Why Are Hybrid Cars Not Allowed To Tow?

[geo13647]

Having a bit of a Monday morning here, (yes I know it's Tuesday)

but can't remember why you can't tow legally with a hybrid.

Of course, it would muck up all the MPG benefits, (but towing with anything does that).

Is it just a manufacturers decision, not submitting it for type approval, wanting to avoid bad mpg stories,

or is there a technical/ physical reason?

Roll on Tomorrow, when I hope my brain is working again.

Regards,

G...

[theoilburner]

As I understand it, the Atkinson cycle the Prius uses means that the engine has less power reserves (running closer to maximum power is more efficient in an ICE, the Prius engine has lower revs for its max power, so runs closer to that most of the time, unlike a standard car engine) and relies more on the Battery to step in and make up the shortfall when climbing hills etc

Therefore, if you were to tow, the car might continually be draining the Battery (due to the extra effort, depending on what you're towing) and you'd soon find yourself crawling along without enough power from the engine alone to move things along.

Remember, in the Prius there is, effectively a single fixed gear, and the torque of the electric motor(s) helps overcome that resistance.

I believe in the Lexus RX400/450h the engine there is so massive that there's a surplus of power, so you can tow.

Theoretically, if you were to drive up a large enough mountain, the Prius would run out of Battery power and, relying on the engine alone, would crawl along to the summit, for the same reasons. I don't think there's many places in the world where this is possible mind!

Edit: Lexus RX450h - towing limit 2000kg! There's one hybrid that really can tow.

Edited July 30, 2013 by theoilburner

[johalareewi]

The only reason they can't legally tow is because Mr T hasn't done the paperwork to get them approved.

[ToyotaAurisHybrid]

Did you by any chance watch top gear last night ? 😉

[Parts-King]

Did you by any chance watch top gear last night ?

Very funny....great series :D: :D:

[Awebb180]

in a nutshell on the Toyotas its to do with the two motors on the hybrid system mg1/mg2 then cant get the power/possibly overheat whislt towing so thats why no type approval where as 1 lexus vehicle uses differnt layout of the motors and can tow a small trailer

Alex

[sanzomat]

Its a shame they couldn't allow even a small trailer load - just 250kg would be enough to tow a track motorcycle/trailer combination so that I could pursue my new found desire to ride on trackdays. I was looking into buying a track bike rather than run my pride and joy R1 on the track then realised I can't tow anything. I hadn't thought to check towing capacity before placing my order and I vaguely recall being told by the guy in the dealer that the reason the regular Prius can't tow is that the batteries are under the boot floor so prevent a bracket being fitted and as the batteries are in the centre console on the 'plus it could have a bracket fitted. Towing 250kg would put considerably less load on the drivetrain than loading the 'plus up with seven adults and some luggage. This would also allow many small box trailers to be used so people could take their rubbish to the tip without putting it all inside the car. I'm not sure what hybrid drivetrain the Peugeot uses but that can tow up to 500kg. I suppose if they type approved a bracket then it would be up to the user to ensure they didn't exceed the weight limit and Mr T would start to get warranty claims from folks with worn out drivetrains who would obviously say "I was only towing 200kg"

[Parts-King]

You answered your own question I think

IF there was a tow bar on it, you would find the car abused at day 1, nobody would stick to a towing weight resulting in very unhappy customers when it all goes pear shaped

Kingo

[theoilburner]

The PSA Hybrid system fitted to the 508 and 3008 etc is completely different to the Prius, it has a normal 2.0 diesel engine with stacks of power reserve, no Atkinson cycle there.

Another Hybrid that can tow is the super rare Volvo V60 Hybrid. That can tow 1800 kg, thanks to having a beefy 2.4 diesel engine.

I don't believe the old wives tales about "Prius can't tow because of Battery location" or "Prius can't tow because the motors would overheat". Clearly, the Lexus RX450h doesn't have those problems and that uses the same Hybrid drive train (except for the whopping 3.5 V6 engine) as the Prius. Also, the Prius + can't tow and that has the Battery pack in the centre console!

