If I could leave 6 stars I would. Great! I am 183cm and 84kg and the large (L) is tight with a think under-armor base layer under it (probably like a think t-shirt). It stretches so it works perfectly with the think base layer. If I was just wearing this (like spring wear) the L might even be a bit loose/not race fit.
Size M for 173cm 68KG is good. Quality is perfect, warm enough for 0 degree with a base layer if you don't take a coffee break and keep moving. Very good seller.