Try hot water(hotter the better) with a squirt of washing-up liquid (even cheap brands) will shift those stubborn marks. I've been doing in for years and it works better than many wheel cleaner sprays...BUT you must rinse it all off soon after with lots of plain water as the washing-up liquid can eat into the laquer or alloy coating.
Here's a handy tip for those grubby alloys...
Try hot water(hotter the better) with a squirt of washing-up liquid (even cheap brands) will shift those stubborn marks. I've been doing in for years and it works better than many wheel cleaner sprays...BUT you must rinse it all off soon after with lots of plain water as the washing-up liquid can eat into the laquer or alloy coating.