I meant no scapes or bulges from curbing I appreciate they not new but might be of use to somebody.
Sorry I did not try to mislead . I’ve modified the post.
When I advertise tyres I never list the best measurement, you always advertise at the lowest point. So this is probably what the OP has done.
5mm may be like... 45% worn going by your calcs but in the real world 7 or even 6mm is seen as nearly new. So 5mm still has plenty of life/use.
I’ve sold surplus tyres with around 3mm tread. So that’s probably something stupid like 85% worn. Still a market for them tho.
OP, I’d advise listing on other platforms like Facebook. You’ll find a buyer pretty quick at £50 for a pair. You may struggle on here, predominantly because the Z4 is a ‘performance’ car. So many will want to choose premium or mid-range over budgets!