Race suits that are sized XS, S, M, L, XL or XXL fall into the striped bands in the size charts. If ANY of the sizes you come up with when measuring parts of your body are on the limit of, or go over the size range you need to move into the next row below. So, even if all your sizes fall in the size 56 row except for one, for example, you need to move down into the next row, suit size 58, to ensure the correct levels of comfort and to avoid having any restricted movement.
All measurements should be taken on your actual body and measured with a fabric tape. Record the actual measurement, don't add any girth for comfort, the manufacturers have allowed for this in their size charts. Remember not to assume your trouser size is your waistline size, the waistline needs to be the largest circumference around your middle, similarly, the chest size needs to be the largest circumference around your chest or the largest breast circumference for ladies.
Please be aware that all these different suit brands are not the same as each other, You NEED to take measurements of your body as stated above and then decide on the correct size, using the relevant brand size chart. DO NOT assume that because your last suit for example, was a size 56 from Alpinestars, that you will fit a size 56 from Sparco, this WILL NOT be the case...