Wire Wheels
Background
I thought I knew a bit about wire wheels but when I started looking for information on this topic. I found out how little I did know. This article will start from the basics and hopefully fill in a few gaps as we go.
History
Wire Wheels were invented by engineer George Cayley in 1808. Although Cayley first proposed wire wheels, he did not apply for a patent. The first patent for wire wheels was issued to Theodore Jones of London, England on October 11, 1826. Eugène Meyer of Paris, France was the first person to receive, in 1869, a patent for wire wheels on bicycles. As you can see they have been around for a while.
Bicycle wheels are not strong enough for cars so auto use had to wait for the invention of the tangentially spoked wire wheel. This design called the Rudge-Whitworth patented detachable and interchangeable wheels was designed by John Pugh in 1907. We will explain tangentially later in the article.
Advantages
Why wire wheels? There are three reasons.
- Weight. Wire wheels were developed because they were lighter for the same strength than other wheels of the time. Of course, now alloy wheels are lighter for the same strength.
- Ventilation. They allow more air to circulate around the brakes. Remember, when they were developed, brakes were all drum brakes.
- Looks. They look sexier than solid wheels.
Basic design
The easiest way to explain is to use some diagrams. I will explain each component as we go.
In theory, a wire wheel could support a static vehicle with one spoke. In the diagram, the yellow spoke is attached to the wheel at the top. It is attached to the hub at the bottom. The car (which of course is attached to the hub) is suspended from a single spoke.
An obvious and key point is that wire wheels work in tension rather than compression. The weight is taken by the spokes that are being stretched rather than squashed.
Also, note that there are two circles on the hub. The inner hub has long spokes that attach to the rim and ensure the rim is circular rather than oval.
The next thing to look at is how the rim stays round, not oval.
In the example, there are only four spokes. By tightening and loosening spokes, the rim can be moved left, right, up and down. The idea is to move it so that is both circular and has the same centre, as the hub. If not, the car will bounce along as the wheel turns.
If the wheel is not circular, and the horizontal diameter is less than the vertical diameter, the answer would be to tighten the vertical spokes. You also need to loosen the horizontal spokes otherwise it will bulge between the spokes.
Rotational forces
If the wheel were just holding up the car, a set of straight spokes would probably suffice. Another thing the wheel must do is handle acceleration and breaking.
If a car accelerates, the hub rotates – in this example clockwise – and the tyre and rim want to stay still. If we relied on only straight spokes as in the initial section, we would risk breaking the spokes or distorting them.
This is where tangential spokes come into play. The trailing spoke (because it slopes backwards) from the hub is more able to take the twisting force of the hub and get the rim to follow.
The term “Tangentially Spoked Wire Wheel” refers to the spokes that are aligned as a tangent to a hub (or in that general direction) and transfer the turning motion to the rim.
If the same spoke was used to handle the load of breaking, it would not work. It would be in compression and bend.
in that diagram, the hub is dragging the rim and tyre in the opposite direction. Think of it this way. All is in equilibrium and the car is travelling towards the right of the diagram. Hub and rims are travelling at the same speed and there is little attempt by one to turn at a different speed to the other.
The brakes are applied. Now the hub is trying to rotate anti-clockwise in relation to the rim. The rim wants to keep going at the same speed, but the hub is trying to slow it down. The force is the opposite to acceleration. The red or leading spoke now takes the load to slow down the rim and tyre.
If you put it all together, you have the long spokes from the centre of the hub which keep the wheel round and centred, and two tangential spokes (the leading and trailing spokes) handling breaking and acceleration. In this case, there are groups of three spokes. The diagram is exaggerated in size in order to simplify understanding.
Lateral stability
The best way to describe lateral stability is to imagine a wheel made of thin sheet metal. It might stay round, and it might support the car, but if you grasp it at the top and bottom, you can wiggle it. How does the design of a wire wheel provide lateral stability?
The power of the triangle. The two short spokes – leading and trailing spokes – form one side and the long spoke forms another. The hub is a rigid attachment point.
The rim cannot move left or right on this diagram unless something bends or flexes. The wheel is laterally stable.
Lacing
What I have described is a basic wire wheel. In this wheel, there are 48 spokes. These were the original TR wheels which we curse because spokes keep breaking. The 48 spokes are divided into groups of 3. There is a long spoke, a leading spoke and a trailing spoke. There are 16 groups of 3 spokes distributed evenly around the rim. They are referred to as single laced. The spokes all end in a single row on the rim. In other words, the dimples are on a single line drawn around the inner circumference of the rim.
48 spoke wheel
For years this was the standard but an MG TC (sometimes described as a coffin suspended by four harps) and a sports car of the 60s were different beasts. Eventually the 60 spoke double laced wheel evolved. This wheel has a second row of dimples running around the rim. It is far stronger than might be expected with the addition of only 12 spokes. The wheel is double laced as the spokes run from outer ring of dimples on the hub to the inner ring on the rim. They also run from the inner ring on the hub to the outer ring on the rim.
You can think of 48 spoke single laced wheels as having a “V” configuration. The tops of the “V” are the inner and outer rings of spokes on the hub. The point of the “V” is the single row of dimples on the rim.
Think of 60 spoke double laced as an “X”. One leg of the “X” has 40 spokes from the inner row on the hub to the outer row of dimples on the rim. The other leg has 20 spokes from the outer row on the hub to the inner row on the rim. They cross over one another.
60 spoke wheel
Photo source: Ebay
Photo credit: Moss Motors
Finally, we get to 72 spoke wheels.
It uses the same pattern as the 60-spoke wheel but instead of 20 outer spokes and 40 inner spokes, it is 24 and 48. It squeezes a few more spokes into the wheel.
Finally, there are triple-laced wire wheels.
The one on the right is a 17” x 7” 100 spoke, triple-laced wire wheel. As your head has probably exploded by now, I will not attempt to describe the lacing pattern. Just imagine your TR with 17” x 7” wheels.
Photo credit: Truespoke Wire Wheels
Summary
Wire wheels have been around for over 100 years and from bicycles to cars to motorcycles have supported us as we travelled around. They look great and stamp the era from which sports cars were built. They are a pain to clean, but would you give them away? I wouldn’t.