RXSF

A majority get either dunlop grantrek or michelines and few get bridgestones.

mtnhigh799

Regenerative brakes should not have been an issue as it has always worked the same way as it does on RX450H -- what is different about the RX450H is that is does regeneration even when you are not pressing on the brake pedal, the result being that, on ice, after the wheels have locked due to braking (regenerative), they remain locked when the brake pedal is released as the regenerative system is trying to generate energy from the wheels, thereby preventing the wheels from starting to turn. In other vehicles, when one releases the brake pedal, the wheels immediately start to turn and you regain steering control but in the RX450H, you do not regain steering control even after you take your foot off the brake. I think there are potential software fixes (e.g. not trying to capture energy from the wheels for so many seconds after a locked-wheels condition is detected. I realize that it's not an easy fix but it would allow the RX450H to take full advantage of regeneration while making it safe to drive in snow conditions.

mtnhigh799

You're not listening to what I'm telling you. I have driven on snow my whole life and know how to drive, even without anti-lock brakes. The problem is that the wheels were in effect locked as a result of regeneration, thereby keeping the wheels from turning. The only way to make them turn is to push the gas pedal, something that is not natural when you are headed for a guardrail.

mtnhigh799

good question about wheels locking when taking foot off the gas -- I never noticed that happening -- what caused the problem is that when I initially braked, the wheels locked (this condition is documented in manual) and then when I released the brakes, the wheels remained locked as the regenerative system tried to capture energy from the wheels but they never started to turn.

Cruiter

I don't know where you get that info but in plain language, you're just wrong. Post that from a reliable source.

DunWkg

Not sure I got everything in the manual about ABS, but here is what I found

Cruiter

I agree with all of that. And what it means is if your tires or worn or it's just plain ice maybe you ought to not drive. The original poster I think said something about our car needed a dash light to warn of bad winter conditions. Well DUH , I guess Lexus just did CYA with that page in the manual. They knew there would be people w/o enough sense to know safe from hazardous.

In thinking it over, I can actually imagine a situation where the tires are so badly worn and/or there is enough ice that traction is zero and if you hit the brakes hard enough and long enough w/o rolling resistance enough to force the wheels to rotate, the system might think you're trying the 'hill' brake system to keep you from rolling backward and just letting off the throttle might cause the car to skid (as the wheels will be locked). Well if you get into that situation than shame on the driver for being there in the 1st place.

Having one of my retirements from the car business I've driven a lot of cars through a lot of winters in a lot of different conditions. Up to now, I'd say the best snow car was my Audi Quattro back in the 80's. But I have to give the edge now to my (h), best yet by a lot

rcy

Really? Where?

mtnhigh799

Sorry for not making myself clearer -- the wheels did not lock up when I took my foot off the gas -- you are correct that I locked them by depressing the brake on snowy condition -- the problem is that when I realized the wheels were locked, I took my foot off the brake to get the wheels turning again but they never did -- I just kept sliding with no steering control -- that's where the regenerative system became a problem on the RX450H -- on my former RX400H, whenever I locked the wheels (which happens in snowy conditions all the time where I live), I would simply take my foot off the brake (as one always did before ABS) and the wheels would start turning, thereby giving me steering control.



I've only owned an RX450 for two winters, which makes me less than an expert. However, I've never noticed my wheels locking up when letting up on the gas pedal. When that happened mtnhigh, that was some slick ice. Inertial is gonna rule in that situation.

I was hoping to get into the online manual to find the reference to ABS not working, but Lexus has just updated the Drivers' page and things must be busy 'cuz everything is slow loading.[/QUOTE]

JimH2

To clarify further, did you actually turn the steering wheel once you let up on the brakes ?

Cruiter

[/QUOTE]

Based on your post, here's what happened and if you think it through it's sorry to say driver error.

