Rear Brakes on Tow Car Wearing Prematurely

Michael - I find your experience interesting because I have the opposite 'problem'! I've had our Touareg, from new since 2015.  It's now done 63k and I'm reluctant to part with it because it's the off-road version which they don't make any more. It's a brilliant tow car better than any of the Discos I have owned - weighs two and a quarter tonnes and our caravan (Knaus Starclass) weighs two tonnes fully laden.  I tow between 2000 and 3000 miles per year.  My driving background is similar to yours.

The pads were changed at about 22k miles and this year when it went in for service / MOT, this March I said to my local garage that's looked after it since new - and whom I trust absolutely - that it was bound to need, at least, new pads - if not, discs.  No one was more surprised than me to learn that it needed neither and, indeed, there weren't even any 'advisories'.

I do wonder whether the original pads were not as good as the ones subsequently fitted, but other than that, I can't explain it.  I do use the manual facility on the torque converter gearbox for engine braking quite a lot when towing and descending long hills but I wouldn't have thought that would have made a massive difference.

I have had a similar problem.  I had to have the rear discs replaced early on my Octavia. 

The Skoda garage said this was down to a couple of things.  The first, and main cause was due to anticipatory driving for smooth driving, in other words, frequently slowing down under natural engine braking rather than using the brakes hard (not trained as such, but you need to be smoother when carrying a pillion on a motorbike).  As a biker and ex copper, I expect this is the way you tend to drive.  The low mileage and gentle braking means when the rear discs get rusty, as they do, particularly if you keep the car outside in all weathers, they do not get cleaned off properly due to the gentle braking.  Gentle braking tends to hardly apply any pressure to the rear pads/discs.  I guess, though they didn't say this, that the rust, when it does start to get removed, also acts as grinding paste, so wearing the discs out faster.  

So, like me, and presumably many others who don't do high mileage, I reckon we just have to put up with it.  Perhaps Mazdas are more prone to this due to the pressure split front/rear on the brakes being different from other makes, hence your very regular replacement requirement.  

I can't comment on premature wear reasons from experience but I would agree with richardandros that OEM quality brakes can be superior. If possible find out who actually makes the brakes for the manufacturer & buy that brand - Eg, we had a customer the director of a large company, that when his Jaguar was out of warranty brought it to us for servicing, well.... he insisted on Jaguar original parts. When the brakes turned up from Jaguar, the discs were in a lovely little wooden crate. Upon opening they were Jurid, a quick look up of the part numbers and next time they were almost half the price without the nice little wooden crate.

Sometimes alternative brands will wear better than others in specific situations, trial & error really.

The CX5 is a popular tow car and I cannot recall anyone raising this issue. To me it sounds like incorrectly set brake pressure sensors or distribution system. I would try a Mazda forum and also find a reputable Mazda dealer or independent specialist. I certainly wouldn’t be looking to change the car for what appears to be a fault specific to your car (but may be a known problem).  

Sounds like a brake compensator

Thanks everyone for your really helpful comments and advice. The car does live outside and I do brake very gently. I’ll make further enquiries!

My cars always live outside and as a motorcyclist was taught gentle braking and use of engine braking. Never had premature wear due to surface rust whether towing or not. Not remotely convinced of that scenario. Had corrosion pitting of discs due to leaving a car outside over winter with hardly any use but the discs and pads were not worn.