hypnotized

I have a 2013 Lexus RX 450H AWD CPO from Lexus dealer with 33K miles on it. Bought it with 23K miles on it.

I have equipped what appear to be the OEM original Bridgestone Dueler tires.19 Inch factory wheels. Tire wear appears to be normal. I have rotated the tires every oil change since owning it. (2 times).

I have noticed that there is quite a bit of slip in wet and snowy conditions. There seems to be a delay in the AWD to kick in as well. Its like slip, delay, then AWD kicks in. I have not noticed any TSB.

With that being said, I am a car person getting use to an SUV. I am use to my IS250 AWD with all season Bridgestone Pontenzas. The car is awesome in the snow. I guess I was expecting somewhat comparing performance. Hammer down and go...snow or rain.

Is anyone had a similar observation with the RX that was solved with tires?

It may be just a matter of wearing tires, high center of gravity, different AWD systems, and giant wheels. It doesn't appear the Dueller is a low rolling resistance or hard tire. Just looking for some input.

rayaans

Firstly, you have to remember how the RX450h works. It is actually not AWD but an E-four system. In other words, its front wheel drive unless the car detects slip at which point it activates the rear motors to help traction.

The front and rear are completely disconnected and the rear wheels don't have a lot of power going to them, its just to help you out a little.

The bridgestone OEM are also summer tyres which will theoretically be worse than all-season tyres in the snow. Try something like Michelin Latitude Tour HP (I have them and they are awesome)

It could also be that your tyre pressures are too high. The wheel size won't make a difference as the RX actually has narrower tyres than the IS and should be better in the snow as a result.

Droid13

I don't think that's true, I believe when starting from stop there is always some push from the rear motor, but as you say, it is not powerful so it cannot compensate for the fact that most of the power goes to the front wheels. The rear drive, under healthy acceleration, probably represents no more than 20% of the power output.

Under casual acceleration the rear drive will tend to shut off fairly quickly and go 100% front drive (at about 5 to 15mph). Two things will alter that... Hard acceleration will tend to hold power at the rear until maybe 35mph. Snow Mode even with moderate acceleration will also tend to hold power at the rear, maybe until about 20-30mph.

Hynotized, the IS250 with true AWD and being not so heavy is likely going to get better traction at start. The RX450h is a more graceful giant of sorts, it'll get going calmly in an organized fashion. But whenever I've needed to get going in a hurry, for example, don't want to wait for it to gently exit a side street still snow covered onto a bare main road, I just disable the traction control and hit it. The RXh will abandon its gentle nature and leap out quite decently if you don't mind a little rooster tailing from the front tires. Snow tires will help of course too.

ericsan13

The 450h has VDIM, so it should prevent the tires from even slipping in the first place. Maybe something is wrong with VDIM?

AFAIK only the RX350 F-Sports and RX450h have VDIM. Difference is that VDIM actively prevents slip as opposed to VSC which kicks in after slip is detected.

vlad_a

OP, you are confusing traction control and AWD. There is significantly more torque sent to the front, they start to slip and trac kicks in. Welcome to FWD world.

Here's the question I quiz my wife on all the time: you see snow, what is the first thing that you do?
Put the car in the snow mode! AWD by itself implies part-time secondary axle engagement, with exceptions of some implementations (e.g. IS250 AWD). Early designs relied on mechanical slip to occur before the secondary axle got any torque. Now, the modern version of the center differential relies on electronics and will preemptively send power to all of wheels upon starting. In our case, there is no center diff and it is pure electrons, but the idea is the same. So, the RX will send electricity to the rear motor when you start moving or drive aggressively through a corner. More power is sent to the rear in the snow mode and it stays there for higher speeds. We've got a fancy screen that shows all of this in action.
Alas, once you start moving, it becomes just your run-of-the mill FWD vehicle.

IS250 AWD was based on a completely different AWD architecture. It is full time and is RWD-biased.

