Car Preparation and maintenance

Buying a slot car, like any competition vehicle, is the first step towards racing it competitively. As soon as you’ve hot-footed it back from the hobby shop or, more likely, signed for the delivery from your chosen online retailer, you’re going to want to take a few steps to make sure that it’s ready for action. Once you’re up and running, you’ll also need to maintain your new little friend. Let’s start with the prep:


A large proportion of chassis arrive warped. This could be a design fault, a manufacturing problem or even just having been screwed to the base of the box too firmly. An uneven chassis will have issues with negotiating corners.

Remove the body, guide and axles, place the chassis on a flat surface and inspect it thoroughly. A lot of cars have extraneous details like exhaust pipes mould underneath so use your judgement. The chassis should have a small, consistent gap to the track and should not be twisted.

If there is an issue – don’t worry. Boil the kettle. While the kettle is boiling, strip everything off the chassis in a way that you know how to replace it. Then follow these instructions from the gods at Slot.It:


Traction Magnets

In those classes where traction magnets are allowed, the difference in performance is incredible. Magnets give downforce, generating higher cornering speeds. But no two magnets are born equal.

Whether it is the ferrous ‘Brown Bar’ magnet in our vintage Scalextric GT and BTCC or Ninco GTR classes or the modern neodymium magnet in Modern GT or Super Mag F1, you should always keep a few of the same type of OEM magnet (the only magnets that we are allowed to use) to choose from to hand – they’re available in packs of 5 or 10 for a couple of quid.

Take a piece of paper, a ruler and a chassis screw. Lay the ruler down on the paper and place the screw level with ‘0’. Place your magnet on its long edge and move it up the ruler towards the screw. Stop when the magnet pulls the screw towards it and mark it against the ruler.

Then turn the magnet over and try again with the opposite face. Is there any difference? There usually is.

Using as many of the correct magnets as you can find, repeat this process until you have found the magnet with the best/strongest attraction and be sure to remember which side is which. Use this one, put the rest away for a rainy day!



A lot of ‘deslots’ at Farnham aren’t caused by going too fast but rather from the lumps and bumps in the track surface causing the guide to rise up far enough to stop working. It’s like understeer on a road car.

As well as the bumps (most often found where sections of track are joined together), the guides can struggle to cope with changes in camber and elevation,such as the rise up to the flyover and the parabolic turn back down again. Additionally, there can be an issue with the car’s front wheels acting as a lever to push the guide out of the slot if they are too big, too rigid or out-of-shape.

As of 2017, there is now a ruling that any OEM manufacturer’s guide can be replaced provided that no modifications to the chassis or wiring are required to do so. However, it may not be necessary to go that far very often.

Firstly, take the body of the car off and 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.

Secondly, using a piece of Ninco track (you can pick up a half-straight on eBay for pennies), place the chassis on it and see how well it the guide seated and whether or not the front wheels are lifting it above the optimum. Take the front axle out to see how much of a difference there is with and without the wheels in play – if there is a difference, you have some choices.

Firstly, reducing the profile of the front tyres will help. Using the method described for truing the driven tyres, fit the front tyres to an appropriate powered axle and pare them down. Alternatively, there are ‘zero grip’ tyres available to fit most wheels, which are slimmer and made from a harder and less resistant rubber.

Secondly, some cars come with adjustable ride height for the front axle. For our track the best setup is to have the front wheels just kissing the track, with some upward play available to soak up the bumps.

The most common culprit for front wheels that interfere with the guide is Scalextric, and to help counter this issue its 2017-onwards cars are fitted with a deeper guide as standard. This is available as a replacement part, code C8420.

Alternatively – and really as a last-gasp measure – there are ‘universal guides’ available from manufacturers such as Slot.It, NSR and Sloting Plus that should fit with minimal alteration. They will probably need to be trimmed, but provided that they do not require modification to the chassis or the wiring that comes with the car as standard they are permitted.


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, interfering with how well the car runs. and even fouling how well the guide is seated.

In the first instance, splaying the braids a little will help. There are also a wide range of ultra-thin braids available from NSR, Sloting Plus, SCX and Slot.It.

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 rails on the track. Good braid contact is important for a  smooth-driving car.



Motor response and output are vital to getting lap times are results. Most of our classes are for a single, standard type of motor for parity, although the variance between ‘identical’ motors can be eye-popping because of poor manufacturing tolerances.

Some motors, such as the slimline ‘FF-can’ used in Super Magnet and 1970-1985 Formula 1 cars, are simply untreatable. The only reason that they exist is to allow slot car manufacturers to produce pretty little cars with a motor in them, but for racing purposes they are sketchy at best.

When a motor is brand new, it will have tight bearings and poor brush contact. As the motor runs-in, the bearings will become a better fit to the  motor shaft, the brushes will wear to the same curvature as the commutator and stop arcing, and any loose windings will settle and possibly improve the balance  of the armature. A run in motor is generally quieter, it has smoother acceleration, more top-end speed and better brakes.

