Locomotive Driving Wheels

<...It would seem logical to have a solid wheel without spokes because it would be easier to manufacture without spokes....> These days, yes. However, the steam locomotive as a concept is older than Henry Bessemer's blast furnace of 1859, before which steel was not available in any significant quantity. Robert Stephenson's "Rocket", the original of which resides in London's Science Museum [free admission as of July 2016] in the "Making of the Modern World" gallery, had wooden, spoked, wheels with a wrought iron tyre, because that was the only way of doing it in 1829; the earliest surviving locomotive, William Hedley's "Puffing Billy" of 1813, which stands nearby Rocket in the same gallery, had smaller wheels that were cast iron and the main frames were two baulks of timber! The technology just filtered through from the road stage coach and that was the only way to manufacture a wheel of Rocket's diameter at that time.

It is easier to cast a steel wheel that is spoked than solid and easier to fit-up balance weights to offset the reciprocating masses on a spoked wheel than a solid one; balance weights reduce the impact of the locomotive's travel on the track and sub-structures and more often than not are boxes held on with rivets.

In the UK, a certain Mr. Oliver Bulleid, the Chief Mechanical Engineer of the Southern Railway company, introduced the "boxpok" solid wheel to steam locomotives of the "West Country" and "Battle of Britain" small 4-6-2s, the "Merchant Navy" 4-6-2s that were a bit bigger, and the Q1 class of 0-6-0 goods engines that, because of their ungainly and revolutionary appearance, were known as "charlies". The boxpok type of wheel was an American invention that appeared on the Union Pacific's massive "Big Boy" class of 4-8-8-4s, among other monstrosities from that country. Mr. Bulleid's inventions were a bit wacky, incorporating features not otherwise seen on British locomotives, with many of them being rebuilt more conventionally after nationalisation in 1948. Following trials with one of his experimental "Leader" class locomotives, Bulleid disappeared off to Ireland, building some amazing locomotives that burnt turf as a fuel, incidentally.

As the locomotives started going faster, the counter balance mechanism became more critical, and of course anything to reduce weight would be a plus by minimizing wear of the track surface...

I think it also involves the processes associated with casting a wheel. I suspect that a 'spoked' wheel is easier to cast, cools quicker, and is stronger than a solid wheel.

Then the counterpart question arises: Why not make all railcar wheels spoked?

Cost of manufacturing. Solid wheels, whether cast or forged, are cheaper to produce. They've been made in the millions. And only drivers on steam engines need counterbalancing. With diesel none have spokes.

Hooker

Agreed, but I was following someone's prior rationale, albeit somewhat facetiously.

London Transport's "A stock" electric trains had spoked wheels when originally built.

I stand corrected. However with commuter light rail weight is perceived to be more important.

Hooker

Steam loco driving wheels also have separate tyres[tires], usually of steel, that are manufactured slightly smaller than the wheel. Fitting is interesting: the tyre is heated, the wheel lowered into it, then as it cools it shrinks onto the wheel. Fitting a tyre means that when the tread is fully worn, only the tyre requires replacement.

I would think it would be the same to shrink a tyre onto a solid steel wheel. My thinking is; it is a case of tradition. Wagon wheels were spoked. Track gauge was adopted from Roman wagon wheel tracks. So it appears there is no real reason for spoked wheels. Automobile wheels is the same. They started our as spoked, but now are disks. Spokes look nice, but are they really necessary?

Many wheels for modern "performance" cars are now esentially spoked. Look at the modern alloy rims with only five cast spokes from hub to rim.

"Everything old is new again".

I think one of the important advantages on spoked wheels for "performance" cars is improved cooling of braking rotors.

Reduced wheel/tire weight is also an advantage when considering suspension performance.

Weight, ease of balancing, cost of steel required come to mind

I also believe that a spoked wheel is stronger.

Okay....then why aren't all wheels spoked?

Most likely any advantages of the spoked wheel are outweighed by the cost of the complicated casting.

As another poster noted, only the drive wheels of steam locomotives subject to lateral force from the connecting rods are spoked; leading and trailing trucks are not.

ICE crankshafts, which also are subject to lateral forces of pistons are also counter-weighted.

Back in steam locomotive days, the wheels were all cast, today they are forged. It was a material saving thing to have the spokes, unlike today's method where it is more difficult to forge spokes than sold items.

Wheels are forged these days. Since they don't build steam locomotives any more, there is no need for spokes. All railroad wheels for cars are in the 33" diameter range and are all forged. Going back to the steam era, what would have been the advantage of spokes vs solid? For automobiles, spoked wheels are a cosmetic feature and also a means to reduce sprung weight. On a locomotive, there is no sprung weight to be concerned about. A solid wheel can be counterbalanced just as easily as a spoked one.

As I stated previously, I suspect spokes on locomotive wheels were a carryover from carriage wheels; tradition is a British thing. The 4' 8-1/2" track gauge was probably the same width as the carriage wheels.

Noticed my typo "sold" versus solid. And yes, although it's been a long time since I "worked on the railroad"(actually road bed maintenance equipment) 33" is the most common wheel size. Only other size that really comes to mind are 30" used in Newfoundland and Labrador. If you have ever had the opportunity to watch the wheel sets being made, it is quite an interesting process. Interference fit of the wheels to the axles and then the bearings as well. Both the wheels and axles are balanced separately prior to assembly.

I think you are correct with your "it's the way we always did it" for spoked wheels.