Quote:
Originally Posted by slilley
Yes, you are technically correct - the sensor is not related to mileage at all. The mileages I quotes are based on the wear of the pads, i.e. when the circuit becomes open because the sensor has rubbed away due to contact with the rotor. This happens long before the pad with the sensor is at 1-2mm thickness. It happens when there are still 3-4mm of pad material left. THAT pad thickness is what I'm talking about when I say there are X thousand miles remaining. You need to change the pads before the pad material is completely gone and the backing plate is making contact with the rotor. If you change the pads before you are down to 1-2mm, you are changing them before it's truly necessary. But it's always best to do it early than to do it late, as you don't want to run the risk of running out of pad friction material.
Most pads start at about 10mm thickness when new. As you drive, you slowly wear away the pad material - that's (mostly) what the brake dust is. (Some of it is rotor wear too.) I actually measure my pad thickness during regular services with a brake pad thickness tool (available on Amazon; I recommend the metal version from Steelman p/n 97844). So, if I know that (for example) I use 1mm of pad material for every 2.5K miles I drive, and the sensor goes off with 3mm of pad material left, I know I can comfortably drive another 2.5K miles before I'm at 2mm remaining. That's what I meant when I quoted those mileages. Of course, I only have 17K on the X5, so the wear I quoted is related to my daughter's F48 X1 and our previous F25 X3.
My second comment about inside pads wearing faster is absolutely true, however. Yes, the difference between inside and outside pad wear should be minimal, but it will still often be measurable. Usually it's less than 0.5mm - and can be as small as 0.1mm. But a floating caliper will always wear the pads out on the piston side a smidge faster. I think the brake pad sensors on BMW's are all on the inside pad for this reason. Porsche puts their brake pad sensors on BOTH pads. But you are correct that if you see drastically different pad wear on the inner and outer pads, you've got a problem. In the hundreds (thousands?) of brake jobs I've done on my cars over the years, that's something I've only seen once - and it was actually caused by a failing wheel bearing (on an Infiniti, not on a BMW!).
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Just want to be clear, the mileage you quote is based on your very personal usage, right? Another person's driving habit can and will be significantly different. In one example of my own, I can wear out a set of front in 8K for some usage. The same car, the 2nd set of OEM pad, get me to 90+K and sensor isn't even tripped. The only difference for my 2nd set was, I swapped pads for track events, but the accumulated mileage for track event cannot be more than 500 miles.
As to pad wear fast on the piston side, I am not sure we are looking at G05 properly. The fronts are multi-piston calipers. Pistons are on both sides, as in picture 4 and 5. So which side wear faster?
Sensor on the inside pad is NOT because inside wear faster at all. Going by this logic, BMW only put sensor on front left and rear right, does it mean front left is wear faster than front right?? To me, putting sensor on the inside is a practical choice because you can see the outside pad and get a good idea of the wear condition. The inner, we typically have to guess. With sensor on the inner, it gives a indication of the non visible pads