Yes, but the driver is choosing how and when to use a Jake brake. My point was enabling the brake by lifting off the accelerator or brake pedal doesn't seem acceptable.
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Tesla semi is ill conceived...
- Thread starter jr4488
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Yes, but the driver is choosing how and when to use a Jake brake. My point was enabling the brake by lifting off the accelerator or brake pedal doesn't seem acceptable.
BTW, for those who haven't seen it yet:
Tesla releases ‘expected price’ of semi electric truck: $150,000 to $200,000
Behold, the power of advancing technology and mass production to bring down costs
Tesla releases ‘expected price’ of semi electric truck: $150,000 to $200,000
Behold, the power of advancing technology and mass production to bring down costs
$0.14 a mile, released spec was <2kWh/mile Not 2 mile per kWh.
brucet999
Active Member
I think your math is pretty far off here. Using the old Tesla comparative speed range charts for Model S, increasing speed from 65mph to 75mph produced a 15.6% reduction in range (295 miles vs 249 miles). Given that a minor part of that difference must be due to increased rolling resistance, a 10mph prevailing wind penalty (typical of the plains states) in westbound travel should be 14% or less (from 300 down to 258 miles), not the 33% that you posit.
brucet999
Active Member
Actually, slowing does not affect EVs more than it does ICE vehicles. It is just more noticeable because of EV's comparatively small "fuel tanks".
WannabeOwner
Well-Known Member
It can be bigger, because EV efficiency curves are generally fairly flat in the operating range, while the loss in efficiency in the ICE can mask the decreased loads in the overall picture.
A couple of real-world observations:
First, even were we to use 10mph as the wind #, remember that for eastbound travel that wind is behind you, so the appropriate dV would be 20mph.
Second, axiomatic in E--->W travel in the US is that, from the Allegheny Plateau or the Appalachian Divide, it's all downhill to the Mississippi River, and your fuel economy shows it. After that, it's all uphill to the crest of the Rockies, and your fuel economy really shows it. Combining that with the headwind, and - from the Mississippi onwards - Karen's numbers are pretty spot on.
brucet999
Active Member
Who is Karen? I answered @Farmertom.
@Farmertom did not compare east vs west travel. He just asserted that westbound prevailing winds "in 80% of the US" would decrease range from 300 miles to 200. According to wind charts, prevailing westerly winds are about 10mph from Mississippi river to rockies, less than that east of Mississippi.
Altitude penalty in Model S has been calculated at about 7 miles per thousand feet, so in 850 miles from Mississippi river to foot of Rockies it would cost only about 30 miles; about 3%. Tesla Truck would likely have similar % altitude loss.
brucet999
Active Member
A couple things.
1) Saghost is correct and Bruce is incorrect. ICE efficiencies max out at high torques (~80% or so of max), generally around 2-3k RPM (both diesel and gasoline). This is a fairly high power band. While gearing lets you choose the balance between torque and RPM at the current band, it does not let you choose the power band (which is dictated by the forces on your vehicle in your current driving conditions). As you drop below the optimal power band, it doesn't matter how well you keep your gearing in the optimal range - the efficiency will drop.
2) The ratio of aero to rolling drag is lower for freight vehicles than sedans. So wind will be expected to have even less of an impact on Semi than Model S. At 60mph cruising speed, a 10mph tailwind equates to a 30% aero drag reduction, while a 10mph headwind equates to a 36% aero drag increase. A "normal" semi will have a balance point between rolling and aero drag around 50-55mph, but for a streamlined vehicle like Semi - without much in terms of options for reducing rolling drag - it's going to be higher. Let's be pessimistic and say 60mph (probably well higher). Parasitic losses will be much less significant in Semi than S/X/3 due to scale of the power demands in the drivetrain. So you can (roughly) halve the above differences to get the effect on range.
We can run the numbers for higher windspeeds, but it's important to remember that we're talking about the quadratic-weighted average of the windspeed across half a day's driving, not whatever some peak winds are during a relatively brief period of time.
