10.98" rotors vs 11.8" worth swapping up?

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Ol'forest

Ol'forest

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Hi all, I'm going to put a factory disk brake set up in my duster, and am wondering if it's worth going to the larger rotors on a steep geared street strip car? I know both set ups are heavy, but has anyone notice a great improvement in braking with the 11.8" rotors?
I want to use a manual master cylinder set up too, what size bore should I use, there's a factory cylinder just a tad under 1" I thought that would be the best match.
 
are you going to be running 275 front tires? Id think not but ask an autocrosser.
 
More like 165's maybe 185's on pizzacutters, but I've warped rotors in the past, just want something that stops well and hopefully doesn't warp after 120mph plus rapid stops.
 
I use them on my Barracuda, and they are a step up in braking BUT, I have upgraded pads. The M/C is a 15/16th bore and does have a little more pedal travel. I like it though, the further pedal travel allows a way to moderate the braking. The car stops as well or better then anything I have ever driven. I think the pads have more to do with that then the rotor size. The larger rotor will dissipate more heat then the smaller one. I don't know the weight difference but it's not a big amount. I live in a hilly area and brake fade has been a problem on other cars I've owned (Ford), so I built the braking system to handle those conditions and the deer we live with!
 
Sounds like a good set up, and kind of what I was thinking, my dart which warped the rotors, had the smaller 15/16 cylinder, and a fair bit of travel on the pedal, but it stopped really well.
 
I run 11.75" rotors on my Challenger, and I ran them on my Duster before upgrading again to 13" rotors from Dr. Diff. The 11.75" rotors do make a noticeable difference in braking power compare to the 10.98's, which I ran before upgrading both cars. Although I run 275's on both cars now, the switch from the 10.98's to the 11.75's was made when I was running 235's on the Challenger and 225's on the Duster, so, you don't need to be running 275's for it to be a relevant upgrade. Of course the difference is more noticeable with the wider tires.

I run a 15/16" master cylinder from Dr. Diff in both cars now, manual on both. The Challenger was a power brake car until just recently though with a stock master cylinder. The manual set up gives much better feel and modulation. I'm running semi-metallic pads with both set ups.

Do remember though that the 11.75" brakes need 15" rims in most cases.
 
As said it will help heat capacity and heat dissipation. Brake ducting is a possibility to help further warping.

If you need more whoa power, there are higher coefficient of friction pads for the standard A calipers; EBC Yellowstuff.
 
You'll probably not have any trouble locking up those tires,so I'd go
w/the 1" MC. If you had wider/much stickier rollers, I'd go w/the 15/16" unit for more braking power,sacrificing a little pedal firmness.
As mentioned,upgraded pads and cooling can't hurt you.
 
EL5DEMON340 said:
what upgraded pads did you use
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EBC red, they are a little hard on the rotors but are very good pads. They come in different color coded pads, and they aren't cheap. European Brake Co. is the company. You might try the middle level first, they aren't as expensive and will probably be just as effective.
 
EBC Yellowstuff has a CoF of .5 which is around 30-40% higher than standard semi-metallic pad material. My son has them on his '65 'Cude with the 73-76 discs and the improvement was what you wild expect with a 30-40% CoF increase: it is like power brakes now, and the rear prop vlave is backed out almost 100%, allowing the 11"x2.5" rear shoes to work harder too.

The RedStuff compound looks to have the same CoF as Yellowstuff: 0.5. So the same results would be expected. The red is supposedly less dusting. I can't recall if I could find Red in the standard 73-76 Mopar A pad style...
 
Tnx! I guess I went with the Yellows since they supposedly can handle a bit more heating, being for heavier vehicles.
 
Dont forget , when upgrading to the larger cordoba rotors, you need to use the corresponding cordoba calipers. There is a size difference in the pistons. The smaller A body rotors use a 2.50" diameter piston, the cordoba calipers use a 2.75" diameter piston, this is why the M/C is upsized as well. More surface area behind the caliper pistons requires more surface area behind the master cylinder piston to port fluid.
 
