Model X towing 5,000 up mountain passes at the speed limit?

That's one of the many technical questions I'd like answered about the Model X. Fundamentally, you are asking about how robust the cooling system is. I have no doubt the motor has enough torque and horsepower to handle it.

The question is, is there enough cooling capacity to tow up a mountain for 20 minutes without overheating?

If the Model X has the same cooling system capacity as the Model S, then the answer is no. This is the reason the Model S isn't a good track car. It overheats too quickly. Heck, I was recently driving (fast) on an uphill freeway in 95 degree temps, and noticed that my Model S AC was getting weaker and weaker - the car had diverted all cooling to the battery/motor. After parking for several minutes, I got back my cold AC.

Usually, real cars/trucks that have towing packages come with beefier cooling systems for this reason. So, does the Model X have a beefier cooling system with or without the tow package? Who the heck knows...

7% grade seems like the maximum on major roads in the US, but I assume the average over a few miles will be closer to 5%. Assuming that like the Model S, the Model X can output a constant 67 kW and total weight is 5450 kg or 12000 lb, the maximum constant speed seems to be around 40 mph:

Base consumption at 40 mph: 18 kW (assuming 8 kW increased consumption due to tire and aerodynamic losses of the trailer)
Consumption due to 5% grade at 40 mph: (64 kmph * 0,05 * 5450 kg * 9,8 mpss * 1,1) / 3600000 J/kWh = 52 kW
Total: 70 kW

I guess that raises two questions:

- Has the constant power output been improved on the Model X?
- For how long can the Model X perform above the maximum constant power output?

These two factors determine whether it's realistic that you will be slowed to 40 mph on a 5-7% grades fully loaded.

ratsbew said:

Thanks for doing the math. I'm hoping that the cooling has been boosted enough to maintain 55mph under those conditions since that is the speed limit with a trailer in California. Maybe the X will feature a massive AC system that can cool the cabin rapidly or cool the battery/motors under heavy usage.

45 kW is only 60 horsepower. This wouldn't look very good if it became known that the "700 horsepower" Model X actually can only produce 60 horsepower when trying to tow a trailer.

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It is well known that the motors Tesla produce are optimized for short bursts of power. It says so right in their patents.

Tesla could easily make motors which sacrifice short-term power for constant power, by using permanent magnets. But I doubt they want to do that yet. Maybe if they make a pickup or full size SUV, they could add a permanent magnet motor on the front axle, or something similar.

Of course, another factor is range. Climbing up 8000 ft with a 12000 lb car + trailer means you'll spend close to 40 kWh on the increase in elevation alone. That means if you're driving at 40 mph (using 18 kW), and you have a total of 81 kWh available, the actual driving range is 90 miles (if you can find a 90 mile road with 8000 ft increase in elevation). This is with no added cooling necessary. If you're driving at 60 mph (using 37 kW), the range should be closer to 65 miles (if you can find a 65 mile road with 8000 ft increase in elevation). This would need added cooling.

My suspicion is that Tesla has concluded these use cases are fairly irrelevant. The range will suffer so much driving so fast, so high and with such a load that they haven't seen the need to improve the cooling.

the actual driving range is 90 miles

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Unless that 8000ft climb is 'just' 8000ft and then you glide down to the bottom using 0 kWh, regening back some 20kWh and saving some brake dust.

WarpedOne said:

Unless that 8000ft climb is 'just' 8000ft and then you glide down to the bottom using 0 kWh, regening back some 20kWh and saving some brake dust.

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If you have full regen available after that climb.

Matias said:

If you have full regen available after that climb.

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What do you mean by full regen?
I thought regen is only unavailable if the battery is full (close to full)!

Just like a gas car reaches a power output limit when working hard the Tesla will also have limits. Physics can be tough.

i have maxed out battery output on a P85+ climbing long grades at highway speeds. Push the accelerator and the car says sorry nothing left to give.

It it is pretty common to see vehicles towing a load, near the top of their rated output, going slower than they would like on long uphill grades.

I'd like to see Tesla drive a fully charged Model X with 100% of cabin/cargo load, towing a 100% max tongue weight and 100% max trailer weight from the Supercharger in Sacramento to the Supercharger in Truckee.
According to Google maps, that's 77 miles and I know it's about an 9,000' summit elevation on the asphalt. Maps says it would be 11,240 ft of climbing and 5,650 ft of descending, starting about sea level and ending (obviously enough) about 5,600ft.
Given this must be one of their most common test routes (Fremont being Galactic Central Headquarters and Reno being the Gigafactory) surely they've made that run numerous times and presumably with a heavily disguised Model X in all conditions from 110 degree days with no wind to blizzard whiteout conditions and subzero wind chill.

