Why do we have larger diameter rotors IN THE REAR?

[smlobx]

I’m looking to upgrade my brakes and found out that the rear rotors have a larger diameter than the fronts!.

This is the opposite of what is normally found as the front brakes usually do 60-70% of the work.

I even looked at other pick up trucks and they were either larger in the front or the same diameter…

Anyone care to guess why the Jeep engineers did this?

For reference we have 12.9/13.6” f/r. The Teraflex BBK has 14” rotors and will fit the OEM 17” wheel.

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[Deleted member 57233]

I’m looking to upgrade my brakes and found out that the rear rotors have a larger diameter than the fronts!.

This is the opposite of what is normally found as the front brakes usually do 60-70% of the work.

I even looked at other pick up trucks and they were either larger in the front or the same diameter…

Anyone care to guess why the Jeep engineers did this?

For reference we have 12.9/13.6” f/r. The Teraflex BBK has 14” rotors and will fit the OEM 17” wheel.

Pretty sure the front calipers are bigger than the rears, so they probably had to use a smaller rotor to fit it in the 17" spare.

 

[InvertedLogic]

you should check the thickness of the rotors front and rear and the piston count

 

[smlobx]

you should check the thickness of the rotors front and rear and the piston count

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…

 

[rharr]

This is just a guess but the rear may be a bigger dia to accommodate the parking brake shoes while still providing a certain amount of rotor braking surface to be effective. A proportioning valve can be adjusted to still give front bias with smaller rotors

Front disk spec:
Product Specifications
Warranty:
2 Year LIMITED WARRANTY
UPC:
641801226352
Construction:
Full Cast
Material:
Cast Iron
Style:
OE Equivalent
ABS Sensor Ring Included:
No
Discard Thickness (mm):
26.4mm
Outside Diameter (in):
12.992 Inch
Outside Diameter (mm):
330mm
Studs Included:
No
Center Hole Size (mm):
72mm
Overall Height (mm):
55.7mm
Center Hole Size (in):
2.835 Inch
Unit of Measure:
Each
Discard Thickness (in):
1.039 Inch
Overall Height (in):
2.193 Inch
Cross Drilled:
No
Slotted:
No
Number Of Bolt Holes:
5
Bolt Pattern:
5 On 5 Inch
Inner Bearing Included:
No
Solid Or Vented:
Vented
Number Of Studs:
0
Rust Resistant Coating:
Yes
Surface Finish:
Non-Directional

Rear disk:
Product Specifications
Warranty:
2 Year LIMITED WARRANTY
UPC:
641801255369
Material:
Cast Iron
Style:
OE Equivalent
ABS Sensor Ring Included:
No
Outside Diameter (in):
13.750 Inch
Studs Included:
No
Overall Height (mm):
76mm
Center Hole Size (in):
2.830 Inch
Unit of Measure:
Each
Discard Thickness (in):
0.790 Inch
Overall Height (in):
3 Inch
Number Of Bolt Holes:
5
Bolt Pattern:
5 On 127mm
Inner Bearing Included:
No
Solid Or Vented:
Vented
Rust Resistant Coating:
Yes

 

[Alx63]

I’m looking to upgrade my brakes and found out that the rear rotors have a larger diameter than the fronts!.

This is the opposite of what is normally found as the front brakes usually do 60-70% of the work.

I even looked at other pick up trucks and they were either larger in the front or the same diameter…

Anyone care to guess why the Jeep engineers did this?

For reference we have 12.9/13.6” f/r. The Teraflex BBK has 14” rotors and will fit the OEM 17” wheel.

My guess would be Jeep rotors are larger in the rear to accommodate the vehicle's weight distribution enhancing braking performance, especially for off-road conditions

 

[smlobx]

My guess would be Jeep rotors are larger in the rear to accommodate the vehicle's weight distribution enhancing braking performance, especially for off-road conditions

I thought that might be the case so I looked up the diameter of my F350’s rotors and they are the same front and rear. Clearly the F-350 is a hauling beast compared to our Gladiator…

 

[JT1]

I’m looking to upgrade my brakes and found out that the rear rotors have a larger diameter than the fronts!.

This is the opposite of what is normally found as the front brakes usually do 60-70% of the work.

I even looked at other pick up trucks and they were either larger in the front or the same diameter…

Anyone care to guess why the Jeep engineers did this?

For reference we have 12.9/13.6” f/r. The Teraflex BBK has 14” rotors and will fit the OEM 17” wheel.

I'm guessing because the rear axle was lifted out of the ram 1500 and they didn't want to spend $ changing any more stuff on it.

 

[Hootbro]

Funny also that brake pads for the front have more surface contact on a smaller rotor.

 

[smlobx]

I'm guessing because the rear axle was lifted out of the ram 1500 and they didn't want to spend $ changing any more stuff on it.

So that’s the same exact axle as the 1500? I didn’t know that.

 

[JT1]

So that’s the same exact axle as the 1500? I didn’t know that.

Not 100% positive, but it's why the back half of JTs aren't the same as the JLs and why we got stuck with the crazy short uppers in the rear.

 

[Wheelin98TJ]

I'm guessing because the rear axle was lifted out of the ram 1500 and they didn't want to spend $ changing any more stuff on it.

So that’s the same exact axle as the 1500? I didn’t know that.

It's a 9.25" rear axle in a Ram.

 

[JT1]

It's a 9.25" rear axle in a Ram.

The new ones yes, but the ram classics from 2014- when the JLs were in development uses some version of a dana 44.

 

[Wheelin98TJ]

The new ones yes, but the ram classics from 2014- when the JLs were in development uses some version of a dana 44.

The Ram Classic didn't come until after 2014. Google says 2019 was the first year.

I ran build sheets for a 2019 Ram Classic and a 2014 Ram 1500 regular cab and they both said 235mm rear axle.

 

[JT1]

It's a 9.25" rear axle in a Ram.

I finally found one of the threads from way back that references the rear UCA and LCAs xref to a ram 1500 too. So maybe they saved some cash there, and then just used a lighter duty axle with similar pick up points.

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