One way to resolve the perceived "midget problem"

Oh, come on. If you took two riders going down a straight side-by-side
at 150 and then had them pull in the clutch and slow to half that, one
staying in a tuck and relying on full braking and one popping up to
use his body as a sail but not applying any brakes, which would get
there first? The brake man, no contest. Then take a larger rider and a
smaller one, do the same thing but have both rely on the sail effect
in neutral, and which gets slowed faster? Probably the larger one, but
not by much, his larger sail having to more than offset his greater
momentum through higher weight. And remember that the larger rider
under braking is carrying more weight up high, pretty much as high as
he can get it, which means there is more lever effect on the bike to
do a stoppie, one of the other limitations under braking. And even
with the rider as upright as he can get (limited by the low bars), the
fairing still limits the impact some. And at the GP level you'd expect
that a larger rider would have a larger fairing, so he's also fighting
that. [Fortunately for him, Hayden hasn't had that problem ;<)]

In the wet, the little will need to soften the

Yet somehow we don't see larger riders at the top level of the sport,
even with all these advantages they supposedly have - when was the
last time you saw a competitive rider in WSB or MotoGP at even 170
pounds? And forget about 250 or 125. But we do see plenty of very
small, very light guys, and more every day, it seems. And you admitted
earlier today that you would expect teams in 250 to hire pretty much
the lightest fast guys they could find, in your comeback on my age 18
minimum for GP. Funny how guys like you and sturd rely so much on
esoteric knowledge, even though it runs contrary to real-world
observation...

 

You have been trying to make the case that riding small bikes on the
way up is critical, essentially that at a certain point racing 125s is
better than riding anything else. I don't really agree with that, but
I wouldn't/couldn't say specifically what is better. I just see lots
of guys having made it to the very top who have different kinds of
racing experiences, and I don't really see anything that suggests
racing 125s makes for the best background. Yet today there seems to be
this developing belief that it is so, and mostly based on the fact
that the internal promotional path in GOP today is 125 to 250 to
MotoGP. I see that as an artificial construct, made that way by
politics, money and bikes that probably respond to smaller size and
lighter weight more than they ever have before, and that it has much
less to do with real ability. Today the bikes in MotoGP are being
shaped for the guys with this 125/250 background, but that's just
another artificial impact, I think - put different riders on them and
the development goes in a different direction.

 

Mark N will never win the Nobel in physics:

The drag equation has velocity as a squared term. The
momentum equation has it as a first order term. Sorry,
physics will win this argument.

Lesson over, you can continue to deny that now.

Never. Since the days of Black Bart, there weren't top level guys
that
were really big. I wasn't aware of racing before that but I'd bet it
was true before that.


Go fast. Take chances.
Mike S.

 

Mark N denies as expected:

I rest my case.


Go fast. Take chances.
Mike S.

 

Want to play the stats game? In the last 15 years including this one.

There've been 45 chances to go 1,2 or 3 in the top championship.

33 of those 45 slots were taken by people who came from 125 and/or 250.
73%

13 of the 19 people who've taken 1,2 or 3 in the last 15 years came from
125 and/or 250. 68%

8 from 15 of the last 15 years championships were taken by somebody from
125 and/or 250. 53%

 

so what, the argument isn;t the determining factor of drag,

it the determinig factor of braking of which drag is the lesser (much so)

no, wrong lesson. drag will be factor in achieving top speed, and
a minimal force in braking.


Bruce

 

Bruce Hartweg says:

That's wrong, as I've calculated and posted here months
ago. Aerodynamic drag force is greater than braking force
over some speed, depending on weight, speed, frontal
area, coefficient of drag, etc. But the speed for this to
happen is well within the capabilities of even a 125.


Go fast. Take chances.
Mike S.

 

Brutus says:

That's wrong. I'm not going to do these back of the
envelope calcs again, if you've had a college physics
class I'd love to see your analysis. Hope this pointer
works:

http://groups.google.com/group/rec....6b0a6a332a?lnk=gst&q=frontal#2a89796b0a6a332a

The difference in coefficient is probably negligable. The difference
in frontal
area is probably not, based more on height than weight. I think.

Mark N won't even go through the calcs and tell anybody where they
are wrong. Will you?


Go fast. Take chances.
Mike S.

 

not much. go to the riders page on motogp Nicky & Dani sitting
right next to each other. nicky maybe has an inch or so bigger silhouette
but much of that is behind the bike - when upright, probably just
friomt he logo up (fairly even) and the arms/shoulds (where Nicky is wider)
so take the bike - the majority of the area - same for both, and the body
(already a lesser percentage of total) and the differnec is maybe (pure guess)
10% (and that over mayber 30% total area).

skip the calcs for a minute and think!

when you are stopping hard, all the wight transfer is forward -
your hands and arms *pushing* on the handle bars to keep from
putting your face through the windscreen. the most force is
on the front wheel and the back wheel gets very light and even
off the ground in extreme case (either intentionally or not).
if the riders aero differences were the factor, that wind resistance
is pushing back on the rider head/chest the force to slow the
bike would be pulling back on the bars, s so the front of the bike
would rise not dive. have you ever seen/experienced a wheelie
while stopping? didn't think so.

Still not convinced? OK - try this for absolute proof - no equations
to argue relative weighting factors, no guessing about what the actual
drag for each rider is, etc. - a pure experiment that will answer this.


get on your bike, go out to some isolated area with a fairly long straight,
mark a fixed point as your brake marker. then get going to say 125 mph
when you get to the marker brake and determine how long/far it takes
to get you speed down to 60mph. do 3 runs as follows:

A) aero only - at the marker - popup and make yourself as big as possible,
do NOT apply brakes (and keep the clutch in so there is no engine braking)

B) brakes only - stay as tucked as possible - but brake (front/rear/engine)
as hard as possible.

