Dealing with Tar Spots on your Wheels
Before you begin, make sure that the wheels have been thoroughly washed and all loose dirt removed.
You will need to purchase a good quality wheel cleaner like the Hot Rims All Wheel Cleaner from Meguiar's. You should ensure that the product you chose is safe to use on your wheel type as some cleaners can dull the look of alloy wheels. You will also need a good wheel cleaning brush and a soft cloth.
Firstly apply the cleaner to the worst affected areas of the wheel using a slightly dampened cloth. Leave to soak in for about a minute and then use the wheel brush to agitate the affected areas. You should find that most of grim comes off however there are sometimes a few bits remaining.
I find that using an old toothbrush and the wheel cleaner will eventually remove most stains but there will be a lot of elbow grease involved. Unfortunately in some situations if the stain has been left untreated for too long then there may be a slight mark left.
Finish with the cloth and wipe the whole wheel. Finally lightly rinse or wipe down with a wet cloth and then dry.
Now take a look a removing tar spots from your paintwork.