The book was Sphere. It rocked. I too remember this fact just from that.
which was made into a movie
https://en.m.wikipedia.org/wiki/Sphere_(1998_film)
that is confusingly similar to The Abyss,
https://en.m.wikipedia.org/wiki/The_Abyss
I always get the two confused.
My guess would be one or more of: the above; greater heat capacity; or, something to do with surface area vs. volume meaning that at a large enough size water in a tire is far lower-pressure and easier to contain than air at a high enough pressure to keep it inflated, and/or, relatedly, something to do with heat dissipation from compressing gasses being really hard to deal with once you hit a certain surface-to-volume ratio.
[EDIT] LOL, guess all these were wrong and it's just for the extra weight.