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I always thought the front did all the stopping until the wives VW needed rear brakes FIRST!
VW told me the rear brakes stop first now...
VW told me the rear brakes stop first now...
Most braking done by the front wheels?
- Thread starter nomas
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Bingo. "Trail braking" by having the rears doing more work under light application has become a thing.
Add this to the fact that many manufacturers haven't upgraded the rear brake size (hello 5th gen 4Runner, talking to you) and we've started to see quicker rear brake wear.
I just did the brakes on our cx-5 this past weekend , at 49k miles.
The pads on all four wheels were worn almost the same. The rear pads are smaller than the front on this suv.
I think it's the stability control, as we rarely if at all activated the abs. Maybe some in one trip in snow.
I try to maintain objectivity and be mindful of customers' budgets as well the appearance of a conflict of interest, ie I'm recommending things which make me money.
If something still has service life, I hate recommending replacement....but if the customer is well informed and makes the call, that's fine.
Its purely physics about having front brake bias. Moving forward, a vehicle will transfer more weight to the front when braking than the rear (theory of momentum etc. etc.). Therefore manufacturers focus braking systems to have the more "robust" components up front to handle the stopping forces better.
Rear brakes don't get ignored though, as there is still some braking to be done back there to keep a vehicle stable and moving in a straight direction when slowing, ie; not oversteering (fishtailing) or causing the deadly multiplier effect. If there were little to no braking in the rear, that end would get light and want to swap ends with the slightest of lateral force. Gotta remember, the only contact you and your car has with the road, is 4 patches about the size of your palm each. Under heavy braking, those rear patches get about the size of your thumbprint.
Also, OEMs generally use a compound in the rear pads to keep the coefficient of friction lower to prevent ABS intervention and/or lock-up. This friction material is more often than not a softer compound that wears far more quickly than the fronts will, hence, the more often replacement of that end's pads.
The truly amazing application of a dynamic braking system is one that has torque vectoring stability control. It can detect forces through a myriad of sensors and apply brakes (and control fluid pressure) to each corner individually to control vehicle motion even at the edge of the friction circle. And much faster and more precisely than any human can.
Rear brakes don't get ignored though, as there is still some braking to be done back there to keep a vehicle stable and moving in a straight direction when slowing, ie; not oversteering (fishtailing) or causing the deadly multiplier effect. If there were little to no braking in the rear, that end would get light and want to swap ends with the slightest of lateral force. Gotta remember, the only contact you and your car has with the road, is 4 patches about the size of your palm each. Under heavy braking, those rear patches get about the size of your thumbprint.
Also, OEMs generally use a compound in the rear pads to keep the coefficient of friction lower to prevent ABS intervention and/or lock-up. This friction material is more often than not a softer compound that wears far more quickly than the fronts will, hence, the more often replacement of that end's pads.
The truly amazing application of a dynamic braking system is one that has torque vectoring stability control. It can detect forces through a myriad of sensors and apply brakes (and control fluid pressure) to each corner individually to control vehicle motion even at the edge of the friction circle. And much faster and more precisely than any human can.
Beat me to it - without ABS, physics takes over, so yes, the front brakes will do most of the work.
Look at the size of the front brakes vs rear brakes too. The fronts are always larger, sometimes substantially, and even with ABS, traction control, and so on, automakers haven't changed this much. It does explain why - as many in this thread have commented - rear brakes wear out as fast as the fronts or even before. It's not that they're doing a lot more work than the fronts either, they're doing more proportionally but are smaller to start with.
On my C43 the rear brakes are also used to maintain the selected following distance when using Distronic (adaptive cruise control). I bought the car with 21k miles on it and at 27k it needed new rear pads. Now at 54k the rear pads -and front pads- are still within spec.
Physics takes over under hard braking with or without ABS, in that nose-down pitch will transfer weight to the front tires. As others have mentioned, that de-weights the rears, reducing usable braking force back there. The system(s) may decide to modulate braking force delivered to the front wheels to keep the tires rolling and therefore maintain steering capability.
