Staying raised on a lift/suspension sag?

[New Duke]

I keep lowering my car back onto the wheels after I work on it, rather than leave it up on the lift for a day (or a few). Which is less time efficient than leaving it raised. I only get a few minutes here and there to work on it so jobs are rarely done in one go.

I had a notion ringing in my mind (I think from Dave?) that leaving a car raised for a long time with the wheels on and unsupported can harm the suspension. Have I completely imagined that? If not, would a few days or a week at a time raised be fine?

[BarbedWire]

I think it puts an unusual strain on the rubber bushes. Same reason you're meant to torque the with the car's weight on the wheels.

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[Conan]

Just take the wheels off

[warpc0il]

I think the discussion you're thinking of is tightening the suspension pivot bolts with the wheels hanging, rather than the weight on the wheels, which then results in the car sitting high, as the bushes are in torsion, and this then damaging those bushes.

However, the question as asked is still valid.

With the car sitting normally there is no torsion stress on the suspension bushes, assuming they have been installed correctly.
With the car on a lift and the wheels hanging there will be some torsion stress on the bushes, actually in the opposite direction to that created in the first sentence example.

Could this cause damage to the bushes?

My guess would be "unlikely", purely because, though the angle of deflection from normal to fully extended exactly the same as from fully extended back to normal, in the "to fully extended" case that's as far as it can go.
The damage caused in first sentence is because the angle of deflection isn't limited from "fully extended" up to normal, as it continues up through the spring compression travel, and this is when the severe damage is caused.

Hopefully you can visualise this from my description, as it would be easier to explain the logic with a whiteboard.

The other potentially relevant discussion relates to mothballing a car over winter, when some people like to put the car on axle stands to take the weight off the tyres and thus prevent flat spots.

If these stands are actually fitted under the axles then no harm done, since the entire suspension sits as normal.
However this can be tricky, especially at the front, so it's more common to use either the jacking point or subframe, in which case you're back to having the wheels hanging.

My potential concern in these cases isn't for the bushes but the damper rods.

Leaving the suspension extended exposes much more of the damper rods and, if the environment is not climate controlled and there could be condensation on exposed surfaces, then the rods could suffer from some surface rusting, which would tear the seals when the suspension is lowered back to normal. I have known this happen to a few classic cars in garage storage, however, I can't see it really applying in your case, as the car's not going to be hanging there for weeks on end.

[goodeggbob]

Would taking the wheels off only result in less weight but the bushes remain in tension?

[RenesisRaceBuggy]

Damper rods are exposed in either case, if they rusted before on a vehicle it probably had damage/pitting there anyway that had nicked the seal and the only reason it wasn't rusting was it kept pulling a bit of oil into the pit past the seal.

[warpc0il]

Would taking the wheels off only result in less weight but the bushes remain in tension?

Yes, the suspension would still remain fully extended, just by the pre-load of the springs.

[New Duke]

Thanks for the answers everyone, and particularly to Dave for the detailed explanation. I could indeed visualise what you meant. Thanks.