Why do we have larger diameter rotors IN THE REAR?

[bleda2002]

IF THE Gladiator is like my 2007 Wrangler the braking is biased to the rear. What I have been told is when your down hilling on a trail and you need to slow down you dont want the front brakes to lock up.

Was wondering if anyone would bring this up, the gladiator is more or less 50/50 braking

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[kevman65]

Why do we park on driveways and drive on parkways?

 

[bd100]

On top of everything else mentioned so far, supposedly the JT has the rear axle shifted forwards a bit compared to the typical pickup truck. Slightly better breakover angle, but also more weight on the rear axle.

 

[Sbro2021]

I feel like the most logical conclusion to this as follows:

 

[Splenda]

OK so I decided to do a deeper dive based on what was reported above and here’s what I found..

PERFORMANCE CARS - REAR ENGINE
Porsche 911 S 380/350 f/r
Porsche GT3RS 410/390

PERFORMANCE CARS - MID ENGINE
Porsche GT4RS 410/390
Porsche Spyder 410/390
Chevy C8 Z06 370/380

TRUCKS
Ford F-350 363/363
Ford F-450 391/401

BONUS
Tesla Model Y 355/335

So it is somewhat all over the place…strange

I think the C8 Z06 has larger wheel diameter in the rear than the front too, as does my buddy's Maserati Granturismo

The Chevrolet Corvette C8 Z06 features a staggered wheel setup with 20-inch wheels in the front and 21-inch wheels in the rear. Specifically, the front wheels are 20x10 inches with a +35mm offset, and the rear wheels are 21x13 inches with a +40mm offset,

 

[Supazuk]

I have…
The thickness of the rotor helps in heat dissipation and of course the number of pistons influences the pressure that can be applied but that still doesn’t answer my question.

The distance the pistons are from the center of the wheel influences the effectiveness of the braking, all other things being equal. That is why the front rotors are usually larger than the rears…but not in this case.

I have never seen or heard of larger diameter rotors being in the rears…

its to accommodate the combined parking drum in the rotor and provide ample surface material for the brake pad

 

[LouisvEarlleJT]

its to accommodate the combined parking drum in the rotor and provide ample surface material for the brake pad

This. I believe the WJ's were similar (also with D44 rears) though it's been forever since I had one.

 

[piroman683]

regarding the initial question, it is possible to have bigger diameter rotors (outer diameter specifically), yet have less rotor area that is used in the braking process. I did a detailed comparison on a D60 (Dynatrac) which uses F-150 rear disks vs. the D44 and the D44 actually had more surface area.

I have not done any detailed measurements on the front, and looking at them it definitely looks like there is more surface area for braking. The fronts are also a dual piston vs. single piston in the rear.

The rears do need to fit the parking brake as well which could be one of the many reasons for the designed size (along with varying payload and towing design inputs).

 

[ShadowsPapa]

regarding the initial question, it is possible to have bigger diameter rotors (outer diameter specifically), yet have less rotor area that is used in the braking process. I did a detailed comparison on a D60 (Dynatrac) which uses F-150 rear disks vs. the D44 and the D44 actually had more surface area.

I have not done any detailed measurements on the front, and looking at them it definitely looks like there is more surface area for braking. The fronts are also a dual piston vs. single piston in the rear.

The rears do need to fit the parking brake as well which could be one of the many reasons for the designed size (along with varying payload and towing design inputs).

Yes, many factors, and dimensions enter into it.
The distance from the hub to the outer edge of the rotor rear vs. front, size of the pad, piston diameter vs. psi against it (it's the force that matters, not the psi, the same psi working on less piston area means less clamping force is applied, and the force across the surface of the pad and rotor. Not as simple as rotor diameter alone.

We got into that discussion when people were talking switching their vintage pony car from manual drum brakes to power disk, leverage of the pedal vs. position of the rod on the pedal lever and it got really deep into the math. (people asked "why is the hole in a different position" - basic grade school physics.........)

 

[Janster]

Curious... do the Gladiators have a 'load sensing' valve? Or sensor?

I remember the Tacomas had them or used to have them. They'd sense the amount of load in the bed and adjust the braking pressure accordingly front to back.

The trucks that were lifted..... We'd make these little flat pieces of steal to relocate the Load Sensing valve up the same amount of the lift. This would get the load sensing valve back to 'normal' /stock.

 

[ShadowsPapa]

Curious... do the Gladiators have a 'load sensing' valve? Or sensor?

I remember the Tacomas had them or used to have them. They'd sense the amount of load in the bed and adjust the braking pressure accordingly front to back.

The trucks that were lifted..... We'd make these little flat pieces of steal to relocate the Load Sensing valve up the same amount of the lift. This would get the load sensing valve back to 'normal' /stock.

No.

 

[Vtur]

I think Jeep just trying to goes as big as possible given the 17" wheels. Front calipers is bigger therefore smaller in rotors. I doubt that Jeep's engineers putting in anymore effort than that

 

[Stan H]

Curious... do the Gladiators have a 'load sensing' valve? Or sensor?

I remember the Tacomas had them or used to have them. They'd sense the amount of load in the bed and adjust the braking pressure accordingly front to back.

The trucks that were lifted..... We'd make these little flat pieces of steal to relocate the Load Sensing valve up the same amount of the lift. This would get the load sensing valve back to 'normal' /stock.

Yes its located right behind the steering wheel. The guy who loaded it knows He needs to push harder.

 

[ShadowsPapa]

Curious... do the Gladiators have a 'load sensing' valve? Or sensor?

I remember the Tacomas had them or used to have them. They'd sense the amount of load in the bed and adjust the braking pressure accordingly front to back.

The trucks that were lifted..... We'd make these little flat pieces of steal to relocate the Load Sensing valve up the same amount of the lift. This would get the load sensing valve back to 'normal' /stock.

That's a height sensing proportioning valve. It adjusts pressure to the rear brakes based on the height of the chassis vs. axle. If the height increases, it reduces pressure to the rear brakes under hard braking due to weight shift.
If the height is lower, it increases the pressure to the rear brakes.
I believe the MJ had that.

It's not a necessary thing with modern ABS.

 

[Supazuk]

Yes its located right behind the steering wheel. The guy who loaded it knows He needs to push harder.

but do they do it with their right or left foot?.........

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