micro cracks on road bike tyres

They’ll be fine

No, I wouldn’t ride on those the cracks are a sign of age and possibly sun damage. There’s enough risks in life without adding to them, you might get away with it but you might not.

I'm not sure I'd be riding those, certainly not on a road bike where a failure may result in a face to tarmac interface.

Michelin ?  Found mine did that with age. Binned and got new. The rubber hardens and you don't get the same grip.

After having a look on a larger screen - DO NOT ride on those tyres, any advice otherwise is irresponsible in my opinion. Some of the tread has actually de-laminated and fallen off. All tyres, irrespective of manufacturer deteriorate with age, keeping them cool and dark helps slow the process.

How far you riding? If nothing else, they're gonna be more prone to punctures than not cracked ones...

But I noticed the same on my 2 road bikes, both need both tyres cracking. My question is, they've been stored in the same place as (and for less time) than my MTB, but my MTB tyres are fine. What's the difference - difference compound??

Depends on how far you plan to go, but I'd probably throw caution to the wind and ride them.

Maybe go for a quick spin around the block first to see if you die or not.

thanks all! well the new tyres arrived & I've fitted them - tubeless (not sure if that made the original situation better or worse) and the cracked ones are now in the bin!

If nothing else, they’re gonna be more prone to punctures than not cracked ones…

this was partially my thinking (as well as getting a terminal case of death from a blowout) as wouldn't want to keep slowing up the group ride with punctures!

Michelin ?

Schwalbe.

I would have ridden them and kept them on without any concerns!  Continental 4 seasons always looked like that after not very much use

They're fine! My commuter is far worse than that and never punctured.

I'd not ride that on the front wheel down hill at 50mph, on the rear probs, for slower flatter stuff defo