There used to be a 29cm wheel which was a good compromise between 28 and 30cm
That was the original karlie wood wheel that had struts (issues with those with hamsters having bleeding feet so the cork ones became more popular). Tbh a 28cm wheel should be big enough for syrian hamsters. Before the silent runner came along, the two most popular wheels were the 28cm plastic trixie wheel, the 27cm wodent wheel and the 29cm wood karlie wheel. While the 27cm wodent wheel might not be big enough for a large syrian, I think most 28cm wheels should be. Although they can run in larger wheels.