Motorcycle Modification is an importantpart of the total experience for many motorcyclists either in the search forindividuality, to make improvements or to make the machine more suitable fortheir use.  It also supports a wholeindustry of parts suppliers, modifiers and manufacturers as well as providingthe opportunity for all types of individual effort. All types of modification have one thingin common, the overriding need to see that the change does not make the machineless safe to ride than the original. This book proposes a simple method,based on long established aircraft and aero engine practices, of reviewing anyintended modification at an early stage so that any potential safety problemscan be avoided. The book is more than just a basicmanual and incorporates many memories from a long career, various related andunrelated thoughts and a few original and possibly controversial suggestionswhich occurred to the author at the time of writing. It invites the readers toeither agree or disagree with any or all of these deviations from the basic method. The book avoids much engineering theoryto ensure that it is readily understandable to those motorcyclists who do notclaim to be professional engineers but are contemplating modifying theirmachines or are just interested in all thing mechanical. Originally published in 2020, theopportunity to produce a 2nd Edition has allowed it to be updated to 2024.  During that time I have concentrated onconversion of two wheeled machines into three wheelers and have learned a lotabout the practical problems of this type of modification. The 2nd edition has providedthe opportunity to add a new section in the hope of helping anyone thinking of doingthis type of modification to avoid many of the problems with this type ofchange. Forward into the future but notforgetting lessons learned from the past. What-ever projects come along, theprinciples of failure analysis which are the basis of this book will remain thebest way to ensure safety.