"No problem. It does darken the sidewalls a bit, but they stay clean in the long run. As I'm typically looking to get a few years out of Challenge tubulars, I have always done this in the past.
BTW, those brushes (or those like them from auto…"
"Shaun - are they coated with aquaseal?
Either way, a gentle soap like diluted simple green and a natural fiber brush (like those available at theservicecourse.com) are a good bet to get anything off that hasn't seeped into the fabric.