Rav4 PHEV: Winter, snow ice and AWD for a novice

[Nicolai]

Not too proud to admit this but not really sure what the AWD can't do and what it CAN do?

We've had quite a bit of snow in Denmark. More than normally and hard ice on top of the asphalt. In these conditions, I could feel my RAV slipping depite the AWD and fitted Bridgestone LM005 Blizzak Winter tires. Tire pressure is current 2.9 bar / 42 psi (as when collected at the dealer) but at the time in question it was prob 2.6 or 2.7 bar / 38 - 39 PSI.

I know the sticker in the door indicates less but what is a middle ground for grip and tire longevity?

I get that the acceleration is probably better with AWD. And you probably won't get stuck as much. But besides that, what makes drivers of AWD cars, almost, invincible in the winter? Stopping distance is still long.

I could really use a winter driving course I think. Eager to learn guys. Hit me with advices, YT videos etc.

Thanks,

[Flatcoat]

I think your tyre pressures are far too high! It is not uncommon for dealers to not check pressures or be clueless with what they should be. I don’t even use those pressures when caravan towing. An old trick to improve traction in snow was to drop the pressures very significantly. I personally would be running at 32/33 psi cold and coincidentally in preparing for a 400mile/650km drive to the snowy north of Scotland tomorrow, will be checking and setting my winter tyre pressures at that level. To be honest safety through grip and braking performance and not getting stuck override longevity considerations.  

[philip42h]

29 minutes ago, Nicolai said:

Tire pressure is current 2.9 bar / 42 psi (as when collected at the dealer) but at the time in question it was prob 2.6 or 2.7 bar / 38 - 39 PSI. 
I know the sticker in the door indicates less but what is a middle ground for grip and tire longevity?

The PHEV handbook states 2.3 bar / 33 psi - you really ought to set them to exactly that. Higher pressures may improve economy, but they'll ruin ride and lose you the grip you need in slippery conditions. Once you have corrected the tyre pressures you may also need to reset the TPWS system to avoid redundant warnings.

The dealer should never have delivered the car at 2.9 bar ... 😠

The Blizzaks are as good as any winter tyres so you are already on decent rubber. The AWD system makes the car as "idiot proof" as possible - there's nothing much that the driver has to do, bar:

• Drive with a very light foot
• Drive slowly or very slowly

There's not that much friction available so stopping distances will be long if speeds are 'excessive'.

Oh, and AWDs are far from invincible in winter so if the going gets too exciting, don't go at all!

[Torrox]

Yes the tyre pressure is too high, my current 4 wheel drive Land rover tyre pressure is 2.2 bars / 32 psi. It has no problem with cross climate 2 tyres. 

[ernieb]

As has been said 2.2 bar 32psi and as the temperature drops the tyre pressure will reduce anyway. This morning it was -5oC and two tyres were showing low pressure according to the TPMS. (The feels like temperature was -9oC)

 

[Bernard Foy]

Tyre pressures a couple psi lower, drive as if you’ve got a glass of water sitting on your bonnet and don’t want to spill it😊 and AWD is no advantage to you on ice.

[philip42h]

7 hours ago, Bernard Foy said:

AWD is no advantage to you on ice.

AWD will always provide twice as much traction as FWD or RWD (on equivalent tyres) - from that point of view AWD is always better than 2WD.

Equally, once you get down to zero grip, two times zero is still zero - and staying at home is the better bet!

[Mike2222]

As others have said - adjust pressures, AWD is *not* invincible, and gentle throttle inputs. 

 

Also, important to recognise not all AWD systems are equal. In the Rav, the difference between the front and rear axle EV motors in power terms is ~3.5:1 in a FWD bias (182hp vs 54hp). I can't find a reference for torque figures for them - torque actually is the more important factor in this regard but one can reasonably assume that they likewise are nowhere near an equal split. Thus the rear axle is not going to have the ability to bail you out if you take too much speed into a corner in the way that a Audi Quattro or Subaru system might. 

 

Also, might be stating the obvious, but you need to actually have some throttle input in a corner for an AWD system to work. If you're coasting or braking, there is no power to "send" to a wheel which still has grip. You need to meticulously plan ahead and shed your speed well advance of the turn, so that you can maintain slight throttle pressure throughout the corner. Otherwise your AWD system is just dead weight and you'll drift/slide.

[Mike2222]

Those are power figures for the PHEV btw. Regular hybrid AWD is 120hp front vs 54hp rear axle, so 3:1, but the principle is the same. 

 

Once ICE kicks in, the power differential gets even greater in both HEV & PHEV I would think, tho can't find a reference to confirm. 

Edited January 19 by Mike2222
I misread kW and hp for rear axle

[Nicolai]

Dropped the pressure to 2.5 bars (36 PSI) for now.

Does anyone know how big a difference in pressure the TPMS will accept before the light comes on?

I swear it came on one morning with just 0.1 bar (1,5 PSI) difference (one front lower than the rest), however, I haven't seen it since although, due to the cold, the pressure has dropped further (although fairly equal on all tires. It start up in the morning, I seem to have one front that always "starts out 1.5 psi bellow the rest but this doesn't seem to be enough for the TPMS indicator to come on...?

