2017 Toyota Tundra 4WD Truck - Rear brakes wearing first

why are my rear brake pads worn down almost metal to metal while my front pads still have more than half left.This truck only has 26,500 miles on it. I bought this truck new. I have never had to replace rear brakes before the front brakes on any vehicle. My 2013 tundra still had original brakes at 65,000 when I traded it for this truck.

Your Tundra should have load sensing rear brakes. The proportioning valve could be bad, thinking you’re carrying more weight back there than you are and working the brakes harder.

Things have changed, get used to this. There is nothing wrong with your truck. Cars and trucks now are being designed to use the rear brakes more to even out the pad wear in areas with VERY heavy brake use. LA, for example - hard stop-and-go driving.

For those of us that live in less congested, less aggressive places, that means the rear brakes wear out before the fronts. My 2004 truck has gone through 4 sets of rears in 140K miles but only 2 sets of fronts.

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And, depending on the specific model, this is not necessarily a new phenomenon. My brother owned a '64 VW bug, and its rear brakes consistently wore out in about half the time of the front brakes.

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I don’t agree with that at all…If that was the case then manufacturers would put heftier pads/rotors on the rear brakes…and it’s just the opposite. The rear pads on my wifes Lexus, son’s Mazda 3 and my Highlander all have substantially smaller rear pads. They wear about the same as the fronts do now. Previous vehicles we’ve owned - I’d be doing 2 front brake jobs for every 1 rear brake job.

My ES300 wore out rears twice as fast as fronts.

Heftier than the fronts? No. Heafier than they have been? Also no. Brake parts are sized to perform best at max braking effort. Not the low levels most of us use. Every car relies more on the front brakes at maximum braking than the rears. Even rear-engine cars like the Porsche 911 have larger rotors in the front than rear. That’s just physics.

Also physics is that at low G levels of braking the rear can do a greater percentage of the braking work than they would in a high G stop since the load transfer is far less. It is against FMVSS standards to allow rear lock under any circumstance so the old mechanical systems were set to front-lock at max brake Gs. That meant the rears were used far less optimally than the fronts at low brake Gs. That caused older cars to wear out the fronts first.

20+ years ago a system called dynamic rear proportioning (or electronic proportioning) came to be installed on cars with ABS to address that issue as well widely varying rear loads in SUVs. A nice write-up explains it here;

The harder you normally brake, the more braking is carried on the front wheels. If you are in heavy stop and go driving, the brake wear will be pretty even. If most of your braking is low-G, the rear pads will wear out first.

Never said they were heftier then front…In fact just the opposite. But 30 years go the 4 disc systems I worked on the front and rear pads and calipers were the same.

Yes it is simple physics. I can show you the Formula if you like.

As you brake…the weight shifts forward over the front wheels…thus the front brakes are doing most of the braking. Start applying too much brake to the rear, then the rear brakes will start locking up.

Rear discs have always been less substantial than front discs in my experience. Fronts are ventilated, rears are typically not.

Rear brake swept area is also typically less than front. Here’s an example for a BMW, 50% more swept area in front:

Then calculate along with me as I illustrate. Assume a front engine, rear drive SUV. Calculate the % front to rear braking at 0.2 Gs and again at 1.0 G’s Assume a CG height of 0.8 meters a wheelbase of 3.3 Meters and a 55% front weight bias.

The sum of the moments about the rear axle gives us the equation;

% braking front = (0.24 * braking decel + 0.55) * 100

at 0.2 Gs, a normal braking effort, the front wheel can support 60% of the braking load, 40% rear

at 0.4 Gs, a bit more aggressive braking, the front wheels can support 65% of the braking load, 35% rear

at 1.0 Gs mx brake, the front wheels ca support 79% of the braking load or 21% rear.

So for normal driving with dynamic rear proportioning, the rear can be called upon to provide 41% of the braking load while the base brake components themselves are still sized for the 79/21% split.

Before ABS, the front/rear split, by government spec, would have to be 79/21. With electronics, the rear brakes can now do 40% of the braking now versus a purely mechanical system and, as such, wears out faster.

I see what you’re saying on the braking…What I’m still struggling with is why manufacturers have made the rear brake calipers and pads SMALLER if they are now doing MORE braking.

I’ve not seen any that were down-sized but more than a few that were’t UP-sized either. Some, like my Mustang, have thicker rear pads although the swept area is quite a bit smaller. My GM SUV has the same rotor diameter and thickness front and rear. The pads are very similar. The biggest difference is the aluminum calipers in the rear and iron in the front.

I think they design the base system for proper torque distribution and heat capacity and then live with whatever pad wear they see. But they tend to test for LA city traffic, or alternately, Boston, Chicago or Detroit metro traffic which contains lots of 0.4 G stops. Those of us who spend our days with 0.2 G stops, wear the rears out quicker.

That said, some manufacturers just do a better job of it. My fwd Saab’s first brake job was a 4 wheel complete change. The pads were equally worn, the rotors were close to minimum on all 4. It was a bulls-eye. Our Audi looks to be the same kind of deal based on the pad measurement.

Or, is something different from stock: have you changed wheels, tires, or installed a lift kit, for example?