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This article attempts to explain the most common method of mounting rubber tyres on radio controlled model cars.
The information in this article is based upon my knowledge of the large scale wheels & tyres and the images used throughout the first part of this article are ones based on large scale wheels and tyres, but they are identical in their basic design principles to most of the other scales' wheels & tyres. |
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| The Wheels and the Tyres |
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Remote controlled model car wheels and tyres come in many shapes and sizes, but the majority of moulded rubber tyres use a wheel similar to the one on the right that has moulded channel in it that accepts a tyre that has a lip section moulded onto the bead area. Obviously there are differences in the proportions of the wheels and tyres, but they all share the same basic design principle in the mounting of the wheel.
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| Foam Liners |
| Although the tyre can be mounted onto the wheel by sliding and/or stretching just the tyre over the wheel and then gluing the lip on the tyre into the channel in the wheel, usually a foam liner is used on the on-road cars. |
| As model cars don't currently use true pneumatic tyres, (although I wouldn't be surprised if one is manufactured in the future) foam liners are used in between the wheels and tyres to simulate the stiffness that air pressure gives in their full size counterparts. Liners are usually available in different hardnesses, (which can be quoted with a Shore rating - see glossary left) which allows you to alter the tyres handling characteristics. They can be either glued to the wheel or the tyre and are supplied in two different formats which are discussed below. |
| Ring or Donut Type Foam Liners |
The tyre liner can be supplied in the form of a ring of foam (right), but are sometimes refered to as donuts.
Ring type liners have the advantage of being cut to size and therefore are easy to fit. The disadvantage of this type of liner is that the corners (both inside and out) are not shaped and will usually require trimming so that the tyre is not deformed and/or the hardness of the foam does not increase as it is forced into the corners. |
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| Strip Type Foam Liners |
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Alternatively liners are supplied as a strip of foam (left) and have the advantage of being machined to fit the outer profile of the wheel and the inner profile of the tyre.
The big disadvantage the strip type foam liner has is that you have to join the foam into a ring, which can create problems due to the type of adhesive used to join the foam. |
| The ideal adhesive to use to joint the foam is one that does not alter the density of the foam. If an adhesive such as cyanoacrylate is used then the foam in that area becomes almost solid. The rotating tyre will then have a hard spot, which will make the wheel/tyre bounce, as well as creating heat build up in that area of the tyre. In extreme circumstances this heat build up can lead to the failure of the tyre. Also inexperienced users sometimes have problems cutting the liner to size and can finish up with a pair of tyres where one is effectively harder than the other, as the foam has been cut to different lengths in each tyre. |
| The Wheel & Tyre Assembly |
You can clearly see the benefits of a properly fitting liner in the cross section of the wheel and tyre assembly on the right.
This is especially true when a particularly hard grade of foam is used to make the liners. |
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| Fitting Tyres |
Tyres can normally be fitted with your bare hands, especially if some form of lubricant is used to ease the tyre over the foam. The large scale tyres are somewhat stiffer and can more easily be fitted using a dedicated machine.
The fitting machine shown on the right is made by KP Designs, who were the first to design and manufacture this type of machine for the large scale cars. |
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| The KP tyre fitting machine is easy to use and involves placing the wheel (with foam glued in place) on the main post and then stretching the tyre over the top of the the wheel and the outside of the metal spike. The tyre is then rotated as it is pressed down to ease the tyre fully over the foam liner and into place.The tyre can then be glued up ready for use. |
| Preparation |
| Plastic wheels, like other parts of a model car, are injection moulded and certain chemicals are used as release agents to help in removing the moulded wheel from the die that is used to form the shape of the wheel. As these chemicals are designed to stop the plastic sticking to the die, they will also to a certain extent, stop the tyre from sticking to the wheel. |
| Therefore either a solvent or an abrasive is is required to remove these chemicals so that the glue can perform as expected. |
| Summary |
| This article will be extended to cover other tyre mounting methods and tyre construction methods in the future. |
| Many thanks to Keith Plested of KP Designs for allowing us to use the image of their tyre machine. |
| Further Information |
| If you have any comments or suggestions about this or any of the other R/C car content on the RcTek site, please feel free to ask them on our On-line Forum |
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| Unless stated otherwise all images and content are Copyright (c) RcTek 2000/2001 |
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