Up grade hog brakes to brenbo? Harley Brake Issues Discuss Up grade hog brakes to brenbo? in the Harley Tech & Harley How-to forums; Rotor size/surface AND pad size/surface.............No !?!?...

[evoKENevo]

Rotor size/surface AND pad size/surface.............No !?!?

[tommyglide]

Wouldn't the larger diameter rotor aid only in cooling the rotor faster, because the brake pads are the surface area that does the grabbing, or am I missing something here?

[rjrivero]

Originally Posted by frisco-rigid

What is the diameter of the rotor you speak of..?

Front x2 - 11.81" (299.974mm) x .197" (5.0038mm)
Rear - 11.81" x .276" (7.0104mm)

[rjrivero]

Originally Posted by tommyglide

Wouldn't the larger diameter rotor aid only in cooling the rotor faster, because the brake pads are the surface area that does the grabbing, or am I missing something here?

I can't speak for heat dissipation, but my guess would be that it does. The angular velocity of a larger rotor would create more friction, and aid in braking. Just about any performance brake application will be designed to get the largest rotor on a wheel that will fit. :2cents:

[HarleyCruiser]

Originally Posted by tommyglide

Wouldn't the larger diameter rotor aid only in cooling the rotor faster, because the brake pads are the surface area that does the grabbing, or am I missing something here?

Well it is also leverage, the larger the rotor the farther it is away from the axle, the larger the rotor the faster the rotor moves, and the more heat that you produce. Heat = braking. The bigger rotor has more cooling area to dissipate the heat to prevent fading.

[frisco-rigid]

If rotor diameter is soo important then why are many of the fastest crotch-rockets using little 6" rotors.?

Your 11.81" is only .310" larger than stock HD.. That .310" won't make a hill of beans..
Have you ever run the old OEM HD 10" rotors.?
If so then you would know that going from 10" to the long-time 11.5" OEM HD didn't make much diff..

More pad surface will.. Yes Tommy..

Rotor and pad material will..
Google it and read some.. I have,, and most info I've read confirmed what I learned by experience.. Ductile iron and mild steel are best for rotors (stainless steel the worst) and whatever HH pads are made of for pad material..

Again RJ---Brembo is a fine caliper.. Your opinion about Brembo is based on your experience and the fact that they now sport the Bar & Shield (which means nothing)..
Have a ball..

[milindh]

Frisco

What crotch rockets have you seen that are running 6" rotors on the front? Every 'Busa, R-1, and Duc I've seen have big front rotors. They have little rotors on the rear because when they brake hard with the front the rear wheel is almost lifted off the ground. Large dia. rotors are heavy and if you could get the same braking power with small dia. exotic composite rotors with super high friction coefficients you'd be ahead of the game by lowering unsprung weight. You might have seen something like that on a race bike but your modern day superbikes you see coming from Japan and Italy all have big front rotors.

[rjrivero]

Originally Posted by frisco-rigid

If rotor diameter is soo important then why are many of the fastest crotch-rockets using little 6" rotors.?

Your 11.81" is only .310" larger than stock HD.. That .310" won't make a hill of beans..
Have you ever run the old OEM HD 10" rotors.?
If so then you would know that going from 10" to the long-time 11.5" OEM HD didn't make much diff..

More pad surface will.. Yes Tommy..

Rotor and pad material will..
Google it and read some.. I have,, and most info I've read confirmed what I learned by experience.. Ductile iron and mild steel are best for rotors (stainless steel the worst) and whatever HH pads are made of for pad material..

Again RJ---Brembo is a fine caliper.. Your opinion about Brembo is based on your experience and the fact that they now sport the Bar & Shield (which means nothing)..
Have a ball..

frisco..

Rotor radius does make a difference. Weather that difference justifies the cost, that's up to the buyer. I can tell you the brembo brakes that are standard for HD now are an improvement over the older brakes. I have both style brakes on 2 different V-Rods in the garage. Weather or not the bar and shield is a deal breaker is again up to the consumer.

