Technical

TECHNICAL

Here at Dunlop Kartsport we have no alignment with any chassis or engine manufacturers so every competitor can be assured that they get true and unbiased advice from us on our Dunlop products.

We won’t try to sell you a different chassis to fix your tyre or handling issue, instead work with you and your current equipment to get the best out of your package.

As always our sport, like any other is developing. New and improved ideas and components are being thought of everyday. Let this be just a simple guide for beginners and maybe even some ideas that experienced karters haven’t thought about.

In a car the differential allows the car to turn, in a go kart there is no diff so in order to gain the same affect and stop the kart from going straight you need to lift the inside rear wheel off the ground when cornering. The skill is to compromise the grip of the tyre in order to allow it to turn but not melt or hurt the rubber whilst doing it. If the rear wheel sits flat you will almost certainly experience under-steer because the rear wheels are still driving straight ahead.

Caster is one of the most important factors when aiming to lift your inside rear wheel whilst turning a corner. Another way to induce wheel lift is by narrowing the front track and altering scrub radius. This is done by using spacers, typically 5mm or 10mm on the front stub axle. The narrower you can have the front track, the more intense the turning angle will be and thus should ‘jack’ the inside rear wheel. Lastly ackermann steering allows the inner front wheel on a corner to turn more intense and sharper than that on the outside and again induce greater wheel lift. This can be changed a few ways but the easiest and most straight forward is the offset on the steering column.

The caster angle is the angle of the kingpin and can be identified by  the forward or backward slope of a line drawn through the upper and lower steering pivot points when viewed directly from the side of the kart. Caster is said to be positive if the line slopes towards the rear of the vehicle at the top, and negative if the line slopes towards the front.

From my experience I believe that at a tight and twisty circuit requires some positive caster.

 

Camber is the degree to which the front wheel leans in or out from each other when viewed directly from the front or back of the kart. Camber is expressed in degrees, and is said to be negative when the top of the tire tilts inward toward the center of the vehicle and positive when the top leans away from the center of the vehicle.

The aim is to use enough negative camber to provide good cornering performance while not requiring the tire to put too much of its load on the inner edge while traveling in a straight line. Less negative camber will reduce the cornering ability, but results in more even wear.

Toe in/out is adjusted on a kart by altering the length of the tie rods.  Increased toe-in will typically result in reduced oversteer, Increased toe-out will typically result in reduced understeer, helping free up the kart, especially during initial turn-in while entering a corner. Be aware that intense toe will tend to wear out tyres because of the scrub.        

Let’s say now that we have the optimum steering geometry in our kart, once you have turned in and can see the apex of the corner the most important thing you as the driver can do now is get your body weight over the front outside wheel, which takes weight away from that inside rear wheel and will allow it to ‘jack’ easier.

In terms of rear track geometry a narrow track will increase the weight force but decrease the sideways force and vice versa for a wider track. Therefore in relation to our tyre range something like a low grip compound sl1 you would tend to run a narrower rear track but with the soft compound cik tyre like a DES you can afford to run a wider stance before the grip of the tyre is exceeded.

 Something that I find very important between driver and mechanic is feedback and the right feedback. As a driver sometimes you really have to sit and think about your go-kart and how it is behaving without jumping to conclusions and trying to fix a problem that’s not there or moving in the wrong direction.

 A classic example of this is a driver will normally only remember the last sensation they feel in a corner. If that is one of oversteer than they tell the mechanic they have ‘no rear grip’ and change the kart accordingly. In fact it can well be a problem with the front end of the kart not having enough grip and initial understeer causes the driver to induce more and more steering and by the time the kart finally turns you have that much steering lock resulting in oversteer. In this instance fix the initial understeer and there will be no oversteer because the problem actually is too much rear grip!

On a cold day or circuit with not a lot of grip you can gain an advantage by increasing caster to help initial turn in ‘bite’ and a further step may be increased toe in which will cause the tyres to scrub and gain heat.

Tyre life and looking after your tyres

Remember that any product exposed to the elements will deteriorate and a tyre is no different, if fact being rubber, a soft porous material, it is more susceptible to deterioration from the elements than other parts of the kart so yes there are some simple precautions karters can take to achieve the best life of a tyre.

i) Keep new tyres in a cool, low light area, away from direct sun light.

ii) Keep the protective plastic on new tyres until you are going to fit them on rims.

iii) When fitting new tyre on rims ALWAYS lubricate the bead and inflate the tyres using a tyre band to pop the beads. This will prevent excessive stretching of the tyres which can result in differing tyre diameters and in extreme situations tread delimitation.

iv) Once the protective plastic has been removed, I recommend that the tyres are bagged to ensure that your tyres are kept clean and not contaminated with anything like fuel or solvents that may damage the rubber.

v) Once a tyre is used and the shiny seal on the tread warn off it will deteriorate faster. Think of it like fuel in your fuel tank, leave the lid off and the fuel will evaporate. A tyre is basically the same, solvents will evaporate out of the rubber (at a much slower rate of coarse than fuel from your fuel tank)and the tyre will lose performance so I recommend wrapping the tyres in plastic if you intend storing them away for an extended period of time and again keeping them in a cool place away from direct sunlight.

vi) Keeping your tyres in a tyre bag or something similar is always a good idea.