Of course, that hard braking scenario is different than the day-to-day driving most vehicles see for the vast majority of their miles driven. In those more typical cases, you're absolutely right that trail braking may put a disproportionate workload on the shoulders of the rear brakes, relative to their pad/rotor contact area.
Both my Jeeps wear out the rear brakes almost twice as fast as the front, and both are driven easy. The rear brakes are considerably smaller in size which might contribute to that. OTOH my 88 E-150 rear drum brakes have outlasted the front disk brakes by about 4 times.
This is true and what I was grown up to know. It's because vehicles are mostly front heavy and weight shifts forward towards braking in general but with modern stability control along with driver enhancements more of the rear brakes are being utilized this plus smaller pads some vehicles equipped with non ventilated discs creating more heat are eating through rear pads sooner than fronts.
My 02 Camry (no ABS) gave me a scare on black ice: Locked fronts, rear did nothing. There was no traction so no weight transfer. Bias was heavy to the front. Used my e-brake (which was set up properly), got some rear wheel skid, slowed down as well as the guy in front of me and we didn't have to exchange paint.
My '19 and '21 Prii wear out all four corners at the same rate. The rears are smaller, of course. I expect all sorts of bias shenanigans since of course they also regenerate, but IMO they got it right.
My '19 and '21 Prii wear out all four corners at the same rate. The rears are smaller, of course. I expect all sorts of bias shenanigans since of course they also regenerate, but IMO they got it right.
Yeah, they must be cheaper?
On pickups they kinda make sense because road spray, gravel, mud and mag chloride+mud all gets directed back there.
People are inexplicably afraid of wrenching on drums but they're easy after you mess with a few. My only significant complaint is the difficulty in conducting a quick visual inspection....and older truck axles like 14Bs where you had to remove the entire wheel hub just to get at the shoes were a terrible design
Our VW Tiguan seems need front and back brake replacement at same time. Maybe better distribution of brake force.
It seems like a lot of people read "most braking is done by the front wheels" and thought it said "all cars wear out the front brake pads faster than the rears."
To respond to the original question, this is the kind of question we can solve the answer to with a "Free Body Diagram." This is a diagram of an object with all the forces acting on that object, whether it's at rest or moving. You can see the this exact problem and the solution in Example 1.4.3 on the following link: https://eng.libretexts.org/Bookshel..._Newtonian_Mechanics/1.04:_Free_Body_Diagrams
Doing the math shows you that the higher the center of gravity is, the more weight will be transferred during braking. This is also why making cars taller (i.e. trucks and SUVs) generally makes them not only more likely to roll over, but also makes them bad at braking, because as tires become more loaded they have lower coefficient of friction. I remember when my father-in-law told me how his Lexus GX460 was so much safer than smaller cars, I looked up road tests with him and showed him how its braking performance was worse than the cheapest, smallest car on the market (I forget if it was a Kia or a Mitsubishi at the time). Despite having tiny, cheap tires with drum brakes in the rear, the subcompact could brake from 70-0 in less space than the gigantic Lexus with huge tires and state of the art ABS. So it might be safer to be hit in, but it is not less likely to get in an accident.
To respond to the original question, this is the kind of question we can solve the answer to with a "Free Body Diagram." This is a diagram of an object with all the forces acting on that object, whether it's at rest or moving. You can see the this exact problem and the solution in Example 1.4.3 on the following link: https://eng.libretexts.org/Bookshel..._Newtonian_Mechanics/1.04:_Free_Body_Diagrams
Doing the math shows you that the higher the center of gravity is, the more weight will be transferred during braking. This is also why making cars taller (i.e. trucks and SUVs) generally makes them not only more likely to roll over, but also makes them bad at braking, because as tires become more loaded they have lower coefficient of friction. I remember when my father-in-law told me how his Lexus GX460 was so much safer than smaller cars, I looked up road tests with him and showed him how its braking performance was worse than the cheapest, smallest car on the market (I forget if it was a Kia or a Mitsubishi at the time). Despite having tiny, cheap tires with drum brakes in the rear, the subcompact could brake from 70-0 in less space than the gigantic Lexus with huge tires and state of the art ABS. So it might be safer to be hit in, but it is not less likely to get in an accident.
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