1973 Honda CB350 - how much power?

Discussion in 'Motorbike Technical Discussion' started by Ig, Mar 13, 2007.

  1. I don't happen to think that 120 is a particularly outrageous speed, and
    you'd need to put airplane wings on the thing in order to get enough lift
    to worry about getting light. A bike isn't much more aerodynamic than a
    brick. A 200+mph F1 car, yeah, you want a little down-pressure
    to get your tires to stick a little better in the turns...

    On a bike, in a straight line under 150mph, the friction coefficient of
    the tires isn't particularly relevant. NASCAR drivers run around, what,
    180-190(?) and I don't recollect seeing much in the way of wings on them.
    Some ground-effects stuff maybe.

    If you wanted to talk about how tight a turn one could make at 120mph,
    using the street tire rubber compounds that were available 30 years ago,
    well, friction coefficient would factor in. But not in a straight line.
    Your calculations are incorrect because you are starting with a faulty
    premise. Wind resistance is not a primary factor in terminal velocity in a
    non-aerodynamic object. An ordinary red brick would have considerably more
    wind resistance than a perfectly round lead sphere, would it not? But if
    you drop them from the same height, at the same time they will both reach
    terminal velocity at the same time and hit the ground at the same time.

    Frankly, 120mph isn't all that fast and it really didn't take any
    engineering or mechanical wizardry to reach it with that machine, just a
    simple sprocket/chain change to get a little more out of the top end.

    If I had had any inkling that a bunch of otherwise supposedly
    knowledgeable people in a "tech" newsgroup would take the stand that this
    relatively easy feat was a ludicrous impossibility and start a shitstorm
    of pronouncements that "it couldn't be done", I'd have kept silent.

    Would I start another shitstorm if I said the same modification to a
    Suzuku TS100 would get it to 85mph?

    It doesn't matter what numbers you plug in, your answer will be
    meaningless because the starting assumption is incorrect.

    I am *amazed* at how many people are jumping to tell me I'm full of shit,
    while backing that up with nothing more than theoretical musings of how
    "it can't be done", instead of coming up with some actual, FACTUAL
    information on this machine such as the original factory specs from the
    manual such as horsepower, speed, gearing and ratios and the number of
    teeth on the stock rear sprocket.

    Armed with that information, it would be a relatively simple task to
    calculate just how little (or much) effort it takes to do what I said.
    Since it's been 30+ years, I can't be *completely* sure, but I think that
    I used a sprocket that had only 6 or 8 fewer teeth. Then you all could
    really pound me into the sand with REAL info instead of bullshit...or is
    everybody here unwilling to get the real facts because they might be shown
    to be wrong?

    To that end, I have located someone who owns one of these machines and
    requested that he send me any available info. I will also check any other
    sources I can find such as the local Honda shop, etc.
    Zaphod Beeblebrock, Mar 17, 2007
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  2. Nonsense. It still won't do 120mph without a very steep hill and a
    hurricane tailwind. Do you *really* think that a sprocket change makes
    it as fast a CB750?
    We wish.

    You are still, and it grieves me to say this, full of shit.
    The Older Gentleman, Mar 17, 2007
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  3. Er, that was me.... ;-)
    Er, that was me. For a 360, anyway.
    The Older Gentleman, Mar 17, 2007
  4. Which was my point. Perhaps you missed that part.

    Given a machine designed to particular specifications for a particular
    maximum load capacity, why don't you explain to my ignorant self just
    exactly what happens if you change the gear ratio by reducing the size of
    the rear sprocket say, from 48 teeth to 42 teeth, a reduction of roughly a
    bit under 15 percent?

    Will it hurt acceleration performance?

    Will it increase top speed?

    Suppose we reduce the max load by 50 percent,
    how will this reduction affect acceleration performance?

    Suppose we reduce the max load by another 50 percent,
    for a total reduction of 75 percent, how will this affect
    acceleration performance?

    Is a 50 to 75 percent reduction in load sufficient
    to offset, if not negate, the loss of acceleration
    performance of the 15 percent reduction in the rear
    Zaphod Beeblebrock, Mar 17, 2007
  5. Ig

    Mark Olson Guest

    Hey, I have to admit that I am not married to the idea of power increasing
    by the cube of the velocity. It wouldn't be the first time someone put up
    impressive-looking BS on Wikipedia.

    After doing a few sample calcs of my own it blows up pretty quickly into
    the ridiculous range for real world examples of 300 km/hr bikes that make
    about 150+ hp. So you are probably right when you say it's something
    between the 2nd and 3rd power for the velocities and bike-shaped objects
    that we are interested in.

    Thanks for an interesting discussion.
    Mark Olson, Mar 17, 2007
  6. Ig

    Mark Olson Guest

    No, TOG didn't miss anything. Power/weight ratio is nearly meaningless
    when you are concerned with top speed.
    On almost all bikes, all this will do is make it an absolute slug,
    Without a doubt.
    Almost certainly not. Most bikes have their gearing set up so their
    top speed is limited by the engine's maximum available power, that
    speed coincides more or less roughly with the engine's redline in
    top gear. There are many exceptions to this rule (specifically
    tourers with tall top gears optimized for low-rpm cruisng) but for
    most bikes they're not too far off.
    It will help.
    Any weight reduction helps improve acceleration-- that was never in
    Maybe. Impossible to say without having a specific case to

    Weight reduction has nothing to do with top speed, assuming
    you have an essentially unlimited distance, otherwise you
    are talking about an acceleration contest, as in drag racing.
    Get that concept firmly entrenched in your mind. You keep
    confusing acceleration with top speed.

