I thought... that the discs on my bike were directional. Hence the brake discs go on a certain way. If this is true.. why is it that the front brake cut-out pattern is reverse to the back disc? The back disc makes sence to me as it looks like that the drag direction promotes strength in the disc for stopping. But the front is completely backwards and its that way on all Harley's. Just wondered if anyone had an idea why or actually knew why.

 

Good Question, Goth. Hope someone has an answer.

 

Just a guess here, with my LIMITED knowledge of physical science. I think they're both directional, and I'm not sure I can type what I'm thinking. But, I'll try. The front brake is stopping a force that is pushing. The rear brake is stopping a force that is pulling. Does that make since? I could ramble on here, but as previously mentioned, with my limited knowledge of physical science, that would probably just further confuse the issue.

 

That does sound logical to me.

 

Most of the late model H-Ds come with 2 or 3 discs cut in the pattern you have. If they were truely directional why would the H-D Dealer techs at the first time that you had a brake squeal in the front of your bike with dual brakes simply swap the discs from side to side? I know that they do that all the time. It doesn't look to me like the cut of the disc is anymore than cosmetics. I know that the OEM discs are marked (R) and (L).

Both of my Sportsters came with the front disc(s) mounted with the swirl pattern peaking to the front; while the rear disc was just the opposite. I don't know how the rotors were mounted on my Road King Classic because all 3 discs have been swapped out to floating rotors.

Maybe we could hear a few words of wisdom from a H-D Technichian? .............. BC

 

I would agree with that hypothesis if the front wheel where rotating in an opposite direction. When it gets down to it, both brakes are doing the same thing. Stopping a rotating wheel from turning. If it were a matter of pushing or pulling...what would you do if the bike had 3 wheels? Front, Middle, Rear? What would the middle wheel be classified as in your theory... This is why I am confused. To me, that disc brake (front) should be turned around.

The ONLY thing I can come up with is that it doesnt matter in the strength dept. If the Rotor is turned around on the front, maybe, just maybe the wheel will pull to one side or the other... by reversing this rotor they balance the pull on the brakes to compensate for both discs being on the same side of the bike.. I am still, confused. And I am NOT sleeping....stuff like this bothers the crap out of me. hehe. And no, the drugs aren't helping.

 

No idea!

 

It's just looks, doesn't affect braking strength, you'll lock your wheel up way before you twist the brake disc apart regardless of the direction of the pattern. Why they have them with the patterns reversed........who knows.......... Even the hole drilling doesn't make a substantial difference, it's just for looks since you can see them, that's why car disc brakes are typically just plain steel with no pattern or drilling since you can't see them. If you really want to, you should be able to flip the front disc to match the pattern of the rear, unless they countersunk the bolt holes on one side of the disc so they can only be mounted from one side, I've never looked harley discs that closely, so i'm not 100% sure if they are reversable. You may hear various things from aftermarket disc makers about how the patterns creating greater braking strength, promote even cooling and whatnot, but for the street biker, non of it is going to have any affect, it's just gimmicks.

 

And just to clearify on the possible cooling issue, Like I said before, it's more of gimmick, and not going to affect a street biker. Even on track race bikes that stress the brakes at a much higher rate, the pattern of the swirls and drilling only has a very small affect, and is generally not a major concern.

 

Functionally, it makes no difference. Asthetically, your front one is mounted backwards. Just flip it over.