Thank you for all the replies. Also BIK_116.80 - many thanks for the erudite explanation. Years ago, there was a Boeing statement that it was OK to use reverse idle (B737-200) where tailwind taxying was involved. This was an invaluable technique where long taxying distances often caused increased wheel brake temperatures. With no brake temperature gauges it was impossible to accurately judge the amount of heat build up. If wear and tear figures were available for thrust reverser operation, we never saw them.