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We have a japanese import 2003 Mazda Demio that we got at the end of 2011, it came with a space saver and I've noticed that when I fill the tyre to the specified 60psi it immediately drops when read to about 55psi.

I have just confirmed this behavior at the service station, using their machine I filled it to 60psi, released it and then attached it again and it already read at 57psi. I also have a SCA pressure gauge and this reads around 55psi straight after filling the tyre.

Is this normal (i.e. severe air bleed due from the measurement) or should I expect it to read 60psi?

We are going on a decent road trip soon so I want to make sure the car is in good shape. I am planning to get four new tyres for the car in the next week or so due to sidewall cracking - so I'm wondering if this spare is a problem I should raise with the tyre shop, and if it is then what I should expect them to suggest I do - repair, replacement with another space saver or a full size spare?

Thank you for your help, Mark.

It's not uncommon for there to be a discrepency between gauges, or even a small discrepency in readings taken on the same gauge.
Tyre pressures will also vary slightly with temperature, so variances of 3psi on a reading of 60psi is nothing to be alarmed at.
If your space saver is losing pressure from week to week by a more significant margin, then perhaps you have a leak. However, if you're only getting marginal differences such as the 60 vs 57psi you refer to, then it's not really a concern.
If you have any doubts, have the tyre shop chech the space saver in their tyre bath when you get your 4 road tyres replaced.