Why not in-wheel hub engines?

Why not in-wheel hub engines?

I have read about the Brabus All Electric 4wd , and now it seems it is in production.
Brabus uses wheel hub engines. 4 of them for a whopping 4 x 110 hp. 440 HP. Grip on all wheels. Must be fun. Even in wintertime.

As we know there is no plan for a 4wd Tesla S any time soon.
But wouldn't it be possible for Tesla also to use those Protean Electric motors?
Sure bolting 2 of them in front corners must be cost friendly way to give Tesla S 4wd?

I do see the obvious, that those 2 electric motors will increase the unsprung weight. Are there others?

Maybe possible to do an personal upgrade to the front wheels, slightly modification maybe but should be doable?

Here you can see those In-wheel motors

aaronw2 | 30 janvier 2013

In-wheel hub engines are a bad idea. I had this discussion with a friend of mine (who happens to work for Tesla). You want to reduce the un-sprung weight as much as possible for handling purposes. Heavy wheels won't handle the bumps and whatnot as well as light-weight wheels.

rlpm | 30 janvier 2013

Not to mention any shocks not dampened by the tires will affect the stator, rotor, gears, inverter, etc. in integrated in-hub systems.

EcLectric | 30 janvier 2013

I don't think 'why not' is the place to start. The question is 'why'? I think the current setup is very efficient and 4WD can be achieved the way they have proposed in the model X - with a similar drive-train in the front of the car.

ghillair | 30 janvier 2013

They show a range of 350km vs MS of 480km. They show 0-100km in 6.9sec vs MS of 4.2. They don't show a price but it looks like half the car the MS is so when I can buy one 40K USD I might think about, but they don't show a price.

Timo | 30 janvier 2013

Hub motors are weak generally speaking. You need four to get same result as Model S gets with one. Add one more and hub-motors lose.

evanstumpges | 30 janvier 2013

In addition to adding unsprung weight, hub motors increase the distance between the wheel and the king pin linkages. This has implications that make proper suspension geometry more difficult and will generally increase stresses in all of the suspension components.

With hub motors, there is the advantage of better natural air cooling, but the disadvantage of being more exposed to the elements.

Another consideration, more motors=more motor housings=higher overall motor weight.

RedShift | 30 janvier 2013

" You want to reduce the un-sprung weight as much as possible for handling purposes. Heavy wheels won't handle the bumps and whatnot as well as light-weight wheels."

Zigackly. Which is why I had asked tesla for a smaller diameter wheel than even the 19". Alas, no go.

I'd love light 17" or 18" wheels to be the std equipment. I know, I know car is big, won't look good, etc etc..

nickjhowe | 30 janvier 2013

@Redshift - what's the weight of a wheel compared to a tire? For every inch reduction in wheel diameter you need to increase the tire wall by half an inch. There must be little marginal weight saving...?

jat | 30 janvier 2013

In addition to the unsprung weight issues (which Lotus did some work on and found that for the most part you could work around the issues by tuning the rest of the suspension), a hub motor means that the bearings in the motor itself support the weight of the car, so they are more likely to wear out than if the motor isn't weight-bearing.

aaronw2 | 30 janvier 2013

See for reasons why you want as little mass as possible in the wheels.

DTsea | 30 janvier 2013

Nitpicky engineer note:

An ENGINE is a prime mover- it contains its own energy source. Rocket engine. Internal combustion engine. Jet engine.

a MOTOR is a device that converts energy generated elsewhere to kinetic energy. Hydraulic motor. Pneumatic motor. Electric MOTOR.

There is no such thing as an electric 'engine.'

ltd | 31 janvier 2013

With left/right hub motors I suspect a mechanical failure or software bug would result would have very very bad consequences.

RedShift | 31 janvier 2013

Overall weight savings are better when you reduce the wheel weight. I went for 15" wheels (a lighter alloy than the OEM 16") for my first car, and I recall that the per wheel weight was down by almost 5 lbs. 20 lbs overall may not sound like much, but it made the handling noticeably tighter. The rotational unsprung mass reduction gives you the maxim bang for bucks.

Timo | 31 janvier 2013

It also makes you feel all the bumps onto road. Larger wheel doesn't notice small bumps, smaller does. Larger wheel makes smoother ride.

gianni.terragni | 1 février 2013

Thank you, in Italian there is no such distinction, and I could not tell if there was a real difference in the English language. Now I know

Brian H | 1 février 2013

in casual speech, there is less distinction drawn. E.g., to "go motoring" is to go for a pleasure drive (in your engine-driven car). The electric starter in a car is always called a 'motor', but no one would be confused if you referred to the V-6 as a motor. Except engineers, who might get slightly red in the face for a moment.

Tiebreaker | 1 février 2013

Timo - he's talking smaller wheel (rim) plus larger tire = external diameter remains the same. I know this is probably a language issue, often "wheel" means the whole thing in many languages :-).

