Towing may require differing regenerative braking profile.

[keeney]

When towing heavy trailers (that might weigh twice what the truck weighs), controlling the trailer brakes properly in relation to the truck braking is critical for keeping the combination stable. For best stability, you don't want the trailer pushing the truck from behind. If you are braking hard, and the trailer is pushing hard from behind, and hit some wet or sandy pavement, you have the perfect conditions to push the truck off the road or provoke a jack-knife.

So for the sake of stability, you want the trailer brakes to do most of the stopping of the trailer. That means the EV regenerative braking cannot harvest too much energy from the trailer during braking. Hopefully Tesla figures this out and they include an integrated trailer brake controller that does the right thing in conjunction with the truck brakes and regen.

This need to use the trailer brakes more heavily is an important consideration when estimating range when pulling a heavy trailer up and down hills. I have seen some estimates that presume some high percentage of regeneration of the trailer weight on the downhill segments. But to the extent trailer braking is necessary, that energy will be lost.

 

[Cyber_Dav]

Not sure I agree with the 'will be lost'. If the trailer can feed regen back to the towing vehicle it is merely necessary that the trailer regen be high enough that trailer braking exceeds vehicle braking.

Normal trailers won't do this, of course, but I'm hoping any trailer Tesla provides will.

 

[Carmageddon]

I dont see Tesla going to the business of offering dozens of Trailer trims anytime in the next 5-10 years, so no that seems unlikely.
Maybe offering a retrofitting kit for trailers, if that technically is feasible and economical enough, I dont know?

Otherwise, yes its probably lost energy. I never thought about this, but then I didnt tow braked trailers yet.

This gives one more justification to 500mile trim, unfortunately..

 

[destructure00]

Nearly every tire vehicle out there brakes harder than the trailer it's towing. This is a non-issue.

 

[Cyber_Dav]

Nearly every tire vehicle out there brakes harder than the trailer it's towing. This is a non-issue.

I don't want to argue, but this is a HUGE safety issue. Every heavy trailer needs brakes and a brake controller.

4x8 trailers don't count, we're discussing real trailers of 8,000 or more lbs.

 

[ewoodrick]

Pretty sure that they are aware of this, since they already support towing. Maybe that's why there's a tow mode

 

[destructure00]

I'm not saying the trailers shouldn't brake

I don't want to argue, but this is a HUGE safety issue. Every heavy trailer needs brakes and a brake controller.

4x8 trailers don't count, we're discussing real trailers of 8,000 or more lbs.

A good proportional brake controller should manage just fine I would think. Should be able to detect the rate of decel and apply trailer brakes accordingly.

 

[Cyber_Dav]

I'm not saying the trailers shouldn't brake


A good proportional brake controller should manage just fine I would think. Should be able to detect the rate of decel and apply trailer brakes accordingly.

Agree.

 

[keeney]

Yes, I am pretty sure a trailer brake controller can be made to do the right thing for safety.

My point was more about the range estimates when towing. A video posted online (I can't seem to find the link at the moment) has a very detailed calculation where the guy presumed heavy loads going up and down hills was a wash if the start and end elevation was the same because of regeneration. That won't necessarily be true.

As mentioned, a regenerative braking kit (motors, cables, connectors, controller) for trailers could be created. But it would be somewhat expensive and require a lot of customization to retrofit to the trailer. Unlikely to be built.

 

[Cyber_Dav]

My point was more about the range estimates when towing. A video posted online (I can't seem to find the link at the moment) has a very detailed calculation where the guy presumed heavy loads going up and down hills was a wash if the start and end elevation was the same because of regeneration.

Everybody wants perpetual motion. No, regen does not give back all that was taken out.

 

[keeney]

Here is the video I was referencing:

 

[TIppy]

The maximum grade on u.s. highways is usually less than 6%, so at most 0.06 * 14,000 lbs, or 840 lbs, will be pushing on the rear of the truck during regen while maintaining speed during descent from elevation. The trailer brakes will only be needed to stop quickly.

Rolling resistance and aerodynamic drag will reduce this force. Above a certain speed, it will only serve to reduce the rearward force of the trailer on the truck; the trailer will not push the truck at all. In this case the potential energy is still being recovered. It's used to require less energy from the battery rather than storing energy in the battery.

 

[Karma]

I'd love to see TESLA launch some videos of CyberTruck pulling an 8000 lb Airstream from Ouray, Colorado to Durango, similar to the cross country runs they did 6 years ago. THAT would get some heads turning, and give those of us who do tow some additional insights into capability.

 

[RMS149]

As a truck person this will need to be a significant consideration. There is NO way that regenerative braking on trailers is a viable option. What is going to be needed is a good trailer brake control system that can mitigate handle 80-90% of the trailer braking. I'm not sure where some of the people get their numbers here but these are not even close. There are literally thousands of different trailers from Boats, to camper, equipment trailers, box trailers, small livestock trailers etc. 90% of the energy put into towing the trailer will be lost to heat. this is one of the many reasons that your millage is reduced between 1/3 and 1/2 when towing. I do not care what the energy source is to move the combo, this is conservation of momentum.

 

[alexgr]

I do not care what the energy source is to move the combo, this is conservation of momentum.

It's better be the conservation of energy, as we are usually talk about the conservation of momentum when parts move different ways.

 

[SSedan]

Regen already triggers brake lights if it is strong enough, which is better than the no signal a teailer gets when a manual transmission vehicle downshifts.

I think you presuming Tesla doesn't know what they are doing because someone else is making bad calculations.

 

[keeney]

The maximum grade on u.s. highways is usually less than 6%, so at most 0.06 * 14,000 lbs, or 840 lbs, will be pushing on the rear of the truck during regen while maintaining speed during descent from elevation. The trailer brakes will only be needed to stop quickly.

Rolling resistance and aerodynamic drag will reduce this force. Above a certain speed, it will only serve to reduce the rearward force of the trailer on the truck; the trailer will not push the truck at all. In this case the potential energy is still being recovered. It's used to require less energy from the battery rather than storing energy in the battery.

I agree with the above - (I did qualify with "to the extent trailer braking is used.").

The loss of the regenerative braking will matter a lot more for urban and stop and go driving than it will when maintaining constant speed up and down gradual slopes at highway speeds. There are a few specific local highways around my house that descend into the river valley with intersections. Stopping the trailer at a red light halfway down the hill is going to dump a lot of momentum into the trailer brakes and the regen is not going to capture that energy for the return trip back up the hill.

 

[TIppy]

I agree with the above - (I did qualify with "to the extent trailer braking is used.").

The loss of the regenerative braking will matter a lot more for urban and stop and go driving than it will when maintaining constant speed up and down gradual slopes at highway speeds. There are a few specific local highways around my house that descend into the river valley with intersections. Stopping the trailer at a red light halfway down the hill is going to dump a lot of momentum into the trailer brakes and the regen is not going to capture that energy for the return trip back up the hill.

Any reason why you can't start slowing down early enough to use regen rather than braking?

 

[Uncle Paul]

Tesla just needs to send a signal to the trailer brakes as to how much physical braking is being done, both from legacy brakes and regeneration.

They do this already by turning on brake lights when either regen or brakes cause enough retardation. Should be easy for Tesla to figure this out. Would not loose any sleep over it.

 

[ThomasD]

Diesels have engine brakes that slow the rigs down without turning on the brake lights. I don't see the regen slowing the rig down with a trailer as a problem