What size wheel spacers for tdi?

[polotdi]

hi all,
Im a new member on here.
I recently purchased a vw polo tdi 1.4 2001 51 reg.

Its fitted with the full gti polo kit and has the same gti bbs 15" alloy wheels.
its lowered by 40mm

Whats the size of spacers recommended so that my car looks good but is still practical to drive everyday ...plent of speed humps around where we live.

Are the spacers for £20 odd on ebay good stuff?

should i fit spacers front and back?

cheers