The literal translation is Speed Tribes. They sure liked speed and were an effective and homogenous tribe that lived by their own rules.
There decades of ascension were primarily was the 70's and 80's. I was churning thorough tumultuous teen years of my own in Tokyo.
I first remember seeing and hearing them when I was just ten. They were truly wild. Daredevils. Often riding without helmets (a ticket offence for any other bike rider) they'd have their kamikaze scarves across their foreheads or V-ing across their mouthes. When they went by - everywhere - they'd bang bats together, fill the usually Tokyo serenity with their custom made melodic horns. They'd be sparks. And fire.
I didn't really know it but they also enjoyed fighting amongst each other's gangs and clashing with police.
They were tolerated, though. But mostly all. (Who's going to argue with mad max machined maniacs high on adreniline and who knows what else.
It was like a circus riding through town. They'd shout and swear with an almost over acted enthusiasm.
When I got my own bike in Tokyo, occasionally, they'd appear beside me, outta nowhere. I'd honk and follow as best I could like the youngest brother on his tricyle. Sometimes I'd just enjoy the majesty of a force of nature. It was like Akira, in real life.
It was said that they didn't like foreigners but on the few occasions I encountered them they were good humoured and encouraging. They liked that I spoke Japanese and had long hair. I might have even had a peace patch on my bag. (School bag - not weapons bag.)
They had no fear. They were truly wild and reckless. What sixteen year old kid isn't going to have some respect for that.