Here in Portland exterior car washes do not use tire brushes as the operators do not like to cut the conveyor rails for fear of cars jumping the conveyor as many of the washes here run at very high speed.
With a good chemical; blasters and 4 passes with Rocker Panels the washes get a very clean wheel. Perfect? Not in all cases, but at $5.00 a wash you are not selling "perfection" you are selling value.
You might take a look at Kaady Tire/Wheel/Body chemical, it is a multi-purpose chemical that does a great job on wheels.
When I operated Cuzzin's Car Wash, a 100' exterior wash we had only high volume side blasters; 4 rocker panel passes and used TWB and got very good wheels. At least we never had anyone complain about the wheels and I know it had a lot to do with the chemical we used.
Regards
Bud Abraham