Brakes on 3rd Gen RX450h

[Barry14UK]

One of the few disappointments I have found with my car concerns the Brakes at motorway speed or indeed even when braking on a steep decline at slower speed.  As we know this is a very heavy car and calls for very good brakes.  I am therefore surprised that with the development of the car over the years this has not been better addressed,  Certainly around town the brakes are fine.  Lexus checked my rotors and pads when they fitted my new tyres very recently and said these were good.  My car was also road tested without adverse comment after some adjustments including 4 wheel alignment, so I believe the brakes are typical of the model.  Although one can mostly counter this shortcoming by allowing for it, there is the odd time that better brakes would be helpful.  (Incidentally, I ,don't find the retardation effect of the hybrid matches that of a manual box).

Admittedly this is not a high performance vehicle and this may account for the lack of brake upgrades available but  in an emergency it matters not whether you are in a sports car or heavy SUV, you need to be able stop well.  

Anybody any thoughts on this or done anything to improve their brakes?

[NemesisUK]

If you can invoke the ABS when braking hard then there's nothing wrong and perhaps you need to read the road better and moderate the speed.

There is virtually no retardation through the hybrid transmission, one must feather the brakes to use the regeneration function, hydraulic braking only comes in at lower speed or heavy pedal application.

Pretty sure Lexus has specified the brakes to safely arrest the car all situations.

[Gliderpilot]

If you lift your foot off the accelerator the the car will coast with only light retardation. To get more regen braking start lightly pressing the brake pedal and you will see the power dial go fully negative putting about 30 kW into the Battery. Pressing harder will apply the mechanical brakes, I try and judge the distance to stop so that I can come to a halt with minimal mechanical braking and get the most regen.

[Herbie]

The brakes on my 2013 RX450h Advance are amongst the best I've ever had and will stop the car on a sixpence from high speed, no problem whatsoever.

However, the whole idea of a hybrid is to anticipate stops and do it very gently - apart from emergency braking of course.

The regenerative braking is a form of retardation, but it's primary purpose is to recover the kinetic energy normally lost in friction heat and use it to charge the traction Battery, not just to slow down the car as a traditional electromagnetic retarder would.

Say you're approaching traffic lights - you start to brake very gently from a fair way out. As you do so, the power meter needle dips into the charge zone, possibly all the way down which indicates maximum charge. As you continue to lose speed the needle begins to rise as the rate of charge goes down. When you reach a certain speed (I think it's 3mph but could be wrong) OR if the traction Battery becomes fully charged and can accept no more, then there's a change from regen braking to normal hydraulic braking.

If you're on a long downhill descent and you just lift off the accelerator the power meter needle will drop into the charge zone, but only slightly - put your foot on the brake and it'll drop down much further, indicating more charge.

I don't know what actual figures are but for sake of this discussion let's say that a set of discs and pads on a 'normal' car will last for 20k miles (remember, it's just an example). It's not unusual for hybrids to double that mileage or even triple it before discs and pads need to be changed, if the braking is done correctly, ie, as much use of regen and as little use of hydraulic as possible.

In an emergency stop or just heavy braking, the hydraulic brakes are used straight away, with no regeneration first.

[Mr Vlad]

Perhaps you can remove the pads and see if they are shiny/glazed. You could roughen them up with abrasive paper and even clean the discs up. You should see a marked improvement in braking.

[olliesgrandad]

Please view the Lexus hybrid driving technique video on YouTube. Driving a hybrid requires a different technique to the 'old fashioned' motor car. 

[Lager shandy]

The problem your having is people done tend to brake hard in these bloaty old beasts ,mine was like yours when I first got it and now I drive it harder and tend to rely more on the actual brakes .unlike most here feathering the brake pedal in there slippers hyper milling lol.i will uprate my pads in the future with pads that give more bite .

[olliesgrandad]

4 hours ago, Lager shandy said:

The problem your having is people done tend to brake hard in these bloaty old beasts ,mine was like yours when I first got it and now I drive it harder and tend to rely more on the actual brakes .unlike most here feathering the brake pedal in there slippers hyper milling lol.i will uprate my pads in the future with pads that give more bite .

Personally I would leave the brakes as Lexus intended because in my experience the front pads outlive the discs and harder pads will wear the discs out quickly. I certainly don't hypermile and the braking is more than adequate when required. My discs needed replacing at 50000 miles as they were at minimum recommended thickness. The pads still had 4mm on them. 

