if you are lowered alot or thinking of lowering your car, get 15mm spacers...
since the front track of the beezer is 37mm wider than the rear, the car benefits more from 20mm spacers either side as it makes the car more stable under braking and hard cornering.
i used to have 20mm spacers on and they where great, going back to standard was so hard to get use to as the rear now no longer feels planted