Tuning

Team Slot Lancia Stratos slot car

In this section we'll have a look at how you can tune your cars to make them faster and smoother.

There is no exact recipe for this, as each car is different. But there are tried and tested techniques which have been proven over the years, that can help to achieve three fundamental aims; increasing current to the motor, reducing mechanical drag, and increasing grip.

The techniques here will be fairly simple, and do not require a huge range of specialist tools, though you will need some basic equipment such as small screwdrivers, sand paper, nail file, and toothbrush etc.

Tyre Truing

Making sure that your tyres are round, and have the right profile, is essential to getting as much rubber down onto the track as possible, thereby achieving good grip.

Why?

The Wheels aren't Round
They look round to me.

The wheels and tyres on your slot car may look round, but they won't be. The manufacturing process almost inevitably means that they will be inaccurate. What this means is that as the wheels spin, they also bounce. This reduces the contact the tyres have with the track, and therefore reduces grip.

The Wheels aren't Flat

The profile of the tyres might also be a problem. If the profile is either raised in the centre, or along the edges, the contact area between the tyre and the track is reduced, and again, this reduces grip.

These two problems combined, can result in a big reduction in performance. Fortunately though, this is fairly simple to fix.

How?

Tyre Truing | Time: 5-10 mins | Rating: Essential | Skill Level: Moderate

There are just a few steps to truing tyres, and all you'll really need apart from your track and car, are a small screwdriver and a couple of sheets of sandpaper; a coarse sheet of around 100 grit, and a finer one of around 500 grit or more.

Disassembly

We'll do this with the body shell removed so that the interior doesn't get dusty and dirty. So first, undo the screws on the underside of the car, then gently pull the body away from the chassis. Be careful not to drop any of the screws, and be sure to put them somewhere safe. If any of the screws are a different size, or type, take note of where each one came from.

Rear Tyres

The rear tyres are the ones we will true, and fortunately they are the easiest. You'll need to use sticky tape, or an elastic band to hold down the trigger on one of your controllers to supply full power to one lane of your track.

Hold down the coarse sandpaper with one hand, on a piece of flat, level track, or alternatively tape it down. Take the car with the other hand, and place it into the slot, with the rear tyres held up off the track. With the rear wheels spinning, gently lower them down onto the sand paper. Don't push down too much, you should be mainly just holding the chassis steady, and don't continue for more than a few seconds, as the motor, or the tyres may overheat.

Have a Look

Take the car off the track and have a look at the tyres. You should see that parts of the tyre have been sanded, and are a slightly different color. The parts that have been sanded are the high points, and our aim here is to continue sanding until all of those high points have been removed. The tyre should then be round, and it's profile flat. So repeat the sanding process in short bursts, until the whole of the circumference of the tyre is sanded, and is the same color.

At this point, take the finer sandpaper and give the tyres a light sanding, to create a nice, smooth finish on the tyres.

Rounding Off

Once that's complete, you may well have a sharp, square edge to the tyre's profile. This will need to be rounded off as it tends to make a car tip over more easily.

So take a small piece of sandpaper in one hand. Take the car with the other hand, and place it into the slot, with the rear tyres held up off the track, as before. Gently press the sand paper against the edge of the tyre and change the angle to create a rounded edge to the tyre profile.

And that's all. Well, nearly.

More

Now that you've got the hang of tyre truing, you might also want to look at truing the wheel hubs, and glueing the tyres. If you're going to take these steps you need to do them before you true the tyres. Not everybody takes things this far, as the gains are more marginal, but you might want to squeeze the last drop of performance out.

Tyre Hubs

Hub Truing | Time: 5-10 mins | Rating: Maybe | Skill Level: Slightly Tricky

Just as you tuned up your rear tyres, you can also true up the hubs on which the tyres are fitted. This isn't normally necessary with metal hubs, but can be with plastic hubs. It's generally the same process as truing tyres, but with two slight complications. Plastic hubs often have a central rib, so the shape is more awkward. Also, once the tyres are removed, the hubs might not protrude below the chassis. Both of thes issues can be over come by using a nail file or emery board over the hub.

Gluing Tyres

Tyre Gluing | Time: 5 mins | Rating: Definitely | Skill Level: Moderate

Gluing your tyres to your hubs obviously prevents any slippage between the two. The method is very simple.

Squeeze out a few drops of super glue onto a small piece of waste plastic. Dip a toothpick into the glue so that there is just a small drop of glue on it's tip. Pull out one side of the tyre to make a slight gap to the hub, and dab the glue on the toothpick onto the hub. Press the tyre back down onto the hub, and repeat the process three or four more times at equal intervals around the hub. Repeat on the other side of the wheel and leave to dry thoroughly.

Front Tyres

Front Tyres | Time: 5 mins | Rating: Meh | Skill Level: None

You may have noticed that we haven't discussed the front tyres yet. That is partly because they are much less important than the rear tyres in terms of performance, and partly because there is little general consensus on what's best.

