyres used in “club” races and standard tyres for enthusiasts are branded: they are inflated with a higher pressure than the tyres for dry grounds (it means between 1 bar and 1,3 bar). Modifiable angles Tyres disassembly-assembly This operation is quite difficult to perform and I can advise you to go to a professional mechanic. In fact to disassemble tyres away from rims in a correct way you need specific and proper tools. Since the cost of this operation is not so high (when you buy some new tyres it could happen the setting up and the assembly is free, or it’s very cheap in comparison to the tyres’ cost), I don’t advise you to operate by yourself, with the risk of causing some damages. Rims disassembly-assembly On the other hand, this operation is very easy. For your back rims, you should act with a T allen key. In fact these rims are fixed thanks to 3 allen screws put in a 120° radial position (so they are put at the vertexes of a kind of a hypothetical equilateral triangle) and they have to be fixed in the following way. All screws have to be tightened not too much, then start tightening one screw more than the others, then go tightening the second one and finally the third one. At this point, keeping the back axle still (since it could turn), you have to give a kind of hit to the screws and hear a clean “stac”. Of course, you have to put a lot of attention in hitting it; the hit has to be slightly lower than your strength limit. In order of unscrewing them, the operation is exactly the opposite: keeping still the axle, a hit has to be given to the 3 screws (one by one) and then completely unscrewing them, always one by one. For the front wheels, a tubular wrench is needed (or a spanner with a tubular wrench and an extension) which is usually a 22. To slacken the wheel it’s enough slackening the nut, and to remove it you have to remove the nut before, and being very careful to the spacers. These ones are necessary to fix the front rim: you have to put the spacers, then the rim and finally the nut. Then you have to tighten the nut in a way the spacers are free to move. You have to tighten until they cannot move and then slightly slacken to the point spacers start moving again; it’s a matter of few millimetres.
Kart tyres have a very variable working life. Actually it would be very easy to define but it depends on what we mean with “working life”. Since tyres are the most differential factor in kart performance, we have to consider the working life as the period where tyres can give you the max response and performance. This time is unfortunately quite short: the Cont’s agent said new Cont tyres are competitive for 2 races (sentence said in a positive way, since before they were fine for only one race, as all competition tyres). Now, thinking a race is mainly consisting of 15 minutes of free trials + 5 minutes of qualifying + other 15 minutes of real race, we can say tyres give about 1 hour of best performance use. For this reason, it’s better keeping a set of “race” tyres to be used only during competitions (and when it’s too old start using “trials” tyres) and a set of old tyres to be used during free trials and laps. In order of extending the tyres’ life, you can follow some simple rules. The first rule is not to let them slip too much during braking (locking wheels) or during acceleration (with power), but also during lateral slipping (too much countersteering, for example); tyres working life depends a lot on personal driving style. The second rule to follow is avoiding to enter the pit lane (usually full of rubbles and dirt) after driving some laps very fast; in fact in this way, tyres would be hot and “soft”, easily liable to deteriorate by small stones and specks on the ground. For the same reason the kart should be used in “very clean” places. Finally accidents, bumps and general contacts and the track going out ruin tyres in a not uniform way, and sometimes in such a bad way to have the functionality completely jeopardized. Going back to the first topic we
were talking about, old tyres can be used until the real end, but
your performance won’t be so good. In some tracks, even old
tyres cannot affect your performance: in fact the good grip and
the low speed during most of the bends, flatten differences between
times and having old and weared out tyres doesn’t affect the
final performance. On the contrary, other tracks (rich in very fast
bends) need tyres in very good conditions, not to loose too much
in lap performance. “Rainy” tyres branded
CONT cost generally more than tyres for dry grounds. A higher price
has to be paid for VEGA tyres (they can be used in “club”
competitions).
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