Rear-wheel-drive cars are back and we have EVs to thank
thedrive.com
thedrive.com
While this is not wrong it's also missing the fact that EVs use AC VFD motors that don't need to have a closed loop response under traction loss due to the fact that the AC field will slow down the wheel of it tries to over speed just by nature of how the mechanism works. This helps keep the wheels in the static friction region where traction is highest. In trains this and other factors[1] contribute to a 2x increase in traction over DC motors. With an ICE you have all sorts of momentum in the flywheel and drivetrain that are trying to runaway until the system/driver reacts and compensates.
[1] http://www.republiclocomotive.com/ac-traction-vs-dc-traction...
RWD + traction control is pretty amazing. of course, it doesn't help too much in ice if you're running on summer sports tires, but that's an entirely different problem.
With RWD you need more training for these situations, and it's more difficult to save a car.
With front wheels slipping it's also easier with FWD.
In either case, it's good to go for training lessons to learn how to deal with situations like these. Without practice your first instincts will most likely be wrong ;)
The more things you overload (acceleration, brakes and steering) the harder it is for a tire to do the right thing.
I've done a couple rally instructional clinics, and one of the introductory drills they spent a fair bit of time on was just a giant circle of cones set up on dirt. You go around it faster and faster until the car breaks free into a slide, then you learn how to control and maintain that slide however you want. All 4 wheels have lost traction but you can still widen or tighten the radius by using weight shifts. Basically, you start steering using the pedals more than the wheel.
So you're not totally screwed if you lose front wheel traction, but this is stuff we don't teach in basic drivers ed classes.
I think this is a bad thing, fwiw. The standards of driver safety training here are incredibly low.
Got my license in California, instructor skipped the freeway part of the drive test which is mandatory.
Moved to Oregon, new licensees require both a written and a drive test but the DMV skipped them both because I already had an out-of-state (California) license.
Driver licenses are literally stupid easy to get here in the US.
The DMV lady who handled my application skipped them both anyway. ┐(￣ー￣)┌
I asked the instructor why we skipped it, and they said it was because the freeway portion "is too dangerous for the instructors".
I had a good chuckle that day.
And for the record, no, no part of the driving test is dangerous for the examiner any more than for anybody sitting as a passenger. Routes are carefully designed to cover as much & as little as law requires, conditions allow, and much more.
https://www.dmv.ca.gov/portal/handbook/driving-test-criteria...
I got a surprise in CA when I went to the DMV (waited four hours) and then was surprised with a written test. I guess it makes sense.
Weirdos.
The maturity to make responsible choices is hard for younger kids. It’s probably smart to set limits to licenses to discourage bad behavior, but be real, some driver testing guy isn’t helping.
You can't expect good competency in something like driving from 99% of the public; you're just not going to get it, no matter what it is.
It seems there’s a strong correlation between population density and minimum age one can get a driver’s license.
But in 2000 it had a slightly higher rate than the US.
The road tests did not change, rather Norway changed how its roads are engineered (due to an initiative called Vision Zero!). So I doesn't seem like the more difficult testing actually helps much.
(BTW If you want to lookup numbers be aware most sites quote death/population instead which I find to be a misleading comparison.)
Perhaps that why Norway has such a hard test - they need it!
Brazil has a higher rate than the US, but you wouldn’t be able to tell based on the testing there. Mine was:
- Backup parking
- Parallel parking
- Drive around the city with an examiner for a few minutes
Any mistakes in the first two and you’re disqualified. You have to get them right the first time with no corrections (or at least that was the case back in 2007 or so).
For the driving part, you can make two small mistakes. Any critical mistakes immediately disqualify you.
In comparison, in my WA test when I moved here I botched parallel parking 3 times until I got it right. Then I indavertently speeded and also didn’t fully stop at a stop sign (either of which would’ve been a disqualifying mistake in Brazil IIRC). Still got my license.
Nevertheless, I find it MUCH safer to drive in the US (WA in particular, the only place where I’ve ever seen folks consistently driving at or below the speed limit). Brazilian drivers are crazy aggressive and in a lot of places traffic rules are treated as mere suggestions.
I’m now back in Washington (Seattle), and I’m shocked at how often people run stop signs here.
That seems to be the way it goes in the US.
Running stop signs is not a sign of a bad driver, most stop signs in the US are not necessary (and really should be yield signs, except that's not legal to do that for no good reason).
/s
As an average driver I can floor a modern electric RWD car while turning and despite the strong torque, nothing bad happens.