The only thing that most agree on is that grip is of no concern, in fact zero grip tyres are often used. There are commercial zero grip tyres available, or you can coat the front tyres with clear nail varnish.

Adding Weight

Adding Weight | Time: 1hr | Rating: Important | Skill Level: Moderate

I thought the idea of a race car was to be lightweight?

Yes, but slot cars can actually be faster with a little extra weight to aid grip and traction, particularly if you're running without magnets.

The Basics

Observation

Adding extra weight to a slot car isn't particularly difficult, but it can be as much an art as a science. Observing how the car is driving at each stage is essential. It's important to test the car after each change you make otherwise you won't know which change has made the difference. Of course the final decision will depend on whether the lap times are falling.

Behaviour

The first thing you need to do is observe how the car behaves, particularly at, or beyond it's limit of cornering speed.

What am I looking for?

Typically there are three behaviour patterns...

Tipping

If the car tends to tip over, then it probably needs some weight adding low down and central. It's almost always a good idea to place weight as low as possible to keep the centre of gravity low. This would normally involve putting the weight directly onto the chassis.

Oversteer

If the car is tail happy, and tends to slide off the track at the rear end first, it will probably benefit from some weight added towards rear axle to increase the grip of the rear wheels. Don't put any weight behind the rear axle, as that might lift the front end.

Understeer

If the car tends to deslot at the front end first, or if the car is lifting it's front end on acceleration, then some weight added towards the front of the chassis will probably help.

Tips

Blu Tack

Whilst you're testing, you can use Blu-Tack, which is easy to reposition, and makes it simple to add or subtract weight. Once you are confident of your weighting you can then switch the Blue Tack for some lead weights which are available with sticky pads from most slot car stores.

Central

You should try to add any weight as centrally as possible, by which I mean an equal distance from the left and right hand side of the car. But that's often impossible if there are machanical parts there already, such as the motor. In that case, you'll need to add two weights, of equal size either side of the motor.

How Much
How much weight should I add?

Ideally none. A race car should be as light as possible.

But I said that.

And you were right. Ideally you wouldn't add any weight at all. But if your car isn't ideal, we'd suggest you start your testing with about 5gm, and if necessary build it up from there. If you don't have any accurate scales, 5gm of Blu Tack would be a ball about 1cm across.

Smoothing the Gear Mesh

Why?

Does your car sound like a bucket of nails being shaken?

Well yes, or at least one of them does. What's the problem?

It could be a problem with the gears. Obviously any problem with the gears is important because they are the mechanism through which the power from the motor is translated to the rear axle, and therefore to the rear wheels.

This should be as smooth as possible and there is a very easy way to test this. Simply take your car and turn the back wheels manually.

In an ideal world you would feel almost no resistance to rotating the wheel. In reality it's likely that you will feel a little click, click, click, every time the teeth of the crown and pinion gears engage with each other. The more pronounced that is, the bigger the problem, because it's wasted energy, and therefore it's slowing down your car.

Fortunately there's a fairly easy solution....

Toothpaste.

What? You can't be serious!!

Totally serious.

How?

Smoothing Gears | Time: 5mins | Rating: Helpful | Skill Level: Low

Baking soda toothpaste has a fine grinding action which can help to smooth out those gears. So smear a dab around your gears, and run the motor for a while. Do this with the body removed so that the interior doesn't get splattered with toothpaste, and do it with the wheels off the track. After a few minutes, you should find that your gears are silky smooth, and your car should run smoother and faster.

A word of warning though, make sure you wash off all the toothpaste afterwards, because it sets quite hard when it dries, and it will clog up those gears if you don't clean it off thoroughly. Funnily enough, a toothbrush is ideal for this job.

Serious

A more serious, though less common issue is when you have a deformed or misshapen tooth on one of your gears. Again you can test this by manually turning the rear wheels. If the wheels mostly turn smoothly, but with occasional points where it's stiff, then you may have a deformed tooth.

Reshaping a Tooth | Time: 10-15mins | Rating: Only when necessary | Skill Level: Tricky

Where?

If the stiffness occurs just once for each rotation of the wheel, then the problem tooth is likely to be on the large gear attached to the rear axle, called the crown, or spur. If it occurs two or three times for each rotation, then the problem will be with the smaller gear on the motor shaft, called the pinion.

Dentistry

Remove the body shell, and rotate the rear wheels until you feel the gears stiffen up. Mark either the crown or pinion (depending on where you think the problem is) at the point where the gears engage. This is where your problem tooth will be.

At this point you may need a magnifying glass, and you'll also need a small triangular section file for metal gears, or a sharp scalpel for plastic.

Remove the rear axle, or the motor, and inspect the teeth of the gear around the point you have marked. You should be able to see one with some excess material around it, or perhaps some deformation. Use the file or scalpel to remove any excess material and generally make the tooth the same shape as all of the other teeth.

