Rubber

In an R.C. car restoration, the first part to face is the evaluation of the tyres.
If the tyres are rubber, a restoration can be carried out. The process to restore the tyres can take 4 to 5 weeks. This is the candidate for being the longest part of the whole restoration operation.
Radio controlled model tyre rubber tends to deteriorate over time; these are the factors that cause it to age and lose its original characteristics:

– exposure to sunlight, UV rays ruin the rubber surface and ‘cook’ it, making it less elastic
– exposure to chemicals that can be in the form of aeriform (such as perfumes with added ozone and gases present in the interior of a building) or liquid (such as previous treatments with unsuitable petroleum-derived oils or aggressive cleaning substances)
– environmental factors such as temperature (changes from hot to cold and vice versa worsen the elasticity of the product, below 15°C and above 105°C the rubber hardens) and humidity (when there is little water in the air, dry air tends to take away the volatile elements of the rubber which hardens).

The elastic property of rubber is provided by long chains of molecules bound together. These chains can break or stretch when subjected to continuous tension or exposure to the elements listed above; the rubber becomes dry and loses its softness, shine, colour, elasticity and firmness.
The first step is to assess the tyre: what determines whether or not it deserves restoration is the condition of the tread, the shape of the wheel (is it ovalised or not), the cuts, the colour, the condition of the shoulder.
If it does not deserve restoration, this phase is already over: when possible it is better to look for new tyres.
This solution is not always feasible; there are parts that are very rare, a new set of 4 tyres complete with rims can cost as much as a whole model.
If you decide to proceed with a restoration these are the steps to follow for a complete remanufacture.

Wheels
Remove the wheels (rims and tyres) from the chassis, this operation is generally simple and presents no particular problems.

Separating the tyre from the rim
Often the tyre and rim are glued together. If the tyre is inseparably glued to the rim before venturing into techniques to separate them, it is best to inspect the rim and see if it has any particular damage. Separating the tyre from the rim can always lead to tyre damage. As soon as the rim is undamaged, one can consider subjecting it to the same treatment as the tyre. Glycerine is the substance that regenerates the tyre and is not aggressive to either the plastic or the paint.

If you have chosen to separate the two parts, there are several techniques for separating tyre and rim; the best known are treatment with acetone or boiling water.
Treating tyre and rim with acetone can cause irreparable damage to the rim. Acetone does not attack the tyre, but it dissolves some plastics and glue. The plastic of which the rims are made can suffer from acetone and can lose shape and consistency. This method, therefore, should be discarded unless you have metal rims.
Treating tyres and rims by immersing the wheel in boiling water works with most glues: the high temperature does not affect the integrity of the tyres and rims, but it does attack the glue, which tends to crystallise, becoming very stiff and breaking easily. The procedure to follow is as follows: boil water in a pot, immerse the rim and tyre in the container, wait several minutes, take the wheel and tyre out of the water with very long pliers, handle carefully and try to separate the two parts. Repeat the operation until the glue loses its grip and be as careful as possible to avoid being injured by the water itself.

Washing
First it is necessary to remove years of dust and grease from the tyre. You can wash the tyre using warm to lukewarm water, a toothbrush with soft bristles and a little degreasing dishwashing soap.
The soap emulsifies the grease, which is then washed away; if you did not use soap, the grease would simply be moved from one side of the tyre to the other. Remove as much dirt as possible and try to avoid increasing the size of the cuts.

Repairing any damage
When the tyre has cuts or tears, these can be repaired using glue. There are specific, black cyano-acrylic glues that have been developed for gluing rubber. Repair the tyre from the inside (photo 1) so that aesthetically from the outside the repair is not too visible (photo 2). Allow at least 24 hours for the glue to dry completely.

Regenerating treatment
To regenerate any piece of rubber, the best product is 99.5% (pharmaceutical grade) pure vegetable glycerine. It is a very thick liquid that has many uses; for example, it is used to make skin creams and some types of soap.
You have to soak the 4 gums completely in glycerine. Better to use

1 – a metal painter’s paint can or
2 – a plastic kitchen vacuum container

For both, when closed, the seal is airtight.

Glycerine’s worst enemy is water and humidity. Keeping the gum completely immersed in an airtight jar provides the assurance that the glycerine will not lose its regenerative properties.
The glycerine basically fills the micropores that have formed over time, making the rubber less elastic and less resistant.
In the first 3-4 days, the glycerine starts to penetrate the surface of the rubber, in the remaining days it penetrates deeply. The glycerine replaces the volatile parts of the rubber that have dried out over time and ensures that the moisture in the air is absorbed, leaving the tyre soft.
On average 8 to 9 days should pass, after treatment the tyres change colour (become darker) and are more elastic to the touch.

Emulsifying the glycerine
The next step is to let the tyre squeeze out all the glycerine, place the tyre on a paper towel.

The paper towel should be changed daily to prevent it from soaking in glycerine, at this stage turn the pieces upside down each time so that they purge all excess glycerine. This should be done for as long as it takes for the gum to stop purging glycerine, on average 7 to 8 days.
Note: always place the gum on its side. This is done so as not to risk ovalising the rubber, which is particularly soft and elastic at this stage.

Cleaning the gum
Use a paper towel to dry the parts daily, removing all traces of glycerine. In practice, the gum is still purging glycerine, but in smaller quantities. It is necessary to remove any residue daily with the help of a paper towel or cloth. The tyre is regenerated by changing its colour and elasticity. On average this operation takes 6 to 7 days.

Installation on the rim
You can now reinstall the tyre on the rim.
If the tyre is oval-shaped or deformed, use inserts to be placed between the tyre and the rim to restore the original shape. These are accessories sold separately for rubber tyres; they can be:

– foam, harder or softer rubber and soft plastic
– circular or strip-shaped

They help the tyre keep its shape even under the weight of the model car.

Colouring any friezes
Many tyres have the tyre brand, friezes, initials, direction of rotation… printed in bas-relief on the shoulder with a border outlining them.
It is possible to colour these parts. The technique is very simple, in reality it is not a matter of brushing or applying paint. The material required is the paint can and toothpicks, a very small flathead screwdriver or iron nail. The procedure is as follows: dip the tip of a toothpick into the paint container, the tip takes away a drop of paint, place the tip of the toothpick inside the shape to be coloured, the drop falls onto the surface taking up as much space as possible by standing inside the figure in high relief due to gravity and fluid capillarity, repeat this until all parts have been coloured.

At this point the tyres are ready to be installed on the machine.
Please note that glycerine suffers from moisture and generally from water; it is best to carry out this operation in a dry place. If the glycerine absorbs moisture it loses its characteristic and cannot be used for further treatments, if the glycerine is applied in an airtight container it will retain its function for future treatments of other rubbers as it will not have come into contact with external moisture.
Once regenerated, the rubber will be as good as new: elastic, with a darker – livelier colour, less rough to the touch.
When the model car is used, if these glycerine-treated tyres come into contact with water, the glycerine will be washed away. After repeated use with puddles of water, the glycerine treatment must be repeated.
When the model car has been lying on the shelf unused for a long time, the best solution is to place the model car on a stand that prevents the tyres from touching the supporting surface. The weight of the model car can ovalise the tyres over time.

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