Getting Started on Rollers

Robert Chung says...

Quoted message said:

Looks pretty linear.

Not to me. More like parabolic.

Mad Dog said:

[email hidden] says...

Quoted message said:

That is 0.6 mph. At this ferocious speed, I'd better be a damn good
bike handler to stay upright long enough to crash into the wall 7 feet away.

No, no no! The skid mark was 7'. The crash site was 15'. If you're gonna get
all cutesy quantitative, the least you can do is read accurately.

You've made a few assumptions that skew your result to the down side. For
example, the combined body mass plus bike for me at that time was about 76 kg.
And although my solo on-road flat sprint max at that time was a bit under 40
mph, on rollers it was higher. But the big mistake your model makes is that
after my tires hit pavement, I was still pedaling intentionally (to generate the
7' skid mark), adding enough energy to the system to completely swamp your
flawed model. But if you look back, I never claimed a velocity and never
insinuated that it was like being shot out of a cannon.

I've also accidentally gone off rollers a couple of times - where I wasn't
intentionally trying to do a burnout or to ride away. I never managed to do it
without leaving some kind of skid mark (or carpet damage). Before I got exiled
to the basement, I put a skid mark on the kitchen vinyl floor. That was the
only reasonable place in that house to use a doorway to ride in. And realize
that this was long ago when I was using cleats and toe clips/straps. It's
totally different now when you can hit the brakes, pop a foot out and catch
yourself. 6 to 12" is not a long skid mark on a vinyl or painted cement floor,
even if you're not trying to leave one. I don't miss rollers, that's for
certain. Anyway, take your bogus model there, Physicus Fakicus, and shove it
where the sun don't shine.

You really don't know when to give up, do you??? Try this: don't post
any more declarations or defenses to your goofy-assed claims about skid
marks and eventually most of the folks in RBR will forgot you ever made
the claims. In time, it'll be as if you never said them. We'll get on
with our lives, and you can get on with yours.

So, really, you expect us to believe that from what is essentially a
standing start (albeit with the wheel turning at some speed) that you
were able to propel a bicycle forward for a minimum of 6, or perhaps
12, feet before the traction of the tire overcame the rotational force
of the wheel and laid a skid mark that far???

So, how much do you want for that bridge?

William Asher says...

Quoted message said:

That's plenty of time to figure out something was a little off and stop
pedaling.

I won't blame you for not reading the whole thread. The 7' skid mark story goes
like this (bikees drinking after-ride beers circa early 80s):

Newbie kid: "I wanna get rollers but I'm afraid of falling off of them and
getting hurt or trashing my bike"

Skeptic: "No problem, if you fall off you just plop over on your side. Do it in
a door frame and just catch yourself."

Newbie: "You don't go forward?"

Skeptic: "Not more than a couple of inches"

Me: "I've gone more than a few inches, 2 to 3' easy."

Skeptic: "[censored]!"

etc., etc. The gang assembles in the basement, bets are waged and since they
forgot to tell me I had to quit pedaling, I didn't, hopped off at the highest
wheel speed I could generate, kept pedaling and left 7' skid mark, plowed into
boxes along basement wall. Fresh round of beers, thousand laughs.

Bob Schwartz says...

Quoted message said:

If I told you that riders at constant power on a
velodrome accelerate in the corners, what would
you tell me?

I'd tell you to get out your chalk board & calculator and prove it.

(note that I did not agree nor disagree with your hypothesis)

William Asher says...

Quoted message said:

If the stripe was caused by fear, it seems you invented the bicycling
version of a Cleveland Steamer. Maybe it could be named after you, the
Mad Dog Steamer.

That would never sell.

Quoted message said:

It
is a sad fact that the only person I succeeded in trolling was you, which
is sort of like catching a cunner when you are going for bluefish.

You need to study up on your bait.

Quoted message said:

The fun kids didn't want to play with me regardless of my mom's wishes, but
they're mostly fat and bald now so in a small way there is some justice in
the universe.

