ksoul2084 wrote:FWD introduces significantly negative handling characteristics and was always a "compromise" design choice even in ICE cars. RWD provides superior handling on dry surfaces vs FWD, and if you are in a market where ice and snow are a factor, AWD is again superior to FWD (and RWD). No need for FWD in EVs.
IanL wrote:MassDeduction wrote:..... I'm told that FWD is generally superior to RWD for winter driving in snow/ice (though AWD is better than either).
That is true for ICE and EV as regards traction, but an ICE with AWD derives no benefit as regards braking, whereas an AWD EV will benefit due to four wheel regeneration.
MassDeduction wrote:You raise an interesting point about regen. Is there significantly more regen on an AWD set-up than a FWD or RWD set-up? AWD generally is shorter range than FWD or RWD, I note, which actually surprises me as you might think it wouldn't be much difference (two motors working a little less hard, vs. one motor working a little harder, all other things being equal?).
IanL wrote:I'm beginning to form a view that the amount of regen available to the driver is probably determined by the designer, rather than the physical limits. However, I was thinking that, in conditions of poor grip, it is better to split the available regen between four wheels rather than limit it to two. I have experienced loss of grip under regen on the FWD SoulEV, and thought AWD would help in that circumstance.
notfred wrote:AWD has more driveshafts to rotate and more universal joints on those driveshafts, that gives a small inefficiency.
There are 2 parts to handling in the snow and other slippery conditions. Firstly, can you get traction - this is directly related to where the weight is in the vehicle. A heavy ICE, gearbox and differential in the front of the car gives good traction with FWD. In the case of an EV where the major weight is the battery pack between the wheels and the weight distribution is more balanced then there isn't the concern.
The second part is about what happens when the wheels lose traction. Generally the driven wheels will lose traction first because some of their grip is used for acceleration leaving less available for turning. In a FWD car this leads to understeer, and an inexperienced driver has a natural reaction to turn the steering more and lift off and possibly brake, which will not lead to any surprises. In a RWD car this leads to oversteer, which while being more controllable for an experienced driver is going to lead to an inexperienced driver panicking and potentially spinning out, possibly hitting some other things on the way.
Before my Soul EV I had a Subaru Impreza with manual transmission. It was glorious in the snow, extremely controllable on the throttle, it might not be pointing in the direction it was travelling but it got there and was great fun. If I had to replace my Soul EV, an AWD Ioniq 5 would be high on my short list.
MassDeduction wrote:IanL wrote:I'm beginning to form a view that the amount of regen available to the driver is probably determined by the designer, rather than the physical limits. However, I was thinking that, in conditions of poor grip, it is better to split the available regen between four wheels rather than limit it to two. I have experienced loss of grip under regen on the FWD SoulEV, and thought AWD would help in that circumstance.
I'm speculating here, as I'm no gear head. However, it occurs to me that regen is the motor basically working in reverse. So perhaps a more powerful motor could work harder in reverse? So my current thinking is that we're both right, specifically:
- the power of the motor determines the upper limit of how much regen is possible, but
- the designer can choose how much regen occurs within the range of what the motor is capable of
I can think of reasons why a car might not be designed to produce the maximum possible amount of regen, including potentially excessive wear and tear on the motor, and recharging the battery pack faster than is ideal.