Mixing summer and 4-season tyres?

[Stratman]

I have summer Continental Contacts front and rear, but the rears are nearing the end of their life and one of them has a very slow leak as well. I'm pretty much decided on getting all-season tyres but as the fronts have lots of tread left, is it a complete and total no-no to just replace the rears with all-seasons and leave the fronts for now?

 

[effbee584]

The recommendation for full winter tyres is for all 4 only, I doubt its the same for all-season, but speak to a tyre supplier.