How dangerous is a screw in a good trye??

[rufusgti]

I collected my car from the garage earlyer and was informed i need to get my tyre changed ASAP as it has a screw stuck in the tread.

I have a spare in the boot and am happy to change a wheel at the side of road if needs be.

I also usually have screws in my tyres, no idea where they come from but when I've had tyres changed before they often say "OOOH, you were lucky, you had a screw in that one" and I've noticed them on loads of other cars.

Were obviously told they're dangerous so we go and buy new tyres but really, How dangerous are they. I dont know the answer, but all my punctures have been from either hitting something in the road, hitting a curb, Old knackered/perished rubber, or having them slashed. Never because of a screw.

Now i know if it was running low pressure it can be dangerous but this tyre isnt. Just has a screw in the rubber tread. How "dangerous" can it possibly be??