[Barry14UK]

19 hours ago, NemesisUK said:

If you can invoke the ABS when braking hard then there's nothing wrong and perhaps you need to read the road better and moderate the speed.

There is virtually no retardation through the hybrid transmission, one must feather the brakes to use the regeneration function, hydraulic braking only comes in at lower speed or heavy pedal application.

Pretty sure Lexus has specified the brakes to safely arrest the car all situations.

Never invoked the ABS because I drive the RX like the old man I now am but have been driving cars for over 55 years and motor cycles before that at much faster speeds then than allowed now and before motorways.  I think I have learnt to read the road pretty well and further adapted to optimise hybrid performance but I drive up to 70mph where permitted and appropriate.

Sorry but 'Pretty sure Lexus has specified the brakes to safely arrest the car in all situations' doesn't make sense.  Meet me on dedicated strip and see how much further you need to stop in an RX from 70mph than me in my 18 year old BMW 5 series with standard brakes or the several Mercedes I had among other cars before that..  After I stopped I wager the RX would still be travelling fast enough and further enough to cause more significant damage.  I have had a few near misses over the years with drivers and on one occasion a horse charging out from nowhere visible in front of me so good brakes and good tyres always important to me.  In my opinion Lexus RX brakes should be better to combat it's heavy weight even though not driven hard, certainly for one emergency stop if not for several that more performance related cars can perform. So may see what upgrades (if any) offered in the USA where the RX is sold in greater numbers.

 

[Herbie]

In that case then Barry, I can only suggest that there's something wrong with your car.

As I said above, the RX brakes are amongst the best, if not the best brakes I've experienced on any car and I've driven many brands of cars, as well as many different vans and vehicles during my days as a telephone engineer on BT.

Given that, and also the fact that very few others on here have voiced the same concerns as you, I can only reiterate that you seem to be the odd one out so it must be your car.

[Mr Vlad]

Way hey Barry riding motorbikes fast back in the very early days lol. I too rode very fast in the 80's hence the name given me MadVlad. Yes the RX is a big heavy car but my truck is bigger and heavier and my brakes need changing yearly coz of the mileage but they work very well indeed just like the brakes on the F sport I had  (yes I miss it) and I drove that fast too lol. As I suggested clean your pads of glaze and the discs with a solvent cleaner. Flush out the brake fluid and renew with fresh fluid. You should then have good brakes that Work.

[Richard Fixter]

Pretty sure as most modern cars have it the Lexus will be equipped with emergency brake assist, this works by how quickly the brake pedal is being applied. If you need to stop in an emergency and stamp on the pedal it increases the force. I have an rx3oo and when I hit the pedal in an emergency ABS certainly kicked in,didn't need that much force either.

Try stamping on brakes quickly just once and see if it makes a difference.

 

 

[Barry14UK]

Thanks to those who have posted thoughts.

As  intimated  at the outset, I find the braking fine at about town and 30 mph.  There is no judder or vibration and car does not pull to one side at any point.  The car was maintained by Lexus from new and any new rotors/pads fitted within the 37K miles at which point I bought it, would have been Lexus. Lexus reported brakes OK when they fitted new tyres recently.  The car may have brake assist in an emergency but I have not found the need to brake really hard yet, although I have done so fairly hard to deglaze the rotors as one does from time to time.  (Incidentally, I am aware that rotors don't usually warp with normal road use.  What can happen is that when hot a minute amount of pad material can transfer and be deposited on the rotors which then induces uneven rotor wear. This can happen if new pads are not properly broken in and particularly if after heavy braking producing a lot of heat the car is brought to a stop with the brakes still held on. EBC provide a small depth of different material on their 'Green Stuff' pads to assist breaking in or did when I tried them). Over hard use producing too much heat can cause crystallisation. The type of sliding caliper with only a sole piston pushing on one side is never going to be as good as a multi pistoned caliper with pistons pushing pads towards rotor from both sides as found on some standard cars or those fitted with 'Performance' brakes. Anyway, when the opportunity arises I will take pads out clean and lube as appropriate.  I will then take a view on possible upgrade of some sort but no point in fitting competition type pads for road use.

By way of example, using standard brakes, in comparing the RX 450h of 2015 with a 5 series BMW of the same year, the front overall rotor size  and curb weight respectively is 328mm and 4650lbs against 348mm and 4090lbs.  So the RX has smaller rotors but is considerably heavier, indicative of why it will be outbraked by the BMW.