Tuning Tips

Secrets that have been cast into the public arena:

 

Sail

Battens Sail battens are perhaps the hottest topic of blokart tuning. It is very much a personal preference thing and what works will change according to setup and weight. A basic rundown on battens goes like this:
The original battens are very stiff. Softer battens gives the sail more shape and allow it to generate more power. This is especially important in light winds. You can soften your battens by sanding them down. Where and how much you remove is the art. Perhaps before beginning, talk to people in your club to gather information, read up on batten shaping for boats on the internet, keep tabs on blokart forums, and allow yourself some room to experiment (you can always remove more later). Basically the front 40% of the length of the batten is where you want most of your shape. You will see this when you put a bend into your standard battens. Keeping the rear of the batten stiffer might give you less shape, however it may also increase the stability of your sail when the wind gets up. This is perhaps more important at the top of the sail where the leach twists off. To begin with, you don't really want to change the shape of the bend too much, only the pressure it takes to bend them. You can keep an eye on the pressure under which your battens bend by using a set of kitchen scales. Put the tip of the batten on the scales and push down on the other end to measure the amount of pressure that it takes to flex it. Use this and visual checking of the bend to see what effect you are creating. Check your shaping efforts using the battens above and below the one that you are working on to guide you. Keep your shape smooth. Your aim is to have a clean and even sail shape that sets nicely in the wind range that you are aiming for. Study your sail as you are sailing - what are the effects of wind loading and downhaul tension? A light and a heavy wind set of battens will also allow you more room to play around. Experiment with allowing more shape lower down in your sail, keeping the top of the sail stiffer and more stable. You might find that this suits you more in gusty conditions.

If you want to be sure that you are getting the best shape out of your sail then you can purchase a new set of battens. Batten sets ensure that the curve characteristics are the same all the way up your sail. Different sets have different characteristics depending on what you are looking for. For more information on batten sets check out:

Downhaul The downhaul tension makes substantial changes to the characteristics of your sail. With the tension off you have a sail with a heap of shape and therefore power, but therefore not so streamlined. More downhaul gives you a tight flat sail that will generate less grunt at low speeds or in lower winds but will cut through the air more cleanly. The retro downhaul kit shipped on the blokart is prone to jumping out at low tension and does not allow for easy adjustment while sailing. You can replace it with a two pulley system with a clam cleat located in an accessible position. They are commonly mounted on top of the steering bar or on a side strut. Info:

The Ratchet Pulley This is a fantastic little invention that takes the pull of the sheet rope off your hands, cutting back on arm strain in big winds or on long journeys. It improves your sailing by cutting down on jerky sail movements, thereby maintaining a smooth airflow over the sail surface, and allowing you to focus your concentration on elements of your sailing rather than fighting with that sheet rope. Replacing the pulley on the mast base of the blokart, the basic ratchet block will only turn when pulling the rope in, locking off to prevent the rope from running out again. Shaking the rope lets it run back through the pulley. These blocks can slow your sheet out reaction time. Better ratchet blocks have an adjustable tension allowing the pulley to freewheel until the set load comes onto the block, engaging the ratchet. Releasing the rope releases the tension, disengaging the ratchet and allowing the rope to run free.
Info:

Bearings

The factory grease and bearing seals create a huge amount of friction. Remove the seals, get rid of the old grease (Disolve out with a solvent or blow it out with compressed air) and lubricate with Inox spray. You can replace the outer seals. The internal seals are not really necessary. Run the bearings without seals if you want it really slick, but clean them out regularly. You can tell how slick your bearings are by holding the wheel and spinning the axle stub. On a really sweet setup the axle will spin freely. Steel bearings are harder and run smoother than stainless. They are perhaps the bearings of choice for racing. They are not good when it comes to corrosion however. Take good care of them. Any moisture will affect them but get salt water on them and you'll be binning them. Many racers have two sets of rear wheels, one with steel and the other stainless.
Pulley Whip

Shorten it! This allows more pull on the end of the boom which tightens up the leach (trailing edge of the sail). This allows you to flatten the sail just by hauling in the rope, stops it spilling air in big winds and gives you maximum mast rake for improved upwind ability. Performance class of bRacing specifies a minimum length of 350mm. The pulley whip is slightly tapered - Remove the length from the top of the pulley whip to ensure you keep a tight fit when you click it into place.