Remember also that the Toyota system is the only one using a power split device with the fixed gear ratio - this requires motor assistance otherwise the 1.8 engine wouldn't have enough torque to turn the road wheels from a standing start! Other Hybrid systems (Honda, PSA, Volvo etc) get additional power from the electric motor (which they don't really need) and conventional gear boxes.

I think Kingo has it right, in that if Toyota did allow a very low towing limit (within the capabilities of the drive train) then people would abuse it and there would be bad publicity.

[Parts-King]

Ive seen Hilux and Landcruiser towing far in excess of it's plated towing capacity. Then when the clutch burns out they wonder why, you would have the same scenario if you put a bar on a Prius, obviously not burning out a clutch tho

[Cyker]

Another problem is the smaller than usual brakes on most hybrid vehicles. The HSD isn't really rated for high torque and over-torquing an electric motor can cause the windings to burn out, which would pretty much write-off the car. I suspect Toyota didn't want to risk that and hadn't done extensive enough testing on what is a relatively niche thing so they just left it.

The Lexus RX 400h is a totally different beast; For one, the main engine isn't an Atkinson cycle but a conventional V6, and secondly the HSD system is also very different (Presumably beefed to cope with the extra torque, plus it can have up to 3 leccy motors rather than just two! The extra one is for the rear wheels.)

I almost want one but even second hand they're waaaay out of my budget! (Plus it's about as appropriate as a Nissan GTR for my usage purposes! )

[theoilburner]

Another problem is the smaller than usual brakes on most hybrid vehicles. The HSD isn't really rated for high torque and over-torquing an electric motor can cause the windings to burn out, which would pretty much write-off the car. I suspect Toyota didn't want to risk that and hadn't done extensive enough testing on what is a relatively niche thing so they just left it. The Lexus RX 400h is a totally different beast; For one, the main engine isn't an Atkinson cycle but a conventional V6, and secondly the HSD system is also very different (Presumably beefed to cope with the extra torque, plus it can have up to 3 leccy motors rather than just two! The extra one is for the rear wheels.) I almost want one but even second hand they're waaaay out of my budget! (Plus it's about as appropriate as a Nissan GTR for my usage purposes! )

Exactly what I said, more or less - it's the Atkinson cycle that's the main problem. Brakes can be beefed up, but the lack of reserve power in an Atkinson cycle engine means there isn't anything left for towing, so you end up with a power deficit in very ordinary driving conditions, meaning the batteries have to keep making up the shortfall, which they can only do for a while...

I noticed that the new Lexus IS300h with it's 2.5 Atkinson cycle engine can't tow either.

And yes, I'd love an RX too. It'd probably get better MPG than my auto diesel Mondeo, and it'd be a better towcar, probably!

[Birty]

Sorry but confused? Is it legal in uk to tow with prius or not? I want to fit a tow bar to fit a cycle carrier and was thinking of getting a small trailor for skip run etc... Will the fuzz pull me over, handcuff me and lock me up and throw away the key or will mr toyota say sorry mate u just lost your warranty or worse still - both!!

[steverally]

Sorry but confused? Is it legal in uk to tow with prius or not? I want to fit a tow bar to fit a cycle carrier and was thinking of getting a small trailor for skip run etc... Will the fuzz pull me over, handcuff me and lock me up and throw away the key or will mr toyota say sorry mate u just lost your warranty or worse still - both!!

Toyota did not get type approval for fitting a tow bar. I do know of others on this forum who have fitted them for the use of cycle racks, but as you rightly say If you do tow a trailer and then have a problem then maybe you'd have a real fight about warranty claims.

This link may be useful, especially the comments from 'partsking' who is in the trade http://www.toyotaownersclub.com/forums/topic/128669-tow-bar/

[Birty]

Thanks... Tow bar yes for my bikes but trailor i will forget?? Bet it still voids warranty though??

[aCactus]

Thanks... Tow bar yes for my bikes but trailor i will forget?? Bet it still voids warranty though??

Not sure about the "ordinary" Prius but for the plug-in then it is a no for any tow bar use. It is quite clear in the manual (page 399)...

"Your vehicle is not designed for trailer towing or for the use of tow hitch mounted carriers"