Get some good snow tires and the RX won't let you down. However, it will never drive the same way your IS250 did.

hypnotized

I believe the Dueller is an all season tire. I would have to confirm unless there are other trims of it.

To my knowledge, this vehicle is not like an Audi where it distributes torque and power to wheels in varying amounts.

As it relates to snow tires, I talked it out with a guy at NTB on my IS250 AWD and did some research. I believe the operating temperature for snow tires (Blizzak) suggests 40* F and below. My logic was even if it is 35* F out and I drive a ton of highway miles on my normal commute, I assume the tires would heat up some. He said above 40* F you may experience rapid wear. I only need snow tires for like 10% of my daily commute, when I exit the highway. It just didn’t seem like a good fit for my situation.

So my point is, snow tires aren’t always a good solution unless you’re constantly in a deep freeze on roads with poor plowing or chronic ice issues (NE, MN,…). My all-season Potenza’s on my IS250 AWD are shockingly good and I have driven aggressively, confidently, and arguably moronic in horrible weather with them.

The “snow mode” should just be called “retard mode” in the sense that it retards your ability to accelerate rapidly. Like starting in 2nd gear is how it feels.

Again, more of the issue I am noticing is under normal acceleration there is a noticeable delay in traction responding. I would say that “detecting” a slip is noticeably slow. Again I am not mashing the gas.

For comparative purposes, I believe some RX models have a TSB for the delay in the back up camera loading when putting the vehicle in reverse. Again it works, but it just is something you go “well that is taking longer than I would expect to respond”.

Anyone have any knowledge of this TSB:
L-SB-0106-14
November 25, 2014
HV Transaxle Repair Components Available
Service Category
Drivetrain
Section
Hybrid Transmission/Transaxle
Market
USA

Applicability

Introduction
The purpose of this general information Service Bulletin is to announce sub-component diagnosis and replacement is now available for the Hybrid Transaxle assembly equipped on 2011 - 2015 model year CT 200h, 2010 - 2012 model year HS 250h, 2006 - 2008 model year RX 400h, and 2010 - 2015 model year RX 450h vehicles.

Warranty Information
Hybrid Transaxle unit repair is available as warranty and is now recommended wherever appropriate for warranty repair. Warranty times for these procedures are included in the Flat Rate Manual. Reimbursement will be managed under the warranty policy.

What is the symptom this TSB is addressing?

vlad_a

I gave up on Blizzaks a long time ago. The silica compound that they use is only on the top half of the tread.
So, they wear out immediately the moment you hit any warm weather and dry roads. For that reason, there was a period of time when I was running all-seasons during winter on my RWD IS300.
I became a believer when I put Michelin XIce Xi2 on the IS300. Those then moved to the '15 STi that replaced it.
The RX also has XIce Xi2 in 255-55-R18 size. I could drive them to Florida if I wanted to. Absolutely no issues with warm weather wear, or cold for that matter. RX is on its 4th winter season and the winter tires are in a great condition.
The S4 has Xice XI3 installed and I couldn't be happier. I had to get 18" tires, or I would've reused the set from my IS300.

vlad_a

I would actually view traction control kicking in late into the tire spin as a benefit rather than a detriment. That's part of VDIM tuning, which common RX350 with VSC doesn't get. It's more fun to drive, LOL.

hypnotized

I would agree if I was in a Mustang. However I am driving a $60K old man SUV across a few lanes of traffic closing in at 55 MPH. Imagine lightly accelerating in dry weather, tires spin suddenly, brief stall as power is reduced to the motor from the traction control intervening, then the traction kicks in when it senses it ready to help out which seems like an eternity.

Ish gets real when you stall in front of on coming traffic!

I am just curious if there may be a re-flashing in the works to improve the timeliness of the response. Otherwise, I need to lower my expects and get new tires!

vlad_a

I am experiencing none of those issues. You really need to invest into new shoes for your car. At 4,600lbs, that's a lot of weight riding on them, especially being mostly FWD. Apply less throttle and you'll be quicker off.
I know exactly what an overactive traction control is. 2 of my IS300s had it. It was impossible to drive with it on, particularly in the situation you're describing. Trust me, you don't want that.

