question Ground pressure

[bobthebolt@hotmail.com]

Does anyone know about vehicle ground pressures? I'm trying to find out the difference between a FV432 and a Bedford 4 tonner, for use on paving during a parade through a town.

[Marmite!!]

Hi..

 

welcome to the forum, I'm sure someone will be along shortly to answer your question in he meantime maybe you could tell us a bit about yourself & vehicle in the Introductions & Welcome section

 

http://hmvf.co.uk/forumvb/forumdisplay.php?f=13

 

Cheers

 

Lee

[Tony B]

Very roughly, the ground pressure of a wheeled vehicle at rest will be the pressure of air in the tyres ie 40psi air pressure = 40 psi ground pressure. Tracked vehicles spread load over area hence about half the ground pressure of an equivalent wheeled vehicle. Into this little pot goes tyre diameter, elasticty of tyre material, type of suspension, load distribution. tyre tread pattern, even the slopping about of the fuel.

[Marmite!!]

http://en.wikipedia.org/wiki/Ground_pressure

 

From Wikipedia, the free encyclopedia

 

Ground pressure is the pressure exerted on the ground by the tires or tracks of a motorized vehicle, and is one measure of its potential mobility,[1] especially over soft ground. Ground pressure can be measured in (for example) pounds per square inch (PSI) or kilopascals (kPa). Ground pressure can be calculated with the formula (loaded weight divided by ground contact area)[2] The ground pressure of motorized vehicles is often compared to the ground pressure of a human foot, which can be 9 - 12 PSI while walking or as much as 1,920 PSI for a person in spike heels[3].

Increasing the size of the contact area on the ground (the footprint) in relation to the weight decreases the ground pressure. Ground pressure of 2 PSI or less is recommended for fragile ecosystems like marshes.[4] Decreasing the ground pressure increases the flotation, allowing easier passage of the body over soft terrain. This is often observed in activities like snowshoeing.

 

All example are approximate, and will vary based on conditions

Human on Snowshoes: 0.5 psi

Rubber-tracked ATV: 0.75 psi

Diedrich D-50 - T2 Drilling rig: 3.8 psi

Human Male (1.8 metre tall, medium build): 8 psi

M1 Abrams tank: 15 psi

1993 Toyota 4Runner / Hilux Surf: 25 psi

Adult horse (1250 lb): 25 psi

Passenger car: 30 psi

Wheeled ATV: 35 psi

Mountain bicycle: 40 psi

Racing bicycle: 90 psi

 

Note pressures for Man and Horse are for standing still. A walking human will exert double it's standing pressure. A galloping horse will exert up to 500 psi

[Tony B]

Eh , for the horse at gallop ground prseeure become zero during part of the cycle. The sequence is off hind , near hind , off fore together , near fore and suspension. At least a wheeled vehicle or tracked vehicle , should , depending on driver keep all the bits on the ground. :coffee:

[antarmike]

Doesn't the ground prssure of an adult male depend onhis boot size?

[antarmike]

The same vehicle will have a lower ground pressure on soft ground, than it does on hard ground.

 

On soft ground it sinks increasing the amount of tyre contacting the ground, so ground pressure drops...

[croc]

The same principle applies to changing tyre pressures, a softer tyre will have a greater ground contact area = lower ground pressure.

[Topdog]

Try running over someones foot and see how loud they yell.

[abn deuce]

Vehicles like the DUKW and many recent post war Vehicles which have central hub inflation systems that let the operator adjust the tire pressure on the move , lower pressure for sand and soft condition's and re-inflate for paved road and or to keep a leaking tire inflated until it can be changed .

[croc]

Vehicles like the DUKW and many recent post war Vehicles which have central hub inflation systems that let the operator adjust the tire pressure on the move , lower pressure for sand and soft condition's and re-inflate for paved road and or to keep a leaking tire inflated until it can be changed .

 

That all sounds a bit posh to me, but you could have great fun with the police if you ever got stopped... did you know you have a flat tyre sir? which one officer? :-D

[antarmike]

And of course when actually driving accross an area by the back wheels, the ground pressure on the front axle reduces and the ground pressure on the rear axle increases due to the torque reaction, and the resulting weight transfer to the back axle, as the driving axle tries to pick up the front of the vehicle

[AlienFTM]

Ground pressure of a CVR(T) ISTR is remarkably low, in the region of 15psi (as you can see above, not significantly greater than a human being) because it was designed to be light.

 

That said, there is always some daft tw ... person who will, on being told a CVR(T)'s ground pressure is not greatly in excess of a human, will allow a CVR(T) to drive over his foot and wonder why it's crushed.

 

When 15/19H deployed to BAOR with 3 Armd Div in late 1977, we collected Saracen ACVs because Sultan was still being built. For two years we were spoilt, being allowed to park RHQ and FHQs in barns. Then we got our Sultans and suddenly German farmers did not like us. "Keine Ketten" - "No tracks" was their universal cry. Then the RSM started taking German Colloquialist Tpr Alien on his pre-exercise recces where I'd explain to said farmers about the Niedriger Bodendrueck (low ground pressure) of the Aufklaerungspanzer (CVR(T)). The fact that somebody bothered to explain it to them in technical terms in their own language did the trick. Trouble was I was cursed thereafter with carrying out pre-exercise recces.

 

If I ever find my one remaining batch of service photos, I must show you one I took at Lulworth Ranges in 1977. As Squadron Leader's driver, I drove into the squadron leaguer after everyone was settled, following the tracks of the Saracen ACV. The Scorpions hadly left a mark on the boggy ground we had been allocated, while the Saracen dug in to a depth of about six inches.

[Tony B]

The Dodge WC range, is reputed to have the same ground pressure as a Camel. Pedrails, tracks, double tyres, all used through history to reduce ground pressure. The old joke about the bloke stopping on the side on the side of the road and hitting the side of his van comes to mind. when asked why he kept doing this he replied 'It's a three ton van, and I've six ton of budgies on board. got to keep half of them flying'.

(yes I know it wouldn't work)

[ArtistsRifles]

Interestingly - I've just done the math to convert the quoted ground pressure of the OT from the stated 0.6 kg/cm2 to PSI to compare. If I've got it right dividing this figure by 0.07 gives the PSI value. This comes out at 8.57 PSI

 

Not bad considering the size and weight of the vehicle and the width of the tracks!!

[Richard Farrant]

Does anyone know about vehicle ground pressures? I'm trying to find out the difference between a FV432 and a Bedford 4 tonner, for use on paving during a parade through a town.

 

Hi Bob,

 

The ground pressure for a FV432 is 11.11 lbs sq in, or 0.78 kg sq cm..

 

Have not found the details for Bed MK yet, but should be easier to work out by finding axle load (unladen I guess) and measuring area of footprint of tyres.

 

Richard

[abn deuce]

so that makes the OT-90 102.48 lbs per square foot and the FV432 133.32 lbs per square foot ?? am I correct ?