Dainese Men's D-Air Smart Jacket Sizing

There is a reasonable degree of expansion in the Smart Jacket, and it should fit under / over most items based on your standard chest size. The only variance could be over a big, bulky touring jackets, for example. If you are planning to wear the Smart Jacket under your riding jacket, measure your chest size first wearing what you will wear when riding (base layers, t-shirt, fleece, etc.). If you are planning to wear the Smart Jacket over your riding jacket, measure your chest over the jacket.