So the effect is quite the opposite: less bumpy with the smaller rim + bigger tire.

gianni.terragni | 1 février 2013

You will lose, but it is a gain: the reduction gear, the differential, the semiaxis and omocinetic joints
  You gain, but it is a loss: 31Kg per wheel and all power and signal connections to each wheel. The 4 motors have to work under extreme acceleration and in contact with the dirt of the road.
It will be interesting to see the developments

jat | 1 février 2013

Personally, I think in-wheel motors are perfect for small, non-performance EVs. You use up less space in the body of the car, which is most at a premium in small cars, and non-performance car buyers won't care as much about unsprung weight. Lighter cars also lessen the weight being born by the motor spindles as well.

Protean | 5 février 2013

All - I have to jump in here on in-wheel motors. Don't get me wrong, the Tesla powertrain is fantastic. But we make in-wheel motors so I wanted to say something.

Each of our in-wheel motors is 80kW so it would take four (not two) to get us to the Model S (310 kW) for power. But,each of our motors is 800 N.m peak torque and more torque feels better.
We can also provide torque and regen on each wheel individually, so torque vectoring around corners is doable.

Unsprung mass is legit, but can be overcome the added 31kg per corner with conventional ride engineering work on shock damping, springs, etc. Here's a study from Lotus you can read if you wish:

We use a conventional automotive bearing so we have an answer for road loads without creating load paths through the motor itself.

Besides, I would like to free up the space occupied by in-board motors, drive shafts and stuff and put in more battery (range), more people space and make the car look completely different.

We are still in the prototype stages so I'm not "selling" here. I just want to add some more to the conversation.

Superliner | 5 février 2013

I see.. increased complexity, increased cost, minimal "if any" gains in efficiency as far as range propulsion etc. While I'm sure there are specialized platforms that might benefit from such an arrangement. It does not appear to be a setup that would drive down costs significantly towards a goal of a viable affordable to the masses mass produced "on road" BEV.

kilimats | 5 février 2013

I dont see in wheel becoming the norm anytime soon, people need to swap their tire for winter wheel, please like to change the look of their car with new wheel, people don't want their crazy expensive in wheel motor to be stole with a few bolt out, etc...

RedShift | 5 février 2013


I think in wheel motors are perfect for all wheel drive applications like off roaming vehicles.
Even though the added unsprung weight can be somewhat offset by suspension design and spring rates, it's
Not 'ideal' for a sports car/sedan.


DTsea | 5 février 2013

Gianni- Anch'io parlo la bella lingua Italiana. (Dopo un anno a Foggia). Vero, pensando un attimo, che si usa la stessa parola. C'e' un convergenza bella pero' dicendo 'ingeniere' (con la radice che sarebbe in inglese 'ingenious' oppure 'gene' significando il momento di creativita, di nascita; in America, i primi ingenieri erano quelli progettando motori di vapore- quindi 'engine' mentre 'motor' scende dalla radice 'muovimento.'


nickjhowe | 5 février 2013

That's easy for you to say.

DTsea | 5 février 2013

Well nickjhowe, it makes more sense in Italian but I will try.

The word for engineer in Italian is ingegnere which comes from the same root word as gene, genius, ingenius- relating to creation, or maybe birth. The first American engineers were guys who designed or operated steam engines. Back then an 'engine' was any designed machine but steam engines became so prevalent that 'engine' took its modern sense. However the root word of 'motor' is the same as the root of 'movement' so you could say that a motor is anything that makes motion, but an engine is the real spark- the prime mover- and that the juxtaposition of those words is pleasing and meaningful.

So I don't get red in the face about it, as Brian H suggested... I just like using the right word because of the compact and beautiful historical connotations.

DTsea | 5 février 2013

Ingenious, I meant. Engineers, as all know, are poor spellers.

lph | 5 février 2013

Did you not have 120kw wheel motors under development at one time. That would be about 630 hp if installed on all wheels.
Also, how much breaking can be done with these motors? If all of breaking can be done through regen (using resistors if battery / supercapacitors can't take it) then we save some of the unsprung weight here.

Brian H | 5 février 2013

breaking is to be avoided at all costs. Very expensive to repair. It's best to brake before they break.

lph | 5 février 2013

Opps, should had checked before sending.

aaronw2 | 5 février 2013

I doubt they'd ever allow for all electronic braking. I think mechanical brakes would still be required by the NTSB. Mechanical brakes are designed so that there's no single point of failure, i.e. dual master cylinders, etc. You might be able to get away with smaller brakes, like the Prius does. Inductive motors require excitation power to generate electricity so if your main power supply (i.e. battery) dies or have an electrical fault you'd have no brakes.

Timo | 5 février 2013

@Protean; But,each of our motors is 800 N.m peak torque and more torque feels better

Tesla Model S standard 85kWh version gives peak motor torque of "only" 440Nm, but that then gets multiplied by reduction gear so that output torque is 9.73*440Nm = 4281.2Nm. 800*4 = 3200Nm, or 4281.2/4 = 1070.3Nm. That's with single motor. Doubled to AWD you get over 2000Nm measured from the wheels.

