racerdude5
Well-Known Member
Do the 11.8 inch actually have more surface area than the 10.7? How much more do they weigh? Is there a noticeable improvement?
is it worth swapping 10.7 inch discs for the 11.8 inch?
- Thread starter racerdude5
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The pad dimensions are the same, yes. BUT, the area swept out by the pads on the rotor is bigger.
If you figure the outside of the rotor is 11.75" and the width of the braking surface is ~1.8" ( I measured it),
then the total braking area is π (11.75/2)^2 - π(9.95/2)^2 = 30.67 square inches for the 11.75" rotors
For the 10.98 rotors (stock size) the braking area is π(10.98/2)^2 - π(9.18/2)^2 = 28.5 square inches
Yeah, sure that doesn't seem like much, but that's an 8% increase in surface area.
Next, and this is where the real advantage is, the larger rotors actually multiply the force that's applied by the caliper more than the smaller ones. This is because the "lever arm" acting on the spindle is longer.
On the stock 10.98" disks, the middle of the pad falls at ~4.59" from the spindle axis. On the 11.75" disks, it's 4.975". Once again, not a huge difference, but that's another 8% increase in braking force. The calipers apply the same force, but because of the larger diameter of the rotor the braking power increases by 8%.
Yes, it is a noticeable difference. I converted both my Challenger and my Duster from the stock 10.98" rotors to 11.75" rotors, kept the calipers the same, and you can tell the difference. The 11.75" rotors are definitely heavier, but they also provide more braking power, and better cooling (more surface area). On the street the improved surface area and cooling isn't as big a deal as on the track, but the increase in braking power is a definite advantage if you have the tires to take advantage of it. I know it probably won't translate into an 8% shorter stopping distance as it wouldn't be linear like that, but I've been in a few situations where a foot or two would have made a big difference in the length of my front fenders.
If you figure the outside of the rotor is 11.75" and the width of the braking surface is ~1.8" ( I measured it),
then the total braking area is π (11.75/2)^2 - π(9.95/2)^2 = 30.67 square inches for the 11.75" rotors
For the 10.98 rotors (stock size) the braking area is π(10.98/2)^2 - π(9.18/2)^2 = 28.5 square inches
Yeah, sure that doesn't seem like much, but that's an 8% increase in surface area.
Next, and this is where the real advantage is, the larger rotors actually multiply the force that's applied by the caliper more than the smaller ones. This is because the "lever arm" acting on the spindle is longer.
On the stock 10.98" disks, the middle of the pad falls at ~4.59" from the spindle axis. On the 11.75" disks, it's 4.975". Once again, not a huge difference, but that's another 8% increase in braking force. The calipers apply the same force, but because of the larger diameter of the rotor the braking power increases by 8%.
Yes, it is a noticeable difference. I converted both my Challenger and my Duster from the stock 10.98" rotors to 11.75" rotors, kept the calipers the same, and you can tell the difference. The 11.75" rotors are definitely heavier, but they also provide more braking power, and better cooling (more surface area). On the street the improved surface area and cooling isn't as big a deal as on the track, but the increase in braking power is a definite advantage if you have the tires to take advantage of it. I know it probably won't translate into an 8% shorter stopping distance as it wouldn't be linear like that, but I've been in a few situations where a foot or two would have made a big difference in the length of my front fenders.
racerdude5
Well-Known Member
What about the bigger brakes vs just getting drilled and slotted rotors?
Drilled and slotted rotors will not increase your stopping power.
They may slightly improve cooling, but a lot of people are going away from drilled rotors and just doing slotted. But, again, that still doesn't actually increase your stopping power. And on the street your brakes aren't going to get, and stay, hot enough for either of those things to be really useful.
Yes, my disks are drilled and slotted. But I couldn't tell the difference on the street vs the plain ones, I just was able to get the drilled and slotted version cheaper when I bought them for my challenger. I run the drilled/slotted 11.75's on the Challenger and had plain 11.75" rotors on the Duster. If anything the braking on the Duster was better with the plain rotors, but I assume that's because its a lighter car and had nothing to do with the plain vs drilled/slotted rotors. I did get my 13" rotors from Cass in the drilled/slotted version instead of just slotted when I upgraded the Duster, but I don't think it makes much difference.
