Super Speed/Analysis

Required Secondary Powers
These characters are somehow immune to the effects of friction - specifically, the chafing that would naturally occur from using extremely rapid speed for extended periods of time, especially while wearing spandex. Again, this is only for characters that aren't explicitly described as Nigh Invulnerable; presumably, that would also cover friction damage. The same applies to the materials in contact with speedster, especially clothes (that should be bent to move): either invulnerability is extended to them or they are going to be damaged and possibly disintegrated/incinerated. For instance, the various speedsters of the The DCU related to The Flash each have a thin invisible aura that protects their bodies from air friction (and, presumably, the impact of their feet hitting the ground at several hundred miles per hour several hundred times per second). This aura also allows them to survive the rigors of outer space.

And they face a problem the other direction, of having too little friction. Feet coming down at superspeed would presumably have super impact, and push them off the ground and at least a few feet in the air. Even once that's explained, someone going at superspeed over the slightest hill, or up stairs, or just random dips in the ground, would lose contact with the ground, they would keep going in the 'same direction' as before, into the air. The faster ones would be launched into orbit, especially while doing the 'run around the world' trick. They have to have something that holds them in contact with the ground better than gravity if they don't want to end up hurtling comically though the air every other step like a Wuxia character.

Speedsters also must possess a very powerful and efficient metabolism, which keeps them from needing to drink several times their weight in pure nectar every day (In recent years, this element has been often used to justify faster healing). Sometimes, this is partly averted - more than one character like this has been shown to be a Big Eater to power their abilities - though not even spending 24/7 in front of an all-you-can-eat ice cream and candy buffet could provide enough calories to power more than a second or two of supersonic running speeds. Which means that every Speedster really is a PerpetuumMobile. Also, they have to have a very high stamina, as running from New York to Los Angeles all at once should be impossible no matter how fast they do it. They also have to have super friction powers (again with the friction), so that they can actually keep their footing when turning on surfaces that aren't specially constructed for high-speed travel. Cars turn easily at sixty miles per hour on (properly angled) asphalt, but they'd have a much harder time on tile.

And if their speed is too high for a given viscosity, there's no time for collisions to be resolved quietly, so normally soft substances (like water or plastics) are going to behave like hard ones: literal blades of grass, glass puddles, buckshot raindrops, shrapnel snow, fragile clothes, that sort of thing. Speedsters who pick up or put down anything while speeding also have to have some power that cushions the impact. Otherwise, attempting to grab a person when you're running at a hundred miles an hour wouldn't pick them up, it would snap them in half.

If these characters approach the speed of light, they would experience time dilation. Furthermore, speedsters never get specks of dust caught in their eyes...

They would also need some type of super-concentration. Given that they must have some form of Super Reflexes so they can react normally to things at super-speed, they should perceive normal speed to be horrifyingly slow. Imagine trying to hold a conversation with people who take several hours to speak a single word. Similarly, if a speedster does something like typing millions of password combinations into a computer, he must somehow avoid getting bored after the first few hundred. It is also possible that the refresh rate of a monitor (normally 60 times per second) would be too slow for them, or for extreme examples, even the response time of the processor to something like a keyboard interrupt. Alternatively, they may have nervous systems that can multitask at different speeds, allowing them to perform (for example) simple manual tasks at superspeed while only being consciously aware of a few seconds passing.

Characters with super speed must also be able to withstand massive g-forces caused by rapid acceleration/deceleration, since most of them are shown to be able to start/stop instantly (rarely applies to those who lack this talent, but they may end up going Too Fast to Stop as a result and find that Inertia Is a Harsh Mistress). This must make the character somehow able to anchor to the ground while stopping too, since friction with the ground can only go so far - but often they just instantly stop. More than likely this uses some form of Inertial Dampening rather than actual friction, as it normally fails to tear up the roadway or set it on fire.

Normal humans moving at very high speeds without a protective barrier would forcibly ram-scoop air into their lungs. It'd be like driving without a windshield... on a supersonic jet. So their "aura" must either slow the air, or redirect it safely around them (while still allowing in enough to breathe). There was a real life incident where the navigator in a US Navy KA-6 Tanker ended up hanging out the cockpit of the aircraft. His seat had become detached from the floor due to metal fatigue and ended up pretty much floating on the ejection guide rails. His helmet and oxygen mask were taken off by the wind. Through his apparently being one of the luckiest guys in the world, he survived, and later compared trying to breathe during the ordeal to trying to drink from a firehose. This on a subsonic aircraft with the pilot deliberately flying as slowly as he could (unlike most vehicles, aircraft stall when they fly below a certain speed due to the lack of lift).

Also traveling at very high speed would generate shock waves that even if they won't affect the speedster would affect everyone around.

And in the cases of extremely high speed, there is also the risk of the radiation (principally Gamma Rays) produced by the Doppler Effect of traveling a such high speeds.