Front and rear disc size difference

[RumbleBee383]

Hey Guys!

I'm building a '69 Dodge Super Bee and I'm looking to add some rear disc brakes.

I have a Wilwood 10.75 front disc kit right now (am going to upgrade to the 12.19" Wlwood kit at some point, but might not be right away).

I have the choice between 2 rear disc kits, a 10.7" and an 11.7" kit (both use Mustang Cobra calipers and rotors I believe).

Although they certainly aren't huge, I would like to go with the larger 11.7" kit, so they will fill the planned 18" rear wheels a bit better.

I would like to add the rear discs BEFORE I upgrade my fronts (again), and I guess my concern is that somehow having too large a rear disc brake relative to the current front 10.75" rotors will negatively affect the overall braking of the car. I do have an adjustable proportioning valve already on the car.

This is my first post here, so thanks guys for any advice you can provide! Lots more questions to come.
:thankyou:

[Apogee]

I would suggest going with the larger kit since you intend to upgrade the fronts in the future. Since you have an adjustable proportioning valve to the rear brakes, you should be able to tune things enough to achieve front lockup before rear. Push come to shove, you can always play with the coefficient of friction of the rear pads if you can't get things where you need them to be with respect to the front to rear brake balance.

Tobin
KORE3

[RumbleBee383]

Hey tobin, thanks for the advice.

Do you think there would be any difference in braking if I ended up going with the 10.7 brakes? I am a bit concerned with losing the ability to put a 15" wheel on the rear for trips to the strip.

Thanks again!

[Apogee]

...Do you think there would be any difference in braking if I ended up going with the 10.7 brakes? I am a bit concerned with losing the ability to put a 15" wheel on the rear for trips to the strip....

Of course there would be a difference, just not a huge one. You'll lose some brake torque due to the smaller effective radius of where the pads contact the rotors (about 9% less) and you'll have significantly less thermal mass to play with assuming the friction surfaces are the same thickness between the two diamter rotors. Less thermal mass means higher operating temperatures and less capacity for abuse, which may or may not be an issue for you. I'd be surprised if you couldn't fit 15's over a brake kit with an 11.7" rotor diameter, but you should definitely track down a the wheel fitment specs and verify, especially if you already have your 15" drag wheels.

Tobin
KORE3

[gsxrken]

Stoptech has some interesting white-papers on braking dynamics. Prepare to spend an hour or so.

http://www.stoptech.com/tech_info/tech_white_papers.shtml

http://www.stoptech.com/tech_info/wp_rearbrake_upgrades.shtml

[RumbleBee383]

Thanks for the help guys!

Wow, those Stop Tech articles are really interesting!

[Bryce]

Articles look good I need to read them completely.