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Thread: "Mass Centralization" was good engineering, or better as marketing hooks?

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    Member Endopotential's Avatar
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    "Mass Centralization" was good engineering, or better as marketing hooks?

    Happy Holiday folks! As we couch surf in our post-turkey haze, thought I'd stir the pot and give us something to debate. And for me to learn more about our bikes.

    First off, please don't take this post wrongly as a rant against Buells. I actually love the rumble, the torque, and the quirky soul of the design. So much so that I have two - an '09 XB9SX and Nic's XB12R cafe racer. Motorcycle reviews breathlessly talk about how "light and nimble" these bikes are. Yes, maybe compared to a 1,000lb Harley cruiser... but compared to an R6 or Triumph Daytona, my bikes still feel very top heavy and deliberate.

    So were Buells really designed optimally from an engineering perspective, or were these more flashy ideas to capture marketing headlines?


    1) Fuel in the frame - OK, this one I'll buy. The frame spars do sit lower than a typical gas tank, so a lower center of gravity (CoG) here. But at the expense of a widened frame, which makes it harder for a height-challenged rider to flat foot. But overall 1 star to Erik!

    2) Oil in the swingarm - another cool idea. More sprung weight for the rear suspension, but lower CoG and unique design. 2nd star to Erik.

    3) ZTL / perimeter brakes - A very thorough discussion here:https://www.southbayriders.com/forums/threads/44780/
    If you buy the calculations, a Buell front wheel is about 4.5lbs lighter than a typical dual disk design, which is a significant decrease in sprung weight for the fork. But overall moment of inertia and angular momentum are about the same, so no advantage in acceleration / deceleration. And supposedly more brake fade from the decrease in surface area of the rotors, especially if you push them hard track riding. If it was such a great idea, then why don't top tier MotoGP bikes adopt / license this technology? @Cooter and @outthere - as our resident racers, what say you?

    4) Underslung muffler - Sure, it's better sitting down there that up on the side or under the tail. But if lower CoG was the prime objective, wouldn't it have been better to mount the engine down lower? An engine block is full of heavy metal and oil, while a muffler is basically a hollow tube stuffed with cotton candy. For a similar volume, I gotta guess an engine block has 5-6 times the density of a muffler. If there's concern for scraping the engine, then just install some light metal plate beneath it instead.

    So overall, I score two valid claims and two debatable design ideas. Still makes for a fun ride any day.

    Let the flame war begin!!!
    Last edited by Endopotential; 11-30-2019 at 08:08 PM. Reason: EriK, duly noted!!!

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    " So were Buells really designed optimally from an engineering perspective, or were these more flashy ideas to capture marketing headlines? "

    I think it was a combination of both but more towards the engineering side.

    " 1) Fuel in the frame - OK, this one I'll buy. The frame spars do sit lower than a typical gas tank, so a lower center of gravity (CoG) here. But at the expense of a widened frame, which makes it harder for a height-challenged rider to flat foot. But overall 1 star to Eric! "

    There is always the SCG model.

    " ) ZTL / perimeter brakes - A very thorough discussion here:https://www.southbayriders.com/forums/threads/44780/
    If you buy the calculations, a Buell front wheel is about 4.5lbs lighter than a typical dual disk design, which is a significant decrease in sprung weight for the fork. But overall moment of inertia and angular momentum are about the same, so no advantage in acceleration / deceleration. And supposedly more brake fade from the decrease in surface area of the rotors, especially if you push them hard track riding. If it was such a great idea, then why don't top tier MotoGP bikes adopt / license this technology? @Cooter and @outthere - as our resident racers, what say you? "

    Though I don't know much about technical aspects of engineering brakes, I suppose that makes sense about them.

    " 4) Underslung muffler - Sure, it's better sitting down there that up on the side or under the tail. But if lower CoG was the prime objective, wouldn't it have been better to mount the engine down lower? An engine block is full of heavy metal and oil, while a muffler is basically a hollow tube stuffed with cotton candy. For a similar volume, I gotta guess an engine block has 5-6 times the density of a muffler. If there's concern for scraping the engine, then just install some light metal plate beneath it instead. "

    I think this is where the cool factor comes in, because that's how I look at it. I also read recently that the days of putting the exhaust neatly under the seat of the bike are over due to the expense of putting it there, much easier to run it on the outside someplace.

