10.95 to 11.75 rotors with 2.6 calipers

[Wvbuzzmaster]

So my 1972 Duster is set up with 1973 brake system all replaced 3 years ago. I know 11.75” front brake rotors is an upgrade but is it worth the hassle when using (and keeping) 2.6” piston calipers?

Basic specs of my current brakes include:
1-1/32” master cylinder with 9” booster (12” engine vacuum)
Front:
10.95” rotors
2.6” piston calipers (rear mounted)
Rear:
10x2.5” drums
.906” bore wheel cylinders

Front tires: 215/65R15
Rear tires: 255/60R15

 

[Professor Fate]

The difference may not be extreme, but it is noticeable. That's why Ma Mopar went to the effort to go to the bigger rotors in the first place on the HD and police packages. If it wasn't worth it, the bean counters would never have let the new parts through.
As far as it being a hassle, it's just a matter of installing the upsized caliper brackets and bolt on the new rotors, nothing else necessary; you don't even have to rebleed the system since you never need to disconnect the calipers.
By the way, is there any particular reason you went with a 1 1/32 master? Power brake systems used a 15/16 from the factory, and the smaller master does give you a little better feel- even with manual brakes.

 

[abodyjoe]

So my 1972 Duster is set up with 1973 brake system all replaced 3 years ago. I know 11.75” front brake rotors is an upgrade but is it worth the hassle when using (and keeping) 2.6” piston calipers?

i did the swap last june on our dart. kept the calipers.. i could definatley feel a difference in stopping power..

 

[72bluNblu]

So I did the math on the the 10.95” to 11.75” rotor diameter increase.

Just the change in the diameter of the rotor gives you an 8.4% increase in braking power, nothing else considered. The rotor change also adds 7.6% to the rotor surface area, which will improve both heat build up and heat dissipation.

Even that is a noticeable increase, and it’s super easy to just bolt on new rotors and caliper brackets and like @Professor Fate said you don’t even have to bleed the brakes.

If you do go up to the later calipers with 2.75” pistons, the combined improvements give you a 21.3% increase in braking power compared to a 10.95” 73+ brake system. Now, that’s not to say you’ve improved the stopping distance that much, but assuming the line pressure is the same the force at the pads increases 21.3%.

Having run the 11.75’s, they are a noticeable improvement over the 10.95’s.

 

[Wvbuzzmaster]

By the way, is there any particular reason you went with a 1 1/32 master? Power brake systems used a 15/16 from the factory, and the smaller master does give you a little better feel- even with manual brakes.

The aftermarket offered only that size in aluminum casting 4 bolt OEM style and I thought that was better than watching a cast iron one rust and look bad.

 

[Wvbuzzmaster]

And to answer the second part I do know all I need is the hub rotors and caliper brackets and I did not want to bleed the brakes again is why I wanted to stick with the 2.6” calipers. DOT 5 and Stainless Steel lines was a fight to get to seal finally.

It’s rare to see anyone go to the 11.75” rotor and not be using the 2.75” caliper but I did know the caliper body is the same so that only like $200 for taller brackets and 11.75” rotors.

 

[Wvbuzzmaster]

72blunblu,

Thanks for providing the math on the by stage percent increase in performance.

 

[MoparLeo]

The other thing that will make a marked improvement is to upgrade the pads and rotors.
You have to replace them anyway.

 

[gzig5]

The main aspect that a larger diameter rotor improves for a given application is the ability to repeatedly stop the car before fade sets in. Stock 11 inch rotor is sufficient to clamp hard enough to stop the front tire from turning and cause it to skid. The larger diameter is only going to increase that capability because of the larger lever arm, for a given tire. By increasing the diameter and thus the mass of the rotor, you are increasing the thermal capacity of the rotor-pad system, and prolonging the time under load before the pad overheats and starts to fade. The best way to improve stopping distance is with a stickier tire. Improving the ability to stop repeatedly goes to pad material and rotor mass.

And of course, larger diameter rotors typically look better.

 

[72bluNblu]

The main aspect that a larger diameter rotor improves for a given application is the ability to repeatedly stop the car before fade sets in. Stock 11 inch rotor is sufficient to clamp hard enough to stop the front tire from turning and cause it to skid. The larger diameter is only going to increase that capability because of the larger lever arm, for a given tire. By increasing the diameter and thus the mass of the rotor, you are increasing the thermal capacity of the rotor-pad system, and prolonging the time under load before the pad overheats and starts to fade. The best way to improve stopping distance is with a stickier tire. Improving the ability to stop repeatedly goes to pad material and rotor mass.

And of course, larger diameter rotors typically look better.

Run them yourself?

Because I’ve changed from 10.95” brakes to 11.75” brakes, kept the same tires and calipers, and the stopping ability of the car improves even when the brakes are cold.

The ability to lock up a tire isn’t a good, or accurate, way to evaluate a brake system.

 

[gzig5]

Run them yourself?

Because I’ve changed from 10.95” brakes to 11.75” brakes, kept the same tires and calipers, and the stopping ability of the car improves even when the brakes are cold.

The ability to lock up a tire isn’t a good, or accurate, way to evaluate a brake system.

Not yet but it's on the to-do list before I go to a larger front rotor system. I am prepared to be wrong. I guess I just don't expect see a big improvement in a single stop stopping distance on street tires like BFG TA's or Cobras. That's where I was coming from on experience with my Cuda after a fresh brake rebuild, with a 255/60-15 tire. Tire was a limiting factor. After the first couple of hard stops the bigger rotor will absolutely make a difference though.