Spring (<13C) – 3/4 roubaix bibs and an endura jetstream jersey, it’s it’s a bit nippier (<8C) maybe a very thin baselayer under that.
Cold (<6C)- As above but with a merino Ls baselayer, if it gets much colder (0-3C) swap to long john bibs with thicker roubaix fabric.
Bitterly cold – as above but swap the jetstream for a softshell.
My general tips would be:
Think carefully about what each layer does, it’s not always obvious.
*Base layers can either be lycra based or polypopylene (or something natural). If it’s Lycra it’s drying and cooling, if it’s polyprpylene it’s drying and warm. Same applies to any layer, super expensive winter gloves are great, but if they get soaked a £2 pair of fleece gloves from decathlon will stay warm even when soaked.
*Mid layers need to add insulation but also need to breath
*Outer layers need to be windproof or waterpoof as appropriate. But rarely offer any insulation.
So wearing a windstopper type jersey under a waterpoof all day is expensive and pointless. As are lycra baselayers in winter. But a lycra baselayer under a windstopper jersey will allow very effective temperature regulation if you open the zip, but will otherwise leave you feeling clammy and wet.
Spare stuff for the extremities is useful to carry. Even with waterproof boots a spare set of waterproof socks can save a ride if you missjudge the depth of a ford in January. Ditto gloves. The cheap £2 fleece gloves form decathlon are pretty rubbish, but they do stay warm even when soaking wet and dry out quickly. I had a ride in the Dales before Christmas that went from a pootle to ‘f*** this, it’s getting dangerous’ after getting washed away by what was supposed to be a small stream that turned out to be 3ft+ deep. Didn’t take my own advice and had a very cold and exhausting 15miles back to the car. Wasn’t life threatening but if it had been another hour then it could have gotten serious.