Added: 3rd September 2007
The fact that the sport has attracted quite a few new drivers lately has highlighted the difficulties of learning the skills needed to drive successfully on sections in all parts of the country and under all weather conditions. One thing that is obvious is that trickling is the most difficult skill of all to learn but choosing when to use it is just as hard as actually doing it.
What is trickling? It is nothing to do with speed, or even power, trickling is no more than driving without wheel spin, as you would on the road. However on trials surfaces, and with the low gearing of trials cars, it is not so easy. The best way to think of it is imagining you are on snow, so you use the minimum of throttle necessary to keep moving at whatever speed you choose.
Why do we use it? There are several reasons, but most important is the fact that grass and other vegetation exudes sap when broken. Sap is an excellent lubricant for rubber, and a wheel spinning on grass immediately becomes nicely coated in sap, which usually prevents any further progress. Other reasons include the fact that a spinning wheel can travel in any direction, whereas a trickling wheel will tend to travel in the direction of rotation, and not to slide sideways (or even backwards!)
When should we use it? This is the tricky one, as watching the experts will soon convince you that there is no hard and fast rule, but basically on grass, heather or bracken, you would normally use trickling. You would also use it on any surface where there is a risk of sliding off camber into a pole.
Where not to use it? The reason for doing the opposite (blasting) is where you need to clean the treads because they are slicked over with mud, or where you think digging down to the surface underneath is likely to be better that the one on top. Wet mud is a typical time for blasting, and trickling is unlikely to be useful here, due to the tread blocking effect of the mud.
Why is it so difficult? The problem is that it is often counter intuitive, you need to accelerate smoothly on the easy bits (when your instinct is to drive slowly) and to ease off (sometimes right down to the stalling point of the engine) when the hill gets steeper (just as you feel the need to accelerate). You have to be confident that your engine will continue to pull at very low revs and will not stall just when you need it most.
How fast and what gear? This depends entirely on the terrain, but on wide grassy sections which get steeper as you progress, it is often necessary to go quite fast, so as to be able to back right off on the difficult bits. In these circumstances it is often easier to use a high gear because this brings down the engine speed for any given car speed, and therefore there is less torque available at the wheels to cause them to spin. The problem is where you have to slow right down for a tight or twisty bit further up the section, you may find the engine is unable to pull at a low enough speed in the higher gear. If there is a level or downhill bit before the tight section you can usually change down a gear, but this is difficult if the whole section is uphill.
Should you mix techniques on a section? Yes, but only if you have a plan in mind, although if you have ground to a halt whilst trickling then blasting might be worth a try, particularly if you have seen someone else get away with it. Generally you will need to mix techniques where conditions vary on different parts of the section. The typical scenario is when the first part (where other drivers blasting on the grass have wrecked it) there is a mud base showing through, but further up the grass is undamaged. This is where you must plan, you need a blast to get going but you have to drop down to the trickle as you hit the grass. This is difficult since you do not know beforehand what speed you will have as you reach the grass, but generally easing off smoothly as you get to the grass will be the best bet. It is a most satisfying technique to master. It will be remembered by those who competed at the recent November Sporting Trial at Wyton Piece Farm, that Barry Wright's section in the left hand corner of the field nearest the paddock required this technique. There was a trickle on grass from the start alongside the fence, followed by a descent to the lowest level where there was a muddy blast followed by a right turn up the bank again. The only way up was a full on blast through the mud to get speed and then back right off to a trickle on the grass. As the event went on the muddy bit extended further and further up the hill, but the successful technique remained the same all day.
How can I practice? By far the best method is to do it on the site on the day, where conditions are the same as those on the sections. Do not ever drive on the sections themselves until the event is over, but you can drive on other parts to try out your technique, provide there are no reasons not to (such as the Eaton site for the Johnson, where parts are designated as an SSSI, or where the area alongside the paddock is restricted like the Fedden site at Dyrham Park).
What else? By far the most important thing to do is to watch others do the section, and see how they get on. For this reason it is a good idea to keep up with the flow during the event, and not spend too long looking at sections. If you let a gap appear in front of you in the running order you will not see anyone else driving the sections, and will be driving blind. If the driver in front of you is less experienced than yourself, then you need to be even more on the ball, so as to see the driver in front of him driving.
Any useful technical tweaks? There are several simple things that are important. The throttle action must be smooth and progressive, but not too lightly sprung. Your foot must be comfortable on the pedal, particularly at the beginning of the movement. You should have something (like a heel stop) which causes the foot to be steady on the pedal. A panel (like the side of the car) alongside the footpad on the pedal can make a difference in preventing the foot sliding around, and it can also add a bit of friction to the movement when you hit bumps. Your engine must run well at very low revs, right down to the stall. Note that you can often score one less mark on a section when you let the engine gradually run out of steam and stall rather than hitting the throttle and spinning to a halt immediately. Getting the mixture and ignition timing right at very low revs can have quite miraculous effects on an engine's ability to run slowly.
I am still having problems trickling, how can I get help? Trials is one of the friendliest sports around, and you should ask more experienced drivers if you are unsure about anything. Obviously do not interrupt their concentration just as they are about to tackle a section, but if you ask at the right time you will get constructive advice, and, if they are running close behind you they may be able to watch your progress and make useful suggestions as the day goes on.
In summary: If you are going to trickle, then trickle properly, and if you are going to blast then blast with a vengeance. Do not pump the throttle, and do not shilly shally around between the two techniques. When you blast, continue to blast until either you reach a different surface, or you are going faster than you are happy with. A common mistake is to blast successfully only to back off too soon and grind to a halt. Another problem is blasting without using full throttle, or for some reason being unable to get full throttle. The last bit of the throttle movement is where all the power lies, and if you cannot achieve it you will get nowhere in mud. When you trickle, drive using just enough throttle to keep moving, and if possible back off as you reach the difficult bit. At the very least keep the throttle position (not the revs) constant as you get to the steep bit. Increasing the throttle at this point is a sure way to grind to a halt. An advanced tip is to ease off (but not to slow down) as the car goes light, for example over bumps. This is the sort of thing is that makes the difference between the novice and the expert.