Hydroplane/RWD

[Terence Murphy]

I wonder if one pedal driving could be the issue. If I recall correctly you want to coast through puddles.

I was thinking the same thing, and trying to work through the mechanics. With RWD, the regenerative braking is only on the rear tires. So let's say you either feel traction start to go, or see a problem, and you instinctively lift entirely off the throttle to coast through. With 1PD, it'll start regen on your rear tires. This isn't the same as braking. The tire is driving the motor as a generator to feed back power, so to a first approximation it shouldn't be able to break traction, but it could come close. And just on your rear axle, which is very atypical braking behavior. It's like using the parking brake in an ICE car (but just a bit, not full on locking the rear wheels to induce drift, only on a closed course naturally!). So I can see regen through AWD having an advantage in this low-traction situation.

What I'm now curious about is how differential low traction factors into regen. With this same RWD scenario, let's say one tire has better traction than the other. Will the differential favor regen from the tire with more or less traction? If it's the one with more traction, is there a risk of that inducing the other tire to start to slip? And what nanny bots will or won't kick in to help compensate? It's not an ABS situation. More like a traction control type split, but that cuts power and we're already not feeding power to the motor.

Can any regen experts here shed some light on this? Or does it need some research on a wet skidpad?

On a related note, there was a recent review in Car and Driver of the BMW i4 eDrive40, with RWD (335 hp). They commented how on the track there was a noticeable weight transfer that happened as it transitioned from predominantly regen braking on the rear axle to harder braking predominantly on the front. I haven't seen this mentioned in any other reviews of other EVs, but most reviews tend to look at high-end models which mostly have AWD. Is this weight transfer issue noticeable in the MME RWD? Or is it something you'd really only notice at the track?

Sponsored

 

[Blue highway]

I was thinking the same thing, and trying to work through the mechanics. With RWD, the regenerative braking is only on the rear tires. So let's say you either feel traction start to go, or see a problem, and you instinctively lift entirely off the throttle to coast through. With 1PD, it'll start regen on your rear tires. This isn't the same as braking. The tire is driving the motor as a generator to feed back power, so to a first approximation it shouldn't be able to break traction, but it could come close. And just on your rear axle, which is very atypical braking behavior. It's like using the parking brake in an ICE car (but just a bit, not full on locking the rear wheels to induce drift, only on a closed course naturally!). So I can see regen through AWD having an advantage in this low-traction situation.

What I'm now curious about is how differential low traction factors into regen. With this same RWD scenario, let's say one tire has better traction than the other. Will the differential favor regen from the tire with more or less traction? If it's the one with more traction, is there a risk of that inducing the other tire to start to slip? And what nanny bots will or won't kick in to help compensate? It's not an ABS situation. More like a traction control type split, but that cuts power and we're already not feeding power to the motor.

Can any regen experts here shed some light on this? Or does it need some research on a wet skidpad?

On a related note, there was a recent review in Car and Driver of the BMW i4 eDrive40, with RWD (335 hp). They commented how on the track there was a noticeable weight transfer that happened as it transitioned from predominantly regen braking on the rear axle to harder braking predominantly on the front. I haven't seen this mentioned in any other reviews of other EVs, but most reviews tend to look at high-end models which mostly have AWD. Is this weight transfer issue noticeable in the MME RWD? Or is it something you'd really only notice at the track?

Regen braking is not a problem on snow covered roads let alone wet roads in my RWD MME.

 

[ctenidae]

Regen braking is not a problem on snow covered roads let alone wet roads in my RWD MME.

Never had an issue in the Tesla, either. As soon as the system senses wheel slip it reacts.

 

[Terence Murphy]

Never had an issue in the Tesla, either. As soon as the system senses wheel slip it reacts.

In what way does it react, if only slowing by regen with wheel slip? What systems are engaging to help control

my hypothetical scenario would definitely require rare conditions. Loss of traction enough to exceed regen force, plus unbalanced traction side-to-side. I remember some old ABS tests on a half-wet lane. That would be interesting to experiment with, especially if it can be set up with enough water to hydroplane one side of the car.

what can I say - I’m a scientist so I want to experiment….

