A wheel (cakka) is a flat circular object that turns as it moves and is considered one of the most ground-breaking inventions in the history of technology. The ancient Indians used the wheel as a symbol for political sovereignty and dominion. The first Buddhists used it as a symbol for sovereignty too, but for spiritual rather than for worldly and political sovereignty. As most meditators will know, the Buddha’s first discourse is called ‘Setting in Motion the Wheel of the Dhamma’ and a wheel flanked on either side by a deer has long been a symbol of the Buddha’s teaching this first discourse in the Deer Park at Sarnath. The Buddha sometimes made elusions to the wheel in his discourses; for example, he said: “Generosity, kindly speech, doing good for others and treating them with impartiality are to the world what the linchpin (ani) is to the wheel, keeping it turning smoothly.”
Some modern commentators have gone further than this, ascribing meaning to the different parts of the wheel. According to this approach, the rim of the wheel (mukhavaṭṭi) supposedly represents movement or progress, the hub (nābhi) represents the coming together of multiple things into a unity, and the spokes (ara) represent the Noble Eightfold Path. As for this last point, depictions of Dhamma wheels today, almost without exception, show them with eight spokes supposedly to represent the steps on the Noble Eightfold Path. Further, these modern Dhamma wheels are usually shown like the steering wheel of a ship, with rounded grips on the outside of the rim extending from each spoke. Such a ‘nautical’ Dhamma wheel may well be able to turn, but it could hardly roll forward, which is what it is said to do. Such Dhamma wheels only started to appear in the 20th century.
An examination of some 300 images of ancient Dhamma wheels on Google Images reveals only one with eight spokes, on a gold coin from Afghanistan, circa 100 CE. Unfortunately, this beautiful object was melted down by the Taliban in 2001. 
Did the Buddha have anything to say about what the Dhamma wheel should be thought of and envisaged? Indeed, he did! In his first discourse he said that each of the Four Noble Truths “was realized,” “can be realized,” “will be realized,” and thus they “are turned in three ways making the sum of twelve” (tiparivattam dvadasakaram). So, it could be expected that Buddhist wheels would have twelve spokes, although few in early Buddhist art do have this number. But in the Mahāsudassana Sutta of the Dīgha Nikāya, the Buddha called the wheel either the Supreme Wheel (brahmacakka) or Highest Dhamma Wheel (anuttaraṃ dhammacakkaṃ) adding that it was “a thousand-spoked” (sahassaraṃ). Consequently, for about the first 800 years, all Dhamma wheels were depicted with multiple spokes which were clearly meant to represent a thousand.
The earliest known depiction of a wheel in a Buddhist context is on the capital of King Asoka’s pillar from Sarnath, which has 24 spokes. In comparison, the numerous Dhamma wheels depicted on the gateways of the Sañchi stupa have between 16 and 32 spokes (the 16 Arahants described in Mahāyāna Buddhism and the 32 marks of a Supreme Being?). A Dhamma wheel from the great stupa at Kanaganahalli in South India has 28 spokes (the 28 Buddhas before Gotama?) and others from Amaravati dated from around the same time, have a generous 65 spokes (possibly an attempt at a thousand spokes?). It is clear from all this that the number of spokes on Dhamma wheels was rarely meant to symbolize any Buddhist doctrines and that the great variety suggests that even if some numbers happen to coincide with some numerically expressed doctrine, it is probably just a coincidence. This begs the question: Is the number of spokes on the Dhamma wheels important? Probably not. But maybe we must not assume that how we see and interpret some aspects of the Dhamma today is the same as our ancient Buddhist predecessors did. Further, it’s easy to get involved in concern over symbols and cultural expression to the degree that less attention is given to the essentials such as virtue, wisdom and meditation.