TAG, Clutched or Direct Drive? The Options
Formula TKM offers the widest choice of any class in the world in selecting the format you want to drive, be it TAG, Clutched or Direct Drive. So what are the differences, and the advantages and disadvantages?
In general driving terms on the track there is little to tell because the clutch on the TAG & Clutched models are always engaged like Direct Drive unless you come to an almost stop. In the wet the clutch has the advantage of allowing you to brake and lock the rear wheels without stopping the engine which can be a problem on a direct drive. Here are some more detailed points:
TAG (Touch And Go)
FOR – The easiest with an on board electric starter system just like a car coupled to a small but high power battery. An automatic centrifugal clutch so you just press the throttle and go. Ultra easy to start by driver with stop start push buttons, quick re-starting should the engine die if you go off and therefore maximum confidence for the driver. Simply press the starter button and accelerate away. The engine is modified with larger exhaust and raised compression ratio to increase power and therefore overcome the additional weight on the crankshaft of the starter system. Pole positions and wins at top championship level confirm its performance.
AGAINST – It adds about 4.5 kilos to the weight of the kart which is fine if the driver is well under the weight limit but could be a problem for drivers near the weight limit. It is more expensive to buy and more complicated to look after requiring good care to wiring etc to ensure no problems.
FOR – Gives all the ease of an automatic centrifugal clutch and the benefit that brings should you spin off, but without the downside of the complication and weight of TAG system. The engine is simply started by a mechanic with a remote hand held electric starter unit (a bit like F1) and if the tickover is correctly set up then the engine will not stall if the driver spins off. It is only a shade heavier than direct drive and nice and simple with no on-board wiring to worry about. If you don’t like clutched or simply want to test it as a direct drive unit then it can quickly be converted by removing the clutch assembly and fitting in its place a special long direct drive sprocket and nut.
AGAINST – You have a fairly heavy hand held starter unit to carry around. If the engine does stall engine in a spin on the track then you can only re-start with this hand held starter. Clutched engine costs about more than direct drive + extra cost of about for the hand held starter. Purists will say it is slower than direct drive engine but a clutch has been used to win the British championship so don’t take too much notice!
FOR – The simplest and lightest and cheapest. There is less to go wrong making it pretty idiot-proof. No wiring or battery chargers etc to worry about. Purists will say it’s quicker. Certainly gives the driver the most absolutely direct connection with engine and kart. You can use a smaller 9 tooth sprocket on tight tracks which the TAG & Clutched units cannot.
AGAINST – The chore of lifting and push starting. In the pits at least you can use a wheel pusher device to help, but if you spin on track then it is down to the driver to do it themselves which is hard work. Juniors will only get re-started on-track with a helper. A definite no if you have any back problem. The new optional EeziStart De-Compression valve will now make starting of this model much easier.
The Direct Drive and Clutched models are now available with the EeziStart De-Compression Valve option which allows the engine to be started much easier. Eezistart Valve will not work on TAG engines as the starter speed RPM is too low. The EeziStart valve is a factory fitted option which is installed in the cylinder head. You simply press down the blue button on top of the valve which then reduces the compression of the engine. This lower compression will then make it much easier to start engine especially the direct drive model. As soon as the engine fires up and starts then automatically the valve closes and you can then pull away as normal.