Is .31 inches a big difference? Let's hypothetically crunch some numbers:

an 11.5 inch diameter circle has a surface area of 103.81 square inches. Let's assume the brake pad is 2" wide. (I don't have a pad here to measure.)
The area of the non friction circle is 70.84 square inches. The friction surface is 33.01 square inches.

an 11.81 inch diameter circle has a surface area of 109.49 square inches. Again, assuming the brake pad is 2" wide, the area of non friction inside that circle is 75.55 square inches. The friction surface is 33.94 square inches.

The area of friction surface area difference is 0.93 square inches. But you have pads on 4 surfaces, so your area of friction is 0.93 square inches x 4 or 3.72 square inches.

So actually the .31 inch difference in diameter equals a 3.72 square inch difference in surface area. Little things add up. The effect of increasing the radius is 4 x r x r in relation to surface area.

Note, I'm not concerned about the composition of the brake pads, most folks in the V-Rod circles use the Lyndall Racing Brakes Z-Pads in both types of calipers. The rotors are all factory HD, just different diameters. I am assuming the rotor compositions are similar.

[frisco-rigid]

You made my head hurt..

I really dig that you figured that all out, but,, I don't agree with it being more efficient.. Now, don't get me wrong,, it might be but my experience (not math) tells me diff.. Also, if the pads are still 2" on either (11.5 or 11.81) rotor then there is NO more friction contact surface obtained..
I submit to you that the friction contact surface is only the 2" pads X's 4 in contact with the rotor suface-- and if those rotors were 36" across the immediate real-time friction contact area will still not change.. It'll still only be 2" X's 4.. It is the friction contact area of the pads against the rotor that Works.. The leverage thing might have some cred, just not sure..

As I stated, when I went from the old OEM 10" rotors to the newer 11.5" I felt very little diff that I remember.. I made that change well over, ahh, many years ago is all I can say..
Now, here's more of My personal exp.. I can lockup the front wheel on my 120" sickle in a heartbeat with 2 cheap thirty dollar mild-steel 10" rotors..
Soo, maybe now you can see why I put very little store in the benefits of super long fancy rotors..
In this discussion I can only offer my personal Hands-On..

Mil--
You made me curious cuz my last 2 foreign bikes were in the 1960's so I went on-line and to a Kaw dealer today..
From casual observations over time, what to me looked like 6" or there-abouts rotors,, turned out to be only rear and actually from 8 to 8.75" rotors.. I guess I never paid attention to the fronts.. Today I found them from 11" to 13"..
But now I'm dis-appointed cuz all these years I was mistaking what is really 8" for 6",, jeeeeze,,, I coulda had a totally different career,, dag-nabit..

[rjrivero]

Originally Posted by frisco-rigid

You made my head hurt..

I really dig that you figured that all out, but,, I don't agree with it being more efficient.. Now, don't get me wrong,, it might be but my experience (not math) tells me diff.. Also, if the pads are still 2" on either (11.5 or 11.81) rotor then there is NO more friction contact surface obtained..
I submit to you that the friction contact surface is only the 2" pads X's 4 in contact with the rotor suface-- and if those rotors were 36" across the immediate real-time friction contact area will still not change.. It'll still only be 2" X's 4.. It is the friction contact area of the pads against the rotor that Works.. The leverage thing might have some cred, just not sure..

As I stated, when I went from the old OEM 10" rotors to the newer 11.5" I felt very little diff that I remember.. I made that change well over, ahh, many years ago is all I can say..
Now, here's more of My personal exp.. I can lockup the front wheel on my 120" sickle in a heartbeat with 2 cheap thirty dollar mild-steel 10" rotors..
Soo, maybe now you can see why I put very little store in the benefits of super long fancy rotors..
In this discussion I can only offer my personal Hands-On..

I don't want you to think I'm discounting your experiences. I can see your point of view, and it makes me wonder if the extra diameter is to reduce rotor warpage, as opposed to improving braking. I need to get the pads off the 2006 (brembo equipped) and compare them to the previous brakes. Maybe there is more pad surface, which would account for the better stopping power. (It's my experience that the Brembo brakes ARE better)

FWIW, I enjoy this healthy discussion.