[Richard Wood]

Almost 8000 miles up on our e-Niro and I notice that the rear brake discs are looking a bit iffy. Front discs are smooth and shiny but one side at the rear is quite scored and on the other the pads are not sweeping the whole width of the disc. Obviously, the brakes don't get a lot of use on an EV. I deliberately hit the brakes hard yesterday till the ABS chattered on a dry road but that's not a pleasant experience. Do EVs possibly need a 'brake test' mode that temporarily disables regen so you can exercise the brakes every now and then?

 

[DBMandrake]

Rusting front brake discs is a constant battle for me on my Ion. The slightest whiff of wet weather and every morning the pads are grinding noisily on fresh rust and they have lost their "sensitivity" and bite due to the layer of surface rust which is clearly visible looking through the wheels. I actually replaced the front discs and pads 2 years ago because the originals had plenty of thickness left but the discs were severely rusted (at the lips etc) from lack of use causing them to be pretty useless. Within just a few months the same has happened to the new ones.

My conclusion is that due to regenerative braking the friction brakes simply don't get used enough in normal driving to keep them properly "maintained" as they do in an ICE. I've resorted to occasionally putting the car into neutral when I'm going down a hill where I will need to stop so that I can stop entirely using the friction brakes. (Since neutral disables regen) A few applications like this seems to spruce them up again - for a while.

And for the rear drums which also suffer similar lack of use problems I occasionally pull the (manual, hand operated) hand brake on partially for a few seconds while I'm driving to give them a slight buffing up, and that also helps them again - for a while. But it's annoying to need to do any of this in the first place.

I think all EV's probably suffer to some degree or another from lack of friction brake use, unless they are actively programmed to reduce regen and favour the friction brakes on a periodic basis as you suggest.

Putting friction brakes that were designed for ICE vehicles into EV's with regeneration without any changes to the design or materials certainly seems sub-optimal. Yes, friction brakes will not wear down as quick in an EV as an ICE, but they will often not last any longer due to corrosion build up that can't be easily removed, (eventually requiring disc replacement) and not work as well because they are not kept clean and rust free. The surface characteristics of brake discs is critical for them to bite well and operate correctly, and those characteristics can only be maintained when the discs are allowed to get hot from use (to drive out moisture) and are used enough to keep the layer of rust worn off.

 

[Richard Wood]

Interesting. I'll have to try the neutral idea. There's a steep hill near me that would be ideal. Is there a physical clutch in an EV, e.g. magnetic?

 

[DBMandrake]

Interesting. I'll have to try the neutral idea. There's a steep hill near me that would be ideal. Is there a physical clutch in an EV, e.g. magnetic?

No clutches in EV's. The gearbox is a single ratio permanently engaged whether you're in drive, neutral, reverse, park.

Neutral on an EV simply removes the power from the motor and also disables regeneration. The motor is still spinning as you coast down the road but offers so little resistance that it feels like neutral in an ICE and doesn't retard movement at all.

While park engages a locking pawl in the gearbox (same as an ICE auto) all the other modes are purely electronic changes in how the motor is controlled.

 

[Richard Wood]

Thanks for that. What you describe is what I'd assumed, so it's good to have that confirmed. I had thought it would spit it's dummy out if I tried neutral on the move. At speed I did get a warning message 'Shift conditions not met' but it went into N anyway. At least I now know all the brakes are working (all hot) and signs of scuffing on rusty bands on rear discs. I'll have a few more goes down local hill on the way home in future. Doesn't do much for the efficiency, though. 2.5 miles round trip, 1.8 miles/kWh!

 

[Gif]

My i3 was the same. Permanent one pedal driving meant hardly any use and no confidence in them when I needed them.

The one time they would get used is when the car was 100% SoC and there was nowhere for regen to store electrons so it didn’t cut in and brakes were used instead. First thing in the morning therefore I would always get the grinding on the downhill section from my house.

If the car was only charged to 80%, this wouldn’t have happened and the discs would have been even worse. I’m assuming the Niro does the same when fully charged so maybe a bit of heavy braking at 100% SoC would help in cleaning them up.

 

[DBMandrake]

My i3 was the same. Permanent one pedal driving meant hardly any use and no confidence in them when I needed them.

I had to do a "soft" emergency stop the other day. Not a life or death situation but narrowly avoiding someone doing something stupid in front of me at about 40mph.

My reflexes are pretty good so I stamped on the pedal fast and hard and while I stopped in time I felt like I was pushing the pedal pretty darn hard for the amount of braking I was getting. The braking force wasn't enough to trigger an ABS response as it wasn't strong enough to lock the wheels, and normally with good brakes if you stamp on the pedal hard at speed you should be able to get an ABS response even on dry roads as the brake force should be able to exceed the grip available so that grip is always the limiting factor of braking distance.