The braking system on both the RX350 and 450(h) has an anti-roll backward feature for hills. If stopped and you press the pedal hard enough it will beep and keep the wheels from turning when you take your foot off the brakes long enough to reach the gas. It sounds like when you braked on the ice, (braking on ice w/o studded tires just doesn't work) the wheels locked and you pushed harder trying to stop the car. If the wheels were not turning due to '0' traction the system thought you were activating the anti-roll back feature and when you took your feet off the pedal they remained locked for a few seconds. It really sounds like that happened to you.

The way to keep it from happening again, is don't drive on ice. If you go from dry pavement to ice, don't push so hard while on the ice to lock the wheels and fool the system. Near 5000 lbs sliding on ice will not be stopped as you're used to with rolling wheels either. It will be stopped when it impacts a solid rooted to the ground mass tho , such as a guard rail.

Assuming that's happened, the braking system performed the way it's designed to. Even tho it's a heavy car, there was not enough friction on the ice to keep the tires rolling when you pressed hard on the brake pedal.

BlueSurf

The best performance in bad weather is the FWD system. AWD is a false sense
of security. AWD is NOT 4Wheel Drive and doesn't behave like it in any way.
Not only was I trold this by two different dealerships and mechanics, I have experienced this while living in NY and Cape Cod Ma. for over 10 years.
Also you have greater maintenance costs in AWD down the road with high mileage on the clock.
as the saying goes... "A fool and his money are soon parted"

DunWkg

This discussion has become a "beauty is in the eye of the beholder".

I drive an RX450h FWD with RWD assist, called Lexus AWD. I think I know it's limitations and my own limitations. If I wanted to go everywhere in all conditions, I'd drive a John Deere articulated loader. Crappy mileage, takes up four parking spaces and currently not available in obsidian black.

Whether an RX450h or a JD 844K loader, you may have to go to a snow-filled, vacant parking lot a see what they'll do.

pasi

Based on your post, here's what happened and if you think it through it's sorry to say driver error.

The braking system on both the RX350 and 450(h) has an anti-roll backward feature for hills. If stopped and you press the pedal hard enough it will beep and keep the wheels from turning when you take your foot off the brakes long enough to reach the gas. It sounds like when you braked on the ice, (braking on ice w/o studded tires just doesn't work) the wheels locked and you pushed harder trying to stop the car. If the wheels were not turning due to '0' traction the system thought you were activating the anti-roll back feature and when you took your feet off the pedal they remained locked for a few seconds. It really sounds like that happened to you.

The way to keep it from happening again, is don't drive on ice. If you go from dry pavement to ice, don't push so hard while on the ice to lock the wheels and fool the system. Near 5000 lbs sliding on ice will not be stopped as you're used to with rolling wheels either. It will be stopped when it impacts a solid rooted to the ground mass tho , such as a guard rail.

Assuming that's happened, the braking system performed the way it's designed to. Even tho it's a heavy car, there was not enough friction on the ice to keep the tires rolling when you pressed hard on the brake pedal.[/QUOTE]

If you are heading to an other car, a wall etc. The thing you are supposed to do is

1. Brake hard and lock your wheels (to kill the speed a bit)
2. Release the brakes so that the wheels start turning again and steer away to the safest direction, if there is any.

If the wheels doesn't start to spin again, there is a safety issue and should be fixed asap! The Hill assist/anti-roll thing should not activate when vehicle is moving forward. If they do and it's intentional by manufacturer, it's a flaw, big time.

Locking your brakes will reduce the distance and speed, unlocking will give you chance to steer.

pasi

And just to clarify my thoughts.

With proper tires, a vehicle with ABS brakes, there is only one thing to do, push brakes as hell and steer at the same time.

With poor tires on ice/snow, ABS brakes can actually be locked and car will slide on the surface. You must release brakes to be able to steer. Same thing with cars without ABS brakes. If this anti-roll system doesn't allow to do that, it's even more important to have
good winter tires to avoid these "sliding with bad tires" situations.