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Topic starter
13/07/2026 2:06 am
Has anyone used math (pressure readings & piston area) to calculate car weight with any accuracy? I played around with standing pressure @ bottom landing, figured put piston area and then subtracted piston weight. I know we could try hanging from the middle but is usually a PITA. I've also seen load cells used with a porta-power that xould
be used to lift the car from underneath.
be used to lift the car from underneath.
13/07/2026 5:42 am
I have not but calculate with empty car then again with rated load and see how close the difference is to capacity.
13/07/2026 5:21 pm
I have found that a good rule of thumb to get close to the empty car weight is that it is roughly the same as the capacity. Once I was told that Ive checked it against a lot of cars that have the cross head tag with all the weights and it seems to be right on (+/- couple hundred pounds)
17/07/2026 11:54 pm
Determine you piston diameter
Then determine your piston area by Pie Times Radius Squared.
Piston Area = 3.1416*((Piston Dia/2)*(Piston Dia/2))
Now take a gauge and get your load PSI
NL PSI * AREA OF PISTON = MT Car Weight
Then determine your piston area by Pie Times Radius Squared.
Piston Area = 3.1416*((Piston Dia/2)*(Piston Dia/2))
Now take a gauge and get your load PSI
NL PSI * AREA OF PISTON = MT Car Weight
18/07/2026 6:45 am
i agree with Bowtierooster after checking 100s of cars hydo car weight is a couple hundred pounds shy of capacity. Holds true for traction cars as well. Front and rear opening are closer capacity,
Topic starter
18/07/2026 7:05 am
Originally Posted by ashley
Determine you piston diameter
Then determine your piston area by Pie Times Radius Squared.
Piston Area = 3.1416*((Piston Dia/2)*(Piston Dia/2))
Now take a gauge and get your load PSI
NL PSI * AREA OF PISTON = MT Car Weight
Then determine your piston area by Pie Times Radius Squared.
Piston Area = 3.1416*((Piston Dia/2)*(Piston Dia/2))
Now take a gauge and get your load PSI
NL PSI * AREA OF PISTON = MT Car Weight
yes this is what I did, but I also subtracted the piston weight from the calculated weight. (This was a holed unit).
This hydro was originally 2200# car weight with a capacity of 3500#. this was from the original layouts, my math I used above was about 2450#. I just weighed 2 traction cars and they were 4150# & 4700# (front&rear) both with a capacity of 2500#. none of these units had crosshead tags btw
Last edited by tayto; 07/17/26 11:06 PM.