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Old 12-14-2015   #1
AnswerMeister
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Things that make you go Hmmm. (brakes)

In general there is a lot of experience and wisdom on this forum. I have been on other forums that have the same traits. I have joined another forum for one of my bikes and there are a lot of inexperienced riders and members that just donít have a clue of how mechanical things work or general rules of physics. There was a thread started about if it better for a bike to have one front brake rotor or two. Someone said that there needed to be two, otherwise under braking situations that the bike would pull to the side that the rotor was on. I was waiting for him to get blasted by older riders for that idea. But he was actually getting people to consider it and think that it was a valid premise.
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Old 12-14-2015   #2
icantdrive55
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Re: Things that make you go Hmmm. (brakes)

Hmm. Lemme think about that for a bit...

Dave, you got any vaca planned for St Augustine this winter? Send me a PM--might want to see if I can arrange a trip that way.

Ciao--Bubba
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Old 12-14-2015   #3
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Re: Things that make you go Hmmm. (brakes)

That's why you put the brake rotor on the opposite side of the rear to equal it out. Even Erik Buell knows that!

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Old 12-14-2015   #4
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Re: Things that make you go Hmmm. (brakes)

Quote:
Originally Posted by icantdrive55 View Post
Hmm. Lemme think about that for a bit...

Dave, you got any vaca planned for St Augustine this winter? Send me a PM--might want to see if I can arrange a trip that way.

Ciao--Bubba
And since St. Augustine isn't too far from me let me know if you plan to take an extended ride while down here. I'm about 1.25-1.5 hours (in the car to Orlando) which I'm sure is faster on 2 wheels.
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Old 12-14-2015   #5
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Re: Things that make you go Hmmm. (brakes)

Whoa, dewwd, then how do it work with a drive schprocket on only one side?? Hmmmmmmmmmmmm???
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Old 12-15-2015   #6
Dave Bannister
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Re: Things that make you go Hmmm. (brakes)

That's funny because until bikes got heavy and or faster there was only 1 rotor or better yet one mechanical drum which are too much fun
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Old 12-15-2015   #7
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Re: Things that make you go Hmmm. (brakes)

I wonder if they know that shaft drives can't wheelie?
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Old 12-18-2015   #8
AnswerMeister
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Re: Things that make you go Hmmm. (brakes)

Quote:
Originally Posted by witttom View Post
That's why you put the brake rotor on the opposite side of the rear to equal it out. Even Erik Buell knows that!

TTTom so I was drunk last night and took your lead and posted this
No wait, they must be right .... that is why Buell has the front rotor on the right and the rear rotor on the left to counter act each other to allow you to brake straight. One pulls right one pulls left so you are safe,

They then replied with:
The problem will introduce itself when you add the ss front brake pads, and ebc pads, jam the front brakes, and it will twist the bars out your hands.. Had a few fellow buellers tell me it has happened to them. What helps is having the front fork brace on .

So I followed up with:
Impossible, it's the same wheel it's the same axis. you can not slow down half of an single item faster than the other half.

I think Vinny said it best

https://www.youtube.com/watch?v=QVGXUrKJVCU
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Old 12-18-2015   #9
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Re: Things that make you go Hmmm. (brakes)

You might want to suggest these "riders" (term used loosely here) loosen their do-rags a bit. They must be cutting off the circulation to their brains.
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Old 12-18-2015   #10
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Re: Things that make you go Hmmm. (brakes)

Post a picture of a supermoto doing a stoppie and watch their heads explode. Problem solved!



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Old 12-18-2015   #11
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Re: Things that make you go Hmmm. (brakes)

This year before EBR closed it's racing program Pegram and Canepa both had difficult steering under braking with the single rotor. Bike wanted to stand up. Both went to the double setup.
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Old 03-06-2017   #12
bigjoepainting
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Re: Things that make you go Hmmm. (brakes)

there's a reason why all the manufactures use 2. but I guess they're just going with the trend...
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Old 03-07-2017   #13
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Re: Things that make you go Hmmm. (brakes)

Hopefully everyone here is joking. If not....the bike does not care if it has one rotor or two, or where the rotors are mounted. The frictional forces at the brake pad to disc interfaces are completely canceled by the reaction forces at the caliper to fork mounting interfaces. The braking force at the contact patch is the only external force the bike reacts to. A tendency to stand up under braking is also common to many twin rotor set-ups, and has everything to do with the geometry of the front end (rake, trail) and nothing to do with how many rotors the bike has or where they are mounted.
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Old 03-07-2017   #14
icantdrive55
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Re: Things that make you go Hmmm. (brakes)

When it comes to braking forces, you're correct. However, where the differences come into play is: 1) unsprung weight, and 2) rotational mass of the rotors and the distance from the axle center. The farther the weight is from the center of rotation, the greater effect it has on the ability of the wheel to change it's plane of rotation (turning). Think back to the spinning top and the forces required to change it's plane of rotation to understand. I've always assumed that Buell's single rim brake was much lighter overall than the conventional two-rotor set-up and thus, it benefited primarily from a reduction in unsprung weight. Whether the mass and large circumference of the rim brake--at greater distance from the axle--was sufficiently lighter than smaller diameter dual rotors to reduce the resistance to change plane (turning) was a guess, but knowing that Buell was an engineer, I'd guess he did the math! I always wondered, too, how much more difficult it would be to do a wheel/tire change for longer endurance races. Seems like there would be a time penalty for the rim brake, but I never worked on one.
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Last edited by icantdrive55; 03-07-2017 at 07:11 PM.
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Old 03-07-2017   #15
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Re: Things that make you go Hmmm. (brakes)

You are absolutely correct regarding the effects of unsprung mass and rotational inertia. I never did the math, but since rotational inertia is a function of the square of the radius it always appeared to me that the single Buell disc likely had significantly more inertia than a comparable dual disc set-up. Whether the reduction in unsprung mass is enough to make this compromise worthwhile is the question. As you say, he surely did the math so I would give him the benefit of the doubt. Heat rejection properties and resistance to fade would also seem to be factors, and in terms of pure surface area you would think that the single disc would be better. As a side note, my Blackbird, which is already a heavy pig of a motorcycle, has a ton of unsprung mass hanging on the front end due to Honda's ridiculous linked braking system. I've considered de-linking the brakes just to see the effects of the reduced mass, but so far have been too lazy to do it. If it was a sportier motorcycle I would be more highly motivated.
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