This question came to mind while watching an overloaded vehicle tilting down the road ahead of me. Are Kryptonians Height & Weight Proportional (H/W/P) to humans? I'm curious to know if Clark has to fly (hover just a little bit) in order to adjust his weight and level load a cars suspension system so he blends in when he travels with earthlings in automobiles.
No, Clark Kent doesn't have a weight problem. But he should. Superman has since the late sixties been portrayed as having the height and weight proportions of a normal human male, despite his superhuman strength.
DC Comics has not bothered to address this issue with Superman in any of the previous iterations of the Man of Steel. He has almost always been listed around 6 to 6.5 feet tall weighing approximately 225 - 250 pounds, sometimes a bit more.
Scientifically speaking Clark Kent, indeed all Kryptonians should weigh, at least a bit more, and have a greater molecular weight than normal humans. Coming from a world which was supposedly significantly larger, they would have to have been much stronger to maintain their human-like appearance.
His strength, since the Golden Age has not depended on his arrival from a heavy gravity planet, and in many iterations, Krypton is not even considered a heavy gravity world. In those cases, Superman's superhuman strength is strictly a product of his solar-powered infusion/conversion of energy into superhuman strength and his other powers.
No, this has not been portrayed consistently; particularly during periods where Kal-el might lose his powers or during the period as Superman Blue/Red when he had no superhuman strength at all.
In the Marvel Universe, for example, the Asgardians to partially compensate for their superhuman strength (even a normal Asgardian can lift ten tons) have three times the bone, muscle and overall tissue density of normal humans. Yes, in the case of some Asgardians they have even greater strength, but we assume there is a magical component for those who are lifting far in excess of that.
None of this makes strict sense and with multiple versions of Krypton, Superman, writer and editor inconsistency, it is not surprising the details have gotten lost or glossed over. Just look at the modifications for the planet Krypton over the decades:
Krypton and its history has been altered to a great extent from its previous versions. In the post-Crisis Krypton, sexual reproduction was considered obscene, and thus, all children were conceived in birthing matrices. After Infinite Crisis, this was taken out of Kryptonian culture.
Also in post-Crisis Krypton, this planet was located in a solar system within the Milky Way galaxy close enough that the radiation from the explosion (traveling only at light speed) was able to reach Earth (Action #600).
But after Superman: Birthright it was suggested that the planet Krypton was from an entirely different galaxy. In current continuity however, Krypton has been revised back to its previous position and is confirmed to be in the sector of space that borders that of Earth.
The Green Lanterns have dubbed Krypton's sector of space 2813 (Earth's being 2814) and was under the protection of Green Lantern Tomar-Re when it was destroyed. Another element to the previous version of Krypton was that all Kryptonians were unable to leave their planet or they would die instantly. This was a result of the Eradicator altering the genetic codes of Kryptonians to keep them planet-bound after a group of them left Krypton to explore and colonize other planets. The Eradicator punished these Kryptonians by altering their genetic codes to be vulnerable to lead, which resulted in the Daxamites.
Originally, Jor-El had a serum that he invented that would allow a Kryptonian to leave the planet safely; which he gave to his son Kal-El upon leaving for Earth. This was created to maintain the rule of Superman being the only Kryptonian survivor which was the theme of the post-Crisis Superman mythos.
This was reversed after 2003 when it was revealed that Superboy (Conner Kent) was half Kryptonian and then in 2004 when Supergirl (Kara Zor-El) arrived on Earth. The Eradicator did not place the planet-bound restrictions on the Krypton of the current DC universe but it still seems to be responsible for the Daxamites' lead vulnerability.
The Krypton of the current continuity was at one time an expanding empire that conquered other planets for years but was dismantled after the Kryptonian high council decided that their methods were too aggressive. The city of Kandor had a lunar city named after the planet bound city and when the lunar colony was destroyed, Brainiac kidnapped the real Kandor.
Other multi-ethnic versions of Kryptonians that resemble African-Americans and Asians also make an appearance in current continuity. Though previously, "black" Kryptonians were mainly confined within the Kryptonian continent of Vathlo Island. In the New Earth continuity, dark-skinned Kryptonians are more integrated into Kryptonian society than they were in the silver and pre-modern age DC universe. The other racially diverse people of Krypton came from a continent called Twenx. --Wikipedia > Krypton