Using a 9v ‘E’ battery is often a good idea to run the motors in. Some folk do this underwater and then dry the motors with WD40 but this seems an extreme way to do it. An occasional squirt of electrical contact cleaner will always help a motor – particularly those like SCX which are open to the elements.

Gears and Axles

Check first of all that the main gear on the axle (the contrate) runs true, by removing the motor and slowly rotating the rear axle. You should be able to see any ‘wobble’ quite  clearly. If there is contrate ‘wobble’, you’re going to have a noisy,  power-robbing gear mesh. So throw the contrate away and find a good one.

Next, check that the contrate sits centrally on the axle by seeing whether the rear wheels are equidistant from the rear axle bearings and/or the chassis.  Quite often they aren’t! If this is the case, remove the rear axle from the  chassis. Then grip the axle on a nonbearing surface with a pair of long-nose  pliers and gently rotate the contrate relative to the axle to centre it. Hold the contrate in place with a drop of superglue. Make sure that an axle bearing  doesn’t slide against the contrate at this point, because the glue will run into  the bearing by capillary action and ruin it.

To move, fit or remove a pinion, it is far better to use a specialist  gear puller like the one supplied by Ninco. This avoids the risk of damaging other parts of the motor with the forces involved.

Pinions can move along the motor shaft and out of mesh with the contrate  gear. When this happens, exchange the pinion for the same make but with a  tighter fit (normal production tolerances). Alternatively hold the original  pinion in place with a small amount of solder (brass pinions only!) or glue,  making sure that none gets into the teeth.

It is very important to achieve a good, smooth, quiet gear mesh. A noisy gear mesh is robbing power, it can give uneven acceleration and braking, and it is a psychological disadvantage to have a car sounding like a bag of nails! With the motor and rear axle in place but the body removed, turn the rear axle very slowly and lightly by hand in the direction of normal wheel rotation. A good gear mesh gives a consistent feel for the complete rotation of the rear axle. Any irregular resistance to rotation is going to be problematic.

A ‘sticking’ point is caused when a tooth on the contrate binds against the pinion as it tries to come into mesh. To eliminate the problem, you first need to determine which tooth on the contrate is at fault. Mark the sticking’ point with a marker pen or Tipp-Ex and carry on rotating the rear axle because it is possible  that there will be more than one.

Then use a sharp scalpel to take off the tiniest sliver from the leading  side of each marked tooth on the contrate. This is usually enough.

The standard gear ratio for most box-standard slot cars is 3:1. It is only permitted to change the ratio from factory fit in the Slot.It Group C class, where generally, a lower numeric gear ratio will give worse acceleration & brakes but a higher top speed;  conversely, a higher numeric gear ratio will give better acceleration &  brakes, but a slower top speed.

Body Float

The optimum setup for a racing slot car is for a degree of ‘float’. This means that the body sits loosely on the chassis rather than being done up as tight as a drum. ‘Float’ acts like suspension for cars that aren’t fitted with any, allowing the chassis greater freedom to absorb bumps without coming out of the slot or losing traction.

Loosen the body mounting screws by about  ¾ of a turn to a full turn. This should loosen the body. If you need to go looser than one turn, it’s advisable to put tape over the screw holes in case they get loose and fall out, causing a short circuit.

Ideally there should be a little body movement but many chassis will rub or catch somewhere against the body. Go around the edges of the body and chassis with some fine sandpaper, just enough to break any seals, snags or catches. Some cars can’t achieve ‘float’ due to their design – like the Scalextric Ferrari 330 P4 for example – because the chassis and body are integral. Not much to be done about that, sadly.


A car’s handling can be fine-tuned by adding weight and subtly altering  the weight distribution. The added weight improves cornering, reduces sensitivity to bumps and makes the car more robust in clashes on the track, but it worsens acceleration and braking.

You shouldn’t need more than 5g of weight for most cars, and it’s most often used to balance ‘sidewinder’ cars with the motor located across the chassis in front of the rear wheels. This can cause the front end of the car to run light and bounce around, so sticking 5g up front under or behind the front axle will work wonders.

In the case of inline motored cars, you need to imagine a triangle between the contact patch of the rear tyres at the bottom and the guide at the top. What you want is to equalise the pressure on those three points, so 1-2g of weight just in front of the rear wheels and behind the guide should help – but only use it if needed.

Some people use plasticene when experimenting with the position of additional weight. Once you have found the  ideal position, it is better to use small pieces of lead sheet to keep the centre of gravity as low as possible – Pendle Slot Racing sells this sort of thing with a self-adhesive backing, although there are many other solutions.

The ideal is to have a car that does not need weight at all, but what will work and what you feel comfortable with is far more important. And only trial and error can teach you.