11.75 rotors, vs 10.87 rotors

[ga66mopar]

I have been thinking about the advantage of the larger rotors. I have used both sizes and I didn't see any real huge difference. Both use the same size calipers and brake pads so the contact area is the same. The larger rotor would rotate at a slightly slower rate at the same tire speed than the smaller rotor. That could make the larger rotor run a little cooler under extreme use but I wonder how much they really improve on stopping distance.

Most high performance brake kits have a larger caliper for more clamping power and a larger brake pad for more contact area but using factory mopar brake components these are the same.

I have to admit I like using the larger rotor because they make me feel like I have better brakes but I'm not sure there is much of a difference under normal use.

 

[tallhair]

I have been thinking about the advantage of the larger rotors. I have used both sizes and I didn't see any real huge difference. Both use the same size calipers and brake pads so the contact area is the same. The larger rotor would rotate at a slightly slower rate at the same tire speed than the smaller rotor. That could make the larger rotor run a little cooler under extreme use but I wonder how much they really improve on stopping distance.

Most high performance brake kits have a larger caliper for more clamping power and a larger brake pad for more contact area but using factory mopar brake components these are the same.

I have to admit I like using the larger rotor because they make me feel like I have better brakes but I'm not sure there is much of a difference under normal use.

i'm wondering if the larger ones have better heat dissipation due to larger surface area and possibly are stronger and more durable / less likely to warp??

 

[kb67mopar]

i'm wondering if the larger ones have better heat dissipation due to larger surface area and possibly are stronger and more durable / less like to warp??

This should be true but they will not provide any extra clamping force therefor not doing much more in the means of stopping the car. one thing that can be said is the farher you move the clamping force out away from the center line of the rotor the better braking will be. This has to do with the leverage action of the distance from the axis of rotation...so yes even with the same caliper you would experience slightly better braking....though not sure how much, thats a road test sorta thing....anybody want to donate some parts...I'll try it out!

 

[Meep-Meep]

I understand what you are saying in that there is probably little difference between the two. I got the 11.75 brakes with the tall spindles for my 69 RR because while I was shopping for disc brakes I thought I'd just go straight to the top.

Not sure if I understand your comment about the larger rotor turning slower. I think the larger rotor will have a higher surface feet per min speed out at the edge (fins). I'm somewhat of a machinist (have a couple of lathes, etc..) and when I have a large diameter part in the chuck I tend to slow it down to maintain proper cutting speed for the material used. So to me the outside edge of the larger rotor would actually go faster. But again, like you said, is that worth anything with the same caliper? Perhaps it's a leverage thing - the caliper squeezes on a larger radius. There must be a balance of pad area vs. the radius of the rotor to keep things happy.

 

[dpstark2]

I had the small rotors and stock calipers and pads on my Charger. I was never happy with them. I believe I had sub-par parts, but once a rotor warped, I went with The Ram Man's drilled and slotted large rotors and EBC red pads. The difference in my case is very, very noticeable. I got to test them yesterday when a truck decided to make a right turn in front of me into my lane. The old setup would not have saved me there. These did. I am much happier with this setup than the old one.

 

[5.7 hemi]

Given apples to apples, I dont think there is a huge difference. But, there are some things you need to take into consideraton. The larger rotor has more surface area which leads to better cooling, and being bigger it has the advantage of leverage. Better pads also make a huge difference on either size rotor setup, so imho, a larger rotor with better pads will give you better braking than the smaller rotor and better pads.

 

[ga66mopar]

I understand what you are saying in that there is probably little difference between the two. I got the 11.75 brakes with the tall spindles for my 69 RR because while I was shopping for disc brakes I thought I'd just go straight to the top.

Not sure if I understand your comment about the larger rotor turning slower. I think the larger rotor will have a higher surface feet per min speed out at the edge (fins). I'm somewhat of a machinist (have a couple of lathes, etc..) and when I have a large diameter part in the chuck I tend to slow it down to maintain proper cutting speed for the material used. So to me the outside edge of the larger rotor would actually go faster. But again, like you said, is that worth anything with the same caliper? Perhaps it's a leverage thing - the caliper squeezes on a larger radius. There must be a balance of pad area vs. the radius of the rotor to keep things happy.