It didn't inspire a lot of confidence in the brakes in a real emergency situation I have to say. However after just two or three firm brake-only applications in neutral down a hill to rub off the surface rust, totalling only 15 seconds of braking time the brakes were back to being fairly sharp and sensitive again, and more than capable of triggering the ABS as I would have expected.

Yet after just a few days of conservative driving (mostly regen and no hard braking unless needed) I know they'll be back to being insensitive again due to rust build up, and it does worry me that I'll get caught out one day when they are not working at their best due to that rust build up. I've considered swapping the discs again for a different brand as some cheaper brands do corrode more quickly due to lack of corrosion inhibitors in the metal.

The only real solution in EV's is probably to use something other than steel for the discs, something that doesn't corrode with the slightest hint of moisture.... but since anything else will be more expensive than cheap steel, I don't think we'll see it for a while!

 

[Richard Wood]

My i3 was the same. Permanent one pedal driving meant hardly any use and no confidence in them when I needed them.

The one time they would get used is when the car was 100% SoC and there was nowhere for regen to store electrons so it didn’t cut in and brakes were used instead. First thing in the morning therefore I would always get the grinding on the downhill section from my house.

If the car was only charged to 80%, this wouldn’t have happened and the discs would have been even worse. I’m assuming the Niro does the same when fully charged so maybe a bit of heavy braking at 100% SoC would help in cleaning them up.

e-Niro (and Soul + Kona) has a good 3.5kWh of headroom above the nominal 100% charge (Soul EV Spy reports around 95% of total capacity at 100% charge limit) so regen works even under 'fully charged' conditions. The answer as regards exercising the brakes seems to be to switch to neutral every now and again when descending a hill. Just tried that successfully today.

 

[Richard Wood]

I had to do a "soft" emergency stop the other day. Not a life or death situation but narrowly avoiding someone doing something stupid in front of me at about 40mph.

My reflexes are pretty good so I stamped on the pedal fast and hard and while I stopped in time I felt like I was pushing the pedal pretty darn hard for the amount of braking I was getting. The braking force wasn't enough to trigger an ABS response as it wasn't strong enough to lock the wheels, and normally with good brakes if you stamp on the pedal hard at speed you should be able to get an ABS response even on dry roads as the brake force should be able to exceed the grip available so that grip is always the limiting factor of braking distance.

It didn't inspire a lot of confidence in the brakes in a real emergency situation I have to say. However after just two or three firm brake-only applications in neutral down a hill to rub off the surface rust, totalling only 15 seconds of braking time the brakes were back to being fairly sharp and sensitive again, and more than capable of triggering the ABS as I would have expected.

Yet after just a few days of conservative driving (mostly regen and no hard braking unless needed) I know they'll be back to being insensitive again due to rust build up, and it does worry me that I'll get caught out one day when they are not working at their best due to that rust build up. I've considered swapping the discs again for a different brand as some cheaper brands do corrode more quickly due to lack of corrosion inhibitors in the metal.

The only real solution in EV's is probably to use something other than steel for the discs, something that doesn't corrode with the slightest hint of moisture.... but since anything else will be more expensive than cheap steel, I don't think we'll see it for a while!

Our son-in-law has an old Lotus Elise with aluminium discs. They're still perfect years on, and don't seem to wear either.

 

[Richard Wood]

Our son-in-law has an old Lotus Elise with aluminium discs. They're still perfect years on, and don't seem to wear either.

If Kia can justify the cost of aluminium hub carriers and lots of different hot-pressed steel in the e-Niro compared with the Niro hybrids, they could do the same for the brakes, especially if rusty/malfunctioning brakes are going to be a real issue.

 

[Gif]

e-Niro (and Soul + Kona) has a good 3.5kWh of headroom above the nominal 100% charge (Soul EV Spy reports around 95% of total capacity at 100% charge limit) so regen works even under 'fully charged' conditions. The answer as regards exercising the brakes seems to be to switch to neutral every now and again when descending a hill. Just tried that successfully today.

The i3 has headroom too but was simply programmed not to use it in those circumstances. I’ve not really tried the Niro to see what happens.

I did get caught out once when the person in front stopped on a roundabout to give way to someone from the left. Yeah I know, I still don’t understand why

I literally stood on the brakes as hard as I could and still managed to contact bumpers. Like @DBMandrake said, the car just didn’t stop as well as it should have under full emergency braking conditions.

When I had the Niro first, I was touching the brakes and standing it on its nose. Some of that was the move from the i3 which drove differently but some of it was new clean brake discs and pads I’m sure.

 

[Surface Effect]

Our son-in-law has an old Lotus Elise with aluminium discs. They're still perfect years on, and don't seem to wear either.

