Replacing old scuffed wheel for the new spare: different treads help

[172saints]

Last service was only a few weeks ago, have 4mm up front tread wise.

the front nearside wheel is scuffed badly (previous owner)

i would like to change it for the brand new un-unused spare wheel... but the tyre is brand new 7mm

Is it dangerous? have any after effects? 1 front wheel with 4mm and the other brand new

Cant swop fronts with rears as both rears are 2.5mm! Thanks

 

[Fred@BTM]

have the tyre swapped from the curbed wheel onto the spare?????