1) Saghost is correct and Bruce is incorrect. ICE efficiencies max out at high torques (~80% or so of max), generally around 2-3k RPM (both diesel and gasoline). This is a fairly high power band. While gearing lets you choose the balance between torque and RPM at the current band, it does not let you choose the power band (which is dictated by the forces on your vehicle in your current driving conditions). As you drop below the optimal power band, it doesn't matter how well you keep your gearing in the optimal range - the efficiency will drop.
2) The ratio of aero to rolling drag is lower for freight vehicles than sedans. So wind will be expected to have even less of an impact on Semi than Model S. At 60mph cruising speed, a 10mph tailwind equates to a 30% aero drag reduction, while a 10mph headwind equates to a 36% aero drag increase. A "normal" semi will have a balance point between rolling and aero drag around 50-55mph, but for a streamlined vehicle like Semi - without much in terms of options for reducing rolling drag - it's going to be higher. Let's be pessimistic and say 60mph (probably well higher). Parasitic losses will be much less significant in Semi than S/X/3 due to scale of the power demands in the drivetrain. So you can (roughly) halve the above differences to get the effect on range.
We can run the numbers for higher windspeeds, but it's important to remember that we're talking about the quadratic-weighted average of the windspeed across half a day's driving, not whatever some peak winds are during a relatively brief period of time.
That's how they're activated, they are also tied into the cruise control. By cruise they can be programmed to engage in either two or three stages depending on the engine configuration.
ICE is most efficient at one speed. Slowing down below it will increase fuel consumption/mile (engine idling). Same is true for an EV, but difference is smaller. I don't know what this most efficient speed is for truck. It could be higher for ICE than EV.
There is a big thing about wind in the real world everybody is missing.
Trucks traveling in the real world experience direct on wind tunnel headwinds about .01% of the time. The vast majority of the time winds are hitting highway trucks from the front corners and anybody that's ever been in a semi will tell you that causes a significant increase in drag. A car is shaped like a bubble, air currents from different directions on the body are going significantly less effect on them than a truck.
Has this truck even been on the road yet other than on a drop deck behind a dirty diesel?
Trucks traveling in the real world experience direct on wind tunnel headwinds about .01% of the time. The vast majority of the time winds are hitting highway trucks from the front corners and anybody that's ever been in a semi will tell you that causes a significant increase in drag. A car is shaped like a bubble, air currents from different directions on the body are going significantly less effect on them than a truck.
Has this truck even been on the road yet other than on a drop deck behind a dirty diesel?
I thought the maximum allowed for a vehicle is 80,000lb pounds. So you were driving illegally by having 25% more weight than is allowed?
And a Tesla Semi shouldn't have any problem doing that trip on a single charge. The 500 mile range is fully loaded and your first 270 miles weren't fully loaded so they wouldn't have used as much energy leaving enough for the return trip. (Unless the trip there was all downhill and the return trip was all uphill.)
Information that's theoretical and being spoon fed to us...
So far all we got is semi information based on the model S. Cars and trucks are two different animals and they will discover this when they finally get a truck on the road.
The motors they are using in the trucks should be designed for less than a five percent duty cycle at full load it'll be interesting to see their life cycle in a truck.
Still no information on the tare weight of these units.
It's hard to predict when you look at the total system level. You have to go down a level or two - and operating strategy can make a big difference, too.
An engine is converts fuel into mechanical energy with varying levels of efficiency depending on the rpm and throttle settings (a bunch of engine design parameters change the details, but most engines are most efficient at full throttle at speeds near the peak torque.)
The loads change based on speed, especially the aerodynamic loads, and this is the same for any car (though the size and shape of the car will change the magnitude of the changes.)
Traditional ICE cars have engines that are much larger than they need to be to move the car down the road at freeway speeds. Therefore, they normally are operating at very poor efficiency on the freeway - and they move further into the inefficient ranges as they slow down. It won't actually burn more fuel overall at the lower speed with the lower power requirement, but the increased inefficiency will prevent you from seeing the full benefits of the reduced loads.
Perfectly legal. This is Canada, tandem truck, triaxle trailer = gross weight of 46,500kg or 102,515lb.
Where is it stated range is based on loaded milage only?
