What determines whether monster vehicles are given treads or really big wheels?
The conventional wisdom, as I understand it, is that tracks perform better on off-road, unprepared surfaces, while wheels perform better on roads. Thus I suspect that the decision comes down to whether the vehicle is expected to be used to any significant degree on roads or road-like surfaces (and to what extent speed of movement is important on those roads). Obviously, in any environment where soft surfaces are likely to be encountered often, tracks have to be the default option because the diffusion of the vehicle’s weight across a much broader contact area makes them much less likely to sink down into the mud or sand or snow or whatever.
Also, if you do[ have a prepared road surface, aren’t wheels inherently capable of going a lot faster than tracks? What’s the fasted a tracked vehicles has ever gone? And since someone is inevitably going to bring up snowmobile racing, what’s the fastest a heavy tracked vehicle has ever gone?
…Civil Guy considers briefly the idea of tracked vehicles traveling very far over any kind of rigid, prepared surface like asphalt or concrete - considers what the tips of all the track blades would do the surface, and vice versa - and cringes…
Tracks for soft and wet surfaces with otherwise poor traction, tires for paved surfaces.
I would s’pect that tracked military vehicles, tanks and such, will be the fastest. Gotta figure that they’ve got good reason to scoot right along - so perhaps some military types here could suggest a conservative range of speeds that might be achieved.
Right. That’s why I added the bit about whether speed of movement on roads is important. Wheels are faster on roads, but you may not care if you’re operating a piece of heavy equipment that’s on roads occasionally but speed doesn’t matter.
Assuming that military vehicles count as “heavy”, the British Stormer Armoured Reconaissance Vehicle is capable of 80 kph, and the British Warrior tanks are capable of 75 kph. Other sources I’ve seen suggest that this is near the upper end of the range, and that tracked vehicles operating at high speed on hard road surfaces are highly susceptible to failures of the track mechanism, making their typical operating speed on roads much lower.
Tracks have several disadvantages compared to tires:
- they are more complex mechanically, thus more expensive to build, and to maintain.
- they are slower than a vehicle with tires.
- they weigh more than tires, thus reducing the gas mileage further.
So for economic reasons, tires are preferred whenever possible. Tracks are used only when the vehicle has to operate off-road. (And, of course, for military vehicles like tanks & half-tracks, economic considerations hardly enter into it.)
Up in northern Minnesota, on the Mesabi iron range they have open pit mines with gigantic dump trucks there–as tall as a 2-story house. They operate on tires – huge ones, taller than a person’s head.
On the other hand, the upper limits of wheeled vehicles is dictated by your ability to manufacture and deliver tires to your site. Very large tires can be made (within limits), but getting them to your Gigantor truck is limited by the availability of barge transport, or failing that the height and width of roadways.
I suppose that there is no real limit on the size of a tracked system that can be assembled on site from a large number of small(er) components.
I have a vintage textbook on tractor engineering in my book collection.
The author notes that tracked vehicles have terrible road handling properties, which, I suspect, means that aside from battle tanks, everything that is expected to ever travel on a road gets tires.
Another consideration is maintenance: tires are easy to change. Fixing a screwed-up track can get messy.
I propose the Ripsaw. The site claims 0-50 in 3.5secs and a top speed of 80 mph. Pretty impressive until you realize it takes 1300 HP to achieve that performance.
I had an old Honda 350 that maybe put out 30 HP and it could hit 80. So, yeah tracks are much less efficient.
Well, you could go the other way and distribute the weight by having lots and lots of smaller wheels, but then you open for another maintenance nightmare as the number of bearings, tires and suspension components skyrocket - particularly if you need to power all those wheels.
Speaking of things that skyrocket, one ultra-heavy vehicle - the Apollo crawler - was made with tracks, even though one would assume that the budget would have been available to pave the road between the vertical assembly building and the launch pad to any spec necessary. The engineers went with gravel beds and (huge) tracks.
Another example is this fair-sized bucket excavator - movable, sort of, and definitely on tracks.
Paved with what? That crawler weighs about 6,000,000 lbs. Any concrete or blacktop would be reduced to gravel after one pass. Paving isn’t even an option.
Further, the issue would be getting the Mothers of all Tires from Ohio (say) to Florida.
Another consideration is that unless you’re travelling in a straight line, a track tends to shred whatever surface it’s traveling on. You cannot turn a tracked vehicle without skidding the track across the surface. The sharper the turn, the greater the damage.
Wiki says the fastest military tank in the world is the CVR (T) Scorpion tank, 82kph.
Snowmobiles are tracked vehicles, and are capable of almost 120mph (193kph)…
Yes, that;s why I mentioned heavy tracked vehicles. A snowmobile only has the one track at the rear, which I think would make it more manoeuvrable over a two-tracked vehicle of the same size. Or would it? With two tracks, you can make one go forward and the other go back, and spin in place. Hmm.
Although the M1 Abrams is capable of 60+mph with the engine governor removed. There is an increased risk of damage to both the tank and the crew, though.
My post, #14, was only directly answering the question “What’s the fastest a tracked vehicle has ever gone?”, which is why I quoted it. Heh. Sorry. Please forgive!
With your new snowmobile question, I think that two tracks are more manueverable than one. Steering is accomplished by moving (or stopping) the tracks out of sync with the other. You can spin in place. Also, snow mobiles are built with emphasis on speed, not maneuverability, so having a single track makes more sense.
The Scorpion is only an “8” ton tank, the Abrams a 60 tonner. I have heard of the figure that Valgard mentions, but wiki was silent on the matter. The production variants are a little more reasonable in speed. (45mph cross country)
Basically, as I see it, tracks are for cross country use, as well as spreading the wieght of the vehicle out more on soft ground. (You don’t want to rush across uneven terrain at high speed. Hard on the tail bone.)
Tires are for flattened or paved areas, and so offer higher speeds, as well as cheaper maintenance costs.
So speed isn’t the only consideration when selecting your type of locomotion.
I think that would be the Mars Rover vehicles, which reached about 17,000 miles per hour about 10 minutes after launching abord the Delta 2 rocket.
Of course, that was not under their own power – but you didn’t specify that.