Magnetize as in have an extreme amount of grip so they can turn against the severe rotational drag that is applied while underwater. Gravity vehicles don't have extra grip, they just change the direction they fall, which makes them a completely impractical suggestion for any race not specifically designed for them.
That won't help, though. Even with friction of 500 (enough to make my car flip over while turning normally), steering underwater is very sluggish. Handling was sluggish even when rotational drag was set to -50 (something you absolutely do not want in normal conditions). There seems to be far too much acting on the vehicle for any change in handling to fix this problem.
Have you considered or attempted building a section that just
looks like it's underwater, using building techniques instead of workarounds?