The logic I'm using with the larger rotor turning at the slower rate per tire rotation is if you put a 15 inch tire on one side of the rear of a car and a 13 inch tire on the other side and rotate the 15 inch tire in one rotation the 13 in will rotate more than one rotation. Kind like when you put shorter tires on a car the gear ratio becomes lower. I'm talking about the larger rotor turning at a slower rate per tire rotation. That's what I'm thinking anyway.

I guess it really depends on how adequate the smaller rotors are.

- - - Updated - - -

Given apples to apples, I dont think there is a huge difference. But, there are some things you need to take into consideraton. The larger rotor has more surface area which leads to better cooling, and being bigger it has the advantage of leverage. Better pads also make a huge difference on either size rotor setup, so imho, a larger rotor with better pads will give you better braking than the smaller rotor and better pads.

I understand what you're saying about the advantage of leverage. But would the more leverage come with a larger caliper with a larger piston area or a larger rotor. The contact area between either rotor is the same until it has been spun a complete rotation?[/?

 

[kb67mopar]

I understand what you're saying about the advantage of leverage. But would the more leverage come with a larger caliper with a larger piston area or a larger rotor. The contact area between the rotor and brake pad is the same until it is spin a complete rotation?

The farther out from the axis of rotation the greater the leverage even with the same size caliper (example ratchet vs breaker bar since you are the same size force) Now go to a bigger rotor and a bigger caliper and you get even better....

and your logic on slowing it down is both correct and incorrect, that works with a tire because its in contact with the road and dictates the speed of the vehicle, but if you take the same size tire with the different size rotors the rpm of the spindle will be the same. Since the circumference of the rotor is larger but spinning at the same rate the linear feet per sec of the outer edge will be greater then the smaller rotor.

(sorry I am an engineer, I can't help myself )

 

[ga66mopar]

and your logic on slowing it down is both correct and incorrect, that works with a tire because its in contact with the road and dictates the speed of the vehicle, but if you take the same size tire with the different size rotors the rpm of the spindle will be the same. Since the circumference of the rotor is larger but spinning at the same rate the linear feet per sec of the outer edge will be greater then the smaller rotor.

(sorry I am an engineer, I can't help myself )

I understand what you are saying about the rotation of the larger rotor being the same but I'm talking about the rotor rotation in relation to the tire rotation. I think were talking about the same thing. These are good dicussions

 

[5.7 hemi]

Just get a 6 piston caliper and 14 inch rotor and bingo, you just went thru the windshield, lol!!!!

 

[kb67mopar]

haha, or a cloud of smoke from the tires.

Moral of the story here is that the bigger rotor should help some but probably not a giant amount.

 

[q-ship]

The only difference (and it can be a BIG difference) in brake performance is modulation (control).

Either system will lock up the brakes, but locked brakes are a very poor stopping solution (as it then becomes a tire contact patch/wear situation, with no directional control)! Not to mention ruining tires.

The larger the brakes, the more control you have over true braking vs lock-up.

I have used more than a few sets of the smaller brakes over the years, but the larger units provide much more control. More than the small difference in diameter would suggest.

I only use the big brakes for decades now on my daily drivers. .... Don't forget that you have to drive on the same road that the ultra braking imports also use. You have a fighting chance with the big units, but your odds go down dramatically with smaller disks, or (GOD FORBID), drums. .... I personally believe that drum brake cars should not be allowed to be licensed for street use!

If you just use your car for the occasional show, or controlled cruise, anything is fine, but if you daily drive like some of us hardcore psychos, the big brakes are essential, and just barely adequate.

 

[HT413]

Good discussion. i agree with a lot of your points...

I was thinking the same as q-ship. The bigger rotors will give more force, but you wont need any more if your current brakes are set up correctly cuz they already lock the tires up. What it will help with is pedal feel. The extra stopping power theoughout the pedal travel should make the brakes more responsive and offer less pedal effort. We're talking 0.88 inch increas over the 10.87, but if you figure the pistons clamp a little in from the edge, the 10.87 becomes more like 9+ inch radius. so 0.88 inch increase means almost 10% increase in leverage, which is pretty decent (all other things staying the same.)

Btw, i agree, bigger rotor means better heat dissipation for sure but unless you're road racing you wont notice a difference. And like i think meep and kb said above, bigger rotor does give higher 'surface velocity' of the rotor at the caliper, not slower velocity, though i dont see how it makes a difference at all.