Sure you can. A tire, any tire on any axle, will start to slide iff you're asking it to do too much work vs. the available traction. That's it. You can always do one (or both) of two things: ask the tire to do less, or increase the traction available to it. You have controls available to change both of these variables (steering and throttle).
Accelerating transfers weight to the rear wheels and lifting off the throttle (deceleration) transfers weight to the front wheels. The steering controls how much work you're asking the front wheels to do.
Once you grok this, it follows that RWD is easier and more controllable at the limit of traction due to separation of controls. The steering controls front traction and the throttle controls rear traction (but I'm simplifying, as the throttle also controls weight transfer thus traction on both axles). In FWD cars you have less fine-grained control since the throttle and steering are both using up traction of the front axle and the rear wheels are merely along for the ride. In a RWD car you can steer with the throttle without changing steering wheel angle.
All of this is car control 101. Which I wish was taught in the US as a prerequisite for getting a drivers license but sadly it is not, so approximately nobody has any experience in how to control a car when traction is less than optimal (rain, snow, oil on the street, etc.)
I urge everyone who drives to take a few car control courses to learn these basics. It can save your life, or the life of others, or maybe just some car repair bills. Totally worth it.
You can reason about the physics when reading about it online but there is no way to train your muscle memory to do the right thing other than by actually spending time practicing these skills in the real world, ideally with a car control instructor next to you.
Eventually they could all do a 'controlled slide' around a corner and continue uninterrupted. They've all reported how useful this skill is later (they're all 25+) when they encounter slick conditions - they can feel what to do and respond quickly and intuitively.
I do welcome RWD EVs, but let's not get carried away. Honda has demonstrated again and again that FWD vehicles are capable of very high track performance.
That's the day I fell in love with 50/50 weight distribution, rear wheel drive, and low and light weight.
It sounds very intentional and reckless.
You know what's not fun? Reading about a RWD car that slid into a roadside tree, killing the mother and child who had no training in drifting, like 99% of drivers.
RWD cars, even with modern ESP etc, should simply not be sold to untrained drivers.
The torque steer in my FWD EV (BYD Atto) is horrendous. Sure its possible to use clever engineering to manage it, but just switching to EVs isn't going to magically make torque steer go away.
Not everyone needs or can afford a multiple motors SV.
Once cheap EVs become more common, FWD will return because having the motor in front allows for much more efficient energy recapture with regen braking.
I think you are on to something.
If you want an extreme visual example, check out stunt cyclists who brake so hard the rear wheel comes off the ground. Pretty easy to see that the rear wheel isn't contributing to braking when it's in the air.
Obviously, front brakes are capable of more braking, but the limit at the end of the day is the regen of the battery itself and how much the inverter can handle regen. RWD-only EVs are already capable of ~75kW of regen. Moving to FWD to try to gain regen is only marginally going to give you better efficiency, if anything. It only matters for harder braking.
It wasn't until I got older and faster that I realized that braking just in the back is not as effective, since the braking action makes your nose dive and puts more weight over your front tire. I now brake with both sides, but always first in the back.
Also it might be a decent config for learning some BMX tricks because if you want to be able to do a barspin you can not have both brakes.
And if you have a bicycle with a coaster hub and a front brake and your chain is off than you are effectively having only front brakes.
Unless you are in a big rush to stop, you can keep the balance pretty even between wheels.
The more you brake, the more weight shifts forward, which results in less traction available to use to recapture.
People vastly overestimate how much traction is available at the rear during braking, and running out of traction at the rear typically results in the car spinning (especially in an EV with low rotational inertia with most of the weight between the axles) so regen tends to be very conservatively tuned to not cause rear lock up, thus using even less of the little traction available.
Yes, when braking strongly rear wheels alone certainly don’t have enough traction: signs of strong front wheel braking are the nose of the car starts to dip and your passengers are complaining! Similar issue with slippery surfaces and no ABS (regenerative traction control)?
I would be interested to see some real-world figures of how often rear-wheel-only regenerative braking hits limits and wastes power.
In addition, are there limits to the amount of power regenerative braking can push into the batteries? I presume that even on front-wheel regenerative braking, when heavy braking occurs the front calliper is engaged and energy is lost. The theoretical difference between front and rear regeneration might not matter in practice?
Disclaimer: I don’t know much about this, and I suspect you are technically correct, but my guess is that it doesn’t matter in reality, and other constraints/costs/benefits matter more for deciding on front vs rear wheel drive.
