sd card size

Hi I'm waiting for my new dashcams to arrive and was wondering what size sd card I should go for? As its a front & back would I need 2? Also is there a certain class I should go for? Any advice?

Hi all, What's the optimum size of SD for a dash cam? 32Gb and 64Gb are common - is the 64Gb really essential, or is 32Gb fine? And does it need to be a high write intensity card, or is that just a marketing gimmick? Thanks for your input!