Ah, these would be the famous MMC (metal matrix composite) rotors fitted to the Elise S1. These are made from an Al/ceramic composite that is much lighter, thermally more conductive and lasts a lot longer than the cast iron discs that were fitted to the later Elise S2. The downsides were extra cost, the requirement for special MMC-compatible pads, and occasional loss of braking in very wet conditions. It may be the last characteristic (and fear of litigation) which has steered mainstream manufacturers away from these lightweight beauties, although the electric RAV-4 is rumoured to be have been fitted with them.

 

[freddym]

One change to reduce disc rusting that can be tried is to fit aerodynamic wheel covers, that block ingress of rain and reduce flow of salt contaminated road mist.

A bit like the original Deese wheel trims.

Long descent brake cooling is taken care of by regeneration in any case.

 

[Richard Wood]

Ah, these would be the famous MMC (metal matrix composite) rotors fitted to the Elise S1. These are made from an Al/ceramic composite that is much lighter, thermally more conductive and lasts a lot longer than the cast iron discs that were fitted to the later Elise S2. The downsides were extra cost, the requirement for special MMC-compatible pads, and occasional loss of braking in very wet conditions. It may be the last characteristic (and fear of litigation) which has steered mainstream manufacturers away from these lightweight beauties, although the electric RAV-4 is rumoured to be have been fitted with them.

Thanks for the technical insight. I expect you're right about litigation concerns, apart from possible cost implications.

 

[donald]

Almost 8000 miles up on our e-Niro and I notice that the rear brake discs are looking a bit iffy. Front discs are smooth and shiny but one side at the rear is quite scored and on the other the pads are not sweeping the whole width of the disc. Obviously, the brakes don't get a lot of use on an EV. I deliberately hit the brakes hard yesterday till the ABS chattered on a dry road but that's not a pleasant experience. Do EVs possibly need a 'brake test' mode that temporarily disables regen so you can exercise the brakes every now and then?

I comment routinely on discs on EVs especially rears.

They are simply not designed for such duty cycles where most of the deceleration (in an efficiently driven EV) is from the traction system.

Discs require constant rubbing to ensure the surfaces remain clear. Be careful what you wish for, if the brakes were designed to touch the discs to keep them clean (which is a thing done in some high performance cars) then you're efficiency would plummet. EVs are very sensitive to the slightest additional loads because they are already so efficient. Not so obvious when you are only turning a quarter of your energy to traction power anyway.

So the answer is ... just let them rust.

... and the management of that is ... strip them down every year or two, give them a nice cleanup and reassemble. Unlikely any need to even swap the pads, though the cost of those might be so low as to justify swapping out even if the old ones look barely worn.

If you don't follow this advice, feel free to tread your own path, which will probably include replacing your rusted up discs every 4 years or so, which might have also sent rust into your calipers also requiring their replacement.

Maintenance is the key here. There is no 'cure'. Disc brakes are the wrong sort of technology for EV rear axles, and aren't really that clever on the front either.

 

[Richard Wood]

I comment routinely on discs on EVs especially rears.

They are simply not designed for such duty cycles where most of the deceleration (in an efficiently driven EV) is from the traction system.

Discs require constant rubbing to ensure the surfaces remain clear. Be careful what you wish for, if the brakes were designed to touch the discs to keep them clean (which is a thing done in some high performance cars) then you're efficiency would plummet. EVs are very sensitive to the slightest additional loads because they are already so efficient. Not so obvious when you are only turning a quarter of your energy to traction power anyway.

So the answer is ... just let them rust.

... and the management of that is ... strip them down every year or two, give them a nice cleanup and reassemble. Unlikely any need to even swap the pads, though the cost of those might be so low as to justify swapping out even if the old ones look barely worn.

If you don't follow this advice, feel free to tread your own path, which will probably include replacing your rusted up discs every 4 years or so, which might have also sent rust into your calipers also requiring their replacement.

Maintenance is the key here. There is no 'cure'. Disc brakes are the wrong sort of technology for EV rear axles, and aren't really that clever on the front either.

The e-Niro actively pulls its pads away from the discs. There's the rub (or lack of it). Since discovering the trouble (until recently the rears were looking OK) I've been descending a nearby hill returning home in neutral and braking. Early days but the rust is beginning to shift.

 

[donald]

The e-Niro actively pulls its pads away from the discs. There's the rub (or lack of it).

Yes, exactly, for EVs to squeeze those extra miles this is what they do now.

I wish you well trying to keep it at bay by simply braking, but I've never found this to work very well if there is any serious corrosion, and if there is not serious corrosion then it is probably just splash marks of no consequence. Good luck with that, but I recommend heeding my advise, the simple step of just cleaning up the brakes every year or so.

The situation is exacerbated because often people, including garage techs, merely examine the amount of pad left as indicative of the need to service the brakes.

