Brake rotor thickness

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psychomotors
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Brake rotor thickness

Post by psychomotors » Tue Oct 09, 2018 3:15 pm

I have a 70 Nova with drum brakes. I bought a disc brake setup off a guy that said id came from a 72 Olds Vista Cruiser. I know its a straight bolt up except for the steering arms. My actual question , is- the Olds rotors are 1 1/4" thick versus 1" thick. I there anything to be gained by using the 1 1/4" rotors? The car will be used for street/strip and eventually have a BBC in it, but for now just a SBC. I was thinking ,possibly less rotor warping ? Anyones thoughts?
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Re: Brake rotor thickness

Post by bigblockmopar » Tue Oct 09, 2018 3:50 pm

More metal is a larger heatsink, meaning you would be able to brake harder, longer.

I personally *think* rotor-warping 'mainly' happens when you do some hard braking, and come to a complete stop while keeping the brakes applied.
The location where the brake pads are on the disc makes it cool down much slower then the rest of rotor and cause warping in that area.
Although this is not something I have scientificly measured or confirmed.

I personally have grown the habbit that when braking hard, to ease off the brakes a bit and let the car/wheels slowly rotate further a bit, so the pads cover more area on the rotor.
This means of course you'd have to stop well short ahead of the object you were braking for anyway. :wink:

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Re: Brake rotor thickness

Post by FC-Pilot » Tue Oct 09, 2018 8:08 pm

bigblockmopar wrote:
Tue Oct 09, 2018 3:50 pm
More metal is a larger heatsink, meaning you would be able to brake harder, longer.

I personally *think* rotor-warping 'mainly' happens when you do some hard braking, and come to a complete stop while keeping the brakes applied.
The location where the brake pads are on the disc makes it cool down much slower then the rest of rotor and cause warping in that area.
Although this is not something I have scientificly measured or confirmed.

I personally have grown the habbit that when braking hard, to ease off the brakes a bit and let the car/wheels slowly rotate further a bit, so the pads cover more area on the rotor.
This means of course you'd have to stop well short ahead of the object you were braking for anyway. :wink:
Great theory. I have questioned that at some of the companies I have worked for (as well as my current) and have been able to invest the time to test it as there are other factors that are more important. Rotor "warping" is mainly done based off of the uneven rotor wear while doing higher speed braking or constant high temp braking (like coming down a steep grade). It causes what we call DTV (disc thickness variation). It is amplified by how much rotor run-out the rotor has when installed on the vehicle. regardless of how well they were machined, as soon as you bolt the rotors up they deflect a little bit, and depending on how you torqued your wheels, you can induce quite a bit of run-out. That run-out provides high spots that inherently get greater wear on the rotor, and as they wear you start to get the vibration. That gets multiplied as the rotor reaches even higher temps and thus the snowball begins to build.

So, thicker rotors are bigger heatsinks and also resist runout when bolted up. It is a constant fight between the brake group and the ride and handling group (wanting to reduce spring weight) as to the rotor size we can get, and then after that fight we battle with chassis (wanting to reduce total vehicle weight) and then powertrain as they want to accelerate as fast as possible while having no rolling mass which could rob even just a .001 MPG. What we find is that until the customers whine enough, we keep getting cut out on upgrades and upsizing. Then once there is a problem, then we get in trouble because we did not improve the brake system earlier (like we wanted to do years ago LOL). It is a vicious cycle.

Paul
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Re: Brake rotor thickness

Post by MadBill » Sat Oct 13, 2018 9:44 pm

Re you doner discs, the big GM wagons I've worked with all had bigger rotors than the sedans, with 5" vs. 4.75" BCs...
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Re: Brake rotor thickness

Post by psychomotors » Wed Oct 17, 2018 4:23 pm

MadBill wrote:
Sat Oct 13, 2018 9:44 pm
Re you doner discs, the big GM wagons I've worked with all had bigger rotors than the sedans, with 5" vs. 4.75" BCs...
These are 4.75. Regardless , my memory is horrible , so I checked them again and they are only 1" thick. I'm guessing that I confused them for my truck rotors. I dunno. :oops:
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Re: Brake rotor thickness

Post by pdq67 » Wed Nov 07, 2018 10:11 pm

Probably the truck and van rotors are 1.25" thick whereas the A/F/X ones are 1" thick.

You might be interested in my, "pdqCBB", four wheel disc brake conversion I put on my '67 Camaro. 13" dia. late '80's 'Vette front rotors and 11.75" dia. Camaro rear rotors all on homemade caliper brackets that mount the big single piston calipers in front and Cad Seville e-brake calipers in back..

https://www.camaros.net/forums/16-brake ... lates.html

https://www.yellowbullet.com/forum/show ... ?t=1445506

pdq67

PS., it's been years so I may have installed 12" dia. rotors on the front?? I honestly forgot??????

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Re: Brake rotor thickness

Post by FC-Pilot » Thu Nov 08, 2018 11:58 am

Going with that larger diameter rotor is a good upgrade for these cars. The only problem is you have to use 17" wheels if I remember correctly.

Paul
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Re: Brake rotor thickness

Post by psychomotors » Thu Nov 08, 2018 4:37 pm

pdq67 wrote:
Wed Nov 07, 2018 10:11 pm
Probably the truck and van rotors are 1.25" thick whereas the A/F/X ones are 1" thick.

You might be interested in my, "pdqCBB", four wheel disc brake conversion I put on my '67 Camaro. 13" dia. late '80's 'Vette front rotors and 11.75" dia. Camaro rear rotors all on homemade caliper brackets that mount the big single piston calipers in front and Cad Seville e-brake calipers in back..

https://www.camaros.net/forums/16-brake ... lates.html

https://www.yellowbullet.com/forum/show ... ?t=1445506

pdq67

PS., it's been years so I may have installed 12" dia. rotors on the front?? I honestly forgot??????
I'm using the stock diameter fronts and the 79 Trans Am rotors in the rear with 79 Cadillac Seville brackets for a salvage yard. I bought Wilwood D52 calipers for the front and I'm going to use stock D52s for the rear. I didn't like the Cadillac rear calipers. Thanks for the links pdq. I already have tires and wheels and didn't want to buy new , for larger rotors. I would buy the Wilwoods for the rear also , but I am going to install a narrowed 9" I got for a song , eventually and I will probably install 8.8 rears discs on it then.
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Re: Brake rotor thickness

Post by psychomotors » Thu Nov 08, 2018 4:37 pm

FC-Pilot wrote:
Thu Nov 08, 2018 11:58 am
Going with that larger diameter rotor is a good upgrade for these cars. The only problem is you have to use 17" wheels if I remember correctly.

Paul
Yep , you are correct.
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