As the inexorable rise of the bicycle continues, many casual cyclists are moving into a more serious brand of cycling, riding in road races, groups or in cycle clubs--and stumbling straight into a minefield of etiquette. From how to wear your socks, to the position of your tan-line, to the eternal quandary of leg-shaving, there are things that any serious cyclist should know. ''The Road Cyclist's Companion'' covers all this and more. Divided into chapters covering kit, bike, group riding and training, it imparts all the essential knowledge that those who have grown up in clubs instinctively know. Peter Drinkell, author of ''The Bike Owner's Handbook,'' writes clear, accessible text, which is accompanied by beautiful photography and illustration. Interviews with pro-cyclists, clothing designers and established figures in the field add further attractions for the true enthusiast.