Says it's pH neutral on the carton.
As a Foaming pre-wash is not strictly a cleaner or the 'wash phase', it shouldn't be acid or alkaline. Cleaners that are that caustic are generally wheel cleaners anyway (I wouldn't put any of those on my wheels either). Detergents are roughly pH neutral. I only use detergents and in different concentrations for different parts of the van on an 'as required' only basis e.g. ... as I clean the wheels very regularly and the van doesn't get particularly heavy use, Autoglym Bodywork Shampoo at bodywork dilution cleans the wheels perfectly well, so I avoid the dangers of unnecessarily using caustic products with their associated side effects.
.