Gas to Performance Hybrid?

Converting a car to 100% electric is a big leap. I don’t have the skills or the $$ to do it, but I was wondering if there was an easier way to get started? Why not take the intermediate step of converting the car to a performance hybrid?

Basically what I would like to do is take my FWD car and put a pair of wheel motors and a small battery pack in back. I think a good performance number would be 25 hp and 100 lb/ft torque for 5-10 seconds.

I am looking for suggestions for wheel motors. PML Flightlink’s Hi-Pa drive system is interesting but I am scared to ask how much it costs.

What do you think?

I’m wondering if one could take an AWD car and pull the drive shaft to the rear diff and bolt up a motor to be run direct drive. That might be a bit less expensive. If done to an old subaru brat or wagon there would be room for a bit more battery capacity and maybe then a PHEV would be the result.


That’d be a great idea if one had a car that came with an AWD option.

i think that would be harder actually.

Bolting on wheel motors would be easier, but they are extremely expensive at the moment.

[QUOTE=Olie;649]i think that would be harder actually.[/QUOTE]

Why? If there is a transaxle in front you could just disconnect the rear and it would be FWD. Then you put a motor on the rear like a direct RWD drive car. The good thing is that the suspension and mounting points at both ends of the car are already engineered to take the loads.

Adding wheel motors to the rear of a FWD car would require a complete redesign and fabrication of the suspension and mounting points to carry the hub motors.


Adding wheel motors to the rear of a FWD car would require a complete redesign and fabrication of the suspension and mounting points to carry the hub motors.


Why? The brakes probably make more braking horse power than the motors make propulsive horse power. And “pothole horse power” is probably greater than either one :eek:

PML Flightlink put wheelmotors on the rear of their AWD Mini. I don’t know that they didn’t make changes to the rear suspension, but I suspect that they didn’t.

Ok… Here goes. *****DISCLAIMER: The post that follows is my enthusiast’s theoretical rambling supporting my personal opinion. In no way am I issuing a professional opinion nor recommendation… *****

I could not find any pictures or diagrams on the AWD Mini’s rear suspension. An educated guess would be the illustration I have attached of a Benz rear multi-link. According to Edmunds the Mini also uses a multi-link rear. The illustration shows a common multi-link setup. I would say that Flightlink could have a serious achilles heel in their conversion if they do not reinforce the rear arms. Here’s why.

If you look at the illustration you will see that the links act primarily as a wheel locator. The majority of drive torsional forces are transfered directly to the diff carrier by way of the half shafts. The center section is then transferring the loads to the body of the car through its mounting points. Braking forces at the rear are not nearly as strong (in a torsional sense) as acceleration forces would be for a few reasons.

  1. the load is actually more lateral than torsional since the ground is essentially trying to “wipe” tread from the tire much like a sanding block on a bat. Yes, there are still torsional forces transferred by the brake caliper to the links at its mounting point, but this force is still much less than acceleration forces.
  2. vehicle weight transfer under braking shifts to the front of the vehicle whereas accelleration transfers weight to the rear. This change in weight distrubution lessens the amount of traction the wheel is able to maintain. This is why front brakes are much larger than rears. A great example of the difference in braking force capable by the rear compared to the front is to perform a burnout. Step on the brakes and stomp on the throttle while holding the brakes. The (rear) drive power easily over comes the braking power while the front still holds the car in place with no problem.
  3. weight transfer during acceleration increases traction and therefore greatly increases the forces that are applied. The ground is not moving, the car doesn’t want to move either so the suspension links take all those forces. Again, these are largely torsional forces that are designed to be carried through the halfshafts to the center section. Since we are talking about rear suspension on a FWD, it is only meant to take the forces of braking and normal suspension travel. The engineering will be for the wrong type and level of forces. The engineers at “Automaker x” will have only designed for forces foreseen in the intended application. The more “economical” the vehicle the less additional strength (breathing room) will be added.

Let’s assume for a moment that the multi-link is engineered coincidentally to be able to carry such forces imposed by wheel motors which would be mounted at the ends of the links therefore transfering ALL torsional and lateral loads through the links to their mounting points. There is still geometry to consider.

