Brakes Question

[MikeS]

I have taken an i3 for a test drive a couple of times and will probably look to buy one very soon. I like the fact that the regenerative braking means that with normal driving you can almost totally avoid using the brake pedal once you get use to how the car drives. However, that does lead me to suspect that owing to the much reduce use of the disc brakes that they will be liable to suffer from excess corrosion. On a ‘normal’ car the brake disc will normally get a light layer of rust if left standing for a day or two but as soon as it is taken out for a drive this is rubbed off by the brakes. On an i3 this is unlikely to happen unless you purposely use the brakes. Anyone any real life experience of this?

 

[woof]

Anyone any real life experience of this?

On the ActiveE and the Tesla Model S (both cars with heavy regen) the rust appears...and isn't a problem. The first few times the brakes are used it's a awful feeling as the pads grind away, but even at very slow speed braking one does to hold the car still at lights it goes away soon enough. Every now and then I do some heavy "panic stops" on purpose to clean things off.

The biggest issue I find is when the rotors are wet and the car is parked overnight, the brakes aren't hot enough to dry off and the pads "stick" to the rotors. When one goes to back out of the garage it takes a bit of extra power to move the car and a sickening "crack" sounds as they break free. For whatever reason, the Model S is worse than the ActiveE with this.

Several on the Model S forum are annoyed that the brake rotors aren't some fancy alloy (zinc?) that doesn't show the rust...(apparently the Chevy Volt has shiny rotors all the time). Perhaps the i3 has these type of rotors.

--Woof!

 

[MikeS]

Thank you for your response. When I drove the i3 I did not feel the need to use the brakes at traffic lights or any other time except when something unexpected happened and I had to reduce speed suddenly.

 

[i3me]

Anyone any real life experience of this?

On the ActiveE and the Tesla Model S (both cars with heavy regen) the rust appears...and isn't a problem. The first few times the brakes are used it's a awful feeling as the pads grind away, but even at very slow speed braking one does to hold the car still at lights it goes away soon enough. Every now and then I do some heavy "panic stops" on purpose to clean things off.

The biggest issue I find is when the rotors are wet and the car is parked overnight, the brakes aren't hot enough to dry off and the pads "stick" to the rotors. When one goes to back out of the garage it takes a bit of extra power to move the car and a sickening "crack" sounds as they break free. For whatever reason, the Model S is worse than the ActiveE with this.

Several on the Model S forum are annoyed that the brake rotors aren't some fancy alloy (zinc?) that doesn't show the rust...(apparently the Chevy Volt has shiny rotors all the time). Perhaps the i3 has these type of rotors.

--Woof!

The rotors on the i3 are indeed made of a shiny stainless steel that doesn't rust much or not as much that I've been able to see it.
I've had no sickening crack from the brakes yet although there was enough opportunity the past weeks!

 

[ecoangel]

The car has an active stability programme that uses the brakes independantly which is similar to having a limited slip differential eg: when taking a corner at high speed. The parking brake also uses the calipers.

The only sticking you might get is with a parking brake left on for a few weeks or after a wet run as suggested by woof.

The solution to that would be to park in N with brake off and use bricks to chock the wheels.

More concerning is the REX engine which is fired up from cold very occaisonally and then run at high RPM to charge a low battery. The wear and tear there would be significant. The exhaust system needs to get hot enough to expel the H2O by-product of combustion and if not it will rot the exhaust pipe - Similar to buying a low mileage ICE car used for shopping runs vrs a motorway car that has always got up to temperature.

 

[Lecram]

I don't think that the engine will run at high rpm. I think that it will run at that rpm where the highest torque is. That's the most efficient rpm.
Beside that, the engine will run much less than a petrol car engine, compared to the mileage

 

[AndyW]

I have taken an i3 for a test drive a couple of times and will probably look to buy one very soon. I like the fact that the regenerative braking means that with normal driving you can almost totally avoid using the brake pedal once you get use to how the car drives. However, that does lead me to suspect that owing to the much reduce use of the disc brakes that they will be liable to suffer from excess corrosion. On a ‘normal’ car the brake disc will normally get a light layer of rust if left standing for a day or two but as soon as it is taken out for a drive this is rubbed off by the brakes. On an i3 this is unlikely to happen unless you purposely use the brakes. Anyone any real life experience of this?

