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Comment by bananapear | Hacker News Reader

I’d love an electric car but I also like my caravan (nice cheap (£20 a night) walking holidays in the countryside). I had to settle for a small diesel instead.

Towing isn’t something a lot of electric cars seem to be homologated for. I think the only current exception is the Tesla Model X.

Unfortunately the post-1997 EU licence restrictions (in the UK) mean that lots of people are restricted to a total gross weight of 3500kg for the car and trailer, so towing even a small caravan with a car that has batteries would need the driver to do another driving test.

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Towing should be a strong point of electric vehicles, with all that torque, shouldn't it?

Towing kills the range

Additional batteries in trailers doesn’t seem unreasonable.

Or, you could just put a generator on the trailer, and get unlimited range! =)

There was an excellent old website (it when by the name Mr. Sharkey but is sadly no longer around except in some archives with missing photos) which detailed a guys experiments with an old VW Rabbit EV. He actually built a range extender trailer for it based on the front of another VW rabbit. One interesting thing is he wasn't powering a generator but actually pushed the car via the tow ball and the engine and transmission from the donor car.

Found it on archive.org: http://web.archive.org/web/20121105135914/http://www.mrshark...

>but actually pushed the car via the tow ball and the engine and transmission from the donor car.

I'm sure that handled spectacularly on on-ramps. It would be like flat towing another vehicle and coming into a corner too hot.

I did say it was interesting! Safe, not so much.

To be fair, I think he basically fired it up when he got to the interstate, manually set the throttle to the speed he wanted to cruise at then turned it off again before coming off the interstate.

The early days of EVs reminds me of the early days of rock crawling. People tried all these wacky things because there was no instruction manual to follow, they were writing it.

That project was inspired by a pusher trailer built by JB Straubel[1] (co-founder and former CTO of Tesla), and in Straubel's write-up he addresses this:

> Dynamics:

> Despite the facts that I shortened the trailer of the Gen-2 pusher by two feet and added more IC horsepower and much more pushing force with the ability of the AT to downshift...I have still found it basically impossible to get into a condition of oversteer. (This is where the car would want to turn into the direction of the turn if you take your hand off the wheel, normaly if you release the wheel a vehicle will straighten itself out of a turn) Even in relatively tight turns with the trailer at nearly full power, the car wants to straighten itself out. The shortened trailer also drafts behind the EV much better further improving the mpg.

[1] https://web.archive.org/web/20120319173545/http://www.jstrau...

That contradicts the experience of basically everyone that's ever towed anything. I'm gonna ignore a bunch of second order variables here but if you come into a turn too hot for the weight of the trailer compared to the tow vehicle the trailer can and will push the rear of the car straight (over-steer). This is exacerbated by long trailer axle spreads and short tongue length (hence why flat towing a car feels the way it does).

Maybe he just drives really conservatively everywhere (wouldn't surprise me since a light foot was key for extending range on early EVs and many people developed that habit) or maybe the trailer is just light enough and being single axle makes it easy to steer enough that the natural tendency of the car to straighten out is greater.

I wouldn't trust anyone crazy enough to build this contraption to evaluate how safe it is. I mean, it's probably fine for him, but you wouldn't want your [stereotypical poor driver of choice] to be driving it on a wet day.

Honestly that isn’t a bad idea. It would also allow you to go on road trips where there is no charging network. Better than buying a fully ICE car instead.

I wonder if a electric car with a generator in a trailer would still be tax exempt...

No electric car I'm aware of allows you to charge while driving, even with software mods and hacks.

I'm not sure what the rocket equation for EV battery capacity would be, but EV batteries are very heavy, pretty bulky, and they need fluid heating/cooling for optimal performance. It's not as simple as hooking up the lights for a trailer.

You know, there might be more to that than meets the eye. If you are adding batteries to the trailer you might as well add a pair of electric motors and make it almost self propelled (like a multiple unit train). It would avoid needing to make the tow car overpowered.

I would think so, but I wonder what effect that has on the range? You can certainly feel the difference a 1300kg trailer makes to pulling away and accelerating, it effectively halves my miles-per-gallon.

Wow - interested to hear it is that dramatic. My only experience is towing a folding camper - this fits nicely in the 'slipstream' of my car, and I assume weighs less than your caravan no doubt.

But since you are limited to 60mph towing, I often find that my MPG is the same if not better when towing, though pulling away and uphill is affected. Not sure my current car would cope with a caravan!

I think the air resistance is the main factor. Even with the roof bars/cycle carriers on I notice maybe 5-10 less average mpg. They’re the Thule aero ones which are designed to reduce drag!

Also my car has a 6th gear for more efficient cruising on the motorway, but you can’t tow in 6th, it just sounds like it’s struggling.

The main limitations for towing with cars and car-like platform is tongue weight (not a big deal if you don't mind going slow) overall power and cooling. Don't get me wrong, easy starting from a stop is worth something but 90% of the benefit in that regard is gotten by going from a manual to automatic. Going EV isn't nearly as big of a jump in ease of use and it doesn't really solve any of the pain points so don't expect electric cars to revolutionize towing.

As others have pointed out, the range also tanks when towing (it tanks with gas cars too but not as badly). This is a bigger deal in an EV because you can't just gas up in 5min but not that big a deal if you're taking a pre-planned trip IMO.

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