 

[AKgrampy]

I have had my Mach-E for 10 months now. I absolutely love it but noticed during rain that I would sometimes feel as though I was hydroplaning. Unfortunately I am now finding out that living in south Florida + RWD was possibly a bad combo for me. On Sunday my car spun out and landed in a ditch. Thankfully I was not injured and neither was anyone else. The car however is likely totaled. Has anyone else experienced this? Is this a Mach-e issue? A tire issue? Or a RWD issue? Or just purely bad luck? I was not speeding. The tires were not worn (14,000 miles). In fact I moved to the center lane several minutes before to stay away from puddles because I felt as though I was sliding a bit. I have to make a decision as to order another mach-e or to move on to a different car so any input would be appreciated. Thanks!

Plenty of comments on the why of it. You also asked about getting another or moving on. I would say that if you liked it then get another. If only a so-so feeling then shop around and see what you can find. Glad you are alright as that is the most important thing!

 

[portlandg]

I find that my ER RWD will "skid" when I am in OPD and slowing down or going downhill and I hit a drain cover in the road in the wet. I can feel the rear wheels lockup briefly then release. Has also happened on painted road markings. I can definitely see that a major problem could occur if you take your foot completely off the "go" pedal while going round a bend in the wet with OPD on. Especially in a RWD variant. I turn my OPD off just in case when it is extremely wet.

 

[MacherAWD]

I find that my ER RWD will "skid" when I am in OPD and slowing down or going downhill and I hit a drain cover in the road in the wet. I can feel the rear wheels lockup briefly then release. Has also happened on painted road markings. I can definitely see that a major problem could occur if you take your foot completely off the "go" pedal while going round a bend in the wet with OPD on. Especially in a RWD variant. I turn my OPD off just in case when it is extremely wet.

I notice the same in my AWD, there is a manhole in the street near me, it's approaching a stop, so always in 1 pedal approaching and can always feel it hop or slide when I hit it.

 

[satchel prefect]

Speaking in general terms (not specific to the OP), perhaps the lack of sensation at speed could be a factor here. It is likely quite common for drivers to subconsciously drive faster than they normally would in a more conventional vehicle--especially an older or less luxury-oriented one.

Pretty much all EVs (and many ICEVs) in this price range do a great job making 70 mph feel like 35. You have quite a bit of splash/hum/whoosh insulation from the heavy, flat battery below, and in some cases, rain drop "ping" noise completely smothered by a heavy glass panel above. And of course, all of the additional damping and padding in the interior panels, acoustic glass, etc. Not to mention the lack of combustion noise.

In the case of a situation like the OP, if there were no other cars around, that would be another reference point removed, possibly masking speed even more.

 

[ctenidae]

In what way does it react, if only slowing by regen with wheel slip? What systems are engaging to help control

my hypothetical scenario would definitely require rare conditions. Loss of traction enough to exceed regen force, plus unbalanced traction side-to-side. I remember some old ABS tests on a half-wet lane. That would be interesting to experiment with, especially if it can be set up with enough water to hydroplane one side of the car.

what can I say - I’m a scientist so I want to experiment….

For wheel slip it just reduces the amount of regen to the point the tires continue to grip. Same basic principle as ABS - reduce the braking force until the wheels grip again, just with a more delicate hand. I got pretty decent using compression braking on snow with my RWD manual, but could only do it down into 2nd gear without using the gas pedal too. It was good to have the braking force at the back so the weight up front was always pulling you straight- it was only after I switched to brakes that the rear end could come around

Tesla (and I suspect the MME) does a similar thing under power, too - on pure slick ice you could floor it, and the tires wouldn't even skip once. You'd accelerate like a nonagenarian grandmother on her way to the market, and probably top out at 12.4 mph, but no wheel slip.

Question is how well the system handles different slip rates on two sides, and front to back. Having two motors is better than 1, since I think regen can be more finely controlled than friction brakes. 4 motors would be better still since you'd have independent control at all four points. Tesla definitely applied brakes independently on each wheel, which led to some odd feeling traction control moments, some of which I never got used to. Tesla's massive advantage in driver miles data showed in the nuance of its traction control, I think.

All that said, I'd be surprised to find that Ford's TSC system is so bad that it induces a total loss of control in a hydroplane scenario. Maybe not completely surprised, but at least a little - the principles are the same no matter the drive train, but some options for application are different.

 

[ctenidae]

I find that my ER RWD will "skid" when I am in OPD and slowing down or going downhill and I hit a drain cover in the road in the wet. I can feel the rear wheels lockup briefly then release. Has also happened on painted road markings. I can definitely see that a major problem could occur if you take your foot completely off the "go" pedal while going round a bend in the wet with OPD on. Especially in a RWD variant. I turn my OPD off just in case when it is extremely wet.

