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Towing a Tesla at 70 MPH replenishes battery at fast charger rates

insideevs.com

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Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#361

Earlier quoted context omitted.

> However, towing for awhile ... is something that could presumably be done by just about any passing car A Tesla model 3 weighs over 4000 pounds. A base model Toyota Tacoma isn't even rated to tow that weight, there's no way any passing sedan could. Now remember that for regenerative _braking_ to work, the tesla's brakes have been on! Definitely not something any passing car can handle.

All modern trucks are conservatively rated in the towing department because of the grade pulling requirement in the test all the OEMs use.

The SAE J2807 tow grade test is done on a real highway in Arizona, not some made up crazy scenario.

If you can only tow a certain load in ideal circumstances (no hills, no sudden braking, no wind, etc) then you actually cannot safely tow that load. The real world has hills and the occasional need to slam on your brakes.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#362

Earlier quoted context omitted.

It’s actually really dangerous and generally illegal to tow a vehicle with a simple, easily stored strap.

It's more dangerous than sitting in an air conditioned office and posting on HN but if you're not trying to keep up with stop and go traffic it's not substantially worse than flat towing. You have to drive like a responsible adult and trust your buddy to do the same but that kind of goes without saying for any situation where you're moving double or more the weight you usually do.

This is really terrible advice.

It's super dangerous, especially at highway speeds (i.e., fast enough to charge a tesla). Granted, leaning on the brake regen makes pulling a tesla a little less dangerous than pulling a gas car around at speed.

There's a reason this is illegal most places. It's also, generally, pretty hard on both vehicles to tow on a non-rigid connection because there's a lot of shock transmitted between vehicles whether the rope goes slack.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#363
post #139

Earlier quoted context omitted.

> Just embed some wires in the road... No offense but that is the most loaded phrase I've heard this week. That would be a major overhaul of both roads and electric car designs.

Sure, but it would be worth it. The cost is that you'd have to re-engineer maybe ten or twenty percent of major freeways and interstates (like have two miles of charging per every ten to twenty miles of regular road), and you'd need to establish a standard for trucks and passenger vehicles and get automakers to adopt it. (Or make it simple enough that it can be added as an aftermarket kit.) You'd also need to install…

With oxidation concerns of copper, I doubt it would be worth it.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#364

Earlier quoted context omitted.

All modern trucks are conservatively rated in the towing department because of the grade pulling requirement in the test all the OEMs use.

The SAE J2807 tow grade test is done on a real highway in Arizona, not some made up crazy scenario. If you can only tow a certain load in ideal circumstances (no hills, no sudden braking, no wind, etc) then you actually cannot safely tow that load. The real world has hills and the occasional need to slam on your brakes.

>The SAE J2807 tow grade test is done on a real highway in Arizona, not some made up crazy scenario.

So? That doesn't make it representative of typical conditions.

>If you can only tow a certain load in ideal circumstances (no hills, no sudden braking, no wind, etc) then you actually cannot safely tow that load.

So someone in Kansas or Florida should be limited by grades that aren't even with a day's drive of them? Do you seriously believe this?

This line of reasoning is even more comical in light of how the current SAE test almost always results in engine power being the bottleneck.

There's a pretty massive amount of safe behavior you can do outside the confines of the magic rating number and even more options of unsafe things you can do within the number. At the end of the day some amount of good judgement and discretion is required because there is no shortage of variables that are static in the SAE test

Your position is only a stone's through from the pitch of the slimy RV salesman who says you can tow something anytime anywhere because it's less than the magic number. I think you (and the hypothetical RV salesman) need to take your appeal to authority and desire to substitute a nuance-free number with critical though and shove them somewhere unpleasant.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#365

Earlier quoted context omitted.

It's more dangerous than sitting in an air conditioned office and posting on HN but if you're not trying to keep up with stop and go traffic it's not substantially worse than flat towing. You have to drive like a responsible adult and trust your buddy to do the same but that kind of goes without saying for any situation where you're moving double or more the weight you usually do.

This is really terrible advice. It's super dangerous, especially at highway speeds (i.e., fast enough to charge a tesla). Granted, leaning on the brake regen makes pulling a tesla a little less dangerous than pulling a gas car around at speed. There's a reason this is illegal most places. It's also, generally, pretty hard on both vehicles to tow on a non-rigid connection because there's a lot of shock transmitted bet…

You don't need to go 70mph to regen a Tesla. They went fast in the article in order to get the wattage up to an impressive article-worthy number. 20mph would work but more slowly.

There shouldn't be much if any shock loading because the towed vehicle will be on the brakes the whole time.

Obviously some good judgement is advised. Roads with hairpin turns or the shoulder of a major urban interstate is not the place for this.

Obviously a tow bar would be better than a rope but nobody winds up in a situation where they need to regen tow a vehicle because of an abundance of alternative good options.

I guess I was a little too generous to HN when I assumed I didn't need to include a bunch of "be reasonable about it" disclaimers in my original comment.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#366

The Mercedes got 5 MPG while towing the Tesla at freeway speeds. [1] 1: https://youtu.be/nILM_DEdBqM?t=336

I'm surprised it was that good. I get 8 MPG from my F250 when towing a travel trailer that doesn't have the brakes engaged.

Your travel trailer makes up for it by punching a very big hole in the air.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#367
post #68

Earlier quoted context omitted.

Teslas have no resistor banks? A great omission.

Why would a resistor bank be better than mechanical brakes? Both get rid of excess power as heat, and you probably need the mechanical brakes anyway.

> Why would a resistor bank be better than mechanical brakes?

Resistors don't wear out like frictional brakes do.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#368
post #68

Earlier quoted context omitted.

Teslas have no resistor banks? A great omission.

A resistor bank of the required wattage would simply be a big lump of dead weight most of the time. And it would need its own cooling fan which would add even more weight.

There's a free 1000+ lb steel heatsink - the chassis of the car.

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#369
post #210

Earlier quoted context omitted.

> This is commonly called power braking, usually called up in an emergency. I've never heard it called power braking, always engine braking or j-braking. It isn't just useful in emergencies but also in steep descents with heavy loads to make sure your brakes stay cool enough to be useful. It may be obvious, but the other technique that really helps keep your brakes cool is descending more slowly.

Talking a little bit out of my ass here making some assumptions, but I'd guess that in this context, 'power braking' refers to grabbing an low gear and letting out the clutch to assist the front brakes when you're trying to stop really fast and maintain the handling dynamics of the car. It's hard to explain, but if you've driven a manual sports car for a while it's easy to learn. And it isn't the same as simple engin…

> And you do have to be careful not to grab too low a gear and/or don't let the clutch out too fast, or you can mechanically overrev the engine.

A.k.a. the "money shift" as it results in spending lots of money, typically from grabbing 2nd instead of 4th (each being relatively down and to the left).

Re: Towing a Tesla at 70 MPH replenishes battery at fast charger rates

#370
post #237

Earlier quoted context omitted.

The residence won't charge anywhere near as quickly as this, though.

The Tesla charger at my residence charges the car at ~30mph

The tow charge was registering 65 kw. In a Model 3 or Y, this would be over 200mph.
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