There are only two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.
— Albert Einstein
Introduction
I have been reading some military history on tank operations during the WW2 and the subject of the ground pressure exerted by the tank's tracks has figured prominently in the discussions on the Eastern Front. The T34/85 was mentioned as a particularly mobile tank because of its low ground pressure. Since I am working diligently on improving my web scraping skills, I decided to generate a short table of the ground pressures of some famous tanks.
Since most WW2 tanks were much lighter than modern tanks, I thought I was going to see a major difference in the ground pressures exerted by the tracks. It turns out that all the tanks I examined exert ground pressures in the range of 10 lbf/in2 to 16 lbf/in2. To make these numbers meaningful, you should compare them to something you see in everyday life. Consider the examples shown in Figure 2.
Figure 2: Everyday Examples of Ground Pressure (Source).
So most tanks exert somewhat less ground pressure than people.
Background
Definitions
- Track Ground Contact Length (lGC)
- The area of the track in contact with the ground at any time.
- Track Width (w)
- Track width is simply the width of the track. You do need to be a bit careful though because most tanks have two types of track: (1) a narrow track used when being transported, and (2) a wider track used for combat. For this exercise here, I am only interested in the combat track width.
- Ground Pressure (PGC)
- The pressure exerted by the tank track on the ground. It is computed using the formula
.
Analysis
Table 1 shows the results of my web scraping and simple calculations. It looks like the Tiger 1 and M1A1 have the highest ground pressure of the tanks I examined. The T34/85 had very low ground pressure, which historians often cite as numerical support for their claims of its excellent mobility.
| Tank | Country | Intro Year | Weight (lbf) |
Weight (US ton) |
Track length (in) |
Track Width (in) |
Ground Pressure (lbf/in2) |
Ground Pressure (kg/cm2) |
|---|---|---|---|---|---|---|---|---|
| Mk IV | Germany | 1939 | 55,116 | 27.6 | 159.8 | 15.7 | 11.0 | 0.77 |
| Panther | Germany | 1942 | 100,310 | 50.2 | 156.5 | 25.6 | 12.5 | 0.88 |
| Tiger 1 | Germany | 1942 | 126,214 | 63.1 | 141.9 | 28.5 | 15.6 | 1.10 |
| Tiger 2 | Germany | 1944 | 139,600 | 69.8 | 162.2 | 31.5 | 13.7 | 0.96 |
| Leopard 2 | Germany | 1979 | 121,584 | 60.8 | 194.7 | 26.5 | 11.8 | 0.83 |
| T34/85 | Russia | 1940 | 73,193 | 36.6 | 151.6 | 23.0 | 10.5 | 0.74 |
| IS-2 | Russia | 1943 | 101,412 | 50.7 | 171.7 | 25.6 | 11.5 | 0.81 |
| T54 | Russia | 1947 | 78,264 | 39.1 | 155.1 | 21.3 | 11.9 | 0.83 |
| T72A | Russia | 1973 | 97,900 | 49.0 | 168.5 | 22.8 | 12.7 | 0.89 |
| T80 | Russia | 1976 | 101,200 | 50.6 | 169.2 | 22.8 | 13.1 | 0.92 |
| Churchill Mk VII | UK | 1944 | 86,240 | 43.1 | 149.6 | 22.0 | 13.1 | 0.92 |
| Challenger 2 | UK | 1998 | 137,789 | 68.9 | 188.6 | 25.6 | 14.3 | 1.00 |
| M4 | USA | 1942 | 66,800 | 33.4 | 147.0 | 16.6 | 13.7 | 0.96 |
| M26 | USA | 1945 | 92,355 | 46.2 | 153.5 | 24.0 | 12.5 | 0.88 |
| M48 | USA | 1953 | 99,000 | 49.5 | 157.0 | 28.0 | 11.3 | 0.79 |
| M60 | USA | 1961 | 102,000 | 51.0 | 166.7 | 28.0 | 10.9 | 0.77 |
| M1 | USA | 1980 | 120,000 | 60.0 | 180.0 | 25.0 | 13.3 | 0.94 |
| M1A1 | USA | 1985 | 130,000 | 65.0 | 180.0 | 25.0 | 14.4 | 1.02 |
| M1A2 | USA | 1990 | 139,000 | 69.5 | 180.0 | 25.0 | 15.4 | 1.09 |
Conclusion
It certainly does look like the T34/85 had excellent ground pressure numbers. When you are battling winter and mud along with an adversary, I can see where this metric could tip the balance.
Do you look into weights including up armouring? or is these just the basic weights?
