Fun and fear

> Sometimes I like to acclerate really hard, taking the bike to near redline
> in first and then banging second gear.
>

If the wife doesn't mind, why would we?


> I can feel the front end "get out of shape" at the point of shifting. I
> guess I could best describe it as a "head shake". If you watch the pros
> (IOM. MotoGP, Superbikes) I think you see what I think I am feeling when
> they really get on the throttle.
>

No...because when the tire clears the road surface, presto, no more head
shake. THATS where the big boys spend lots of time accelerating out of
corners.


> What causes this?

Accelerate harder, you'll feel less of it, if its bothering you.
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On Oct 11, 4:33 pm, "BryanUT" <nestl... DeleteThis @comcast.net> wrote:
> I admit it, sometimes I engage in squid like behavior.
>
> And this leads to a question about motorcycle behavior and handling.
>
> Sometimes I like to accelerate really hard, taking the bike to near redline
> in first and then banging second gear.
>
> I can feel the front end "get out of shape" at the point of shifting. I
> guess I could best describe it as a "head shake". If you watch the pros
> (IOM. MotoGP, Superbikes) I think you see what I think I am feeling when
> they really get on the throttle.

In a straight line headshake & wobble with steep steering geometry
without a steering damper is pretty common. On one-track day I rented
an R6 & it was pretty bad over bumps as was my 1st SV-650 was but my
GSXR-1000 never did (had a steering damper).
On the GP bikes I think they get wobbly because they're putting too
much power to the ground and it's the rear wheel that is slipping,
thus causing a temporary wobble as the wheels try to come back into
alignment.

> What causes this? I never felt this sensation on my noodle framed Nighthawk
> 750 (with much less HP). Although I distinctly remember the noodly
> sensation in the corners on the Nighthawk, but never on the F4i.

The Nighthawk prolly had more power than you thought it did for the
weight distribution. My old Z1 "83"HP would do 1st & 2nd gear power
wheelies. Those old UJM's were notorious for rubbery frames and would
even go into straight-line wobbles. That little RZ-350 has a max speed
"on sweepers" of about 110, above that it starts to wallow. Old bikes
were also more sensitive to front/rear tire combinations.

> So I know the F4i has a much more rigid frame. Anyway, when I make the
> bike behave like that it is really fun and yet I believe rightfully puts the
> fear of god in me.

It's not really the frame but the front wheel coming off the ground
misaligned with the rear tire particularly over a bumpy road. On a
turn you're looking at more at a rear traction problem as the front
will likely let you know it's about to loose traction by going wide in
the turn or sliding a bit to the outside.

Bob Nixon.
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>> >What causes this?
>>
>> With 100 horsepower on tap and a high center of gravity, you are
>> accelerating
>> at about 3/4ths of a g, and you are transferring most of the bike's
>> weight to
>> the rear tire, so the front tire loses its grip on the pavement and the
>> front
>> end wiggles.
>
> Exactly. Feels a little uneasy when she comes back to the ground.
> Childsplay. You want uneasy, take a third shift job in a gas
> station...at night...anywhere in America...with a road name "Martin
> Luther King."
>

RACIST!!!
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"BryanUT" <nestle12.DeleteThis@comcast.net> wrote

> Sometimes I like to acclerate really hard, taking the bike to near redline
> in first and then banging second gear.
>
> I can feel the front end "get out of shape" at the point of shifting. I
> guess I could best describe it as a "head shake". If you watch the pros
> (IOM. MotoGP, Superbikes) I think you see what I think I am feeling when
> they really get on the throttle.
>
> What causes this? I never felt this sensation on my noodle framed
> Nighthawk 750 (with much less HP). Althought I distinctly remember the
> noodly sensation in the corners on the Nighthawk, but never on the F4i.
>
> So I know the the F4i has a much more rigid frame. Anyway, when I make
> the bike behave like that it is really fun and yet I believe rightfully
> puts the fear of god in me.

Lots of bikes will exhibit some headshake under hard acceleration. It's also
known as "shimmy", "wobble", a "tank-slapper", or even a "death wobble".
It's why lots of people put steering dampers on their bikes.

I've felt mild headshake quite a few times -and during deceleration as well
as acceleration- but have been in a really serious tank-slapper only twice:
both occurring at the track and under exactly the same circumstances;
accelerating WFO out of a slow corner and hitting a stretch of very rough
pavement while still leaned over with the front end *very* light.

