08-06-13, 11:37 AM
Every bike shop I've ever worked in has had a pretty even consensus that even on z rated tyres mushroom plugs are o.k., up to 2 in any one tyre, all other things considered. I'm betting that, even though most people who work in bike workshops have just learnt their trade over time without any "official" qualifications, the tyre manufacturers would include them as experts! Whilst some are more knowledgable than others, I've worked with enough very experienced people to trust the two-plug-per-tyre line.