How could I float a pump in a pond using a car-tire or anything? Would removing air from the tire help?

Using less air pressure will not really make a difference, because air is very, very light.

The weight of the steel rim is the problem. You could cut some away, but this is hard work.

You can also get a bigger tire. I assume you don't want to do this.

Here's what you do: get some sheet styrofoam, maybe some external house insulation or packaging material. Paint it black so it isn't obvious (make sure the paint doesn't melt the foam, and best if non-toxic). Cut it into a hollow ring, like a donut shape, and put in inside the bottom of the rim. Put enough in to float the pump, multiple layers if necessary.

You could use some other floatation material, but hard to beat styrofoam.

Good luck!

Removing some of the air may help, but not by much. Try it.

But I'm confused. A modern auto tire cannot be inflated without the wheel, which weighs a lot.

Older tires came with separate tubes. Is this what you are talking about? A tube, not a tire? In that case, removing air won't help much if at all, as removing air causes the volume to decrease, decreasing the buoyancy.

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The mass of the air in the tire can be found using Boyle's law if you know the volume of the tire. It would require a huge tire to have even 1 kg of air mass. So there is not much to be gained by letting air out of the tire. You are better off getting a larger tire, like from a truck. Tire stores have these used, as do wrecking yards.

Good luck.

The mass of the air is nothing, ~1 Kg per CU meter

The more you inflate, the bigger it gets, the more it floats

All vessels will sink so to displace the amount of water equivalent to its mass.

Hope this properly answers your question

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