Both times I immediately got off the throttle and both times the steering
settled right back down to normal after a few more zigs of decreasing
magnitude. (Disconcerting feeling, though!)

Saddle is being overly dramatic when he implies that you're automatically
dead if "the bike doesn't straighten itself out", because you *can* get back
under control by simply backing off of the throttle very quickly if the
shake shows signs of getting progressively worse. But if you *don't* get it
back under control and it progresses rapidly from a slight shimmy to a
pronounced wobble to a lock-to-lock tank-slapper, then you're going to be
highsided a second or two later!

If you look around the web you can find videos of riders being spit off of
their bikes by tank-slappers, and the bikes nearly always have this in
common: they're very powerful bikes, they're accelerating WFO, and they're
being ridden by squids. Inexperienced squids.
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BryanUT wrote:
> I admit it, sometimes I engage in squid like behavior.
>
> And this leads to a question about motorcycle behavior and handling.
>
> Sometimes I like to acclerate really hard, taking the bike to near redline
> in first and then banging second gear.
>
> I can feel the front end "get out of shape" at the point of shifting. I
> guess I could best describe it as a "head shake". If you watch the pros
> (IOM. MotoGP, Superbikes) I think you see what I think I am feeling when
> they really get on the throttle.


Lashings of power make the front end light and you may have a death grip
on the bars and be unintentionally pulling one side harder than the other?



>
> What causes this? I never felt this sensation on my noodle framed Nighthawk
> 750 (with much less HP). Althought I distinctly remember the noodly
> sensation in the corners on the Nighthawk, but never on the F4i.
>
> So I know the the F4i has a much more rigid frame. Anyway, when I make the
> bike behave like that it is really fun and yet I believe rightfully puts the
> fear of god in me.
>
>

Do it, enjoy it!......as often as possible.......
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BryanUT <nestle12.TakeThisOut@comcast.net> wrote:
>
> Sometimes I like to acclerate really hard, taking the bike to near redline
> in first and then banging second gear.
>
> I can feel the front end "get out of shape" at the point of shifting. I

I believe the other Brian answered the question. I would just mention
that when it comes to bringing the bike up to redline, there isn't much
point unless you are WOT (Wide Open Throttle).

- Kurt
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> I would just mention
> that when it comes to bringing the bike up to redline, there isn't much
> point unless you are WOT (Wide Open Throttle).
>
> - Kurt

Is that like WFO?
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"Le Chaud Lapin" <jaibuduvin.DeleteThis@gmail.com> wrote

> Well reading this post makes me feel a lot better. I've been taking
> my VFR-800 up to 140-150 on straight and hard surfaces, and I could
> swear that it starts to vibrate in the front for no reason. Never
> experienced it on a dirt bike, so I had no idea why it was doing
> that. Now I know.

If the bars are vibrating horizontally it's most likely just a front wheel
that's out of dynamic balance, because high-speed headshake isn't a problem
endemic to VFRs. -I've had mine up to those speeds quite a few times, and
it's *never* vibrated in a headshake mode at high speeds at all: only when
accelerating WFO from fairly low -circa 60 MPH or below- speeds. And when
that happens it isn't a "vibration" at all: it's a rapid back-and-forth
jerking of the bars that rapidly increases in magnitude and is too powerful
to control.

What *does* happen at very high speeds is that your suspension simply can't
absorb the minor pavement irregularities that are occuring in rapid very
succession -'specially if you've got your suspension set up stiff for a 200
pound rider such as myself- and it translates into a *vertical* pounding
that's severe enough to make it hard to focus on your instruments at
anything above 140 or so. This happens even on the super-smooth paving at
the California Speedway NASCAR oval.

I recall whipping past the start-finish line and thinking "Gawd, if the
NASCAR stockers shake like this I'd hate to drive one for 500 miles!" (That
and "Boy do those fence posts go past fast when you're only ten feet away
from them!")
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BryanUT wrote:

>What causes this?

With 100 horsepower on tap and a high center of gravity, you are accelerating
at about 3/4ths of a g, and you are transferring most of the bike's weight to
the rear tire, so the front tire loses its grip on the pavement and the front
end wiggles.