I think front wheel drive cars were probably about economics instead of traction or braking. In fact front wheel drive always had weird transient effects on steering. I'm guessing economics of no driveshaft plus a transverse mounted engine.
But with EVs the drive motor is small and can fit anywhere, so that's where they will put it - anywhere.
That said tere are still manufacturers, like BMW, producing 50% of their as rear-wheel drive (and 33% as AWD).
Snow tires makes more of a difference than being FWD or RWD in heavy conditions is the real truth here.
Snow tires are essential. I went out one day on Dec 31 without snows and made it about 300 feet from my driveway before I went in the ditch and rolled my car.
Circa 2008 I drove a FR Buick for a few weeks that had traction control and I was impressed with how it handled in the snow.
FR is front engine, rear wheel drive
The engine can be placed front (in front of the front axle), mid-engine (between the axles), or rear over/behind the rear axle.
It affects weight distribution and therefore the vehicle’s handling.
And snow tires is what makes a difference, true, but you can mount them on any car and same thing for traction control. So a same age AWD with snow tires drives better than a RWD with snow tires, specially if you come from a stop on an upwards icy road.
AWD is better than FWD or RWD, yes, but driving in the winter without snow tires.
AWD matters exactly 0 when emergency braking and little as long as you aren't driving flat and not accelerating.
Snow tyres help when accelerating, braking, driving straight forward and through curves, uphill and downhill.
There is a reason why snow tires are mandatory here and AWD is not.
Correct. All cars, whether they are FWD, RWD, or AWD are All-Wheel-Brake. The most important aspect of stopping safely are your tires.
Yeah. They do.
I've driven pretty much every combination of FWD, RWD, 4WD, and AWD, with and without snow tires, in a variety of winter conditions. The "other tires" were regular all seasons, not high performance summer tires or anything.
RWD with all seasons is really bad in snow, and mine generally didn't leave the parking lot in winter, because it simply couldn't. When you can start it, put it in reverse, let the clutch out, get out, and watch a wheel turning without the car having moved an inch, it's not a good day to take that car.
FWD with all seasons is better, because there's typically more weight over the drive wheels, but they're not great in snow.
4WD/AWD with all seasons (I lump them together because while there are some differences, it doesn't matter in typical snow) is far better, and hysterically fun to drive (drift all the wide corners), but it's still somewhat tricky in snow. And, yes, you do get better braking with 4WD, because the front brakes slow the rear wheels too (most of the braking force is on the front wheels, especially at initial application). The catch is that when you lock the wheels, you lock all four and have zero guidance, vs just locking the front and at least continuing mostly straight (or, usually, whatever the local downhill is).
FWD or RWD with snow tires is, by far, better than AWD with all seasons.
And then AWD/4WD with snow tires is just a case of "What snow?"
Why is it so hard to believe that a product that advertises 30-50% improvement in traction results in a lesser improvement than doubling the area over which tractive force is applied?
I used to drink the snow tire kool-aid until I bought a set for the FWD car of and realized that better straight line stopping distance and cornering ability don't actually help you because being able to controllably put power to the ground is still the bottleneck in the "is it reasonable to drive in these conditions" equation by a mile and while they help they are nowhere near a replacement for doubling the contact patch that force goes through.
Sure, they get me a little bit of margin to be an idiot and come into turns too hot or stop short but I wasn't really doing that stuff in the snow anyway so the benefit is lost on me (and people adapt their driving style to the performance they have available so how big is the benefit really?) and they still don't make the FWD car climb my damn street like the AWD car does so I don't buy them anymore. I keep chains in the trunk for the really bad days.
The FWD/RWD nit picking is mostly irrelevant IMO because any fundamental difference is far less than the vehicle to vehicle difference within or outside a given category. Better handling in the dry more or less directly leads to better handling of the same type in the snow. A RWD box truck will out hill climb a FWD minivan but the latter will out corner the former and a Miata and hot FWD hatch will be better than both at everything.
> better straight line stopping distance and cornering ability don't actually help you because being able to controllably put power to the ground is still the bottleneck in the "is it reasonable to drive in these conditions" equation
I take this to mean the answer is no. I drive in serious winter conditions, and AWD with winter tires is great, but it doesn't matter how many wheels are applying traction when you slide into a ditch.
The reduced ability to stop and turn has lead to in my snow driving experience, far, far fewer "that could have easily gone worse" situations than a lack of ability to gracefully put power to the ground.
I don't get why everyone obsesses over stopping and turning and shills snow tires. There's a reason that everyone and their brother buys an AWD vehicle and far fewer people buy snow tires. Everyone(TM) can't be wrong.