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I didn't change the calipers, it might be something to do in the future. The smaller ones work fine right now and I can keep the same M/C. My next step is the 1.03 torsion bars for a stiffer front end. I want to upgrade from the 892/893.
 
i can't see how the larger rotor can improve breaking..
in repeated lock ups maybe dissipate a little more heat.Stock
callipers where 2 5/8,the 'cuda challenger and later cordoba
pin style callipers were 2 3/4" and will make a noticeable improvement!
 
ir3333 said:
i can't see how the larger rotor can improve breaking..
in repeated lock ups maybe dissipate a little more heat.Stock
callipers where 2 5/8,the 'cuda challenger and later cordoba
pin style callipers were 2 3/4" and will make a noticeable improvement!
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Even just keeping the stock A-body calipers and using the 11.75" rotors increases braking force. There are several things going on here...

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". That might not sound like a huge difference, but that represents an 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%.

You're also increasing the braking surface area. The pad area is the same, but because the pads are further out they sweep out a larger area as the rotor turns. Applying the same amount of force over a larger swept area means the brakes don't heat up as fast, and there's more area to dissipate heat as well. 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 the braking area is π(10.98/2)^2 - π(9.18/2)^2 = 28.5 square inches . That's an 8% increase in surface area on the rotor.

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 a bit 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/traction 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.
 
all good points..but the amount of friction,pad surface and pressure don't change
less heat would certainly be a bonus for repeated hard braking.
the outside of the larger rotor would be travelling slower and should
theoretically be easier to stop....
 
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ir3333 said:
all good points..but the amount of friction,pad surface and pressure don't change
less heat would certainly be a bonus for repeated hard braking.
the outside of the larger rotor would be travelling slower and should
theoretically be easier to stop....
Click to expand...

Right, but they don't need to change to see an improvement. Changing NOTHING but the rotor increases your stopping power by 8%. That's not insignificant. And you get better heat fade resistance, although that probably isn't something you'd notice on the street. And if you did change pad compounds or go to the later calipers you'd still have the benefit of the larger rotor.

Like I said, I noticed an improvement in braking both times I switched from the stock 10.98" rotors up to the 11.75" rotors. Both times I did that swap the only thing that changed was the rotors, I left the calipers and pads alone, didn't change the tires or wheels, heck I didn't even bleed the brakes. Just bolted on new caliper brackets and installed the larger rotors with new bearings. It's not a night-and-day kind of difference, but it is noticeable even in just plain old boring everyday driving conditions. And when I swapped the brakes on both cars I was running much more standard sized tires, 235's on the Challenger and 225's on the Duster, so you don't need 275's up front to take advantage of the improved braking. Although the larger tires definitely improve stopping as well.

I'm not saying everyone should throw their 10.98" rotors in the trash, or that changing the brake pad compound or switching to later calipers won't help, those are also great upgrades. But, if you're doing a brake job and you need to buy new rotors anyway you can get the larger caliper brackets from Dr. Diff for $100. If you've already got 15" rims and need rotors anyway that's a heck of a deal.
 
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..i have never done the swap but you have and can give a qualified answer.
so i would have to think there is some gain...good post.
 
check out The Ram Man for brakes on You Tube (Mopar Disc Brake Conversion doctorate), He knows a lot about Mopars and he knows his stuff. He talks about the different disc brake rotor sizes. 10.98" and the 11.75" rotors in his video, the 11.75" are the way to go, if you have a choice! Another video of his to see is 11.75" rotor upgrade, High Performance.
 
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I had a couple of Dodge Diplomats one the road at the same time one had 10.8 rotors and the other the 11.75.....with power brakes you could not notice any difference, after a while I forgot which car had the bigger rotors until it came time to change the tires after a few years...unless you have big sticky front tires on the car and do repeated stops I would be surprised if you could measure any significant difference in performance....but if you have the parts or need new rotors it can't hurt to bigger, unless your 14" wheels won't fit.

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