Please note that this only applies to “rubber” tyres.
RC tyres do tend to degrade over time – both in terms of deformation (pressure from sitting on one “side” while on the shelf – and degradation of the material through a number of means:
- Cold/heat – and especially variations, and very low temperatures, which tend to have very low humidity associated with them;
- Exposure to ultraviolet radiation – the dangerous bit of daylight;
- Humidity – extremely low humidity can suck the volatile components (plasticisers) right out of rubber parts;
- Indirect chemical attack – i.e. fumes from paints, oils & other chemicals found in & on typical outbuildings;
- Direct chemical attack – usually inappropriate tyre treatments, such as dousing with WD40 or equivalents.
Oxidisation (e.g. exposure to air) does not seem to be an issue – I don’t know of any cases of tyres being found to be rotten in NIB (new in box) kits or NIP (new in pack) spares. From this we can probably assume that UV is a bigger problem.
It should be obvious that this is a lot of theorising and informed guess work – obviously I didn’t start full testing back in the late 1970’s ;)
In general, I’d suggest that best thing to do with rotten tyres is to replace them with new old stock parts, or even tyres from re-releases, but in some cases that just isn’t possible – the Wild Willy and Lamborghini Cheetah for example – and sometimes, the cost is prohibitive – like vintage Sand Rover / Holiday Buggy rear tyres.
Tyre Types, and Overview of my Method
According to Tamiya, all their tyres (obviously excepting foam, and the short lived “Diplo” tyres) are “rubber like” rather than actual rubber - from this, and the lack of other information, we can assume that the formulation is proprietary – meaning it’s difficult to know what to use to re-invigorate tired tyres.
However, I have observed that tyres, broadly speaking – though there does seem to be a lot of variation in compounds, falls in to two types:
- “Rubber”: e.g. Wild Willy/Blazing Blazer, Sand Rover/Holiday Buggy, Sand Scorcher/Grasshopper, Super Champ/Hornet, Brat & so on – i.e. the very old cars, and their re-releases;
- “Plastic”: Hotshot/Bigwig etc, and the Monster Beetle, i.e. the “middle age” of vintage cars, later ones seem to have got a bit less plastic...
Regardless, both types dry & crack, and permanently deform under load – i.e. “flat spots” from sitting on a shelf.
“Rubber” can also go soft, swell a little & lose tread/sidewall detail, it tends to craze in a traditional rubber perishing pattern, with emphasis around the moulded details.
“Plastic” tyres tend to crack in a larger, more random pattern, breaking up into fingernail (or larger) size “biscuits” in extreme cases – especially on the Monster Beetle.
A bit of experimenting on my part has shown that whatever the compound, a sound process of preservation consists of:
- Thorough cleaning and drying;
Repairing any tears/splits (and curing time for the adhesive used);
Treating with glycerine and adequate soaking/drying time;
Improving the shape with foam formers if necessary, and improving the looks by lettering the sidewalls;
Protecting from further environmental damage and deformation.
Overall, this is not a quick process; or perhaps I should say that the longer you give it, the better the results. I’ve also found that tyres can continue to improve (especially firmness) for some time after initial treatment – tyres I’ve treated have been better 1 year after I’ve “finished”.
As a guide, the steps should take something like:
- cleaning & drying time – 1 day
gluing & curing – 1 day
glycerine treatment – 7 days
glycerine removal – 7 days
post drying time – 7+ days
lettering & paint curing – 1 day
... so I’d suggest allowing at least a month. In the case of most full restorations then, the tyres are something you should probably start on first.
This doesn’t have to be anything too involved... in fact I’d suggest the less elaborate the cleaning product the better – just give the tyres a soak in warm water to loosen any dried on smeg, then give it a scrub (both inside and out) with washing up detergent on a cheap toothbrush. Rinse thoroughly & allow to dry naturally overnight.
Cheap cyanoacrylate (superglue) is the obvious choice for rebonding any cracks in tyres – but I’d suggest you use something more flexible for longer lasting results, either a “flexible” variety of superglue, or a synthetic rubber glue – I’ve been trying out Stormsure “Black”.
Whatever you use, I’d suggest there are two main things to consider – firstly to prepare the edges of any cracks that go all the way through the carcass by gentling roughening with a small file or piece of wet & dry paper, and secondly, not to apply any more glue than you need – a pin can help you lay very small amounts of glue in the cracks.
Allow plenty of curing time – I’d suggest leaving the tyres overnight again, especially in the case of synthetic rubber glues.
Glycerine, also known as glycerol is an oily, sweet-tasting liquid principally used in the food industry as a humectant – a substance that helps things stay moist. On RC car tyres, not only does it initially replace some of the volatile substances that may have evaporated over the years, it can also continue to do so by sucking moisture out of the atmosphere.
It’s a by-product of the biodiesel industry so is cheaper and far more widely available than it used to be, although I am aware that its sale is restricted in some countries – this does tend to be in terms of quantity rather than a total ban though.
The basic idea is to wet your cleaned, dried, glued & cured tyres in the stuff, then keep turning/basting them for several days until no more can be absorbed. You’ll see initially that the tyres will repel the glycerine in places, but after 2-3 days they should begin to absorb it all over.
I’d suggest you use airtight containers at this point – glycerine is hygroscopic, and will take moisture out of the atmosphere, losing its viscosity over a day or two as it becomes more diluted.
How long you continue this process for is up to you, but I’d suggest at least a week.
At the end of this period, pour off the excess glycerine; if it hasn’t become discoloured or thinned out you could keep it for use on further tyres.
You can now leave the tyres uncovered, and over the next week (or more), check the containers daily & pour off any excess glycerine – this will be easier at it will get thinner. Turn the tyres over to allow even draining. The longer you can keep this part of the process going, the better, but at some point you will want to move on – blot up any remaining glycerine (especially on the inside) with lint free cloth – i.e. not cheap tissue.
Here’s a set of Sand Rover tyres that I started several weeks before the Hotshot tyres:
This is important: as glycerine is water soluble, getting the tyres wet (i.e. by using your RC car) will tend to mean that it’s sucked out of the tyres, rendering them less moist & flexible. On balance though, it really does seem to be the best thing to use.
Flat Spots: Foam Formers
Where glycerine treatment has failed to deal with flat spots in a tyre, I’d suggest stuffing the inner void with foam.
Once the tyres are properly dry and are fitted back on the wheels, lettering will improve the look of the tyres – and the car overall.
My preference is to use thinned down polycarbonate brush paint (e.g. Tamiya PC-1 white), applied with a small cross point jewellers screwdriver for tyres with larger lettering (Hotshot, Holiday Buggy, Brat etc), and a white paint pen with a tiny point (e.g. Pilot Super Color White with the EF “Extra Fine” nib) for finer lettered tyres (Sand Scorcher, etc).
From the list at the start of this piece you can no doubt see that the “best” storage conditions, for practical purposes, are when your tyres are protected from variations in temperature, have a comfortable humidity, avoid direct sunlight, aren’t subject to fumes, have nothing used as a dressing (with the exception of glycerine), don’t have to support the weight of the car (again, see later). This tends to mean a spare bedroom or converted loft are the best places, a garage or shed is probably the worst.
The only thing I can add to that is that to avoid further flat spots, your cars should also be elevated so the weight is taken off the tyres. I’ve seen various “stands” suggested, my preference is for Perspex tubes cut to such a length that the tyres are clear of the deck.
Written by TB member Jonny Retro