Going Electric.. present small car options.. confusing

[DaveMcT]

Comparing the corrosion risks of today's electric car brakes with a 1980s Citroen is entirely valid, because the BX made so little use of its rear brakes. They rusted away due to lack of use. Today's electric cars do 90% of their braking via motor regeneration so the friction brakes stay cold risking lack-of-use failures. Hopefully, designers avoided this issue. More likely, they hope everything will be OK until the warranty runs out.

 

[Most Easterly Pandas]

Comparing the corrosion risks of today's electric car brakes with a 1980s Citroen is entirely valid, because the BX made so little use of its rear brakes. They rusted away due to lack of use. Today's electric cars do 90% of their braking via motor regeneration so the friction brakes stay cold risking lack-of-use failures. Hopefully, designers avoided this issue. More likely, they hope everything will be OK until the warranty runs out.

It isn’t the temp that stops them rusting, just regular use. They’re still used under heavy braking, and when bring the car to a total stop below circa 7mph.

 

[StevenRB45]

It isn’t the temp that stops them rusting, just regular use. They’re still used under heavy braking, and when bring the car to a total stop below circa 7mph.

I do think there's a point at which regular use is not enough.

You need a certain amount of pressure to clean surface corrosion that's gone beyond a light orange sheen. If it never gets that the corrosion stays largely intact and eventually they end up a pitted mess.

Not an issue if the car is used regularly but the ones on our Citroën got beyond cleaning up surprisingly quickly.

If I'd noticed I'd just have gone out a few times a month and pulled the handbrake but the car was only used very minimally at the time so didn't. If pressure was not important the front ones would be the same.

 

[AndyRKett]

I’d go as far as to say that modern car brakes aren’t made the same as they where 30+ years ago.

If Covid had proved anything it’s that cars these days can stand a long while without turning to dust. Back I the 80s if you left a car in your garden for a week it would start rusting quickly enough that you could see the paint turning brown, obviously it was even worse in the 70s which is why back then they pre-painted the cars in rust colour

 

[Didge3]

I very rarely use the friction brakes for slowing down. I have an app on my phone that connects to an OBD dongle, you can set it to beep when the friction brakes engage (annoying but informative for testing purposes). As MEP says under gentle braking they only come in around 7mph when regen starts to lose its effectiveness.
AFAIK the brakes are original on my car (7 years old in October and ~60k miles), I have no idea how the previous owner drove but even if you brake hard, if you're above 40mph or so regen is still doing all the work until you're below 40mph when the friction brakes are used and you need to be braking hard for that to happen.
One thing that might help the rear discs although I'm not sure if it makes much difference, is the electric handbrake which (if you're lazy) will disengage automatically when you put your foot on the accelerator, there is a small delay where the car will squat and then it releases, I'd guess this creates a bit of drag on the rear discs for the first second or two of movement. Although thinking about it are the regular discs actually used for the handbrake?

 

[varesecrazy]

95% sure the rear discs will be the handbrake too

Ancient set.ups had a tiny drum there too.. but that was probably pre.ABS

60k.. my twinair had only half.worn its original set of brakes also.. but of course they are 'scaled' to the weight of the car.. so no great shock

Our low miles panda doesnt see much use nowadays.. and the discs barely clean after me using it for a week..
But of course I am easy on the brakes

So.. Im still thinking of Electric

 

[Most Easterly Pandas]

So.. Im still thinking of Electric

Any questions then pop them here. As much as I’m all for electric though, and it is the way things are going, still make sure the maths work if mileage is fairly low, unless doing it purely for environmental / new toy reasons

 

[varesecrazy]

Any questions then pop them here. As much as I’m all for electric though, and it is the way things are going, still make sure the maths work if mileage is fairly low, unless doing it purely for environmental / new toy reasons

Its still infrastructure stopping me..

Cars are capable of the 110 mile trip..
But not capable of the return without a charge I cannot access..
Nearest points are :
Tesco ..3 miles uphill
Pub... 6 miles downhill

Neither really work for a regular '90%'
Top.up

 

[Didge3]

Its still infrastructure stopping me..

Cars are capable of the 110 mile trip..
But not capable of the return without a charge I cannot access..
Nearest points are :
Tesco ..3 miles uphill
Pub... 6 miles downhill

Neither really work for a regular '90%'
Top.up

If home charging isn't an option it is hard to recommend an EV to most currently, unless they only do short trips and will only be charging publically once a week, it's a lot of hassle on a daily basis and the reason I didn't go full BEV as I need to make a 120mile round trip with no charging at one end, not easy for the cheaper end of BEVs in the depths of winter

 

[DaveMcT]

I’d go as far as to say that modern car brakes aren’t made the same as they where 30+ years ago.

You think?

The Citroen BX discs were virtually the same as today's Fiats. Vented front, solid back, retained by wheel bolts (not nuts) using single piston sliding callipers. Due to the engine powered hydraulics they had the hand brake working on the front but the mechanism was like any rear disc hand brake. The other difference of course was the mineral oil rather than brake fluid. Mechanically they could have come out of the same factory.

The fronts were fine and considering how the car stopped surprisingly long lasting. The back discs suffered pitting corrosion from to lack of use. The rust almost never got polished away so corrosion soon dug in. My rear discs were scrapped with deep pits of rust after a couple of years. At least they were cheap and easy to replace.

I suspect many owners of electric cars will get similar issues simply though lack of use of the brakes.

 

[StevenRB45]

While brake disc technology hasn't really come on brake controls have.