[nlee]

I don't know what the drop has to be from the set point to trigger the low pressure warning but it would be wise to first get them to the pressure you need them to be, then reset the set point in the settings menu (sorry can't remember exactly where it is in the menu and it could be different if you have the newer display). Then you will get the warning if pressure drops from what you have set them to, rather than what they were previously.

 

[Nick72]

On 1/18/2024 at 2:55 PM, Nicolai said:

Not too proud to admit this but not really sure what the AWD can't do and what it CAN do?

We've had quite a bit of snow in Denmark. More than normally and hard ice on top of the asphalt. In these conditions, I could feel my RAV slipping depite the AWD and fitted Bridgestone LM005 Blizzak Winter tires. Tire pressure is current 2.9 bar / 42 psi (as when collected at the dealer) but at the time in question it was prob 2.6 or 2.7 bar / 38 - 39 PSI.

I know the sticker in the door indicates less but what is a middle ground for grip and tire longevity?

I get that the acceleration is probably better with AWD. And you probably won't get stuck as much. But besides that, what makes drivers of AWD cars, almost, invincible in the winter? Stopping distance is still long.

I could really use a winter driving course I think. Eager to learn guys. Hit me with advices, YT videos etc.

Thanks,

Tyre pressure. As others have said. Totally. I've been running at 1.9bar at 0C not by design. Though I just added a little air to bring them up to 2.1 bar so they'll be close to sbout 2.3 in the summers. Prefer the traction over efficiency.

You need to drop the tyre pressure to about 2.1 bar. 

[Nick72]

7 hours ago, Nicolai said:

Dropped the pressure to 2.5 bars (36 PSI) for now.

Does anyone know how big a difference in pressure the TPMS will accept before the light comes on?

I swear it came on one morning with just 0.1 bar (1,5 PSI) difference (one front lower than the rest), however, I haven't seen it since although, due to the cold, the pressure has dropped further (although fairly equal on all tires. It start up in the morning, I seem to have one front that always "starts out 1.5 psi bellow the rest but this doesn't seem to be enough for the TPMS indicator to come on...?

Mine was coming on at about 1.8 to 1.9bar. 

[Nicolai]

1 hour ago, Nick72 said:

Mine was coming on at about 1.8 to 1.9bar. 

...and what were your "target pressures" at the time?

[Nicolai]

12 hours ago, Mike2222 said:

Also, important to recognise not all AWD systems are equal. In the Rav, the difference between the front and rear axle EV motors in power terms is ~3.5:1 in a FWD bias (182hp vs 54hp). I can't find a reference for torque figures for them - torque actually is the more important factor in this regard but one can reasonably assume that they likewise are nowhere near an equal split. Thus the rear axle is not going to have the ability to bail you out if you take too much speed into a corner in the way that a Audi Quattro or Subaru system might.

So, arew saying the AWD-I of the RAV4 is quite... bad or subpar?

[Nick72]

19 hours ago, Nicolai said:

...and what were your "target pressures" at the time?

2.3bar

[Nicolai]

4 minutes ago, Nick72 said:

2.3bar

OK - that's quite a drop for the light to come on. Thanks.

[Nick72]

8 minutes ago, Nicolai said:

OK - that's quite a drop for the light to come on. Thanks.

Just over 15% so not so much.

[Nicolai]

My difference was 0.1 bar and wondered why it did not come on.

[Mike2222]

19 hours ago, Nicolai said:

So, arew saying the AWD-I of the RAV4 is quite... bad or subpar?

"Bad/subpar" is all relative to what your intended use-case is. If you had harboured hopes of hooning it around gravel forest tracks, paying homage to your wasted youth on the original playstation Colin McRae, or up and down rutted muddy ravines in the ar*e-end of outer Mongolia like Bear Grylls looking for some alone time, then yes the Rav is subpar compared to subaru/quattro/land rover in AWD tech terms. 

 

If you want a large (for UK)/"family" SUV, with fairly comfy suspension, great phev tech, with some AWD to improve road-holding capabilities over FWD options, to provide fairly safe driving dynamics when driven with care, then no it is not subpar. 

 

I think it may have been discussed before, but AWD and 4WD are not the same, nor are they meant to be. AWD actually is not a very precise terminology and encompasses quite a wide variation in technical ability. i-AWD in the Rav means that the rear axle is only driven when the car thinks it's necessary, and the power differential means that if the rear wheels (or only one of them) has traction, there is a limit to how much motive force they are capable of applying to the road. Whereas Subaru and Quattro are variations of permanent AWD, meaning power/torque is constantly being varied between front and rear axles (and depending on system, also to left and right wheels), typically allowing a much larger percentage of total engine output to be applied thru one axle/wheel. 4WD with fixed differentials is another thing entirely (land rover etc). 

 

Most non-offroad-focussed brands use a FWD dominant system, where the rear axle is only driven occasionally, typically allowing a lower percentage of force transfer to the rear. Whilst helpful for improving overall road holding, they're not the same if you plan to hoon it around in dodgy weather. 

[Nick72]

1 hour ago, Nicolai said:

My difference was 0.1 bar and wondered why it did not come on.

0.1 bar is in the noise. Probably the size of the inaccuracy of the measurement device so that's unlikely to be a trigger. 15 to 20% drop is more likely to trigger it but not a few percent.