Yes indeed!

Mad Dog said:

William Asher says...

Quoted message said:

That's plenty of time to figure out something was a little off and
stop pedaling.

I won't blame you for not reading the whole thread. The 7' skid mark
story goes like this (bikees drinking after-ride beers circa early
80s):

Newbie kid: "I wanna get rollers but I'm afraid of falling off of them
and getting hurt or trashing my bike"

Skeptic: "No problem, if you fall off you just plop over on your side.
Do it in a door frame and just catch yourself."

Newbie: "You don't go forward?"

Skeptic: "Not more than a couple of inches"

Me: "I've gone more than a few inches, 2 to 3' easy."

Skeptic: "[censored]!"

etc., etc. The gang assembles in the basement, bets are waged and
since they forgot to tell me I had to quit pedaling, I didn't, hopped
off at the highest wheel speed I could generate, kept pedaling and
left 7' skid mark, plowed into boxes along basement wall. Fresh round
of beers, thousand laughs.

Well now that you explain it, you don't seem nearly so retarded.

--
Bill Asher

In article <[email hidden]>,

Mad Dog said:

Joe Pro says...

Quoted message said:

Not that I do not believe you, but it is impossible. I once was involved in
setting up some roller races at a large regional mall. We had to demonstrate
to the mall manager that if someone fell off that he would not go crashing
into the crowd or a plate glass window. I did the demonstration and hopped
off of the rollers at speed. No forward motion whatsoever, and I did a track
stand.

Dunno what to say about that, Joe. I only know what I've seen. Not only have I
seen forward motion when others rode off, I've ridden it myself into the
basement wall with boxes flying all over the place.

Your "no forward motion whatsoever" claim doesn't make physical sense. If
you're in a big gear and spinning, it's not unreasonable for the wheel to be
going at the equivalent of 40 mph and most folks I know can easily maintain 25
mph on rollers with no load unit strapped on. That's a fair bit of angular
momentum on the average bike wheelset. Are you saying that the angular momentum
of two spinning wheels just evaporates when you go off the rollers? It's gotta
go somewhere. Or did you develop a process to convert it into pizza? If so,
send me a veggie deluxe, light on the cheeze, very heavy on the garlic and
jalapenos because it's gettin' deep here and I want to contribute to the stench.

Hey! I did the math.

Mass of tube, tire, and rim:
M = 0.5 kg

Radius of wheel:
r = 0.35 m

Moment of inertia:
I = Mr^2 = 0.0625 kg-m^2

Angular speed:
w = 50 / 11 * 180 / 60 * 2pi = 85 / sec

Kinetic energy in two wheels:
2 * I * w^2 / 2 = 450 J

Kinetic energy of 100 kg traveling at 3 m / sec:
450 J + small amount in energy of spinning wheels.

Note that 1 m / sec is 3.6 km / hr.

A bicycle and rider in a trainer can build up kinetic
energy in the spinning wheels equivalent to the kinetic
energy a forward speed of ~ 10 km/hr. Of course some of
the energy in the spinning wheel will become skid marks
when the bicycle comes off the trainer. A forward speed of
5 km / hr is plausible.

--
Michael Press

In article
<[email hidden]>,

Quoted post said:

Mad Dog said:

Your "no forward motion whatsoever" claim doesn't make physical sense. If
you're in a big gear and spinning, it's not unreasonable for the wheel to be
going at the equivalent of 40 mph and most folks I know can easily maintain 25
mph on rollers with no load unit strapped on. That's a fair bit of angular
momentum on the average bike wheelset. Are you saying that the angular momentum
of two spinning wheels just evaporates when you go off the rollers? It's gotta
go somewhere. Or did you develop a process to convert it into pizza? If so,
send me a veggie deluxe, light on the cheeze, very heavy on the garlic and
jalapenos because it's gettin' deep here and I want to contribute to the stench.