    I really don't know why I bother responding. At the risk of
    being accused of resorting to an ad hominem attack, you appear
    to be incapable of grasping the most basic concepts relating
    to power, acceleration and top speed.
    Mark Olson, Mar 17, 2007
  7. Indeed. It's a long time since we had such an awesome demonstration of
    total ignorance and stupidity here.
    The Older Gentleman, Mar 17, 2007
  8. No. It will almost certainly reduce it in top gear, meaning top speed
    will be attainable in a lower gear. Unless, of course, the bike was
    massively undergeared to begin with.
    If, by load, you mean weight, it will improve it.
    See above
    We're not talking acceleration - we're talking top speed, in this
    thread. They are two different things. You said gearing up a CB360 will
    make it hit 120mph. Everyone else says you're talking shit, and you are.

    You are truly, truly ignorant. And stupid.
    The Older Gentleman, Mar 17, 2007
  9. May I second that? All this maths goes way over my head, bud it's always
    interesting to see a well-reasoned argument.
    The Older Gentleman, Mar 17, 2007
  10. No.

    I don't know diddly squat about your machine or what modifications could
    be done to it.

    Yeah, I know, you're inclined to say that I don't know diddly squat about
    Zaphod Beeblebrock, Mar 17, 2007

  11. The evidence for that is overwhelming.
    The Older Gentleman, Mar 17, 2007
  12. I apologize if it appeared to be an attack. I just feel that the use of
    the term "terminal velocity" is not correct in this discussion. As I
    understand the usage of "terminal velocity", it refers to the speed to
    which an object will accelerate (at a rate of 32 feet/sec/sec) when
    dropped from a sufficient height.

    To me, assuming that "terminal velocity" has anything to do with the
    discussion is a faulty premise and renders any equations meaningless.

    If I misunderstood what you were trying to say, again, I apologize.

    Yes, I realize that you are the one who has been giving the greatest
    latitude in this discussion, and I appreciate it.

    No, I do not have a degree. I do have, however, *some* education in
    various disciplines as well as practical experience.

    I might concede that two speedometers could be off by some percentage, but
    not by a huge margin. I didn't check their calibration. But I will go to
    my grave swearing that that both of those machines would reach an
    "indicated" (a term someone else used elsewhere in this thread) 120mph.
    When it comes to something *I* experienced*, something that I saw with my
    own eyes, I will not be convinced that it didn't happen no matter how many
    numbers are thrown out to say it "didn't" happen. Yeah, I put the motors
    way past redline.

    After reading some of the other responses I realize that the speedos
    *could* have been off and lacking any calibration data I should not be
    saying it was an "absolutely guaranteed 120mph". But how much error are we
    talking about here?

    I certainly didn't intend to start a shitstorm like this. I only wanted to
    say that those were some pretty damn good motors as far as I was
    concerned. But insinuating that I'm a liar and being flamed as a "stupid
    sod"? I damned sure would have kept silent had I known this would happen.

    That speedo hit 120, and broke there. The cops were pissed about all of
    the time they spent looking for my body because, as bad as the bike looked
    after the wreck, they didn't think the rider could have survived, let
    alone leave the scene under his own power.
    Zaphod Beeblebrock, Mar 17, 2007
  13. I will concede that the speedo *could* have been off, but not by all that
    goddam much. Certainly not enough to justify the trash-talking that was
    dished out right out of the gate. Seems to me that some people are just a
    little too eager to flame.

    The front wheel was the factory wheel. I didn't check the calibration of
    the speedo, in those days I didn't care much about speed limits.
    Zaphod Beeblebrock, Mar 17, 2007
  14. 10-15%. At an indicated 120mph, that means a true top speed of as little
    as 103mph, and that under "favourable" conditions.
    The Older Gentleman, Mar 17, 2007
  15. Oh yes, it could.
    No shit.
    The Older Gentleman, Mar 17, 2007
  16. **** me sideways, this thread is bringing out every ignoramus on the
    The Older Gentleman, Mar 17, 2007
  17. LOL, to think you might have missed out if I weren't so "ignorant" and
    such a "stupid sod".
    Zaphod Beeblebrock, Mar 18, 2007
  18. You are.

    As has been noted, you display an ignorance that's truly impressive. The
    refusal to acknowledge that means your stupidity is just as impressive.
    The Older Gentleman, Mar 18, 2007
  19. We do have a specific case. Since I don't have the specific data as to the
    gearing, etc. I left it general, allowing one to make reasonable
    assumptions as regards the ratios and loads to arrive at a general idea.
    I'll not accuse you of an ad hominem attack. If I read this right, you are
    saying that you believe *I* am saying:

    Less weight = higher top speed (period).

    That is NOT my intention. What I am saying is that:

    1) Taller gearing = higher top speed

    2) Taller gearing imposes a performance hit on low-end acceleration

    3) Less weight means I can AFFORD to sacrifice the low-end
    performance in exchange for the top-end gain.

    That's it.
    Zaphod Beeblebrock, Mar 18, 2007
  20. <Shakes head in amazement>

    ****, you're stupid.
    The Older Gentleman, Mar 18, 2007
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