Body Float

This is the process of loosening the screws that hold the body to the chassis causing it to float or rock rather than being rigidly attached. When cornering, centrifugal force throws the weight of the car onto the outside wheel, so it is the outside wheel which loads up most, with more "weight" and is therefore responsible for that tyre gripping the track surface most, and resisting slide.

Loosening the screws that hold the body to the chassis does two things:

  1. It prevents the body stressing and potentially causing the chassis to flex, which could disturb the grip.
  2. Most importantly, it further throws the weight onto that outside wheel. More weight on the outside means more grip from that wheel and more consistent cornering. Even though you have the same amount of weight to divide between the two wheels, the amount on the outside wheel seems more beneficial.

How?

Body float | Time: 30 seconds | Rating: Recommended | Skill Level: None

All you need to do is loosen the screws by about one full turn but it pays to experiment around that figure until you are happy with the handling. This process won’t magically improve your lap times but it will make the car easier to handle round the twisty bits with less likelihood of deslotting.

Cars with adjustable motor pods such as Slot.It and NSR can also benefit from loosening these up, either in combination with body float or instead of it. Experiment with both until you find the correct balance.

Things to bear in mind
  1. This is primarily a technique for non-magnet racing. It can work with a magnet car but may cause distortion with thin chassis as the magnet will pull it downwards if the body is left too loose. In any case the magnetic attraction of these cars is far more important than mechanical grip.
  2. Cars with a low centre of gravity will benefit most from this and it may not be suitable for high c.o.g. saloon cars as it could cause them to tip over more easily unless you also add weight to the chassis.
  3. Cars where the body sits on the chassis don't achieve as much gain as ones where the chassis sits inside the body.
  4. Some makes of car have internal protrusions which hamper body float and you may need to trim them up with a craft knife to make it work.
  5. It pays to replace the standard full thread screws with screws which have a non-threaded shoulder so the body posts don’t catch on them.
  6. The screws can vibrate loose and fall out, so remember to put insulation tape over them or secure with Blu Tack to prevent them ending up where they shouldn’t.

Running In a Motor

When you buy a new full size car the manufacturer always recommends that you keep the revs down and don’t overstress the engine for the first 1,000 miles. Slot car motors can benefit from this as well but the time scale is a lot shorter.

As you can see from the exploded drawing below, an electric motor has very few moving parts and the bits we are mainly interested in are the commutator and the two brushes which fit round it when the motor is assembled.

The brushes are made of carbon material and, as this is a mass produced item, they are not always a snug fit round the commutator. The break-in process articulates the contact surface of the brushes to the curved commutator surface through frictional wear for maximum contact with minimal power loss due to resistance.

It won’t make an enormous difference to the performance but will ensure the motor runs smoothly and has a long life.

Running in a Motor | Time: 1hr | Rating: Maybe | Skill Level: Easy

Equipment

You will need an adjustable power supply, nothing fancy, just something like the one below which can be picked up for less than £10 on eBay:

Basic Dry Method

You can remove the motor from the car to do this but it is advantageous to leave it in situ and run the gears in at the same time so everything meshes smoothly.

Resist the temptation to run the car flat out straight away.

Remove the body and apply a drop of thin oil to the spindle where it emerges from the motor.

Prop up the rear wheels so they can spin freely.

Connect the power supply and run the motor in the forwards direction for 30 minutes at 3volts.

Apply another tiny drop of oil to the spindle, then repeat at 6 volts.

Job done. Simples!

If you stand nearby while this is happening you should hear a slight increase in revs at some point as things bed in.

Advanced water method

There is a theory that running in the motor under water is beneficial but it is a subject of some debate whether it is any great improvement and it can destroy the motor if you overdo it. SCX motors in particular don’t like it so best to stick to the dry method for these.

If you should wish to try it out you will need the following:

  • Deionised water (the stuff you put in a steam iron).
  • Isopropyl alcohol
  • An air duster canister.
Procedure

Remove the motor from the car.

Lightly oil the spindle and immerse the motor vertically in a container of the deionised water.

Connect to the power supply for 30 minutes at 3 volts. The liquid will become mucky as the worn carbon is expelled. Make sure you run the motor forwards, not backwards.

Change the water.

Apply another tiny drop of oil to the spindle then repeat at 6 volts.

Remove and place in a container of the alcohol and run for 15/20 seconds. Blow dry with the air duster.

Oil spindle again, job done.

Find out more

The SlotRacer forum has a Tips and Tuning section where you can find out more and ask questions.
Tips and Tuning

Slot car tuning tips
http://www.homeracingworld.com/slotcartuning.htm

Tuning 1/32nd slot cars for non-magnet racing
http://www.rockinghamslotcarclub.co.uk/Scalex_files/Tuning%20for%20Non-Magnet%20Racing%20Rev%202.pdf

How do I build a fast car?
http://www.farroutslotcars.com/FarrOut-Slot-Cars/Tuning-Tips/Garys-Car-Tuning-Tips

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