I think the i3 has an auto brake drying system when it detects rain - the pads brush against the discs to wipe away water in readiness for you braking.

 

[MikeS]

Thanks for all the comments. I expect to have a discussion with a ‘BMW i3 Genius’ tomorrow so i will ask the question then!

 

[Bunter]

You don't need anything fancy to make a rotor that does not rust, stainless is good enough (see motorcycles).

The parking brake won't do much to remove rust because it's applied when stationary so it will not sweep around the rotor.

Parking in N and chocking with bricks sounds like a lot of effort. I'd try parking in park and leaving the handbrake off if you are worried by the pads and rotors sticking after rain. My wife's car does that after a single night so it doesn't need to stand for weeks for that to happen.

Bill

 

[MikeS]

I have taken an i3 for a test drive a couple of times and will probably look to buy one very soon. I like the fact that the regenerative braking means that with normal driving you can almost totally avoid using the brake pedal once you get use to how the car drives. However, that does lead me to suspect that owing to the much reduce use of the disc brakes that they will be liable to suffer from excess corrosion. On a ‘normal’ car the brake disc will normally get a light layer of rust if left standing for a day or two but as soon as it is taken out for a drive this is rubbed off by the brakes. On an i3 this is unlikely to happen unless you purposely use the brakes. Anyone any real life experience of this?

I think the i3 has an auto brake drying system when it detects rain - the pads brush against the discs to wipe away water in readiness for you braking.

I sk the local BMW i3 ‘genius’ about this today but he had no info!!

 

[simonb]

spoke to bmw i genius... they advised the brakes are monitored and 'cleaned' when required, i.e. brakes applied very slightly to cause friction and so reducing rusting/issues

 

[ecoangel]

From Alfa Romeo forum:

http://www.alfaowner.com/Forum/alfa-147-156-and-gt/330010-stainless-steel-brake-discs.html

" Stainless steel brake discs for cars don't exist for a very good reason - cast iron performs better. The coefficient of friction between conventional organic friction materials & typical stainless steels is around 20% lower than it is between the same friction material & cast iron. If stainless steel discs were used the lower coefficient of friction would have to be compensated for by changing something else in the system, e.g. increasing system pressure, bigger brake discs or higher-friction pads.

Cast iron also has cost advantages - it's a cheap material easy to manufacture using very simple technology.

Motorcycles do use stainless steel discs, mainly for cosmetic reasons. They use bigger wheels than cars so have room for bigger discs & high-performance bikes use sintered-metal pads which combine very high friction levels with freedom from fade. Sintered pads could be made for cars; however, apart from the high cost they would be deemed unacceptable by most users because of noise - not such a problem on bikes which don't have a big flimsy metal box to amplify the noise! "

 

[oldbillygoat]

Carbon fiber disc's would have saved quite a few pounds.I don't know what kind of pads they'd use, but F1 uses them.

 

[ecoangel]

CF Ceramicbrakes are superb but don't work quite as well with light or relatively slow machines. Racing requires extreme energy transfer. Many airliners use them and a short landing can cause brake over heat and tyre explosion/fire so they have their own cooling fans used when taxiing to terminal!

An example is Cathay Pacific landing with a serious engine problem at way above normal landing speed:

http://online.wsj.com/news/articles/SB125662899989309719

http://news.aviation-safety.net/2013/09/17/report-contaminated-fuel-causes-a330-engine-problems-and-emergency-landing-at-hong-kong/

Cast iron discs/rotors are still best value.

 

[ecoangel]

https://www.dropbox.com/s/7w18m38v1ycfoek/IMG_5949.jpg


https://www.dropbox.com/s/5sa31bc4jqp9d93/IMG_5950.jpg

Front vented discs however seem fine!