P21S Gel will stay wet for a long time. Spray your rims and let them sit for even an hour. Just make sure the solution doesn't dry, keep re-applying chemical if necessary. If that doesn't work you can try a little bit of old clay you don't care about anymore. Last resort is an acid based cleaner. Acids attack metal, all metal. The acid goes to town on the metallic brake particles that have attached to your wheel under extremely high temperatures. Always spot check new chemicals in a small area out of sight first to make sure that there is no unwanted reaction.