If your fastidious with your alloys then it really is worth investing in a few Wheel Woolies brushes of various shapes and sizes. http://www.cleanyourcar.co.uk/wheels-and-tyres/wheel-woolies-wheel-brush-kit/prod_1037.html
http://www.cleanyourcar.co.uk/wheels-and-tyres/wheel-woolie-spoke-back-brush/prod_1252.html
Soft, synthetic wool brushes that hold loads of suds mounted on long, flexible nylon handles. They easily reach right through the barrel to the inner rim and the cranked brush gets behind spokes and round calipers etc. Three different sizes squeeze in most nooks and crannies. Not cheap but I've had mine for a couple of years now and still going strong.