My Formula 4s got flat spots, sounding like a moped when I ride the bowl. I’m looking for larger sizes from 56mm upwards. I need mostly for very smooth surfaces and high speed, but sometimes also rougher concrete. I don’t have a need for ultra soft wheels.
They’re not necessary for ordinary skateboarding. Longboarders use them because their carving puts lots of sideways stress on the wheels. They might prolong the life of your bearings if you skate fast and do many power slides.
The main issue with spacers is that the inside width of wheels isn’t standard, so unless you have spacers that perfectly fit the inside of your wheels, they don’t really do anything useful. They mainly introduce a surface of contact that will slow down the wheel and catch more dirt.
If you have expensive ceramic bearings, you might consider using spacers, but otherwise it doesn’t really matter. I have never had a bearing blow out from sideways stress.
Historically, spacers are casualties of the weight optimization in the 1990s. Some people still swear by them, but it’s mainly superstition. There’s no reasonable explanation for using them.
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The only way I know about is spacers is that I asked the same question myself a while back when I ordered a complete and didn’t get any. I’ve always just replaced parts, so it never occurred to me that they disappeared many years ago until then.
I’m from Denmark in Europe. Mid 40s and still try to skate at least weekly if the weather is nice. There’s not a local park and hardly any skaters where I live (yet), but there are many concrete parks being build in neighbouring towns, so I drive around to those and mostly skate the bowls. I can’t keep up with the kids or even my former self, but I push myself to do at least do 1 new thing on every session.
Next year we will finally have a local park, so that will make it easier for me to get my kids along for longer sessions and maybe practice more efficiently. Being involved in the project has also been really interesting.