Well how you can tell if the skateboard wheels are hard or soft is that rubber is so hard because it is full of rubber
Thin soft racing wheel
It's all a matter of testing the wheels out, there is no scale, they can range from as soft as cruiser wheels to as hard as bones wheels.
How they grip the ground.
soft ones make it easyer to turn
well that depends. a skateboard goes pretty slow on rough terrain unless you have soft wheels. rollerblades are a bit more all-terrain but you can also get all-terrain wheels for a skateboard, too. skateboard just FLIES going downhill. you go really fast.
78a would be a soft wheels those wheels are usally on long boards or cruisers "#a" would be the durometer of a skateboard wheel 90-100+ is usally a hard wheel 80- is softer. harder wheels are for tricks and street skateboarding and they slide easier as well. as for soft wheels they grip better and you glide over cracks and dont feel it pretty cool soft wheels are for vert and crusing skateboarders
soft i think
The speed of a longboard on flatland has more than just how fast you push in consideration. The quality of the wheels is important, as well as how maintained the bearings are, the road condition, and how much wind or force keeping you back there is. A smooth road with harder wheels is faster than a rocky road with hard wheels. Also, soft wheels are slower than hard wheels on most surfaces. Then you have to judge how hard you can push.
Hard x-rays have a higher or faster frequency than soft x-rays.