I think they are electric. The back of the gauge only has 2 wires, and no vacuum nipple. I think it's specific only to S15's too. You can use the holder in S14's though, but you have to cut the top bit of the plastic to fit.
My friend asked me if there is anything that he can do to reduce tyre road noise level in his car. Currently he is using 225/45/18 Good Year Eagle Efficient Grip tyres for this car. These are the tyres that came...