It's my fault.
There's no way around that. I brought it up. I jumped into the Q&A discussion. Given the topic, how could I not? Then, I decided it needed to be readily accessible for posterity. Why shouldn't posterity get to have a few laughs while it learns about superheroing?
You'll thank me later.
Anyway, I made a few minor edits for content here, but it mostly went like this:
WG: Some time ago I was informed that one of my favorite super-heroes of all time is coming to TV again.....The Flash!
Phoenix: “Some time ago”, he says. I told you yesterday.
WG: Here's a question for you comic fans. Who is faster, Flash, Superman, or is it still undecided? If I remember correctly, they only raced a few times in the comics.
ML: Flash, he can accelerate his molecules to speeds Superman can't even touch.
JS: I have a better question: How does Superman fly faster? We always see him make that grimace before he accelerates; and if he's able to, why not fly at that speed all the time?
WG: @Jason. Fly faster than who? Or do you mean when Superman just wants to accelerate, he grimaces? I believe Superman's powers have definitely changed over the years from when he first started (namely growing stronger), and in the Superman movie with Christopher Reeves, he reverses Time by flying so fast (which I think he couldn't do before---you'll have to ask Phoenix about the "Time" thing), but there are different eras of story arc and "rules" with Superman. Again, my Superman lore isn't that strong.
Maybe he grimaces when he accelerates because of the random unfortunate bug that collides with him.
@Michael. Of course, since the Man of Steel gets his "fuel" from that giant fusion reactor in our sky (the more he gets the stronger he is, if I remember), it could be argued that with enough light Superman could indeed outrun Barry Allen.
[Lore note: Superman has indeed gotten more powerful over time. Usually, the pattern becomes that he’s gradually powered up so the writers can have him do bigger and better things to make the stories increasingly exciting. The trap that springs is one that makes him increasingly difficult to challenge because he has become so very powerful. Then, they have to figure out some way to scale his power levels back and start the dance again. He was able to time travel long before the first movie, they just imprinted the concept incorrectly for untold millions.]
ML: Superman can't outrun Barry Allen. The Flash can accelerate his molecules to the point of being able to pass through solid objects. The Flash would lap him 100 times before Superman even got started. Superman has to build momentum, the Flash does not.
JS: I mean he grimaces when he accelerates (The Flash does too). So, where does that extra boost of speed come from? But for Superman its really weird because he doesn't have to move his body at all. Well, except for stretching out his arm a little and grimacing.
Phoenix: OK, Superman varies his flight speed for the same reason as anyone changes speed: need. Silly question. He varies his speed by will. Tough call on who is faster because it changes. For a while, both Superman and Barry (later, Wally) were effectively up to no limit. Then, DC tried an era of limits, restricting time travel and top speeds and other powers. Superman was cut back and his top speed became finite (2000 mi/s) and he could tire. Flash gradually became unlimited again. DC has done a ridiculous mass reboot called New 52 and among the changes Superman has been restored to interstellar capabilities so he too is effectively unlimited again.
Oh, passing through solids is a function of controlled molecular vibration not velocity. Flash can walk through a wall (somehow not falling through a floor).
JS: Well, if it's just a matter of will; then why is it straining him? And don’t say it's not straining him; cause if it was effortless he wouldn't even change his facial expression.
Which brings me to my next point. There's always a scene where the clock is ticking and he has to fly even faster than he already is. So he stretches out and gives out a yell, or some other sign of stress and Flys faster. If he's in a hurry to get somewhere, why wasn't he flying at top speed to begin with?
And what the hell was it that increased his speed? It's not like he's swimming and has to kick his legs.
WG: @Jason. I think the facial expressions are for the fans, duh. How blah it would be to see boredom on Superman's face as he races to keep Zod from throwing a train onto some helpless pedestrians.
Phoenix: I challenge the absolutism of "always". I've found myself engaged in similar questioning with Star Trek and warp drive. Superman lives in a relatively fragile world. He's grown learning to live in it and to control himself. Even a meager Spiderman is capable of crushing bricks, snapping bones and ending lives if incautious. Superman would shatter concrete, rend steel and become a menace in moments. If anything, he should have to encourage himself to push the restraint level that he has conditioned to keep him in check. Facial strain? Let's say its concentration on his control mechanism that keeps unfathomable power leashed. Rocketing across Metropolis to save a falling human whom he doesn't want to turn to pudding or overshoot by a hundred miles means using control, not acceleration to faster than light speed because he can. Unrestrained velocity in an atmosphere, without benefit of Flash's low air friction aura, is reckless. Outracing a bullet doing a mere mach 3 doesn't require the overkill you propose.