--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/sportbike/200710/1
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saddlebag wrote:

>Exactly. Feels a little uneasy when she comes back to the ground.
>Childsplay. You want uneasy, take a third shift job in a gas
>station...at night...anywhere in America...with a road name "Martin
>Luther King."

Binder dundat, in broad daylight in the part of northern Mexico called
"California".

--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/sportbike/200710/1
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On Oct 11, 7:33 pm, "BryanUT" <nestl... RemoveThis @comcast.net> wrote:
> I admit it, sometimes I engage in squid like behavior.
>
> And this leads to a question about motorcycle behavior and handling.
>
> Sometimes I like to acclerate really hard, taking the bike to near redline
> in first and then banging second gear.
>
> I can feel the front end "get out of shape" at the point of shifting. I
> guess I could best describe it as a "head shake". If you watch the pros
> (IOM. MotoGP, Superbikes) I think you see what I think I am feeling when
> they really get on the throttle.
>
> What causes this? I never felt this sensation on my noodle framed Nighthawk
> 750 (with much less HP). Althought I distinctly remember the noodly
> sensation in the corners on the Nighthawk, but never on the F4i.
>
> So I know the the F4i has a much more rigid frame. Anyway, when I make the
> bike behave like that it is really fun and yet I believe rightfully puts the
> fear of god in me.

Last time I raced my F4i (early September), I realized my steering
damper stopped working and sure enough, the bike would wobble all the
way down the front straight (when you need to be wide open). The bike
did not exhibit this problem anywhere else around the lap, but I had
to back off the throttle some to not let it get too out of shape,
particularly just before the braking zone. One thing I did from
Saturday to Sunday was increase trail, which was shorter than stock.
Also, check your rotors and make sure they're not warped. In terms of
riding technique, you may focus more on being very loose on the
handlebars (no death grip, as others said) and sit a little closer to
the front and hunch over the tank more (this will put a little more
weight onto the front). As far as shifting, you're loosest on the
bars if you're doing very quick and smooth clutchless upshifts.
Sometimes people momentarily tense up on the bars, whether they're
using the clutch or not. So you might want to take a look what you're
doing at the moment of upshifting.
 >> Stay informed about: Fun and fear 

On Oct 11, 6:33 pm, "BryanUT" <nestl... RemoveThis @comcast.net> wrote:
> I admit it, sometimes I engage in squid like behavior.
>
> And this leads to a question about motorcycle behavior and handling.
>
> Sometimes I like to acclerate really hard, taking the bike to near redline
> in first and then banging second gear.
>
> I can feel the front end "get out of shape" at the point of shifting. I
> guess I could best describe it as a "head shake". If you watch the pros
> (IOM. MotoGP, Superbikes) I think you see what I think I am feeling when
> they really get on the throttle.
>
> What causes this? I never felt this sensation on my noodle framed Nighthawk
> 750 (with much less HP). Althought I distinctly remember the noodly
> sensation in the corners on the Nighthawk, but never on the F4i.
>
> So I know the the F4i has a much more rigid frame. Anyway, when I make the
> bike behave like that it is really fun and yet I believe rightfully puts the
> fear of god in me.

There's nothing squidly about that, if you are doing it in a safe
area.

And, I know exactly what you mean about the old Nighthawk 750's. I
had '93 for ten years, and it was really a great UJM Standard - but
when playing with sportbikes there was a noodly wiggle in sweepers and
at speed. Unerving, but steady throttle changes, staying loose on the
bars, and leaning back in the seat a little usually kept it
predictable and relatively stable.

Loved that bike, though - toured on it extensively (one summer for
three months!) and put over 50,000 miles on it. Doesn't compare to
modern tech, but it did have a great style. However, I don't miss
that wobbly frame.
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On Oct 11, 7:33 pm, "BryanUT" <nestl... RemoveThis @comcast.net> wrote:

> I can feel the front end "get out of shape" at the point of shifting. I
> guess I could best describe it as a "head shake". If you watch the pros
> (IOM. MotoGP, Superbikes) I think you see what I think I am feeling when
> they really get on the throttle.

Never bothered me enough to do anything about it on the street. On
the track, even my RZ350 and my MZ660 and my EX500 required steering
dampers to quell this. The S4Rs *really* needed one, and GOT one.
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