What I want you to tell me is why I should prioritize braking and steering if they're not the bottlenecks I encounter when driving in the snow.
Most accidents are caused by failure to stop and failure to turn, not failure to accelerate.
> There's a reason that everyone and their brother buys an AWD vehicle and far fewer people buy snow tires.
You clearly live in a very different place than me - very few passenger vehicles are available with AWD (subarus, trucks, some SUVs). But everyone has snow tires.
> What I want you to tell me is why I should prioritize braking and steering if they're not the bottlenecks I encounter when driving in the snow
Great for you? Again, you clearly live in a place with very different conditions than I do. What about the conditions make it so that you can't accelerate, but you can turn or brake just fine?
I regularly drive in conditions in my damned Camaro where the only other vehicles on the road are trucks, with some of them not being on the road anymore.
I agree that tread depth is massively important in the slushy conditions that commutes in the snow devolve into. You need that depth to provide a path for the "thick water" to GTFO so you're not hydroplaning on slush.
A FWD with snow tires or chains will almost certainly have better snow/ice handling than a RWD with snow tires or chains, by the simple virtue of the drive axle being steerable.
If you've played Kerbal Space Program or a similar spaceflight simulator + rocket designer, then the reasoning here should be pretty intuitive: if you can only apply thrust to the reverse, and don't have reaction wheels, then in space you have no ability to steer under your own control. You need to be able to point thrust to the sides if you want to be able to turn (or stop turning).
Same deal on an icy road. RWD means all your thrust is pointed backwards; FWD means you can point your thrust to the sides and control your car's orientation. Having both FWD and RWD (i.e. AWD or 4WD) is even better; sure, it constrains the overall thrust angles, but you also get more of it - which means better control when you're driving on a surface that ain't flat.
This ain't just theoretical; it's something I've repeatedly observed every winter here in the Reno/Tahoe area.
Is that a virtue? it makes steering tougher.
The actual virtue is the weight of the motor over the front wheels (coefficient of friction * basically weight above tires)
Not in my experience it doesn't. In icy or otherwise low-friction conditions, the steerable wheels being powered makes correcting for understeer and oversteer much easier than if they're unpowered - specifically because, per above, you can readily accelerate in directions other than forward/reverse, allowing you to orient the car even when sliding out. You can't rely on the tires' lateral friction to help you steer; a tire at an angle on ice will just slide with the rest of the car, and needs to be spinning to apply any force on said car other than forward.
The catch, though, is that you have to be willing to accelerate at the very moment your brain would otherwise panic and tell your feet to hit the brakes. Hitting the brakes will make things considerably worse by stopping the spin on your tires (especially the fronts, which are the very tires for which spinning is absolutely essential for steering control).
(In snow, this is a little bit less severe; the deeper the snow, the more pushback on the sides of the steering tires when at an angle, which helps a little bit with steering - but not nearly as much as on a dry road, thus still necessitating being able to accelerate with those tires)
> The actual virtue is the weight of the motor over the front wheels (coefficient of friction * basically weight above tires)
This also helps, but not nearly as much as the front wheels being able to accelerate in the direction they're pointed.
I’d tell you about my tactics for going around corners fast in a FF car but I’d get downvoted…
Back in the days this could also be used for performance reasons, to keep the turbo on, preventing it from needing to kick in again upon re-acceleration out of of the corner (back then turbo lag was huge and the "kick" was hard to control).
This technique was known to be very harsh on the engine but some races pilots would do it anyway.
FR = Rear-wheel drive
For anyone else who couldn't puzzle out WTF those meant, I'll save you looking it up.
FF = front engine, front wheel drive
FR = front engine, rear wheel drive
RR = rear engine, rear wheel drive
MR = mid engine, rear wheel drive
FF 4WS
FR 4WS
4WS is for «four wheel steering» (the emphasis is on «steering», not «driving») where – depending on the travelling speed – the rear pair of wheels turns either in the direction opposite to the front wheels (≤ 20 kmh) or in the same direction (≥ 20 kmh). The former makes the parking easier and reduces a turnaround circle. The latter makes the car look moving sideways when going around a bend or disappearing from its lane and emerging in the neighbouring lane during the lane change. 4WS also handles a bit differently on slippery roads around the bends.
Source: was taught this stuff by someone that won SCCA autocross nationals, as well as a few podiums in rally. Go to any rally event and you'll see plenty of FF cars doing every drift you can imagine through corners.
