So I’m planning on riding this weekend and its evident I’m not going to get longer thule straps in time. Any ideas on safely securing 27.5+ tyres to roof mounted carrier? Hopefully something that can be obtained at a local DIY as halfords didn’t seem to want to recommend anything helpful
Holding them is easy, anything from shoelaces to bungi things or ratchet straps will do just fine, just tie it round the rack not the wheel holder. Your bigger issue is getting the tyres into the rack if your rack has the standard wheel holders (which I assume it does given the need for longer straps).
Besides have you seen the forecast? “can’t get my bike on the roof” might be a blessing!