Strong burning rubber smell

I ahve noticed after we've done some long hard drives that if we stop and get out we can smell a kind of burning rubber smell around the car.

Couldn't see anything amiss underneath. Was thinking maybe an exhaust mounting. It's not the same smell as burning oil on pipes.

Noticed it last year when we went to Ireland. Now in Wales we stopped on the way through Snowdonia mountains and it was like burning tyres!. Different to brake pads. Wheel bearings not hot.