Can't get over 50psi in bike wheel I've just replaced my mountain bike tyres/tubes with new 26x1.50 city slicks.
Max psi is 80 but my foot pump won't push more than 50 in.
Is this because it's a schrader valve, or do you think my foot pump is past it.
If it's the valve type is there any work around apart from bying presta tubes.
The valve isn't the limiting factor for the pressure -- you can go well above 80 psi with a Schrader valve. 

If you're holding 50 PSI in the tire (the tire should feel a bit firm, but you can likely push it in a bit with your fingers), you shouldn't be leaking. I'd try depressing the core (pin in the center of the valve) a bit with a key/small screwdriver/finger nail to make sure its free and try pumping it up again. 

If you're not holding the air in the tire, you either have a bad valve or a leak in the tube (in which case, get a new valve core/tube in the former case, and patch/get a new tube in the latter case and check the tire for damage).

Failing that, I'd try a different pump -- not all pumps are able to reach high enough pressures, but 50 psi is on the low end for the limit of a bicycle pump not specifically intended for low pressure situations like fat bikes (then again, a pump designed to do sports balls only needs to pump about 8-10 psi, so its possible). I'd try a floor pump like this one.