The trick, in my experience, is to learn how to get into a tailspin and do donuts. Unplowed parking lots are best for this. When you're familiar enough with the vehicle to do controlled tricks, you're just about prepared for an emergency. I've never owned a FWD car through a snowy winter; it's really down to what you're experienced with.
You only have so much traction to accelerate, brake, and steer. Sharing them on the same wheels seems objectively worse at the limits to me, except in the sense that every car is all wheel stop.
I think some of the safety issues associated to RWD were problems of the days where they were more common. Trucks need weight in the back, we know that, and winter tires are way better now.
You have to learn how the car handles when it's not an emergency to know what to do in a panic. I toss every car I own around in a snowy parking lot at least once so I know what it'll do. This seems insane to a lot of people I've talked to.
That said, I think understeer is safer and more predictable in most situations for people who use their cars as a transportation appliance. You point and shoot, so to speak. Most people aren't driving at the limits.
Strictly speaking, if your car is out of control, you're driving past the limits. The whole point of the parking lot exercise is to learn where the limit is. I drive like a granny, but prepare for the worst. And I've learned over the years to avoid the first day of snow in a season.
You've still got one control working in the rear: brakes. The understeer characteristics of a FWD car are very easy and intuitive to recover from. If someone can't manage traction in an FWD understeer condition, they almost certainly lack the skills to manage oversteer.
This might be true when discussing snap over-steer and throttle induced under-steer on a track but is a complete lie for snow driving where most drivers will just keep steering harder in response to under-steer which is not productive and you don't have enough traction for lifting and braking to induce much extra weight on the front.
That's my point. Make the wrong correction in RWD car and you end up oversteering beyond 90 degrees in an unrecoverable spin. The failure modes of FWD understeer in the snow are all recoverable.
You're making one of those textbook correct but reality wrong statements that clipboard warriors love.
Sure, you can recover from under-steer but if you're already doing the wrong thing and pointing the wheel where you want the car to go you almost certainly won't.
With over-steer if you do the "natural" thing and steer the wheels toward where you want the car to point at least you have a chance. Sure many people might flub it but that's a heck of a lot better than the "no chance" you get if you react the same way to under-steer. Also, if you do over-correct the over-correction may very well not be as severe as the initial over-steer giving you a better chance to get it right the second time.
Sure, under-steer is theoretically recoverable and with over-steer you can theoretically spin or slide backwards but in reality in "on the street" situations (i.e. not what you see someone doing on an old taxiway in a training video) 99.9% of the time you'll have hit something long before either happens.
Edit: Since I'm apparently so wrong anyone care to explain? Or is it just "sideways bad because smart man with vest and clipboard say so".
That is the understated safety factor of understeer, but people prefer to think in terms of never doing mistakes instead that in terms of overall safety
To be fair, they probably wouldn't get stuck in my driveway but I can stop a hell of a lot quicker and turn if necessary. I also find controlling a near spinout to be more intuitive on a RWD vehicle than a FWD one, but that might be just because my first car was RWD as well.
Trying to make two tires do all the going and the lion's share of the turning is just silly for a variety of reasons (competing design goals for suspension/handling, tire wear, performance, etc) and without some big pros to make up for it there's no reason to incur that.
Of course some applications that have cargo space as the utmost priority will remain FWD forever (Promaster style vans, probably some station wagons and subcompact hatches, etc) but for more rounded cars, especially ones with AWD optional having RWD be the default just makes too much sense from a suspension design and handling perspective to ignore.
The only time my FWD Civic struggles is when accelerating uphill in snow.
I imagine that's exasperated by the fact that everything behind the cabin is built to be as minimal and lightweight as possible, but the overall design is made to support a heavy maximum load filling the bed. Without significant weight in the bed, the truck will naturally lean forward.
Unfortunately this all applies to trucks, and does nothing to help my FWD Civic accelerate up a snowy hill.
When I accelerate, the center of gravity moves back to the middle of the car. Accelerating up a hill puts that center of gravity in the backseat near the rear axel.
If I got to choose my drivetrain, I'd go AWD > RWD > FWD.
You got that backwards.
Forward acceleration transfers weight to the rear axle. The harder you accelerate, the more weight transfers to the rear, which means the more traction is available to the rear wheels, less to the front wheels.
It's easy to visualize if you think of the case of extreme acceleration such as in a motorcycle or drag race car - the front wheel(s) lift off the ground entirely and thus have zero traction.
Going uphill only accentuates this even more, so FWD is going to be at an even greater disadvantage.