C) both - stop like normal, hard braking and sitting up.


I bet you will find B far far shorter than A and the C is best but not
that much off of B.

Bruce

 

A bike's tendency to wheelie or stoppie in MotoGP on lots of factors.
But one major one is rider position. A lighter rider is a smaller
proportion of the overall weight and so has to move their body further
around the bike to have the same effect as a heavier one.

 

Bruce Hartweg misunderstands:

You can't without knowing a little of the physics behind it all.

Nobody said that braking forces weren't very important. But aero
forces, at high enough speed, are also.

That experiment doesnt tell you anything more than braking is
important, as is aero. If you measure deceleration during all of your
experiments, and the speed is high enough, you'd see what I"m talking
about.

Here's an experiment I tried once. Turn one at IRP, my first time on
a bigbore roadracer. I'd been racing 550's until then but was hired
gun on an endurance team with a built Honda 750, I think it was a
1012 or something. Whatever superbike of the day was ('82 I think).
First lap at speed during practice. There's a looong straight down
the drag strip, then a 2nd gear right sweeper you have to get stopped
for. This bike was an honest 165 mph bike, at least.

As on a middleweight, I tucked and charged. If I could see you
coming out of the corner coming onto the straight, I was going
to pass you with this beast. It was pretty evil handling though.
Anyway, through the gears, come to a guess at a brake marker
(still practice) and do what I'd always done - pop out of the tuck
at the same time as I grab a handful of brake. Mistake. I hung onto
the bars no problem but my helmet smashed back into my nose
HARD. Sorta scary and I vowed not to do that again.

As I trailed off into turn 2, I realized that my face was wet. Then
I figured out that my nose was bleeding. Back to the pits to clean
up......

C is far faster from 180 to 120, or some other numbers depending
on the bike/rider.


Go fast. Take chances.
Mike S.

 

Certainly with a "high-drag aero optimised for downforce" vehicle like an
F1 car the snap deceleration between upshifts at high speed comes in around
2G (hence the huge advantage gained with seamless shift gearboxes in those
vehicles...) but the fact that a MotoGP bike can do such big numbers in top
speed (say 208mph) with "only" 250BHP or so would suggest to me the bike
has really good aerodynamics!

 

I'm sure it did, but bashing your helmet into your nose didn't
really slow the entire bike that much.

 

You keep knocking down the same strawman here. I'm not saying
125/250's are the "best" path. I'm saying they're important (at least
for many riders) in their development process. They're also important
if you want to go the GP route specifically. I seem to be hearing a
circular argument from you, that GP bikes have developed 250'ish
characteristics because of the riders coming from 250's. So if you
don't like that, I already asked you what you want from the series. I
happen to like any bike with a 250'ish character to it. I like
MotoGP, 250's, and I much prefer 600 racing to superbikes. Not sure
what that means, but just because you or I have a particular
preference, it doesn't automatically bless or doom any one series. I
feel like there is currently a decent spread of different kinds of
roadracing series worldwide for virtually any fan's tastes. Do you
want MotoGP to be more like superbike? That's what I seem to be
hearing.

 

As I stated in another response, we have the other direction -- it's
called World Superbike.

 

You're confusing my argument. If you had two riders slowing from 150
to 75, as you suggest, both using brakes to their fullest potential,
and both relying on aerodynamic drag to _contribute_ to their braking,
then my point holds. In fact, I recall reading a paper stating that a
modern sportbike rider using maximum braking in a straight line at 120
mph can create additional 25% deceleration just from the drag, when
popping out of the bubble. I don't know about you, but I can tell you
for sure that at speeds exceeding 100 mph, one has to really adapt a
different way of thinking of their braking distances when first
dialing it in at a new track precisely because of the aero variable.

 

Knowing the sport firsthand is esoteric to you? Okay...

Now I'm confused. You're saying superbike is not hiring riders over
170 lbs. But they're not hiring from 250 classes directly the same
way MogoGP does. Is that another extension of this European
conspiracy? Or is it because that's what the superbike technology and
rules of today dictate? If it's the latter, could it then be possible
that hiring even smaller riders might be what the MotoGP technology
and looser rules might dictate there?

 

Bruce Hartweg says:

How much force you think that took? And that's just the area
of my helmet.


Go fast. Take chances.
Mike S.

 

obviously enough to bash your face, and the area of a helmet
is pretty similar across a variety of different sized riders.

look, i am not saying there is no such thing as aerodynamic forces,
or that they aren't a factor in breaking, I *am* saying that they
1) are not the largest force in breaking, 2) the percentage they
contribute drops fast as the bike slows, 3) are not dramatically
different between different riders. so I believe there is no advantage
for *larger* riders due to this (or that any small advantage is a
wash due to needing more force to stop more mass).

Bruce

 

This is a little off-topic, but whaaaaaat are you talking about?!

If you're holding yourself up with your arms under heavy braking,
you're not doing it right. Plain and simple. On a modern sportbike,
you should be able to anchor yourself with your thighs, feet, and
lower abs under braking, while keeping your arms relatively loose.

This simply doesn't follow. Take out a piece of paper and draw the
vectors acting on the bike and rider in different places. Wind
resistance vector will be pushing the rider's upper body back, but it
won't be the only force. The bike is essentially acting upon the
rider by creating the braking force between the road and the tire,
decelerating the whole thing. Since the system is not traveling at
its terminal velocity, and neither is any of the 2 components
separately (bike or rider's torso), there is some uncancelled momentum
that has to get eaten up by the braking force. But it's not the full
momentum, had there been no aero drag at all. Is this making sense?
It's a little hard to explain without a visual.