Really, any time he spends as Clark should be seen as exercises in fine-tuning as much as keeping him emotionally connected to the collection of delicates and deadlies he has chosen to juggle.
BP: Bill, if they race on Earth them the flash might win.. but have the race to Mars and back.. no contest.
WG: @Phoenix. You know, the writers could farm much material for story elements off what you just said about Superman. Alas, it seems he never has the same or similar 'human' flaws as other superheroes because he's always so properly aligned towards the forces of good, therefore negating any real need to explore such juicy inner workings related to "control" of the internal strife. Mainly because there is little or none with The Man of Steel (you may correct me). Consequently, such a character would be hard for me to write about. But take Batman or Wolverine…loads of stuff going on in those heads. You see, gotta go dark man, gotta go dark---hehe.
Phoenix: There are a few isolated bits that come to mind with Superman being truly angry or temporarily draconian. People either surrender quickly or things get messy. In the current New 52 era, I hear they have him being a dick and also dating Wonder Woman. I also note, they swept aside most of his traditional supporting cast and ma and pa are dead.
We haven't really talked about the headline event of all this: the races. In the requested spirit of this, it's all going to be from memory, so nobody have a cow if they find a glitch later. As memory serves, the first two Superman/Flash races were pre-Crisis in the era of the mega-Superman. Superman and Barry Allen were racing for charity on a pre-set course around the world. There was a 240,000MPH speed limit and Superman wasn't allowed to fly. Of course, they detoured for rescues. Since the event resulted in heavy betting, though, organized crime factions set traps for each hero and substituted a masked loser fitted with rockets that no one was supposed to notice (70s). The doubles got frustrated trying to run slower and slower so the other would win till they ended up standing on the highway yelling at each other. The heroes eventually recovered, escaped, took out the frustrated doubles and then finished in a deliberate tie to thwart the gamblers.
The next race was a forced rematch. The two rulers of the planet Ventura, habitual gamblers Rokk and Sorban, crashed Justice League HQ and used their alien science to lockdown the heroes. The aliens still had a bet to be settled from the first race and that wouldn’t do. Loser’s home city gets blasted, just for motivation. With the bigger stakes came a bigger challenge: they had to race to the edge of the galaxy and back. Flash’s aura received an alien power charge so that for two weeks (no dawdling) as he ran an invisible runway would be created underfoot and all the oxygen he could breathe. Well, the important thing about this one was that Barry collapsed. He was worn out, exhausted, and spent far short of the goal. Superpowered though he was, mortal Barry was no match for an inexhaustible Superman. All ended well, of course, despite the aborted race. Superman had spotted Rokk and Sorban (the real ones) gambling on Ventura. The imposters back on Earth were actually Flash villains Abrakadabra and Professor Zoom trying to wipe out their nemesis in an elaborate scheme. With the Man of Steel providing a prompt return, the baddies were thrashed and reintroduced to DC’s revolving door super prison system.
The next big race came in the post-Crisis era of the finite Superman. Fifth dimensional imp Mr. Mxyzptlk (there’s one for the spell check) popped in and insisted on a race. He would return home only if Superman won. Wally West was wearing the red tights at this point and sporting the benefit of being “The Fastest Man Alive” (DC’s folk had decided that if he was going to have the title, he should be the guy without the unspoken “except for Superman” tag). So they raced. I don’t remember what Wally’s carrot was, but it was incentive enough to make him work for it. It was a foot race, Superman got exhausted this time and Flash beat him by a few steps. Mxy was pissed because he had lied, intending to go home only if Flash won. He was certain that Superman had figured it out somehow and thrown the race.
Marvel had a humorous bit where their Earth-based speedsters were assembled for a sprint to the moon on an alien-provided raceway. Many of them couldn’t manage the full trip and the rest of the pack was blown away by a lost, disoriented blonde fellow who could only remember a couple of syllables of his name. The extraterrestrial officiant dubbed him “Buried Alien” (a nod to Barry Allen, lost in the Crisis on Infinite Earths) and the clear winner.
The last one I know is also between Superman and Wally. Taking place in Superman the Animated Series, this was another charity event with a finite Superman. Flash rogue Weather Wizard was the disruptor and, though Wally seemed to be given a stamina edge, the two came off as fairly evenly matched.
I suppose I should also mention Smallville. While they had no official race, Barry Allen relative Bart Allen was able to open up and leave young Clark in his dusty wake.
So, limited to foot travel, Flash most likely to have the speed advantage. As with most comic adventures, though, it’s going to come down to the needs of the story. Fortunately, they spend more time on the same side fighting evil, not wasting time racing. I’ll have to tell you some time about the brawl I had with the Justice League and the Legion of Superheroes before we all teamed up to save the world.