Every multi-link rear suspension exhibits a phenomenon called squat. This can be observed as the rear end of the vehicle dropping during hard acceleration. What is actually happening is the weight transfer combined with lateral and torsional forces are making the links articulate and raise the wheel. The mounting locations of the links are designed to place the links at angles around theoretical points of intersection to create a specific degree of leverage to counter squat. This geometry is conveniently called anti-squat. The amount (or percentage) of anti-squat is a delicate balance of acceleration and deceleration forces. This is because the more anti-squat that is dialed in the more negative effect there is in the opposite direction. This being braking. The effect is exhibited as wheel hop.

In the case of a FWD vehicle there is little to no geometric (nor torsional for that matter) consideration for acceleration forces on the rear suspension so squat (or anti-wheel hop) is optimized. Also, the suspension in the rear of a FWD car is designed to be for the most part fully passive during acceleration. Adding a drive force to those links or arms could place the suspension in bind for certain parts of its travel rendering it useless, unpredictable and even dangerous.

This is why I will stick to my earlier post that adding wheel motors to the rear of a FWD car would require re-engineering of the suspension arms/links and their mounting points.

You mentioned “performance hybrid” in your original post. You also mentioned a figure of 100ft/lbs of torque. If you are talking per wheel motor that’s a lot of load! My turbo subaru puts out 250 peak torque at full boost. Since electric motors produce full torque from just off 0 rpm, it’d be like dropping the clutch on my car at 4000 rpm (while somehow managing to achieve full boost with no load)

Sorry for the longgggg post. Suspension can be extremely complex.


Thanks! I suspected in the beginning that the Mini wouldn’t be able to use the rear wheel motors, but gradually came to doubt that position. Do you mind if I repost your explanation elsewhere?

[QUOTE=Jack the R;732]Thanks! I suspected in the beginning that the Mini wouldn’t be able to use the rear wheel motors, but gradually came to doubt that position. Do you mind if I repost your explanation elsewhere?[/QUOTE]

I really don’t care if you do. My post was not in any way a professional recommendation nor opinion. Mainly just enthusiast theorization. My attorney says to issue a disclaimer…:wink:

Oh yeah, if you do post it elsewhere please post here as to where you reposted it. I’d like to see how much the real suspension engineers rip me up (if you goto a susp. engineering forum or something). I’m always up for learning something new.


O.K., Link

Hey Jack,
I assumed you were talking about compact FWD car. Not a Riviera. Take a few pics of your rear suspension and post them here. Your wheel motor idea may still work with that car. You may still have to re-engineer your suspension, but it may be A LOT easier to do on that car. You could possibly go 4 link or even 3 link (my personal favorite). :cool: By the way, I talked to a guy at my local hobby shop. Lipos would be far too expensive to use for a pack. Not to mention it’d take like a hundred 3 or 4 cell packs to make the thing.


Heh, I figured if Tesla could wire up a few hundred/thousand NiMH’s, it wasn’t entirely out of the realm of possibility. The A123 cells are Li-ion though, not LiPo, aren’t they?

I was looking at the HyMotion Prius PHEV pack a couple days ago. I thought that would be perfect, but the bastards say they won’t sell them for converting other vehicles to hybrid.

Something will come available in time :smiley: We’ve still got a couple years before PML Flightlink starts mass producing wheel motors.

As far as re-engineering suspension goes, aren’t there Corvette suspension kits for older cars? Every now and then I read about a 57 Chevy with Corvette suspension.

InSANe Diego,

Only an enthusiast, eh? :cool:

Maybe a PhD drop-out in Suspension Engineering?? Your making some very proper points on these here boards.


I’ve got a JUSTY 4WD. For weight to range calculators, be advised that the JUSTY is just shy of 1800 lbs without creative weight reduction!

There is excellent logic to a hybrid set-up on such a vehicle.

In a difficult quest for a repacement driveshaft (the driveshaft on many a Subaru makes use of ‘staked-in’, non reuseable U-Joints), I was easily able to run the vehicle without the driveshaft as the JUSTY is selectable drive - between FWD and 4WD.

One or two JUSTY owners has made the claim of disconnecting the front axles?! enabling the 4WD-FWD to act as RWD!? :eek:

I’ve got garagespace, tools, and drinks hydrating OR dehydrating… whose up to a winter project!? :stuck_out_tongue:


Thanks RP. Been REALLY busy here lately. Not much time to get on here.

Jack- I’ll have to take a bit of time to look at your pics (if it even matters anymore). I’ve only had time to drop in and glance at things lately.


I welcome your opinion. I don’t plan on buying anything until the cost of li-ion comes down so there’s no rush.

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