The Tesla navigation system should be able to do a "range anxiety off" calculation and report to the driver that it realizes this is a climb. The Model X should be able to report sensor readings for the trailer weight (just by a few acceleration and braking events) and report tongue weight from the rear suspension compensation, as well as report cargo area weight, passenger weights (politely ...) and advise on the desired state of charge if a stopover at Sacramento or Truckee SCs would be advisable in light or weather, traffic, load, etc.


Google Maps
OR
Google Maps

I think the factory should have been able to literally hand code this stretch of road, plug it into their GPS "knowledge" and say "okay, here's how to average 55 mph (say) between the Bay Area and Lake Tahoe towing 80% trailer capacity and six occupants with gear in comfort with the least point to point time required given current state of charge" ... and just keep that as a whole information page somewhere accessible in the dash or relayed to a phone app (so everyone can know ahead of time, and the driver(s) can plan the trip ... hey, let's bring a late night snack and hot cocoa since it's going to be snowing ... : )

You will need 20inch wheels. I just got this from Tesla as I ordered 22inch and tow package

Dear Michael

Thank you for configuring your Model X with the Tow Package.

We want to provide some clarification regarding the towing capacity of Model X to ensure you get the right configuration for your needs. When configured with 22" wheels, the towing capacity of Model X is 3,500 pounds. When configured with 20" wheels, the towing capacity of Model X increases to 5,000 pounds.

Should you wish to alter your configuration to include 20" wheels for a higher towing capacity, please email us and a member of the Tesla Team will reach out within 24 hours to update your configuration. Alternatively you can call us at 888-51 TESLA.

Tesla

There is an SAE standard J2807 that can be used to establish tow ratings. It includes a hill climb test that's 11.2-miles up a nearly steady 6-percent grade to a 3,000-foot summit.

Pickup truck manufacturers are finally using it. Toyota uses it for some of their other models as well. I don't know if Tesla followed it to establish ratings for the MX.

Based on real world experience -

Yes, I can tow 25,000 lbs with my F-350
Yes, I can tow that weight at speed limits, on level terrain.
No, I can NOT tow that weight, at limit, on steep grades.

Pick any two out of three. Not all three. And there is absolutely no reason whatsoever to think that a Model X would avoid this close-to-fundamental law.

So I asked Tesla via email if the Model X was going to get a beefed up cooling system to handle tow loads, this is their reply:

"That is a very good question. At this point we are working on the specs and the cooling systems abilities. Stay tuned and we will have more information before the end of the year."

I thought of this actually in context to track performance, but it could apply to towing. Even with the same cooling system, if Tesla can have a mode that cold soaks the motor/inverters before they hit the incline, that can help improve performance. They can predict the incline from the GPS.

In terms of track performance, this would be a mode you can engage to cool down the motor/inverters to below normal operating temperature before a lap. This is as opposed to how it is now, where the motor/inverter is at normal operating temperature before a lap, it gets to the overheat limit, and then you have to wait for it to cool back to normal. If you can cool it down below normal beforehand, then it'll take longer to reach the overheat limit.

The Model X cooling system would intuitively be larger than the 5.5 kw capacity of the Model S. Tesla has known for a long time that the Model S rear kids seats overheat the kids in the sun as there is no real air back there.

Bigger vehicle, more occupants, more interior space, bigger battery capacity => bigger Heating & Cooling Unit.

How much bigger, good question. Perhaps the response to the question also matches the service center adjustment to my model S HVAC almost 2 years ago, when I complained of insufficient air flow, I got back "no trouble found" and a fan speed that goes to "11" as opposed to "8" like before, or newer loaner cars. It is really quite loud on recirculate, but does the job quickly.

The HVAC unit is a 400 VDC heat pump compressor custom made by Tesla, that works with the front mounted radiators, in a 3 zone (Model S) configuration (battery, driver/front passenger temp zones). It could be 4 zones if indeed it also directly cools the motor, but I have not investigated that far. Tesla doesn't have a rotating drive shaft on an ICE to connect a traditional car air conditioner, so they had to build their own. Most likely the zones are simply a combo of flow restricting valves, and total coolant flow through a multi-loop system. 5 gpm of fluid at 30 degree temp differential has more capacity than 3 gpm fluid, but takes more energy to push through the same hose.

A 3 row Model X would presumably have front / rear controls, so that is at least one more zone than the Model S.

Ludicrous mode could also push a requirement for cooling both front and rear motors, as well as more battery cooling capacity.

If the Tesla compressor is anything like the variable speed HVAC unit I have at home, it can draw very low power at lower speeds, and then ramp up to "full power" which gets noticeably louder, and eventually efficiency drops. 8 or even 12 kw will do wonders for comfort, but at some point the range crashes. Early Model S software included "Range Mode" which limited HVAC performance to increase range, substituting seat heat for air heat.

Thus the real size in the founders edition cars could indeed be 10 kw capacity, but software limited to 7.5 to 8.5 kw range. Unless my intuitive guess of what they should have done is more optimistic than what they really did, in which case, DOLT!

Mark.