What I am unclear on is how the Tesla semi with fixed gearing is going to out pull a standard semi that has a 17:1 (T310M) or 27:1 (T310MLR) first gear along with a 2.7 or so rear axle. Total torque multiplier of ~50 or 70x the engine. A Mack MP8 puts out 1500 lb-ft of torque, so the total is > 75,000 lb-ft to the rear axle. With a 6 motor Tesla tractor, each would need ~12,000 ft-lb to match. The P100D puts out ~900, double the gear ratio to sacrifice top speed and that only gets you to 1,800 each.
Even with one axle with a much lower gear ratio (80 times lower ratio than the P100D to cover the smaller motor of the 3 [450*2*80 = 72k]) and over running (sprag) clutch, it would top out at 2-3MPH, and it wouldn't help with regenerative braking.
On the side of Tesla is that the torque is available from 0 RPM.
What am I missing?
- Model 3 weight around 3,600lbs?
- 40 ton truck 80,000lbs, fully loaded. Unladen it should be half, so 20 tons.
- 22 Model 3's worth of weight fully loaded.
- Top speed of Model 3 is ~130mph?
- 65mph would have /2 the gearing, allowing:
- 11 Model 3's worth of weight loaded at 65MPH.
- Conveniently, a standard 40 ton truck (for comparison) already has 10 wheels using fat wheels (or 18 skinny wheels if you double up everything but front); one Model 3 motor per wheel (or wheel set for dualies). (By the way, I always include the trailer in all of my calculations. I'm not sure why anybody wouldn't, except for a local tractor.) ((I think Tesla Truck might only be a trailer with builtin mini tractor with no driver's seat, or at least one version like that.))
- Using Model 3 equivalency, that would be 750kWh battery for 300 mile range.
- A 40 ton truck has a huge wall moving through the air, but it also has a huge amount of truck behind it that slithers through the air tunnel made by that wall. I wonder how much efficiency comes from that tunnel. Of course, the tunnel sides are still made of air. If it is properly wind-tunneled, perhaps some sort of aerodynamic tunnel could be created by the shape of the front.
I'd like to see aero drag numbers 40 ton truck vs model 3.
The key problem with what I described is that a 40 ton truck isn't built to carry Model 3 passengers (typ. 1) times 10 (so 10 people): it's designed to carry 20 tons cargo. That means the weight of the vehicle unladen needs to be 20 tons, not 40 tons; laden, 40 tons.
How much of that is battery?
Tesla Model S Weight Distribution
Well, how much of it is battery and motor? Apparently, motor is a huge amount. Anyway, battery + motor for Model 3 must be around part of that.
So, battery + motor for Model 3 is wild ballpark ~1,800lbs*10=18,000lbs, or only 9 tons. That leaves 11 tons for skeleton, skin, and brain power, and that seems all quite reasonable. Remember, we can go all the way up to 40,000lbs for an empty tractor-trailer combination as long as it can carry another 40,000lbs inside its cargo hold.
But all of this is using Model 3 and Model S as comparison. Once you get to truck size, you have all sorts of size advantages and disadvantages that make all the numbers way different. You have places to put a huge amount of stuff that you don't with a car. And, you have huge amounts of air to push out the way since you want all of that space available to put pallets into with proper weather protection and security. Also, you have constraints of road weight limits, so that puts a big hamper on reducing wheels.
Perhaps Tesla could be kind and program in some aerodynamics that lifts the truck off the road so it weighs less at top speed, but to do that, it would need rudders and great computer steering. This would save the cost of rolling on the roads. I wonder how much lift a truck can develop in its shape. It would also need flaps to give down-pressure in curves and high winds so it doesn't float off the lane and/or tip. The rudders could help in the wind, too.
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Advertising will be easy: load up an uncovered flatbed with metal-I beam and something in front that's the full height of the legal height limit with everything weighing 79,975 pounds with proper axle distribution with driver, make sure they don't eat, drink or purchase more than 20 pounds net at rest stops, and drive it up every mountain with heavy truck traffic passing every truck at the full car-pulling-trailer speed limit. 55MPH up the Grapevine. 50MPH up Hwy 17. 55MPH up Windmill Hill. 55MPH up 156 toward the reservoir. 55MPH up I-80 into Nevada (there must be a mountain there -- I don't know but I presume). Just do that all day long for 3 days going up every mountain with a Tesla logo on the tractor and on the trailer passing every other fully loaded truck and advertising for the next quarter century is done. (Must follow 35MPH speed limit downhill for legal reasons; braking will be the ultimate limit, so I don't know how good regen is downhill for braking.) Carry sales business cards for fleet managers and indies and advertising budget is spent and done and never to be used again. If anything, the trucks will be a sales profit center, since they will earn sales for the brand that way, not spend on sales. (Tesla will say "we rid the world of polluting trucks!" as a brand positive.)
Tesla doesn't have to do any other reveal.
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The tractor-only electric with traditional non-electric trailer will be a short range non-hill variety, with less power and less range. It would be for in-town and short haul in flatlands. Basically, anything pulling old stock up hills that's electric would have to have some sort of oversized motors and alternate battery implementation. I consider that a side case, something ungermaine to the main product line; it can be done, but with tighter constraints. The main product line in my view integrates the whole combined vehicle for electric propulsion and operation (batteries, regen, motive, aero, etc.).
This is what makes the reveal exciting to me: what will Tesla actually do?
And, as I said above, why do they even need a reveal? Maybe to score brand points more than anything, and keep businesses appraised of what's happening, spurring both innovative competition and regulatory innovation (e.g., allowances in the form of demands).