Potter's wheel? Russian to English

such a strange sentence. Небо is not in dative case as серому is. Are you sure you've wrote it correct?

you've written it correctly.
And not "written" in this context, but "copied."

thanks
was still sleepy

Could you give a bigger extract from the text?

The only weird spot in the original is that the words 'серому небо' don't agree grammatically. Whether they should agree (and it's just a mistake), or not, could be found out with more context.

So here's the whole paragraph.

Серафим еле успел подхватить подмышки Тудора, буквально выпавшего из велосипеда, и мужчины, - старый и молодой, - застыли в изумлении. А рядом с ними лежал, скрючившись, как старая молдавская акация, велосипед, и колеса его крутились, пустым своим верчением напоминая серому небу гончарный круг…

Here's a longer extract, but I'm not sure it'll yield more clues:

Дед, покачав головой, ничего не ответил, и стал нажимать на педали все сильнее. Гул послышался громче. Заинтересованные Тудор с Серафимом ускорили шаг и езду, и вышли, наконец, на край села. Здесь, за последним домом на небольшом, с пару квадратных километров, плато, они увидели двадцать сельчан… выстроившихся возле небольшой, но настоящей трибуны! На ней стоял приятель Серафима, Никита Ткач, и дирижировал. При каждом взмахе руки он что-то выкрикивал, после чего собравшиеся проговаривали хором несколько фраз. Причем, что было удивительно, - поскольку остатки сельской библиотеки сельчане пропали под снегом, ветрами, палящим солнцем и дождем еще лет десять назад, - каждый держал в руке по книжке! По целой, и новой на вид книжке! Было понятно, что творится какая-то непонятная чертовщина…

Серафим еле успел подхватить подмышки Тудора, буквально выпавшего из велосипеда, и мужчины, - старый и молодой, - застыли в изумлении. А рядом с ними лежал, скрючившись, как старая молдавская акация, велосипед, и колеса его крутились, пустым своим верчением напоминая серому небу гончарный круг…

- Камень, - кричал Никита Ткач, - это…

- Снаряд для игры, - ревел хор, поглядывая в книги, - весом 19,960 килограмма и диаметром 31 сантиметр!

- Внимание! - поднял руку Ткач. - Именно 31, а не тридцать, или, к примеру, двадцать девять! Будьте внимательны к мелочам, ясно?

1. You've made a copy error in your original post: it should be "серому небу", not "серому небо"
2. You understood correctly, it is indeed saying that it "reminded the grey sky of a potter's wheel." The point is that Tudor and Seraphim are so astonished by what they see that they've completely forgotten everything else.Tudor is so astonished that he forgot to ride his bike, "literally fell out of" it. No one is looking at the spinning wheels of the bicycle (except the indifferent grey sky).

серому небу. You catch a mistake while copying :)
It is easy: "напоминая серому небу гончарный круг" means that grey sky looks on bicycle as on potter's wheel.

Either it should be like "пустым своим верчением к серому небу напоминая гончарный круг" Its wheels went round and round, and their pointless spinning directed to the grey sky reminded of...
Either the sky is able to recall things according to the author :)

You're not missing anything, the sentence makes perfect sense, but it should not be translated literally. Try to visualize the scene as if watching it in a movie: at the beginning, we're observing the events as participants, with the human eye, but then the shot suddenly changes, and the lying bicycle is perceived from above. It is from above, from the grey sky, that the bicycle resembles a bent tree and its spinning wheels resemble a potter's wheel.

Just my two cents in addition to the above remarks:
Whoever the author of the text is, I think this particular phrase is an example of grammatically incorrect and somewhat mixed up Russian language.
I would accept in the original "showing to (towards) the grey skies", but not this "reminding to the grey sky".
Unless the author tried to imply that some gloomy gods are watching from above... Anyway, I wouldn't translate this literally.

I am royally amazed that two native Russian speakers failed to understand a Russian sentence that is just slightly elevated over the daily level of common discourse. It tells us something about the current generation! In fact, it is rather typical to Russian literature to personify nature or its particular objects. In Russian poetic, imaginative speech, not only the sky can be reminded of something, but trees can be upset, stones can watch you, and clouds be angry with you. This is perfectly normal, rather straightforward Russian literary text. You did understand it correctly, and most people clarified the meaning further. It is also implied that the grey sky is eternal and has seen many things happening underneath, and potter wheels that it (the sky) used to watch for millenia are a much more familiar sight then bicycle wheels that have only been around for merely 150 years, a blink of an eye for something as ancient as the sky over our heads.