Basic weights. I just grabbed the official listings for each vehicle.
mark
He only used the standard weight as listed in official sources, but the reality is that on a main battle tank and added "up armor" isn't really all that much compared to the basic weight of the tank. The worst case I can think of would be the TUSK kit on an M1A2 which adds nearly 5 tons to the tank -- but that is only about a 7% increase in total weight and a corresponding 7% increase in ground pressure.
Today I went to Bovington tank museum. One of the displays mentioned that tank track travels twice as fast as the tank moves forward. Can someone explain how this works please?
I have always found this an interesting fact. Similar the bottom of the track has zero speed relative to the ground. Watch an old WW2 documentary sometime and look at where the track contacts the ground. You will see that it is not moving – as long as the tank is not skidding.
This is a relative velocity problem. There is nothing special about a track. The same speed relationships hold for a wheel. Consider the following figure. Let the vehicle speed be S.
The speed of points on a wheel are measured relative to something, like the axle or the ground. Every point on a rigid wheel moves a the same speed relative to the axle, but with different directions. Relative to the axle, the bottom point of the wheel is moving at -S. If you measure the speed relative to the ground all the speed are shifted up by the ground speed of the tank. The point where the wheel contacts the ground must be moving at the same speed as the ground, otherwise you are skidding. The axle is rigidly mounted to the vehicle and it must be moving at the ground speed of the vehicle. This means that the top to the wheel must be moving twice as fast as the ground speed.
mark
The UK's Scimitar/Scorpion have a ground pressure of just 5psi. This enables them to go places no other vehicle can go. This was particularly useful in the Falklands, where there is a lot of soft wet ground.
Didn't the brits have the Volvo BV 202 on the Falklands?
With respect to the T34, one needs to be careful to be precise about which specific model you are referring to. In 1940, you're dealing with the initial model T-34-76 which had a ground pressure of 9.1 psi and a 19.2 hp/tonne power to weight ratio which indeed made it a spritely performer. The T-34-85 was later, heavier, upgrade of the original that came on the scene in 1943. It had a 11.1 psi ground pressure and a 15.6 hp/tonne power to weight ratio in the 1943 model, and 16.3 hp/tonne ratio in the 1944 model. This was still very respectable compared to other contemporary tanks, but it's the earlier T-34-76 that most deserves the laurels for mobility.
"...ground pressure is a poor proxy for cross country mobility because it ignores variances in pressure along the length of the track. Such a procedure is ok vs hard surfaces where the transfer mechanics are rigid and sinkage is a non factor but on softer ground, where the vehicle sinks in local stresses caused by the pressure rise of the roadwheels make for significant deviations from the hard surface interaction mechanics. The tracks themselves are flexible -along with the soil, which is partially depressable and therefore one is confronted with a mechanic which does not represent a rigid transfer medium anymore.
Rowland worked out the principles. Some of his research papers can be found in the internet. He and later Ogorkiewicz note that a high number of small road wheels will be benefitial in soft soil interaction (f.e. Churchill, Mathilda, IS) but create more rolling resistence than large diameter road wheels (some designs got around this with a large number of large roadwheels using interlocked or overlapping layouts with excellent results).
For the Mean Maximum Pressure(MMP) to calculate You need
W= weight of vehicle in KN
n= number of roadwheels per side
b= track width in m
p= pitch of track links, in m
d= diameter of roadhweels, in m
MMP= .63W/((n x b x c) (p x d)^.5)
where c is the ratio of actual plan area of a track link to the product of p and b"
Source: https://forum.axishistory.com/viewtopic.php?p=2169273#p2169273
Great comment! I am going to update this point per your comment.
Thanks a ton!!!
mark
Quite correct. The German "big cat" Panzers like Tiger and Panther had low aspect ratio tracks which helped prevent rutting. Furthermore the use of interleaved and overlapping full sized wheels gave the best of both worlds: as high a number of contact points as smaller wheels but also the advantage of large diameter wheels in reducing peak ground pressure. It's the peak ground pressure that is going to break up the soil mechanics. The quality of suspension springing and range of suspension travel also played a big part in ensuring the track had full and optimal ground contact everywhere it could. The Panther had 50cm of suspension travel, a number not matched till the Leopard II tank of the 1980s. The terrain Mobility of the big cats was excellent. This should not be confused with mobility issues caused by being big (such as fitting into a narrow bocage or lane)
Thanks, very interesting. I was curious about a story I heard from a friend in the Canadian military, and indeed there may be some truth to it, based on you analysis. Here's the story: The friend was in the Canadian military, and they were doing joint maneuvers with the German 'bundeswehr'. The Canadians noticed the German tank treads were incredibly wide. "Why is that?" (In deep German accent) "So we will never get stuck in Russian mud."