Haven't noticed it on decelerating, but I will look for opportunities to test. Definitely get a bit more skip than I'd expect (or like) on accelerating, though. I chalk it up to Ford still needing refinements to the motor controllers- they feel like they're still kind of on or off, and need more gradations in between.

 

[ctenidae]

Haven't noticed it on decelerating, but I will look for opportunities to test. Definitely get a bit more skip than I'd expect (or like) on accelerating, though. I chalk it up to Ford still needing refinements to the motor controllers- they feel like they're still kind of on or off, and need more gradations in between.

Caught it today decelerating in a turn on bumpy pavement (the things I do for science). It felt like a slip/slide for sure, but it was pretty clearly just the regen cutting out completely when the car sensed "wheel slip," just a quick bit of pucker as it suddenly wasn't decelerating. Fraction of a second, but just enough.

Ford has got to improve the coding for the controllers. They will, for sure, but it can't come fast enough.

 

[Bayviews88]

I find that my ER RWD will "skid" when I am in OPD and slowing down or going downhill and I hit a drain cover in the road in the wet. I can feel the rear wheels lockup briefly then release. Has also happened on painted road markings. I can definitely see that a major problem could occur if you take your foot completely off the "go" pedal while going round a bend in the wet with OPD on. Especially in a RWD variant. I turn my OPD off just in case when it is extremely wet.

As you are the UK, I presume you have a lot of experience driving in the rain.
What are your tips to prevent others from landing in a situation like the OP?
Asking primarily for myself, as I just went from a AWD Select to a RWD CA RT1.

 

[portlandg]

As you are the UK, I presume you have a lot of experience driving in the rain.
What are your tips to prevent others from landing in a situation like the OP?
Asking primarily for myself, as I just went from a AWD Select to a RWD CA RT1.

My commute to work involves a few hills that have metal covers in the road for the utilities. There are also a lot on flat road surface. I usually turn off OPD and engage the "L" button in heavy rain. This seems to make things better. Using the "L" setting stills gives me regen but it seems not enough to cause the rear wheels to "lock up" on the covers. I also turn off OPD in really heavy rain on faster roads (motorways etc), just in case.

 

[bosbruce]

Agreed with what several others here have said... I had RWD (SR/Premium) Job 1 Mach E for 18 months including a Boston winter with no issues due to RWD (I prefer the slightly tail happy feel, and really loved turning traction control off to do smooth, quiet donuts in snow covered parking lots). Might have occasionally preferred the better acceleration of AWD or GT but liked the fact RWD had better range for smaller battery and was lighter (plus I had cars better handling and quicker than GT anyway so that wasn't the purpose here for me).

I did have RWD cars I spun out when I was new to New England and had summer performance tires in a snow storm (luckily never hurt or significant damage but a couple of 360s), and have had a few scary moments hydroplaning but RWD with good weight distribution, appropriate tires, and appropriate speed/acceleration/braking is as safe as AWD IMO and maybe safer as I know sooner of limits as loss of traction accelerating will tell me before it would in AWD.

Just wild guesses here : (1) perhaps speed was too high for conditions, (2) perhaps rear tires were balding if this car was driven spiritedly, (3) perhaps too heavy (acceleration) or light (deceleration if single pedal enabled) use of accelerator contributed to loss of traction.

The latter may be an edge case where RWD could hydroplane worse than AWD if single pedal mode is on (moreso if unbridled), as you DO NOT want to brake/decelerate/... when approaching hydroplaning limits. Best is manual transmission car to slam in the clutch and let the car decelerate optimally without any engine acceleration/braking to aid in loss of traction. Next best is just to let off the throttle hoping your car isn't in a sport mode (which it shouldn't be in slippery conditions unless you want to spin) in an automatic. For EVs, turning off single pedal (or explicity going to snow/slippery mode if available) will help and might help RWD more than AWD.

 

[MrPeanut]

I'm pretty sure RWD/FWD/AWD have little to do with hydroplaning. AWD really only helps you start moving, and gives additional stability when cornering at speed. The RWD MME has 53% of its weight over its rear axle, so it's not like most RWDs people have driven. The stock tires are terrible and I replaced them as soon as I could. Haven't had any issues through rain/snow up here - in fact, it's one of the best performing cars in adverse weather I've ever driven once the tires were replaced.

Also, overinflated/narrow tires usually have less chances of hydroplaning: https://mechanics.stackexchange.com...re-pressure-affect-susceptility-to-hydroplane

What brand/version of tire did you change over to?

Sponsored