Maybe tank isn’t the right word, but I swear I’ve seen vehicles with big guns with wheels. Why would you pick one over the other?
In: Engineering
So the other vehicles with wheels you are talking about are usually “8×8” “Armored Fighting Vehicles” or “Armored Personnel Carrier” or “Infantry Fighting Vehicles” those terms are tossed around quite a bit.
The US Army uses the “Stryker” family of IFVs, the UK/Germany/Dutch/Australians+ use the new “Boxer” family of 8×8, and there are many others. There are also regular 4×4 and also 6×6.
These are different from tracked vehicles like Tanks (US Abrams, German Leopard 2+, etc), Assault Gun/MPF (US just revealed their M10 “Booker”, but it’s very explicitly *NOT* a light tank… it’s an assault gun and they call it MPF) and there are tracked IFVs too (like the US Bradley IFV, etc)
You don’t pick one over the other, generally. These two classes of vehicles serve VERY different purposes. Many armies around the world have both for that reason, and both types serve different aspects needed for combat operations.
Tanks are the heavily armored spearhead for maneuver warfare. But modern MBTs are easily 60+ tons, with the newest Abrams M1A2 SEPv4 reported to be around 75ish tons. Heavy armor comes with weight considerations. So if it was on wheels those wheels would likely have major problems with traction and the tanks would “sink” into most ground if it tried to move, or the wheels would pop constantly, etc. With large tracks, you spread that insane weight over much more area on the ground, and this helps with ground pressure.
Also, tracks allow the vehicle to be truly “all terrain” and do very very well off road. Even in snow and in mud and in sand.
Lighter tracked vehicles like the M2 Bradley IFV, they are tracked because the doctrine is to have the Bradley vehicles be able to KEEP UP with the M1 Abrams tank. The tank is the armored spearhead, the Bradley carries dismount infantry into the fight and keeps them protected and also helps with enemy suppression/defeat.
So now you may ask. “Okay, tracks are awesome, so why not only have tracked vehicles? Why wheels?” Well, because much of modern Earth has roads. Tracks TEAR up roads, even with rubber pads on, they just fuck up roads badly. And heavy armored tracked vehicles also consume tons of fuel for their operation. So the military thought to themselves “hmm, we want something slightly armored, more than a normal truck at least, but we want something that is more fuel efficient in modern life on roads/highways to get TO the fight or fight in urban areas, while still being decent at offroad when needed.”
And boom, the 8×8 armored vehicles are born. By having 8 big run-flat wheels instead of just 4, they spread the weight of the vehicle out better than a pickup truck or humvee or jeep. So they can add a bit more armor to cover small arms fire (up to .50 cal, usually, and also shrapnel protection from indirect artillery/mortars) to protect the people in the vehicle, and they can traverse open ground better.
With the military, there are worries over “Strategic Mobility/Action vs. Tactical Mobility/Action” Strategic is like getting forces to the fight, wherever on the Globe. Tactical mobility is how well that unit can move once in Theater.
In the USA, the Armored BCT (and we’re shifting back to Divisions as the main unit of action, so Armored Divisions…) is the heaviest punch and most protected, and has plenty of Tactical mobility. But shipping hundreds of massive tanks around the world to the theater of operations takes MONTHS to deploy before the fight can start. We all know some fights happen in hours. So the Armored BCT or Armored Div has basically very low Strategic mobility. Takes forever to get them ready.
At the same time, the US Military has Marines on ships around the globe and they have Airborne light infantry. Both have no tanks, very few tracked vehicles. But they can drop in Strategically anywhere in the world within like 72 hours. Sometimes within 24 hours in an emergency. Amazing Strategic Mobility. However, once on the ground, they have no heavy armor or tracked off-road capability. They have only light vehicles and aircraft. This makes their Tactical mobility very low compared to the ABCT.
The 8×8 wheeled AFV/IFV is a mix. In the USA we call it a “medium” BCT. Armored is the “Heavy BCT” with Tanks, Airborne and Infantry BCTs are “Light”, and Stryker BCTs are “medium”. The 8×8 Strykers offer the force a bit more armor than light forces, and more tactical mobility than light forces, but are much lighter weight and size than heavy armored forces and so they can deploy Strategically much faster, and usually have longer range once on the ground. It’s the “good at both, but master of neither” force.
Also, it’s important to say again that 8×8 Wheeled AFVs like Stryker and Boxer… they are *NOT* heavily armored like the Abrams or Bradley. They are not meant for frontline combat. They are colloquially referred to as “trucks” in the US military for a reason. They are battle taxis. They are designed to not directly fight, but to drop off infantry behind the front line. They are just slightly armored to protect the troops inside in chance contact or in rear-guard actions. If a Stryker went into the frontline, an IFV or Tank could destroy them easily with one shot. They are only armored to protect against .50 cal usually. An autocannon or tank cannon would ruin everyone inside.
One aspect not mentioned so far: wheels are more stealthy than tracks (as regards both noise and footprints). This is important for armoured reconnaisance vehicles.
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