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Autopilot and Towing

ohmman

Plaid-ish Moderator
Feb 13, 2014
9,971
18,017
North Bay, CA
I've been thinking about towing a trailer with the Model X, and it occurred to me that AutoPilot may be disabled while towing, or at a minimum not recommended. Specifically, I'm thinking of some of the reports of occasional "jerky" movement, which would be unwelcome when hauling any trailer. I recognize it's going to get better over time, so probably not a permanent thing. However, my guess is that if you're hauling a trailer, you're probably going to be unable to use lane assist.

Thoughts?
 

Cosmacelf

Well-Known Member
Mar 6, 2013
8,421
20,078
San Diego
If you've travelled the freeway route several times before on AP and it has worked without corrections, then it should work fine towing. But you're right, I wouldn't trust it at this level of beta right now on a new route. As the fleet trains the system better, maybe this won't be an issue in a year...
 

SabrToothSqrl

Active Member
Dec 5, 2014
3,698
2,975
PA
My question is... why so few Model X videos w/auto pilot?! Or X videos at all? I've seen the S... I own the S... I need the D. I mean X.

perhaps it would not be best to try auto pilot beta while towing, but in a few years it could be argued that it would be safer than a human driver.
 

BerTX

Supporting Member
May 2, 2014
3,505
3,559
Texas/Washington
I suspect Tesla has done fairly limited testing of the towing system. I suspect Tesla has done fairly limited testing of the AP. I STRONGLY suspect they have done little or no testing of both together.

To me, that spells a strong warning from Tesla not to use the AP system while towing. But people will use it anyway -- hopefully under optimum conditions at first until we get more data.

I wondered about the TACC and towing. The Ford F-150 has adaptive cruise control, and they do NOT warn against using it while towing (except when using aftermarket trailer brake controllers) and simply say it may not work well in hilly terrain or when towing heavy loads because the cruise control disengages if speed drops 10+mph below the setting.
 

ohmman

Plaid-ish Moderator
Feb 13, 2014
9,971
18,017
North Bay, CA
I wondered about the TACC and towing. The Ford F-150 has adaptive cruise control, and they do NOT warn against using it while towing (except when using aftermarket trailer brake controllers) and simply say it may not work well in hilly terrain or when towing heavy loads because the cruise control disengages if speed drops 10+mph below the setting.

This bring up another issue. As we know, the MX will use regenerative braking when slowing. The trailer brakes would need to be connected to the brake light accelerometer if we want those to also be depressed during regen; but to what degree will they be depressed? Or will they only become activated with physical braking?

Someone with more trailering knowledge should chime in here - if the car slows and a heavy trailer is pushing, does that cause any issues other than the obvious reaction time adjustments? Is there any different stress put on the actual hitch? I'm guessing no more than rapidly accelerating with the trailer, but who knows.
 

Cosmacelf

Well-Known Member
Mar 6, 2013
8,421
20,078
San Diego
I think that's the whole point of the tow package. The tow package includes a brake controller. Often trucks and SUVs will have a tow package wiring harness, but they leave it to you to buy a brake controller. Although it isn't spelled out (does Tesla spell out anything important?), I believe the Model X tow package comes with an integrated brake controller which would presumably brake when regenning in an appropriate manner.
 

santana338

Member
Apr 11, 2012
341
47
Manchester, NH
I think that's the whole point of the tow package. The tow package includes a brake controller. Often trucks and SUVs will have a tow package wiring harness, but they leave it to you to buy a brake controller. Although it isn't spelled out (does Tesla spell out anything important?), I believe the Model X tow package comes with an integrated brake controller which would presumably brake when regenning in an appropriate manner.

This is the first I have heard of an integrated brake controller in the X. Are you speculating or did you get that info from a reliable source? What source?
 

goneskiian

Active Member
Nov 16, 2012
2,618
805
Bellevue WA
This is the first I have heard of an integrated brake controller in the X. Are you speculating or did you get that info from a reliable source? What source?
Probably assuming there is one since the Tow Package language implied there was one.

TlePl8Z.jpg


Edit: Or maybe it didn't. I guess the braking language could mean it simply adjusts the braking of the vehicle itself and not the trailer.
 

Cosmacelf

Well-Known Member
Mar 6, 2013
8,421
20,078
San Diego
I got a call back from Tesla (on a Sunday no less) answering my question about the Model X tow package. Unless there is some confusion (I did ask the person some clarifying questions which she will get back to me tomorrow), the Model X just comes with a 4 pin wiring harness that you can then attach to your own third party brake controller to, just like as with other SUVs and trucks. Some people here have asked about regen braking, but presumably regen braking would also trigger the brake controller, just as it triggers the brake lights now.

- - - Updated - - -

Separate question for those that tow more often than I have. I'm looking to tow about 1,000 pounds. I'm thinking that I don't need a trailer than has brakes. I will be towing down a mountain though. What do you guys think?
 

ohmman

Plaid-ish Moderator
Feb 13, 2014
9,971
18,017
North Bay, CA
Some people here have asked about regen braking, but presumably regen braking would also trigger the brake controller, just as it triggers the brake lights now.

To pile on to your question for people who know more than I do about towing - when you feather the brakes on your towing vehicle, I'm assuming the brakes on the trailer closely match how hard you're depressing the brake. If so, then it seems like the regen connection would be more complicated than just an on/off when the brake lights are on. Surely I am missing something, though.
 

Cosmacelf

Well-Known Member
Mar 6, 2013
8,421
20,078
San Diego
Brake controllers usually come with a dial or other way to set braking strength. It has to be this way since the weight of the trailer varies. If you are towing something light, you set it to not give as much braking power to the trailer brakes. But if you towing something heavy, you have to tell it to give more braking strength for any given input. I have found that it takes some trial and error fiddling when you first start towing something to get the right setting (you can feel the trailer brakes dragging the vehicle back if you set it too strong).

I don't know if the brake controller gets a variable braking signal rather than just on/off. I would assume it gets a variable signal.
 

Cottonwood

Roadster#433, Model S#S37
Feb 27, 2009
5,088
166
Colorado
Brake controllers usually come with a dial or other way to set braking strength. It has to be this way since the weight of the trailer varies. If you are towing something light, you set it to not give as much braking power to the trailer brakes. But if you towing something heavy, you have to tell it to give more braking strength for any given input. I have found that it takes some trial and error fiddling when you first start towing something to get the right setting (you can feel the trailer brakes dragging the vehicle back if you set it too strong).

I don't know if the brake controller gets a variable braking signal rather than just on/off. I would assume it gets a variable signal.

In the U.S. 4-pin trailer connectors are for lights only (ground, running, left, right). The 7-pin connector includes +12 Volt power and a proportional, electric brake signal. See Wikipedia: Trailer connectors in North America

I would have hoped that Tesla included a 7-pin trailer connector with proportional trailer brake controls in their tow package...
 

dhanson865

Active Member
Feb 16, 2013
4,404
6,020
Knoxville, Tennessee
To pile on to your question for people who know more than I do about towing - when you feather the brakes on your towing vehicle, I'm assuming the brakes on the trailer closely match how hard you're depressing the brake. If so, then it seems like the regen connection would be more complicated than just an on/off when the brake lights are on. Surely I am missing something, though.

The reality is that trailer brakes aren't strong enough to stop the trailer on their own. They are just there so that the trailer doesn't act in an undesirable manner such as passing the car towing it on the left, right, or over top. :)

So long as you have sufficient braking on the tow vehicle the trailer just needs stability. It doesn't have to exactly match the braking power of the tow vehicle.
 

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