  3. #3
    Senior Member Cooter's Avatar
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    Definitely all engineered. Whether the ideas have proven the test of time or not, I believe Eri(k) and his Buell boffins were only interested in performance. There are always concessions, don't forget there were several things that were mandated by mother H-D

    [IMO below]
    Fuel in frame is still a good idea. Less sloshy and lower weight, but it requires a level of commitment and sacrifice and big money to design both things at once. Safety testing? Most engineers/ designers would prefer to design the frame, then make room for 4 gallons of liquid. Ya Bubbles is barely 5' and can ride an Scg so the width is only a 'small' sacrifice (PUUUUNNNN).

    The oil in swing arm. The added liquid is so close to the pivot, it's not adding much unsprung weight to suspension movement. Probably more of a convenience anyway. Saving space, and still keeping the weight low, and near the C/G. Where else would you put it?

    Perimeter brakes were a great option for Buell to satisfy another obsession of his. Rotating mass is just as big a deal to him as mass centralization and a good thing to show off "different in every way". The aren't the best for racing today, but can hold their own. Thats a very stunning statement considering they were designed and unchanged 20(!?!) years ago while regular brakes have changed considerable and have gotten MUCH, much, larger. 320mm disks and Brembo M50's are the norm now, wow!

    I like to point out the weird underslung muffler to my Panigale, R/1, BMW friends. All of them copy-cats, lol. The problem is you can't make the H-D twin narrower. If it was mounted any lower you'd lose lean angle, Erik's solution was to use that empty space for the muffler.

    Don't forget, Erik also put the first stainless braided brake lines on a street bike and got them to pass the dreaded whip test by the DOT.
    Last edited by Cooter; 12-01-2019 at 12:27 AM. Reason: Oops! spellcheck hilarity...

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    Member Endopotential's Avatar
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    Quote Originally Posted by Cooter View Post
    Rotating mass is just as big a deal to him as mass centralization

    The problem is you can't make the H-D twin narrower. If it was mounted any lower you'd lose lean angle, Erik's solution was to use that empty space for the muffler.
    Good points sir.

    Rotating mass - that's what gets me. Putting the rotor out further to the rim increases the moment of inertia, even if overall weight is the same. Or I guess it did allow for slightly lighter wheel spokes.

    As for lean angle, the cylinders are aligned fore and aft. If they were transverse like for a Moto Guzzi, Honda CX, or old air cooled BMW I can see how that would be more of an issue. The Buell engine block at its bottom isn't much wider than the muffler. And if scraping the sides of the case were a concern, you'd be close to low-side angles there, no?

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    Quote Originally Posted by Cooter View Post
    320mm dicks
    ahem.... this is supposed to be a family friendly site, isn't it?

    12.5 inches? that would surely affect lean angle

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    Senior Member Cooter's Avatar
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    Quote Originally Posted by Endopotential View Post
    it did allow for slightly lighter wheel spokes.
    The whole assembly was made lighter including the hub, as the braking forces didn't include the hub as a path anymore. Just tire, wheel rim, mounts, disk (haha) and then to the caliper. No torsional load on the spokes or hub. The wheel spokes on the EBR are frighteningly thin, but obviously do the job.
    Not perfect by a long shot, but pretty cool for 20 years old

    Check your lean angle by putting a 5' long by 2' tall piece of plywood against the tires, now lift it up and see what hits. Crazy, right!? Can you imagine if the engine was even 1" lower?

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    Senior Member pdksh's Avatar
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    I agree with cooter. The ZTL/ZTL2 braking system may be marginally lighter than a conventional dual rotor system but the added weigh savings of the front rim MUST be considered. The dual Brembo MONO-BLOCKS must weigh a ton compared to the ZTL, for my style of street riding I don't need/use the extra braking of the MONO-blocks. I will say, anti-lock brakes is a MUST with the MONO-BLOCKS, unless low-sides is your thing.

