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Overweight towing question.


Marcusthehat
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Purely hypothetically, since I have 3 or 4 "G" Wagens good to tow 3500Kg, especially the 1999 automatic 461 series SDP Van.

But anyway, apart from possible* gradient or speed dependant stopping issues, I can only presume there is nothing likely** to suffer any harm by towing more than the recommended weights, due to the nature of the epicyclic electro-mechanical transmission without any wearing parts.

*And with properly adjusted and functioning overrun brakes even this should not be an issue.

**Bar attempting a stupidly steep hill start perhaps.

Thoughts, hypothetically, obviously.

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Without addressing the car issue I think your insurance would be null and void if in the event you had an accident as would probably any recovery insurance you had in place?

I’d also be concerned that if stopped the police would have something to say which might not be pleasant to hear?

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6 minutes ago, ernieb said:

Without addressing the car issue I think your insurance would be null and void if in the event you had an accident as would probably any recovery insurance you had in place?

I’d also be concerned that if stopped the police would have something to say which might not be pleasant to hear?

Well, ernie, I knew all that legal/non hypothetical stuff.

keep trying re the mechanical side?

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So, thoughts that may or may not be relevant ...

The transmission is still a box full of cogs however 'clever' these may be. I doubt that you can really rule out wear and failure within the transmission.

How does an electric motor behave when you apply a voltage to it's coils and prevent the rotor from moving. I suspect that you could overload, overheat and prudentially damage the electric motors (but I'm not entirely confident of the physics)

🙂

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3 minutes ago, philip42h said:

So, thoughts that may or may not be relevant ...

The transmission is still a box full of cogs however 'clever' these may be. I doubt that you can really rule out wear and failure within the transmission.

How does an electric motor behave when you apply a voltage to it's coils and prevent the rotor from moving. I suspect that you could overload, overheat and prudentially damage the electric motors (but I'm not entirely confident of the physics)

🙂

If you stall any electric motor the supply will try to move the motor, get progressively hot and eventually burn out unless the is an overload protection system. Even running a electric motor in an overload situation for any length of time is likely to over heat it. How any of this relates to a hybrid car is beyond me. From experience with a non hybrid car towing a caravan within limit and a convention auto gear box you can get problems on a hot day, especially on even a gradual incline.

Without wanting to start a war of words I would be concerned knowing I was driving a car towing combination well outside the manufactures recommendations, not  just for myself but for other road users. I’ve seen first hand the danger of such practices with a neighbour who managed to rip most of the towing hitch out of the back of his car.

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Ernie, the question starts with the magic words:

1 hour ago, Marcusthehat said:

Purely hypothetically ...

so I am assuming that Marcus has absolutely no intention of exceeding the towing weight limit of his Rav4. So the question as I understand it becomes "what part of the Rav4 hybrid 'breaks' if one were to be so stupid as to exceed the towing weight limit of a hybrid Rav4?"

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I

If you own a vehicle that will tow the weight you require why use a vehicle that is not suited for it?

 

Now if the others are for work and you want something to tow a caravan, I would suggest you look to something more in the range of the Mazda CX-60 (not out until September) same engine also hybrid different transmission and a towing weight of 2500KG

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54 minutes ago, philip42h said:

Ernie, the question starts with the magic words:

so I am assuming that Marcus has absolutely no intention of exceeding the towing weight limit of his RAV4. So the question as I understand it becomes "what part of the RAV4 hybrid 'breaks' if one were to be so stupid as to exceed the towing weight limit of a hybrid RAV4?"

I take the point, hypothetically??? 

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Aside from the obvious stuff (Law, brakes, tyres etc. ) I think MG2 (and MGR) might have their lives shortened a bit, esp. if towing up a hill a lot or excessive stop-start - Electromagnets are basically short circuits and the only reason they aren't just very powerful resistive space heaters is the movement dissipates the energy going through them. Without that, all the energy just gets turned into heat. Lots of heat! That's why the car will flash up a warning if it's being held stationary on power instead of the brakes. (As an aside, Tesla were very clever to realize this and use this behaviour to heat up the Battery through the coolant loop when it's cold, instead of wasting space and components on a dedicated heater; Those traction motors can put out a lot of heat when powered statically/stationary!)

Unfortunately the enemy of permanent magnets is heat, lots of heat, and since all Toyota HSD motors are permanent magnet motors rather than magnet-less induction motors like Teslas use they will tend to lose torque over time if exposed to lots of heat repeatedly.

I think the 'power split device' itself would be okay; There is no direct connection from the ICE to the wheels through it so if it was too heavy for the engine to move (Unlikely as that is) it would just spin MG1 while MG2 catches fire :laugh: (Mostly joking - I expect the ECU wouldn't let it get to that point!)

The other thing is the structural integrity of the tow bar and all the stuff it's attached to - Would probably be fine well above the rated weight under normal conditions, but in the event of an accident or emergency of some sort the possibility of the towbar or even rear chassis rail being ripped off and the trailer parting ways gets less improbable.

I reckon you could go a bit over the maximum weight without too much issue but obviously the further you go the more likely something will break!

 

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Thank you Cyker.

More the hypothetical analysis I was after.

Btw. I am a 63 year old farmers son, who grew up with dad and other farmers routinely towing heavy cattle trailers behind saloon cars, with zero fuss, mishap nor incident.

I also, and possibly unfortunately, "pride" myself on driving smoothly and with mechanical sympathy, so in the years since 1978( 44 years) have never therefore had a vehicle break-down to leave me stranded, this despite driving older and self maintained vehicles, 3  second hand and 2 new, until the Rav4  was purchased 1 year ago. My only at-fault accident was in about 1989 when I dunted into a bloke that stopped dead immediately after entering an otherwise empty roundabout. I have also done some heavy towing, without fuss or incident.

I typed that to attempt to explain that I am rather unlikely to hitch 3500Kg behind the Rav4, and even if I did, hypothetically, "in extremeis" I imagine I would be highly unlikely to suffer from mishap or be involved in an accident. Because in those particular hypothetical circumstances I imagine I would be driving most defensively.

In short I am not a witless lunitic driver. Honest Guvenor!

Cheers all

Marcus

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Aye, exceeding the manufacturer's tolerances is never a good idea.

Quite a lot of people ended up with lunched clutches by remapping their diesels too hard. 🤣

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I never had ANY mechanical problems as a result of remapping a diesel and I have had plenty, including one remapped from 120 to 200 horses. However for the OP, if you tow a weight such that it takes your outfit over the GVTW then it is illegal, irrespective of any other factors. 

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That's one advantage of EVs and HSDs - No clutches to burn out! :biggrin: 

(Just motor windings instead :laugh: )

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28 minutes ago, Flatcoat said:

I never had ANY mechanical problems as a result of remapping a diesel and I have had plenty, including one remapped from 120 to 200 horses. However for the OP, if you tow a weight such that it takes your outfit over the GVTW then it is illegal, irrespective of any other factors. 

It's not about the power so much it's about the torque.  I've remapped a few myself and always kept it under the max torque of the the gearbox.

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The point about cooling of electric motors or generators is one to really note as the heat component once generated in electric machines has a rapid increase to a destructive level. There is no graceful build up as in thermic  devices like petrol or diesel engines. I am reminded however of the heavy gun moving machines the germans had which were developed by Porsche, entirely electric and massively high torque.

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