Why do we have larger diameter rotors IN THE REAR?

[JT1]

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.

It was the same truck. They renamed it "classic" because they released the new one in 2019.

The tooling was paid for so they made both trucks for a few years.

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[Wheelin98TJ]

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.

That is correct the rear uppers and lowers are the same as Ram parts.

 

[JT1]

That is correct the rear uppers and lowers are the same as Ram parts.

Good find!
So that explains the funky rear geometry we see. They just slapped that on an M220 and called it a day.

 

[ShadowsPapa]

Too much oversimplification going on.
Pad surfaces (CoF), piston diameters, parking brakes and the fact we have ABS and electronic sway control, traction control and more. The ABS controls the pressure, size of the piston determines the forces applied, the friction materials used...... not all about rotor diameter.

 

[Jteakus]

When you figure out your brake upgrade please share with the class. I've gotta do something to help slow this pig on 38's. Tons and the brakes they bring are the perfect solution but I'm not quite ready to make the jump yet.
The Terraflex brakes and the booster upgrade look like a good setup. If we only had a power steering pump Hydro boost would do the trick, Sigh, thanks Jeep.

 

[MT1]

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

Yup, it appears that the hat on the rear rotor is wider, so the overall diameter must also be wider.

 

[smlobx]

Too much oversimplification going on.
Pad surfaces (CoF), piston diameters, parking brakes and the fact we have ABS and electronic sway control, traction control and more. The ABS controls the pressure, size of the piston determines the forces applied, the friction materials used...... not all about rotor diameter.

I‘m quite familiar with the physics of braking having raced Porsches for over a decade…and that includes building the cars from stock and upgrading the brake systems in several of the cars…. Typically, depending on the class rules, this would include larger diameter (and larger thickness) Cryoed rotors, larger brake calipers (typically 6 and 4 piston) a more aggressive brake pad (Pagid 97’s were one of my favorites) and installing an adjustable brake bias valve to help compensate for the track conditions on any particular day (raining or very hot).

Having said that, I still haven't found an answer to my question, nor have I seen any other vehicle with larger brake diameters in the rears…hence my question.

Has anyone ever seen larger diameter rotors in the rear of any vehicle?

 

[ShadowsPapa]

I never bothered measuring the rotors on our other Jeeps - didn't matter, didn't care - they worked.
The rears on the WJ seemed large but then it was also a drum for the parking brake, so it had to be a very different size and shape to fit that purpose.

Since all of the pressures are managed by the ABS - would it matter?

You'll likely have to ask a design engineer. Anything else will be pure guess or speculation unless someone finds a solid physical reason.

(just like all of the stuff regarding control arms, axles and so on - internet speculation)

 

[Splenda]

While it's more common for front brake rotors to be larger than rear rotors due to weight transfer during braking, some vehicles, particularly those designed for heavy loads or performance applications, may have larger rear rotors. This can be seen in some trucks and high-performance vehicles where rear brakes are designed to handle more heat and stopping power.

Vehicles with Larger Rear Rotors:

• Heavy-duty trucks and SUVs:
  These vehicles often have larger rear rotors to handle the increased braking load from towing and hauling heavy loads.
  
  
• Some performance vehicles:
  Certain high-performance cars or those with performance modifications may have larger rear rotors to improve braking performance and heat dissipation, especially in situations where the rear wheels are heavily loaded.
  
  
• Mid-engine supercars:
  These vehicles may have larger rear rotors due to the rearward weight bias and the need to handle the heat generated by the engine and braking.
  

Why Larger Rear Rotors Might Be Used:

• Weight distribution:
  In some vehicles, particularly those with a rear-wheel drive or mid-engine layout, the rear wheels may bear a larger portion of the braking force, especially during spirited driving or when the vehicle is loaded.
  
  
• Heat dissipation:
  Larger rotors offer a greater surface area for heat dissipation, which is crucial for preventing brake fade during repeated or hard braking.
  
  
• Performance enhancements:
  Larger rear rotors can improve braking performance and responsiveness, especially when combined with larger brake pads and calipers.
  
  
• Towing and hauling:
  Vehicles designed for towing or hauling often have larger rear rotors to handle the additional weight and braking requirements.
  

