Metal tube to lift a car – how strong?

I have a manual car lift that has two platforms that go under each side of the car under the sills and basically lift the car up with it resting on its chassis/floor pan. This is great for access and working on the wheels but…

…my new car has only 4 jacking points, red in the picture, and has various pipes and seams on the floor pan so not ideal to lift the car.

I was thinking of getting two square metal tubes that were the length of the gap between the jacking points, adding a nice rubber bung to fit the jacking points neatly and then rest that on the ramp and use the metal ube to lift the car at the correct jacking points instead of the floor.

The car weight 1.5 tonnes.
The overhang at each end of the jacks platforms is about 500mm
What size and thickness of tube would I need – examples from MEtal Supermarket most welcome (https://www.metalsupermarkets.co.uk/product/mild-steel-square-tube-galvanised/)?

Please film it, whatever you decide to do 😄

But don’t go underneath …

I’d say your car has bigger problems than the jacking points.

Id not use tube… id be looking at a box section id be trying to go 3×4 or 4×4 but my honest answer is id try some and see how it goes

Seriously though, take a look at the arms on a proper lift and decide if it’s worth pursuing or if you can even secure them properly.

I’d be cutting hockey pucks and just lifting it on whatever strong points I could find rather than bodging something.

You’d want it to deflect less than 1% of its cantilevered length thus the deflection would be <5mm.  The formula for that is delta (0.05m) is PL^3/3EI.  Where P is the load in newtons, L is the length of the section from its point of fixing to application of load, E is the elastic modulus of the material and I is the second moment of inertia.  Rearrange the formula to give I.  I for a square section is (a^4-b^4)/12 where a is the outer length and b is the inner length.  You can then play with this to get a section diameter and thickness which suits your purpose.

I moved a ~750kg lathe this year and levered the headstock (where most of the weight is) with a odd bit of scrap from a old garage room. 3mm thick folded into a open box (imagine a box section then removed a stip along one side) section 75mm by 100mm approx, 3m long. This was placed on a fulcrum and about 500mm overhang and levered up. Jumped on, extra counter weight bolted on bla bla. Flex was minimal.

So the 100mm 3mm looks plenty. For 1.5 ton car

I’d suggest they can’t be oversized if you plan on being under it at any point given your reputation. But I’ve seen weightlifters lifting massive weights on (admittedly bending) steel bars of about 1″ diameter, so I assume you’d be able to find something strong enough.

Would I-beam joists, designed for holding house sized weights up not be an option?

I have no qualifying knowledge, but a 1.5t car, front loaded due to the engine, maybe the 4 points would be (pure guess) 500kg each at the front and 250kg each at the rear?  600/600/150/150? You then have a turning moment pivoting around the front of the floor x 500mm, how far to the rear jacking points? Any chance that the whole thing could pivot over the front of the floor, if you were to load or unload by eg: torquing on bolts….if so I’d want the rails fixed down onto the floor, not just sat on it.

I’d say your car has bigger problems than the jacking points.

When the car needs a label ‘car’ just to make sure we know what it is, there’s definitely an issue.

Have a look at http://www.cjautosheywood.co.uk.

They do all sorts of automotive lifter, adaptors etc, etc.

Something like http://www.cjautosheywood.co.uk/product/2-ton-crossbeam-adaptor-cl04/

Sounds like an adapter you can get for detailing lifts.  Basically what @drnosh suggests. When working out the strength it needs to be don’t forget to add a safety factor. 5x is probably the right multiplier. I’d be wanting to buy soemthing off the shelf.

Car ———-> 😂

I have a 2 post lift down the workshop. That has 2 part rectangular hollow sections in a section to allow it to slide for different sized cars. Not measured it but I guess the outer box is probably 120×60 with an 8mm wall size. Inner tube would be 100×40 with a similar wall thickness. The arms  will extend to about 1200mm and the lift is rated to 4 tonne. (so max load of about 1.5 tonne per arm end to account for offset loading). I can measure it but won’t be till Sunday now.

Thanks. That photo is not the actual car :-)

I will check with CJ Autos as they supplied the actual jack I am using. It is designed to tilt so that even though it is a low height you can tilt the end you are working on up higher. Those cross beam adaptors are almost exactly what I am after, although those are designed to go across the car obviously.

I have been working with it on wooden supports with cut outs to miss the pipe work but that was always a temporary solution. It all seems solid but feel it would be better for the car to use the actual jacking points.