If tires don't resolve your issue, the vehicle you're driving may not fit your driving style. You bought a car built on the wrong platform. I would recommend stopping by your local Lexus dealer and test driving an RX350 or RX450h with brand new tires. Do they have the same traction issues? If yes, you need to step up to something with RWD bias.

NateJG

The rear might add just a tad more than 20% because:

The rear motor is provides 103 lb ft of torque; while the front motor is capable of 247 lb ft. It's hard to say definitively, since Lexus doesn't give a "combined" torque rating for the front and rear axle together (it lets us infer a number from adding the two; however, I doubt that the electronics lets it happen quite that simply).

It's also a bit tricky to figure out just how they come up with the 295 HP, given that the engine is capable of 245 hp @ 6,000, and the front motor is rated at 165 HP, with the rear motor rated at 67 HP. Adding those together causes me to scratch my head - given that the engine is rated at 245 HP and 234 lb ft of torque.

We know that the battery is only good for about 50 HP by itself (the battery's 37 kW converts to 50 HP), so even with the engine putting all of its 245 HP into the drivetrain, plus the battery's maximum of 50 HP (assuming 100% efficiency in the conversion of battery electricity into torque), I then infer that the 245 HP plus the 50 HP is how they come up with 295 HP.

There is at least one variable in the algebraic representation of all this for which I cannot yet find a suitable explanation - but somewhere along the way, the battery gets depleted (if you're WOTing it long enough) which would take out the battery's storage of 37 kW - and result in the max usable power limited to something just shy of the engine's 245 HP and 234 lb ft of torque.

So assuming that the electronics "allows" the rear to put out all 67 hp (by using all that it can from the battery plus a slice of the 245 hp from the ICE), one might make a case that the rear is capable of sharing 67/295 or 22.7% of the load -- which is a long trip around the barn to agree with you (with your 20% contribution supposition).

Elsewhere in a thread (perhaps this one?) someone supposed that the rear motor didn't have enough power to be useful in snow - to which I ask: Isn't 67 HP and 103 lb ft from the motor to the rear axle (there is some gear multiplication, right?) enough to spin the wheels in snow for a 5K # vehicle?!?

In my own unscientific testing of my '13 RXh in snow, I find that (in Snow Mode) it's a stellar performer.

What I haven't taken the time to investigate is how much leverage is provided by the gearing of both the front and rear axle setups - which would make a big difference in the amount of torque available to the wheels of those respective axles.

Perhaps someone else has some insight?

Droid13

The missing part of the magic is what is the generating capacity of the MG1 motor, typically referred to as the generator. The generator creates a load on the engine, but it never sucks up the full 245HP of the engine. Some of the engine power stays mechanical and does provide direct rotational force on the front wheels through the PSD. I've never seen a rating for MG1 on the RH450h, so that would be an important part of the equation. With front (165) + rear (67) motor adding to 232HP then considering battery (50) says the generator would need a minimum of 182HP to fully run the show. But I imagine the generator is not able to produce this much power, probably not even close. This means it's very unlikely (probably impossible) for both front and rear motors to be fully energized at once as a significant % of power flows mechanically to the front wheels instead of electrically. So it comes down to, given the drive motors are capable of drawing more power then the generator and battery can provide, how is the power best divided? Given the higher rating of the front motor, I suspect under maximize acceleration while still at a low speed the rear might briefly represent near the 22.7%, but as vehicle speed increases (and likelihood of traction issues decreases) it will quickly drop to 0%. Fooling around on snowy roads with light or modest acceleration at low speeds might see the rear contributing close to 50% with the lower overall power requirements.

NateJG

And don't forget that both the FWD and AWD versions are rated at the same 295 HP.

Do you think there's a hint of "watch my watch" or "Never-mind the man behind that curtain" going on?