Tuning
Your Slot Car - Advice and Tips
by Mark Rampling - Dunton Slot Car Club
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6. Car Set-Up and Tuning
I do the following things roughly in the order written:
6.1 Chassis
The first thing to do is to check that the chassis is flat. An uneven chassis can cause inconsistent handling between right- and lefthand corners, and cause the car to slew sideways under braking.
Remove the body and the guide, and put the car on a set-up block. The chassis should have a small gap to the track and should not be twisted, with one side lower than the other or one rear wheel up in the air! The front tyres should be resting on the surface of the block, and it should not be possible to lift either front wheel off the surface without lifting the chassis. This shows that the front axle is hard against both chassis "up-stops" at the same time, so the front & rear axles are parallel.
Another check is to press one front corner of the chassis downwards, watch the opposite rear wheel, then repeat for the other side - if both rear wheels lift by the same amount for the same downward pressure, and you cannot see any slack being taken up between the front axle and the chassis "up-stop" on the side you are pressing on, then the chassis is holding the axles parallel and the car should corner the same in both left-hand and right-hand corners. The above checks can't be done on a Formula One car, as they have a separate front axle unit independent of the chassis.
Next, remove the front & rear axles and rest the chassis on the set-up block. The chassis should be flat front-to-rear and side-to-side, with no big air gap. Sometimes the lettering on the underside of the chassis stands proud, but this doesn't count!
If the axles aren't parallel or the chassis isn't flat, it is possible to repair it by heating it and twisting it back into shape. My preferred method is to strip the car down to just the chassis, clamp the chassis down hard onto the flat set-up block with a couple of small modeller's G-clamps, and use a hair drier on it's lowest heat setting to gently heat the chassis until it is plastic-deformed into the right shape. It involves lots of trial and error, but it works!
6.2 Magnet
On a Scalextric-type plexi-track with steel contacts, the strength of the magnet and its location in the chassis are dominant factors in the handling of the car. The magnet provides an additional down force, similar to the aerodynamic down force provided by the front & rear wings on real Formula One cars. Just to give you an idea, in some cars the magnet is so strong that it is possible to hold a piece of track upside down without the car falling off!
The effect of the magnet is to clamp the car down on the track, giving higher cornering speeds and better braking. It is more difficult to find the limit of the car, as there is no progressive break-away to warn you when you are getting close - one moment you're on, the next you have flown off at high speed! I find that driving with a magnet on Scalextric - type plexi-track requires a quite different driving technique to driving on a wooden track.
As the DSCC track has non-magnetic copper tape, the magnet in the chassis is redundant. I usually remove it to reduce weight, though I keep the magnet in case we run a challenge event against a club with Scalextric-type plexi-track, when it can be re-fitted.
6.3 Guide
Make sure that the guide can turn freely in the chassis through its full travel. If it cannot, check for any moulding flash and remove it if necessary, and apply a drop of oil lubrication. If the guide is too stiff it can cause handling difficulties. For example the rear end no longer slides progressively and predictably, and it suddenly steps out when the cornering force is sufficient to overcome the friction. A stiff guide will also not self-centre but will stay skewed to one side when the car comes out of the slot, making it more difficult for a marshall to put the car back on again.
Scalextric cars have a unique problem in that they have sprung sliding contacts to the braids, which provide no self-centring to the guide. At DSCC it is permissible to hard wire the guide for selfcentring, provided that neither the chassis nor the body are cut away. This is possible with the Porsche GT1 and the Subaru Impreza, but I haven't found a way to do it on the Jordan Formula One yet!
Remove the old guide and throw it away, remove the metal strips and fit a conventional guide (I have found the SCX guides to work best). You will need to replace the lead wires with something longer and more flexible, such as the wire supplied by Oz-Race. Don't forget that you will need a couple of the small eyelets to push into the new guide (see next section).
6.4 Braids
All cars come with hard braids as standard. They last a long time but they are stiff and tend to lift the front of the car high above the track, raising the centre of gravity. I replace them with soft braids that help to keep the front of the car lower. My current favourite is the ultra-thin braid from Slot It, but sometimes I have to use the slightly thicker Pink Kar soft braid to stay above the new ground clearance limit.
I put a 90° bend at the very end of the braid with a pair of pliers, then I feed the braid into the guide so that the bend is at the top of the guide and helps to prevent the braid being pushed through. I then use the pliers to bend the braid against the lower part of the guide with the sharpest, cleanest bend I can achieve. This helps to keep the guide as low as possible in the slot.
The lead wires from the motor have a small metal eyelet with exposed strands from the lead wire poking through it. When pushing the eyelet into the guide, trap the exposed strands between the eyelet and the new braid, to give the best electrical contact. When pushing the eyelet into the guide, press the guide and braids hard down against the set-up block. I usually remove the front axle when I'm doing this, so that all the pressure is only on the guide. This will ensure that the braids are not pushed down out of the guide as the eyelet is pushed in, the bend in the braids is kept sharp and doesn't bunch up, and the guide is as low as possible in the slot.
With Scalextric cars which cannot be hard-wired, I replace the supplied steel braids with softer braid. As supplied, the Scalextric braid comes up from the track surface into the guide, along the top of the guide against the spring contact, then dives down into the guide again and returns out onto the underside of the guide. This return tends to hold the main part of the braid away from the guide, lifting the whole front of the car. When fitting the softer braid, I end the braid on the top of the guide and hold it there with a touch of glue. So the braid no longer lifts the guide out of the slot, and the front of the car sits lower.
Trim the braids to be the same length as the guide. Splay the braids apart to form a 'V', and slightly turn down the very ends to give best contact with the copper tape on the track. Good braid contact is important for a smooth-driving car. On Blue lane on the flyover section, the groove width varies quite a bit and the track height varies on each side of the groove. It is common to see cars stuttering because of poor braid contact, so give the braids an extra tweak before running on Blue!