Important Note: It's essential to consult your vehicle's specifications or a qualified mechanic to determine the appropriate brake rotor sizes for your specific vehicle.

 

[rharr]

just looked up a 2004 suburban with the 8.1L, a tow pig by all standards, front disk is 325mm OD and rear is 330mm OD, so again as other have said, seems pretty standard for sizes to vary.

 

[smlobx]

While it's more common for front brake rotors to be larger than rear rotors due to weight transfer during braking, some vehicles, particularly those designed for heavy loads or performance applications, may have larger rear rotors. This can be seen in some trucks and high-performance vehicles where rear brakes are designed to handle more heat and stopping power.

Vehicles with Larger Rear Rotors:

• Heavy-duty trucks and SUVs:
  These vehicles often have larger rear rotors to handle the increased braking load from towing and hauling heavy loads.
  
  
• Some performance vehicles:
  Certain high-performance cars or those with performance modifications may have larger rear rotors to improve braking performance and heat dissipation, especially in situations where the rear wheels are heavily loaded.
  
  
• Mid-engine supercars:
  These vehicles may have larger rear rotors due to the rearward weight bias and the need to handle the heat generated by the engine and braking.

Why Larger Rear Rotors Might Be Used:

• Weight distribution:
  In some vehicles, particularly those with a rear-wheel drive or mid-engine layout, the rear wheels may bear a larger portion of the braking force, especially during spirited driving or when the vehicle is loaded.
  
  
• Heat dissipation:
  Larger rotors offer a greater surface area for heat dissipation, which is crucial for preventing brake fade during repeated or hard braking.
  
  
• Performance enhancements:
  Larger rear rotors can improve braking performance and responsiveness, especially when combined with larger brake pads and calipers.
  
  
• Towing and hauling:
  Vehicles designed for towing or hauling often have larger rear rotors to handle the additional weight and braking requirements.

Important Note: It's essential to consult your vehicle's specifications or a qualified mechanic to determine the appropriate brake rotor sizes for your specific vehicle.

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

 

[MT1]

I‘m quite familiar with the physics of braking having raced Porsches for over a decade…and that includes building the cars from stock and upgrading the brake systems in several of the cars…. Typically, depending on the class rules, this would include larger diameter (and larger thickness) Cryoed rotors, larger brake calipers (typically 6 and 4 piston) a more aggressive brake pad (Pagid 97’s were one of my favorites) and installing an adjustable brake bias valve to help compensate for the track conditions on any particular day (raining or very hot).

Having said that, I still haven't found an answer to my question, nor have I seen any other vehicle with larger brake diameters in the rears…hence my question.

Has anyone ever seen larger diameter rotors in the rear of any vehicle?

The current Wrangler has the same rear rotors; look at the hats. The rears need to house the shoes.

 

[ShadowsPapa]

just looked up a 2004 suburban with the 8.1L, a tow pig by all standards, front disk is 325mm OD and rear is 330mm OD, so again as other have said, seems pretty standard for sizes to vary.

And these are tow rated. With that payload and/or trailer holding down the ass-end, it's not like an empty truck. In fact, depending on the rig, heavy braking can actually increase the load on the rear tires and decrease it on the front.

So it is somewhat all over the place…strange

Engineering for purpose. I'd not say strange, it's got a reason.
So you have a really light tow vehicle, say 5,400 pounds, towing a 6,000 pound trailer. You hit the brakes, the weight of the trailer pushes forward and down over it's own axle, increasing the weight on the rear tires as it brakes. You want beefy brakes in the rear of a light-assed vehicle when towing something heavier than you are. Even a light trailer can add a whole lot of weight to the rear axle under heavy braking. The thing also needs to control sway - ESC uses ABS to manage that, braking to change the individual wheel velocity.

I'd bet that there was some engineering and testing done.

It's like we've been discovering up in WI stuff from the old AMC plant up there - they equipment they had for testing oiling systems, ignition systems, towing, differential gearing with quick-change differentials. A lot more computers today, but it shows a whole lot goes into their planning. These had to be able to do those SAE testing for payload and towing, autocross type stuff.

 

[bborc]

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.

 

[ShadowsPapa]

when your down hilling on a trail and you need to slow down you dont want the front brakes to lock up.

Hmmm, I suppose that could be rather bad?

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