People here do it routinely; "Hey, my brakes are great, don't need to be touched, only 25% worn in 5 years!". Yeah, and just wait for those frozen calipers ....

EVs may never wear their pads in their whole lifetime, this is not a way to perform some sort of brake inspection, so the only way is to strip them down periodically.

 

[Stormgrey]

I comment routinely on discs on EVs especially rears.

They are simply not designed for such duty cycles where most of the deceleration (in an efficiently driven EV) is from the traction system.

Discs require constant rubbing to ensure the surfaces remain clear. Be careful what you wish for, if the brakes were designed to touch the discs to keep them clean (which is a thing done in some high performance cars) then you're efficiency would plummet. EVs are very sensitive to the slightest additional loads because they are already so efficient. Not so obvious when you are only turning a quarter of your energy to traction power anyway.

So the answer is ... just let them rust.

... and the management of that is ... strip them down every year or two, give them a nice cleanup and reassemble. Unlikely any need to even swap the pads, though the cost of those might be so low as to justify swapping out even if the old ones look barely worn.

If you don't follow this advice, feel free to tread your own path, which will probably include replacing your rusted up discs every 4 years or so, which might have also sent rust into your calipers also requiring their replacement.

Maintenance is the key here. There is no 'cure'. Disc brakes are the wrong sort of technology for EV rear axles, and aren't really that clever on the front either.

Toyota solvedvthiscwith the 1999 Toyota RAV4 EV the front brake disks were Aluminium and did not have a corrosion issue.

 

[DBMandrake]

The e-Niro actively pulls its pads away from the discs. There's the rub (or lack of it). Since discovering the trouble (until recently the rears were looking OK) I've been descending a nearby hill returning home in neutral and braking. Early days but the rust is beginning to shift.

Any details on how it actively moves the pads away from the disc ? I'm a little sceptical about this.

Normal disc brakes rely on a tiny amount of natural run out of the disc to push the pads away when you release, but don't have any other mechanism (spring, opposing piston etc) to actively pull them away.

You wouldn't want to pull them away as you would seriously impact the response time of the brakes in an emergency stop. You don't want any slack in the mechanical or hydraulic action for fast brake response time.

 

[DBMandrake]

Yes, exactly, for EVs to squeeze those extra miles this is what they do now.

How ?

I wish you well trying to keep it at bay by simply braking, but I've never found this to work very well if there is any serious corrosion, and if there is not serious corrosion then it is probably just splash marks of no consequence. Good luck with that, but I recommend heeding my advise, the simple step of just cleaning up the brakes every year or so.

I think you're confusing severe disc rusting (which use won't shift once it's there) with a very fine surface layer of rust that can form within just a couple of days. This interferes with the interface between the pad material and disc causing a large loss in sensitivity.

The situation is exacerbated because often people, including garage techs, merely examine the amount of pad left as indicative of the need to service the brakes.

People here do it routinely; "Hey, my brakes are great, don't need to be touched, only 25% worn in 5 years!". Yeah, and just wait for those frozen calipers ....

Yes, I groan a bit every time I see EV fanboys constantly claim that the mechanical brakes in EV's last near on forever compared to an ICE. Yeah, the pad thickness does, but the discs corrode badly through lack of use and this is more insidious because it results in exactly the surface corrosion and lack of sensitivity this thread is discussing.

That wear that everyone complains about on their ICE discs and pads is exactly what keeps them in good healthy, sensitive, functioning condition.

EVs may never wear their pads in their whole lifetime, this is not a way to perform some sort of brake inspection, so the only way is to strip them down periodically.

Or use more suitable materials than cast steel. It's not rocket science. Steel is used because it's cheap, and it does the job adequately. It's not optimal even in an ICE and its far from optimal in an EV where corrosion build up through lack of use is a major issue.

Eventually I think we'll start to see EV's use materials other than cast steel for the brake discs, however it will cost more, and at the moment EV's cost so much to produce that manufacturers are willing to skimp on much cheaper items than brake discs, such as the plastic on dashboards in a desparate attempt to get the price down. So I don't think we'll see fancy brake disc material on regular EV's for a long time yet until manufacturing costs are under control.

Another option would be to add more intelligence to the brake controller to disable or reduce regen and use the friction brakes periodically to keep the surface rust worn down. Basically the same thing I'm doing now manually but done automatically for the driver without them having to change their pedal control behaviour.

It doesn't take much use of the brakes to keep them clean. I found a total of about 15 seconds of firm friction brake only force per day is enough to clean them up, so over an entire days driving this would not be much loss of regenerative potential.

Think of it like the automatic DPF regeneration cycle in a Diesel car - the driver is barely even aware it is going on, but it's important to keep the DPF working correctly.