Wheels and Tires

Your tires are probably out of balance. There is a real art to balancing your wheels. Sort out your bearings so there is minimum friction. Don't replace your seals. You will notice that the heaviest part of the wheel sinks to the bottom. Add counter weights to balance the wheel out. This requires heaps of patience. A balanced wheel should favor no particular spot. Blow a tire and you have to start all over again :)
Pressure is essential. Keep them pumped right up. Some will run up to 35psi in the front and 45psi in the rear. The rear wheels are prone to blowouts at this pressure so you might want to back it off a little bit, especially while in storage (the air in the tyres will expand in hot conditions i.e. your car). The old style front rims do not handle such high pressures very well and will start to deform. blokart has released new front rims that are rated to 35psi.
Info:

POD/DirtSkirt

These cut down on your wind resistance. It is all about making your blokart slippery.

Sailing Tips

How good is your technique? Going fast is all about maintaining your momentum. Do whatever you can to prevent yourself from slowing down. Sometimes it might be more advantageous to take a slightly longer path to ensure this.

Upwind Technique: Build your speed up a little before pointing right up.

Downwind Technique: Is it faster to sail off the wind and go further than to sail the shorter route dead downwind?

Telltails or Woolies

A short piece of wool stuck to the surface of your sail with a sticky patch at one end will show you how the wind is flowing over your sail. Put them at a few points on both sides of the sail. You should be aiming to have the woolies flying horizontally on both sides of your sail. If they are flying up or down, then you adjust the sheet rope in or out.

Top Speed!

Having all three wheels on the ground is fastest but no where near as much fun. At a particular windspeed (varies depending on your weight and setup) your 3m sail will be faster than your 4m. Your acceleration and downwind speed may not be as fast with a 3m, but you have less wind resistance and leverage so your top speed is likely to be higher. 3m sails charge upwind too - it is all about choosing when to use it. ;)

General Use and Maintenance

Sail

Packing up your sail. The sail comes to you folded with the long battens out and the boom in two pieces. Many find it easier and quicker to roll the sail up with the battens and boom in. The mast can be rolled into the center. The sail itself requires little maintenance - just wash the salt and sand off it if you have been running on sand.

The blokart

If you have a steel framed kart and are running it on the beach, you need to be washing it down very thoroughly. A little CRC or something similar, sprayed on points of wear will help stop corrosion. Some people recommend using an anti-corrosive coating to protect all the insides of the tubes from rusting. Boat shops stock the stuff.

Bearings

Dust and sand in your bearings can wear them out and slow you right down. The seals and grease are quite effective at keeping the crap out of your bearings, but if you hose your gear down at the end of the day, the water pressure can force its way past these barriers. If you suspect there is something going on, then undo the axle nut, remove the axle and tap the bearings out of the hub. Using a pin or some other pointy tool, remove the seal by slipping your tool between the bearings and the seal and levering it out. Clean out the grease, repack it with new grease and then put it all back together.
Info: Pulley Whip

Pulley whips can break. If this happens, remove the spring clip, saw off the offending breakage, drill a new hole for the spring clip and replace the clip.

Wheels and Tires

Flat tires slow you down. They can give you a little more traction on soft, slippery surfaces, but perhaps that is just because you are going slower. It pays to experiment. Keep an eye on the tire pressure. The recommended tire pressure stamped on the rims is about perfect. If you go over the top, the front rim will distort and the rear wheels are prone to bursting, especially if your blokart is parked up in the sun.

Speedometer

You have got a couple of options here:
Cycle Odometer - A good cheap option. Make sure that the unit can handle the small diameter of the wheel. Mount the magnet in the spokes of the front wheel and the reed switch on the steering arm. Salt water gives these units grief, but sealing everything in plastic can help. Wireless units may not be able to transmit the distance from the front wheel to a mount on the steering bar - think about its placement.

GPS - None of the technical grief but heaps more expensive.