This condition is the negative side of utilising the Regen facility on all EV’s.
Braking using the footbrake is a 80 - 20 ish condition, about 80% of the braking is conducted by the front brakes and the remaining 20% is done by the rear brakes.
Therefore the rear brakes never really display the same level of use / wear that the front pads and discs do.
Add strong Regen into the mix on an EV and the rear brake have almost nothing to do at all.
This lack of use allows rust to form that then develops into deep pitting into the face of the disc’s.
It hasn’t taken long for both dealers and MOT testers to lock onto this premature corrosion problem and it is offered them an opportunity to take some much needed lost revenue from EV owners.
Service time for EV’s have become more of a “Health Check” than replacing engine oil / filters etc etc.
They are NEVER going to let this work opportunity pass them by tbh.
There no real solution to preventing this condition or it repeating itself again unfortunately.
Turning the Regen to its lowest setting will help prevent the decline speed of the rust forming, but most of us like this feature so it’s a battle between head / heart and ultimately your wallet
.
I tried once a week, to remember to lower the Regen to its lower setting to help with the rust, but it’s not a cure
.
On the ZS EV the car defaults to normal Regen and that became my “Go To” setting.
Our S5 on the other hand, it defaults to LOW Regen on start up, this may help a little in the battle of surface rust forming
.
Our ZS EV had covered about 28,000 miles in the three and a half years of ownership.
It passed its first ( independent ) MOT with no problems at all and nothing was reported by dealership on any of the 3 annual service inspections it had.
There was “pitting” clearly evident on the surface face of the discs on the rears, so I expected it would get picked up at some time in the near future.
I think owners would complain less, if the price to replace this items at the dealership, was not so expensive !.
The is nothing really special about this discs or pads, very basic standard stuff.
Now third party replacement parts are available at a highly discounted price point.
