I've read a number of the threads about the 12" brake conversion with the tall spindles. Interesting reading for sure...especially in regards to the debate about the tall spindle conversion. That aside, has anyone done a before/after comparison of braking performance with the 12" brakes?

That's one of the things that bugs me about a lot of the handling/braking mods they do in the mags. They put in a new cam and they'll put it on the dyno to get some HP numbers. They put on a new set of brakes or a new sway bar and you get nothing quantatative!!! No braking numbers. No skidpad times. Aarrrggghhh.

Anyway, I was hoping someone had some published numbers on performance gains in moving up to the 12" brakes. At a minimum, some seat of the pants numbers.

Am toying with the notion of making the conversion but am not sure whether it's really worth it. I could go through the numbers and figure out the theoretical difference (which my gut says is small), but I'd like some good real life data. Thanks!

I have a G-tech and still have the stock 11" disc brakes. I would be interested in seeing the stopping times for a stock 11" setup on my Elco vs the 12" setup I have sitting in my garage collection dust.

The only problem I see is my rears lockup before the front. So, when I install the rear prop valve I know the numbers will be better by just installing the valve. Someday I'll get around to it!

Perfect! You like the G-Tech? That seems like just the ticket for something like this.

Let us all know when you do the prop valve swap and then the 12" swap. Would love to know the real answer!

You having lockup problems with the stock prop valve on ther? Is that typical?

Well,
I can tell you that last week I swapped the 11" stock discs/single piston caliper to a 13" Baer Track/dual piston caliper system and I can hardly believe the difference in brake 'force' that I recognized on my first spin with the Monte. The brakes work so well now that I will have to change my driving style... http://www.chevelles.com/forum/smile.gif

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71 Monte 454 HO 5-Speed "FULMNTE", 100 HP Nitrous
www.71Monte.com (http://www.71Monte.com)

I don't have any hard numbers, but seat of the pants feel tells me that the 12" brakes not only worked a little better, but that pedal pressure was slightly better in my manual brakes. Certainly you will not see a huge difference in performance in braking... we are only talking about a 1/2" further out from the wheel center. But another of the benefits includes more rotor mass for better cooling. This helps reduce warpage which reduces having to turn the rotors as much.

Good luck,
Bill C.


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Bill C.
'71 SS (now with 467BBC)
'70 Nova 350/700r4
ACES #2780
Colo Spgs, CO

Here is a post that I made a few months ago with the calculations between 11" and 12". Sorry I can't give you a real world opinion however.

Here is the braking difference between an 11" rotor and a 12" rotor. These calculations are with the exact same size pad with the same friction coefficent. For my brake system the 11" disc will produce 11523 in-lbs. of braking torque. With the 12" rotor will produce 12786 in-lbs. of braking torque. This is a 10.9% increase in braking torque.
This is the difference between the two size rotors. Even though they have the same size pad there is a considerable difference in brake force.


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R.J.
1972 Chevelle
TC Member #1525
RJ's website updated 12-1 (http://www.buffnet.net/~airrj/)
2003 Northern Chevelle Gathering (http://www.angelfire.com/folk/canam/page35.html)

In addition, it depends on the type of brake pads that are used as well. Changing pads can also improve braking, so there is another factor to consider.

Looks!!
Most of us will not do track days so the "advantages" of the tall spindles and 12" brakes will be lost on us.
Can you lock the fronts at 80, you have enough brake, can you do it 10 times in 1.5 minutes, you might need bigger brakes or more cooling.
Trust me 30 minutes on track at a place like Willow Springs will put the best brakes, even some of the after market stuff, in the trash.

I will not argue that their is a very minor leverage improvement with the 12" GM brakes but there isn't any problem with the 11" factory brakes to begin with and how can there be an improvement in pedal pressure when all the hydralics of the 12" to 11" are the same? And yes the larger rotor will act as a larger (takes longer to heat up) sink but it will also take longer to cool off in sprited driving situtations BTW I have never had a problem with the 11" brakes fading as long as the car had good quality pads. If you really want bigger brakes use the Baer stuff it is a major leap forward in tech. over the 12" GM stuff, just realise that the original 11" stuff is still very good for everyday driving.

IMOP, The 11" disk is as good as any street tire that will fit under the front of a stock "A" body. A lot comes down to where the rubber meets the road. Again, JMOP

Q,
You said that you cannot see any difference in pedal pressure? Do you understand the laws of physics and how forces act and react on each other? Consider the example of trying to remove a head bolt from a motor. You have your socket and a wrench that is 6" long. Do you think it will be hard? You bet... not much leverage! Now take that same socket and put a 3' breaker bar on it and 'POP' off comes the bolt like MM opening another beer! Basically, there is a certain pressure that needs to be exerted to get that bolt to come loose and all you have to do is get to that pressure point. Same thing if we look at locking up the front brakes on the car. Given a certain caliper, with a certain brake pad and certain rotor diameter, it will take a certain amount of force to lock the wheel. Now, keeping all else exactly the same, move that caliper away from the center of the hub a little bit and what happens? The amount of force required to lock the wheel does not change, but the amount of force required by the pads on the rotors is reduced slightly being that now they have an advantage in leverage, just like the breaker bar did in previous example. So since the brake pads don't have to squeeze so hard, you don't have to apply the brakes so hard...

Same principle applies to master cylinder bore size... you wouldn't think changing bore size by 1/8" would make much difference, but it makes a huge difference! That is why power MCs are power and have 1 1/8" bores and manual MCs have a 1" bore!

Is there anything wrong with the stock 11" disks? Not IMO if you are just cruising around, but if you get into spirited stop and go driving or racing, then I think they fall short. My biggest issue is that they don't cool very well and need to be thicker to reduce warpage... that is why I run the Corvette 1.25" thick rotors on my Chevelle versus even the 1LE rotors which are same as stock rotors at 1.1" thick.

Bill C.

BC you are bring up leverage advantage, this will not help pedal height or feel. Oh ya BTW I race in SCCA autocrossing, the 11" rotors and have not had any problem, just use really good pads. I have two cars one with the tall spindles w/12" 1LE brake rotors and a car using 11" stock brakes, the pedal feel in the 11" brake car is better but I don't believe the problem is in the 12" 1LE brake stuff. I like the handling of the stock spindle car better, it doesn't have the steering geometry issues.

Q,
Cool, I like the tall spindles and bigger rotors and you don't.

Best of luck in your racing...

Bill C.

Q-ship
can you suggest a good pad for street driving that may stop me a little shorter and not heat the rotors or wear to excessly? Now running 11in. front and 10 1/2 rears.

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