    Not only did Eric introduce factory steel braided brake lines, I believe the WestWind was the first bike to use inverted forks. Correct me if I'm wrong but thats what I tell all my buddies at the coffee shop.

    When I saw the big ducati's with the underslung exhaust I was re-assured that most, if not all of Erik's ideas were founded in sound engineering. After all, is there anything more sexy than the 916/996 pipes?

    Now just blabbing my ignorance, didn't the RZ-500 (RD500LC) have a underslung rear shock? (as much as I love my Buells, they would all go on the block for a mint RZ-500)
    Last edited by pdksh; 12-01-2019 at 04:18 PM.

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    Hmmm, So I been reading on motorcycle dynamics, and came across where a higher COG requires less lean angle as opposed to a lower COG. Basically how far away from upright the COG is the faster the bike turns given a fixed lean angle? Being I'm mortal and would never realize this on the street, but it is interesting as most improvements are normally a shift in balance of compromises. I love Erik's approach to engineering. Also I love the "that a big brake rotor" comment. Then I mention the inside out brake caliper. You can see the short circuit in their eyes. lol

    I always thought about the oil getting mixed up being in a bouncing swing arm and possibly inducing air into it. However, knowing Erik, I'm sure that was investigated as well.

    Dreaded whip test?...

    found it.
    Uh cant get just the url for the pdf...hope the link works
    https://duckduckgo.com/?q=dot+break+...174-3__&ia=web
    Last edited by rb70383; 12-01-2019 at 06:19 PM.

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    Quote Originally Posted by Endopotential View Post
    Happy Holiday folks! As we couch surf in our post-turkey haze, thought I'd stir the pot and give us something to debate. And for me to learn more about our bikes.

    First off, please don't take this post wrongly as a rant against Buells. I actually love the rumble, the torque, and the quirky soul of the design. So much so that I have two - an '09 XB9SX and Nic's XB12R cafe racer. Motorcycle reviews breathlessly talk about how "light and nimble" these bikes are. Yes, maybe compared to a 1,000lb Harley cruiser... but compared to an R6 or Triumph Daytona, my bikes still feel very top heavy and deliberate.

    So were Buells really designed optimally from an engineering perspective, or were these more flashy ideas to capture marketing headlines?


    1) Fuel in the frame - OK, this one I'll buy. The frame spars do sit lower than a typical gas tank, so a lower center of gravity (CoG) here. But at the expense of a widened frame, which makes it harder for a height-challenged rider to flat foot. But overall 1 star to Erik!

    2) Oil in the swingarm - another cool idea. More sprung weight for the rear suspension, but lower CoG and unique design. 2nd star to Erik.

    3) ZTL / perimeter brakes - A very thorough discussion here:https://www.southbayriders.com/forums/threads/44780/
    If you buy the calculations, a Buell front wheel is about 4.5lbs lighter than a typical dual disk design, which is a significant decrease in sprung weight for the fork. But overall moment of inertia and angular momentum are about the same, so no advantage in acceleration / deceleration. And supposedly more brake fade from the decrease in surface area of the rotors, especially if you push them hard track riding. If it was such a great idea, then why don't top tier MotoGP bikes adopt / license this technology? @Cooter and @outthere - as our resident racers, what say you?

    4) Underslung muffler - Sure, it's better sitting down there that up on the side or under the tail. But if lower CoG was the prime objective, wouldn't it have been better to mount the engine down lower? An engine block is full of heavy metal and oil, while a muffler is basically a hollow tube stuffed with cotton candy. For a similar volume, I gotta guess an engine block has 5-6 times the density of a muffler. If there's concern for scraping the engine, then just install some light metal plate beneath it instead.

    So overall, I score two valid claims and two debatable design ideas. Still makes for a fun ride any day.

    Let the flame war begin!!!
    Ok lets see if I remember this story right. ( getting old sucks) When Eric was trying to figure out the motor placement, he took the maximum lean angels of the tires at the time. He then made a V out of plywood at those angels and then placed the motor in the V and designed the frame around it.

  10. #10
    Senior Member Cooter's Avatar
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    I would totally believe that ^^^^ and a big part of why I'm a huge John Britten fan as well.



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