There are many ways you could manage it, for example tell the car not to use regen for the 1st few stops after a period standing. Or use a method Mercedes used 15 years ago where the abs pulsed the pads against the discs to keep them dry in bad weather, not enough to be perceptible but kept them dry for use would also skim off corrosion.

The fact is most of the cars will have very advanced control of both friction brakes and regeneration and the relationship between them so it wouldn't actually be very difficult to manage it.

As long as you press the brake and it stops in a consistent and predictable manner do you actually care how it does it?

 

[AndyRKett]

While brake disc technology hasn't really come on brake controls have.

There are many ways you could manage it, for example tell the car not to use regen for the 1st few stops after a period standing. Or use a method Mercedes used 15 years ago where the abs pulsed the pads against the discs to keep them dry in bad weather, not enough to be perceptible but kept them dry for use would also skim off corrosion.

The fact is most of the cars will have very advanced control of both friction brakes and regeneration and the relationship between them so it wouldn't actually be very difficult to manage it.

As long as you press the brake and it stops in a consistent and predictable manner do you actually care how it does it?

All of this. Also when I said brakes are not made the same, I thought I was being fairly obvious that I was talking about materials which are much better now than they where in the 1980s, back when a cars brakes would be unserviceable after standing on a dealers forecourt for a couple of weeks in the rain.

 

[Most Easterly Pandas]

While brake disc technology hasn't really come on brake controls have.

There are many ways you could manage it, for example tell the car not to use regen for the 1st few stops after a period standing. Or use a method Mercedes used 15 years ago where the abs pulsed the pads against the discs to keep them dry in bad weather, not enough to be perceptible but kept them dry for use would also skim off corrosion.

The fact is most of the cars will have very advanced control of both friction brakes and regeneration and the relationship between them so it wouldn't actually be very difficult to manage it.

As long as you press the brake and it stops in a consistent and predictable manner do you actually care how it does it?

Oh but any brake application would be wasting energy

Its still infrastructure stopping me..

Cars are capable of the 110 mile trip..
But not capable of the return without a charge I cannot access..
Nearest points are :
Tesco ..3 miles uphill
Pub... 6 miles downhill

Neither really work for a regular '90%'
Top.up

Oh no home charging capability?

 

[StevenRB45]

Oh but any brake application would be wasting energy

Given you're at the point where both brakes and throttle are drive by wire the car can do what it wants pretty much.

If it wants to use friction brakes when you lift off..it could and then next you lift off it could use regen. In the same as if you press the brake pedal the friction brakes may actually do nothing if the car decides it can provide the force with regen only.

If did it once or a trip in a trip the difference in range would be measured in feet rather than miles.

 

[Most Easterly Pandas]

If did it once or a trip in a trip the difference in range would be measured in feet rather than miles.

But from what you describe it’d be using the pads and discs no more than the car already does below 7mph to bring it to a complete halt.

As such you’d need heavier braking, which although won’t reduce range massively, will still waste energy. I’m a tight arse, save all the energy I can

 

[StevenRB45]

But from what you describe it’d be using the pads and discs no more than the car already does below 7mph to bring it to a complete halt.

As such you’d need heavier braking, which although won’t reduce range massively, will still waste energy. I’m a tight arse, save all the energy I can

I was more theorising on possible management strategies they could employ rather than speaking from a position of "they should do this".

The main point was the with no physical connections the brake system can do whatever it needs to do. It may well be they've already considered or it may be they fit better brake discs that don't mind little to no use.

Either way...they seem to be different to a BX.

 

[varesecrazy]

Oh no home charging capability?[/QUOTE]

5 years away I reckon

Double yellows outside the house.. need council to install a post ..or 5.. in our alloted layby

Flat I use for work is on a managed estate..
Weirdly strict (and slow)
I think a yellow disabled space would need 18 months notice.. so supplying electric to a parking area will need a decade plus

 

[AndyRKett]

With brakes really it isn’t essential on an electric car to even have them (with one exception) you can very easily design an electronic system that can stop a car just based off the back emf in an electric motor, or an emf type resistive brake in other words use regenerative braking to completely stop a car very quickly you could lock the wheels like this but obviously that wouldn’t be very efficient as you lose energy if the wheels lock. But that said if you needed to you could probably a lot more expensive than a disc and a cheap calliper on each corner but you could.

The public however might not be so keen if you said ‘this car has no brakes at all’ and also you still need a hand brake. There is no reason why brakes can’t be very easily designed with appropriate materials to not fall apart in the first, say 5 years which is very reasonable.

As for street parking there as something on the radio the other day about a council installing lamp post charging points in a whole street, I think things are going to change surprisingly quick but people think it’s going to still take 30 years to install a charger

 

[varesecrazy]

As for street parking there as something on the radio the other day about a council installing lamp post charging points in a whole street, I think things are going to change surprisingly quick but people think it’s going to still take 30 years to install a charger

Thats how they power our Xmas lights

Not sure how the neighbours power theirs :devil:

 

[DaveMcT]

With brakes really it isn’t essential on an electric car to even have them (with one exception) you can very easily design an electronic system that can stop a car just based off the back emf in an electric motor, or an emf type resistive brake in other words use regenerative braking to completely stop a car very quickly you could lock the wheels like this but obviously that wouldn’t be very efficient as you lose energy if the wheels lock. But that said if you needed to you could probably a lot more expensive than a disc and a cheap calliper on each corner but you could.

I think this has to be the way it goes. There will be a basic drum brake for parking, maybe on the front axle (as Citroen did) as an emergency measure. But thats it. The motors do the rest.

There is not really any need for axle differentials. Use a motor for each wheel with the control system managing how the power is put down.