Nope. You did not misinterpret.
The shorter rear pad life has been confirmed at two Jag dealerships. You could call it a design flaw, but long story short-- whatever computer controls the braking grabs hard at the rear pads to counter-act the car "nosing forward" on hard braking, to keep the car level so the stop feels smoother. Since the rear pads and rotors are smaller, shorter life. Techs at both dealerships say they see this all the time on XK's.

 

If the rear brakes are grabbing the rear wheels will lock up and cause instability. Modern cars RELEASE the rear brakes on hard braking to maintain stability. Older cars (~70's - 90's) had mechanical proportioning valves to do this. Newer cars do this electronically.

Description of the system from the service manual:

Electronic Brake Force Distribution

EBD limits the brake pressure applied to the rear wheels. When the brakes are applied, the weight of the vehicle transfers
forwards, reducing the ability of the rear wheels to transfer braking effort to the road surface. This may cause the rear
wheels to slip and make the vehicle unstable.
EBD uses the ABS braking

Since some, but not all the cars have this problem, I suspect the cause is less than a design flaw. My two current modern Jags, that share the same brake system and components, wear the front brake pads faster than the rear pads, as they should. There is something electrically or mechanically different on cars that go through rear pads in 15K miles. So I don't buy the "design flaw" theory. There is something that can be corrected to get the system to operate in a normal and safe fashion. Are there any TSBs associated with the braking control modules?

 

Interesting. Maybe the high wear rate on the rear pads is due to not having reset the electronic parking brake correctly?

 

I will buy that theory.

 

For whatever it's worth: My brand new 2012 XF had its rear brakes replaced at 32K miles. The fronts were still great all the way until the end of the lease at 42K miles.

 

It seems like the parking brake can cause excessive drag on the XK rear brakes to the degree that the entire rear wheels can become excessively hot without even using your brakes at all! Try using a temperature guage that you can just point at the rotors. You might be quite surprised. There's just no way the rear pads and rotors should wear out before the fronts. It turned out that the dealership techs were not adjusting the parking break drag correctly after new rear rotors!

 

The nosing forwards is a relationship of slowing down the mass with a CG above the roll center. Front or rear brakes, it will nose forwards under braking.

 

As explained by professional race drivers when you accelerate the CG shifts to the rear and when you decelerate (brake) the CG shifts to the front, hence the "nose drop". See the PK4144 post for a more complete explanation.

 

However.
Theoretically if you have electronic brake proportioning, electronic anti lock and electronic shocks, the weight can be shifted backwards.

The only reason a rear end steps out if you gave it majority of the braking power is because its lighter in forward motion. But when done carefully a rear biased brake can stop a car with much less drama. Like gently using the handbrake to counter the nose dive. I would do that with my manual when I did not want my passenger to spill their drink.

 

The CG only shifts when you move objects in the car, luggage, yourself, a passenger, etc.

CG is center of gravity, and aside from burning off gasoline, it will remain about the same if you don't have passengers or luggage flopping around inside.

Weight transfer is what you mean instead of center of gravity.

The grip of a tire is roughly proportional to the force pushing it in contact. As weight transfers off, available grip reduces.

The roll center of a car is not static, it is a sum of the effects of the suspension geometry. For example, if the suspension were "crouching spider like", and attached at the top of the car, the front of the car would pitch up under braking instead of down. This is because the CG would be below the roll center.

All that has to be done to counter the nose diving under braking, is arranging a suspension geometry that creates a roughly neutral roll center to CG.

 

I've got an 07 XK with about 40K miles. It's on the 3rd set of pads. Original owner was an elderly woman and she only got about 15K on the rears. I had to replace them, and the rotors, at 35K. I switched to slotted rotors and ceramic pads. We'll see if that improves the life. I wonder if the brake balance valve is defective. The rear rotors also look very small. I think they're shared with the X Type.

 

Not in this Universe.

 

The way to shift the weight backwards would be to apply significant braking force from above the CG of the car. The leverage of how far above would have to be greater than the braking force applied.

So reverse jet engine on a lifted pod, propeller, etc.

Also a massive air brake positioned high and to the rear with proper leverage would also weight shift to the rear.

 

But I DO drive in reverse all the time! Only time it's in Drive is when I'm "backing" into a space....

 

But what if you NEVER use your parking brake? I'm old school, and am thinking about systems that use a cable (old school!), so I don't understand the electronic parking brake at all.

All I will restate is that neither my regular JLR dealer who does major service nor the shop who did the pads was surprised-- both said they see it on these cars.

 

I can just see the Click & Clack Brothers arguing about this for days and even making a puzzler out of it.

If two people are carrying a beam with equal load between them, then one lifts his end up slightly, because he is going up a step- which in turn makes the beam heavier for the other guy.

Isnt a car suspension doing the same if it softens the back allowing the car to go down and effectively raising the front.

At least by my illiterate observations the weight of a car can be shifted 70% to the rear by lowriders and Chicanas raising the front of the car with hydraulics.

 

The way I proved the rotor overheating was really quite simple. After driving at freeway speeds for 5 miles or so I exited the freeway on a rising off ramp and slowed to a stop using only engine braking. When I checked my rotors and wheels, the rears were hot enough to burn me while the fronts were only mildly warm. The entire rear wheels were hot! Now I use a digital thermometer that can just be aimed using a red LED.
I'm quite well aware that there is normally some contact of the pads and rotors during normal driving. Trust me, the overheating I observed was in no way normal. After arguing with the service advisor who's favorite answer to difficult questions was "Oh they just do that", I was taken into the service bay where one of the senior techs advised the tech working on my car that the parking brake adjustment was being done incorrectly causing the excessive heat and wear! After the correction, my rears are only 10 to 20 degrees warmer than the fronts.
I'm not arguing weight transfer while breaking, just brake and wheel overheating which could be a dangerous cause of the excessive pad and rotor wear.

 

Instead of a lever or pedal connected to a cable that the driver operates manually there's a switch and electric motor that pulls essentially the same cable.

The EBP never activates while driving unless commanded by the driver. It's not part of the DCS or stability system.

 

From what I can tell, the parking break uses the rear rotors and pads and is activated electricly. It needs to be adjusted for clearance and travel when the rotors are changed.

 

Correct. A very simple process even at the DIY level.