Performance version gets even more impressive numbers.

The fact is that hub-motors just are not powerful enough, not for passenger cars anyway. Hub-motors could be useful as brake replacements though, especially for very heavy vehicles with multiple wheels. Regen would be much better I imagine.

Superliner | 5 février 2013

@ Iph .

100% regen braking under current NHTSA regulations would not be allowed. There MUST be a redundant mechanical system, Air or Hydraulic in place.

Timo | 5 février 2013

@Superliner, I imagine that is one regulation that could be removed if the regen as brake could be proven to be equally powerful and more reliable (magnetic brake essentially, with no moving parts it could be more reliable than ordinary brakes).

Brian H | 5 février 2013

Complete stop at low speeds must still be managed mechanically. Unless you run the motor in reverse to apply decel.

Protean | 12 février 2013

To address some of the follow up comments....we can regen as much as we "gen" or about 80kW per motor. Our motors were used on both the Brabus EV and the Brabus Hybrid cars, based on a Mercedes E Class. Just from regen, we can develop about 0.3G of decell, which is enough for most normal stopping maneuvers. However, we also have conventional disc brakes (not breaks) because of regulation requirements. (belt and suspenders)

Finally,we use a conventional wheel and tire, not a special design, as long as it is at least 18". Thanks for listening.

EcLectric | 15 février 2013


On this forum, it's "breaks", not "brakes". You will learn...

Brian H | 16 février 2013

Protean, don't listen to him. Group-think misspellings are still boners. >:p

torst1 | 16 février 2013


Do you think it might be possible in the future to add aftermarket in-wheel motors to the front wheels of Tesla S to get 4wd?

I realize there are not all positive effects from using such motors regarding unsprung weight but for many users the benefits would far outweigh! the downside. And after all, Tesla S is first and foremost an every day car - not a track day car or a trailer queen. For me living in snow and ice 6-8 months a year I do prefer 4wd. Yet I would not like to wait for the Tesla X.

Will it be possible at all to mount your motors in the front wheels?

Benz | 14 mars 2013

The Toyota i-Road has been revealed at the Geneva Motor Show. The two front wheels have in-wheel electric motors. I think Toyota should really start thinking about producing and selling these i-Road vehicles. They are ideal for the city, where there is lots of traffic. This could be a real success. It's better than the Renault Twizzy anyhow.

jat | 14 mars 2013

@torst1 - I don't think it is a good idea to retrofit hub motors, as I think you need to design the suspension around the extra unsprung weight and torques that will be created.

timojames | 4 avril 2013

Retro fitting Hub motors wouldn't require a re-design of the Suspension geometry, a recalculation of the damping and rebound maybe and change the springs and shocks. If you were planning on converting your ICE car you would have to do that anyway.

ecocentral | 16 avril 2014

If hub motors are so useless, can someone explain these 2 youtub videos?

DTsea | 16 avril 2014

Why would you want to build and control four motors when you can do it with just one?

staze | 16 avril 2014

A bit off topic. When clicking on the OP's Brabus link, why is the title of the webpage page "Brabus - Tesla Roadster"? (hint: look at your browser's title bar)

ir | 16 avril 2014

@eccocentral: "If hub motors are so useless, can someone explain these 2 youtub videos?"

Easy! Tesla builds CARS not bikes!

chrisdl | 17 avril 2014

Even the fantastic 4-motor Rimac Concept_One doesn't use hub motors.
They're simply not there yet. Protean may be leader in the field and in case this is definitely something to watch.

But in the future, we may see hub motors in EVs. Nice, neat, and simple.

Webcrawler | 17 avril 2014

Hub motors will not work due to fact that dynamic loading of every component will lead to premature failure. Also corrosion is a big issue. There is no seal that can handle the dynamic loads and water pressure in a wheel that will not leak in short order... With these loads you need a really big set of bearings and this means you need a really big seal. Big seals are more likely to fail and leak...

Right now if your seal fails you have to replace the cheap wheel bearings and maybe a spindle. In a hub motor you replace the motor...

Car t man | 17 avril 2014

Inwheel motor projects are sucker traps for unknowing investors, who don't know much about motor design or manufacturing. Much like Webcrawler described, they simply do not make sense for anything that needs handling and reliability of sealing is nowhere near where it should be to be a reliable option. Maybe for military and applications where money is thrown away on rebuilding and maintenance but not in applications that need to handle and make economic sense in the mid or long run. It only looks good as an idea in the simplest
of terms.

darkhut | 15 juin 2014

I love how random people keep saying how in-hub will never work, for this and that reason, in their humble opinion, blah blah blah. Did anybody bother to read the nice research from Lotus? Doesn't seem so. If Lotus tells me unsprung mass can be dealt with, and Mercedes makes prototypes with in-hub from Protean, then it must be something worth their time. Maybe some of these posts are payed for by the automotive and oil industries who would like to maintain the status quo?