are the spacers hubcentric ? if not then try your best to line them up by eye
If there not hubcentric then ill shall pipe up the band of people who have never used non hubcentrics pipe up and say you need hubcentrics lol.
My experience of using 20mm NON hubcentric spacers on the front and a 20mm and a 10mm non hubcentric together to have 30mm on the rear,
I found that if i didnt align the spacers spot on by eye and tighten every bolt progressivly as in like once the bolts in enough for the wheel not to wobbly around, hold the spacer and tighten each bolt a few turns at a time keeping an eye on how center the spacer is,
if you have got hubcentrics take the wheels off and have a look for anything odd / wrong with the way you have fitted them, for example is the spacer sitting on the hub properly and not being forced over rusty hubs, does the spacer sit in the wheel correctly if its a tight fit then is it seated properly inside the wheel ?
have you got your spiggot ring inside the wheel andthen the spacer sitting ontop of it ? if so try putting the spigot onto the hub then the spacer then the wheel on
all else eliminated then take your wheels to a tyer shop and have them balanced, Could be buckled i had a set of pro race 1.2s that vibrated STUPIDLY at around 40mph turns out they had a huge flat spot. cheers pot holes