They may slightly improve cooling, but a lot of people are going away from drilled rotors and just doing slotted. But, again, that still doesn't actually increase your stopping power. And on the street your brakes aren't going to get, and stay, hot enough for either of those things to be really useful.
Yes, my disks are drilled and slotted. But I couldn't tell the difference on the street vs the plain ones, I just was able to get the drilled and slotted version cheaper when I bought them for my challenger. I run the drilled/slotted 11.75's on the Challenger and had plain 11.75" rotors on the Duster. If anything the braking on the Duster was better with the plain rotors, but I assume that's because its a lighter car and had nothing to do with the plain vs drilled/slotted rotors. I did get my 13" rotors from Cass in the drilled/slotted version instead of just slotted when I upgraded the Duster, but I don't think it makes much difference.
I'm going to take the opposite direction here, and tell you that i swapped over the original disc brakes on the 71 Cuda, that i once owned, to the 11 3/4 inch rotors, back in the day, when the Mopar crowd first started doing this swap.
I never noticed any difference in the braking, wether street driving it for years, after the swap, or hitting the brakes, at the end of the quarter mile, while drag racing it at Sacramento Raceway.
And i used to run 13.20's at 108 MPH, and never had any problems using the first return road, at the end of the run, with the standard brakes, or the 11 3/4 ones.
My 2 cents worth on the topic.
I never noticed any difference in the braking, wether street driving it for years, after the swap, or hitting the brakes, at the end of the quarter mile, while drag racing it at Sacramento Raceway.
And i used to run 13.20's at 108 MPH, and never had any problems using the first return road, at the end of the run, with the standard brakes, or the 11 3/4 ones.
My 2 cents worth on the topic.
The brakes aren't the whole story. Just like having a bazillion HP won't do you any good if you can't put it to the ground, having all the braking power in the world doesn't do you any good either if you don't have the traction to take advantage of it.
I wouldn't be at all surprised if it didn't make any difference whatsoever on a set of factory bias ply's. Or even on a set of 205/65/15 BFG T/A's.
But I do know that with the 275/40/17 modern compound radial tires I have on the front of my Challenger, it makes a difference, and a noticeable one at that. And the physics says they're good for about an 8% increase in stopping power. But that's only if your tires and suspension can put it all to the ground.
I wouldn't be at all surprised if it didn't make any difference whatsoever on a set of factory bias ply's. Or even on a set of 205/65/15 BFG T/A's.
But I do know that with the 275/40/17 modern compound radial tires I have on the front of my Challenger, it makes a difference, and a noticeable one at that. And the physics says they're good for about an 8% increase in stopping power. But that's only if your tires and suspension can put it all to the ground.
The reason that i did the 11 3/4 inch rotor conversion on the 71 Cuda, is because it needed a front brake job, and the rotors were already at minimum thickness, and wouldn't take another machining, without being undersize, discard, thickness.
I already had 15" inch Rallye Wheels on it, and had a pair of spindles, and new rotors, and the taller caliper mounts, waiting to be used.
So i did the swap.
If you have the parts on hand, then go for it, but if you have to purchase everything, then you might want to think twice about doing it.
It will be a diminished return, on your investment.
I already had 15" inch Rallye Wheels on it, and had a pair of spindles, and new rotors, and the taller caliper mounts, waiting to be used.
So i did the swap.
If you have the parts on hand, then go for it, but if you have to purchase everything, then you might want to think twice about doing it.
It will be a diminished return, on your investment.
..........I haven't swapped larger discs on my A bodies, but on my 01 Dodge Ram 2500 4x4 it was a very noticeable increase in braking power by swapping on the 13 in rotors and caliper hangers from a 3rd gen truck, my 2nd gen had 12in rotors.......used the same pads and calipers.......kim.......
Robbie2734
Lambcharger
I did the swap, it isn't a big difference on a flat road but I live on a steep hill and they run a lot cooler at the bottom. Would I do it again? maybe. But first I'd use a better pad on the calipers. EBC makes pads that are much better then the run of the mill stuff available over the counter. Try them first (they are a tad expensive ) and you might not want to add the extra weight of the 11 3/4 rotors. The pads will wear the rotors more then stock pads but they do stop!
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