Yep, it's the wire wheel phenomenon! Seems they think they are propellers! However I had often wondered why is it that the off side wheel can suffer sometimes more than the near side wheel which is generally running in greater levels of water.I thought that perhaps the calliper pistons might be relaxing more on one side than the other and letting water sit there but no, the phenomenon continues. One day when I had nothing better to do and was tidying up around the place I came across a set of old disk guards I had for a Mexico which I had at the end of the 70's. the plastic type that stops brake dust getting on the alloy wheels. With a bit of modding I fitted it to the brake disc and despite the fact I really don't like taking my car out in the wet I waited for the next rain storm and took it for a blast.... The covered disc clearly didn't suffer with the problem and in heavy water when the problem showed itself the car only pulled to the right (protected disc) side. So it was clearly staying dryer. Now I at first thought that it was a hot disc sucking in water after a total soaking and a rapid cooling from same allowing water to flood in between the disc and pads, but I'm not sure how hot my disc's or pads get as I rarely need to hard brake so I reached the conclusion that the wire wheels just can and do give the disc's a thorough good soaking and its just hit or miss as to which side gets it! A quick stab and straight back on the brakes seems to have a clearing effect, a practice I have now adopted if ever caught out in heavier rain.