Physics Boy,
Okay, let's work out this "angular momentum" thing. Suppose my
wheels (both of them together) weigh 2.5 kg. Of that maybe 0.8 kg is
at the hubs and has negligible angular momentum. Let's treat the
remaining 1.7 kg as if it was all at the edge (rims and tires) at
0.33 m radius. Suppose I'm roller-riding at the equivalent of 30 mph
(13.4 m/s). The angular momentum in my wheels is, L=mvr =
1.7 kg * 13.4 m/s * 0.33 m.

Angular momentum is not the quantity to consider.
Kinetic energy is.

1.7 * 1/2 * (13.4)^2 Joule.

Now convert this to 85 kg moving at speed v.

1.7 * 1/2 * (13.4)^2 = 85 * 1/2 * v^2.

Quoted message said:

Now I bunny hop off the rollers and onto the floor. Assume that
I stop pedaling, but my tires instantly grab the floor with perfect
traction, meaning no skidding, and convert that angular momentum
into linear momentum. This is unrealistic (there would surely be
skidding) but gives the maximum possible forward velocity.
The linear momentum is P=L/r = 1.7 kg * 13.4 m/s. But this
has to push the weight of me and the bike, say that's 85 kg.
I go flying forward at ... 0.27 meters/sec. That is 0.6 mph. At
this ferocious speed, I'd better be a damn good bike handler to
stay upright long enough to crash into the wall 7 feet away.

See my other post on this matter.

--
Michael Press

Mad Dog wrote:
[nitpicking about factors of 5-10%]

Quoted message said:

But the big mistake your model makes is that
after my tires hit pavement, I was still pedaling intentionally (to generate the
7' skid mark), adding enough energy to the system to completely swamp your
flawed model. But if you look back, I never claimed a velocity and never
insinuated that it was like being shot out of a cannon.

A bunch of people responded to the OP, saying that when you
fall off rollers, you don't ride through the window, unless you are
crazy enough to keep pedaling. You called these people out by
talking about what a legendary rug-burn you laid down. After forty
posts arguing with you, you finally say Oh by the way, I was
intentionally pedalling.

[email hidden] says...

Quoted message said:

A bunch of people responded to the OP, saying that when you
fall off rollers, you don't ride through the window, unless you are
crazy enough to keep pedaling. You called these people out by
talking about what a legendary rug-burn you laid down. After forty
posts arguing with you, you finally say Oh by the way, I was
intentionally pedalling.

My first reply was to William Asher's reply. At that time, the OP and Bill's
post was all that was showing up on my news server. I don't recall Bill or the
OP saying anything about stopping pedaling and there was no gun to my head to
force all the details about my record-setting skinny-tire burnout.

So I didn't call anyone out. But I did have a lot of fun watching you guys get
all in a huff. I should have sawn that part of the basement floor out, put
varnish over the skid mark to preserve it and then pressented it to the rbr hall
of fame.

William Asher says...

Quoted message said:

Well now that you explain it, you don't seem nearly so retarded.

Hey, man, I'm not nearly as retarded now that I no longer ride off of rollers
after drinking a bunch of beers. But really, thanks for your support.

Mad Dog said:

No, no no! The skid mark was 7'. The crash site was 15'. If you're gonna get
all cutesy quantitative, the least you can do is read accurately.

You've made a few assumptions that skew your result to the down side.

Get psychological help. You've got issues.

JT

****************************
Remove "remove" to reply
Visit http://www.jt10000.com
****************************

Mad Dog said:

I was still pedaling intentionally (to generate the
7' skid mark), adding enough energy to the system to completely swamp your
flawed model. But if you look back, I never claimed a velocity and never
insinuated that it was like being shot out of a cannon.

WTF???

You're an idiot.

JT

****************************
Remove "remove" to reply
Visit http://www.jt10000.com
****************************

"Mad Dog" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Carl Sundquist says...

Quoted message said:

But I think I understand it now: he was using a resolution of 4 kilometers
when he measured the 7 foot skid.

No, no no! I was using a resolution of 4 nanometers when we failed to
detect
your brain!

Can't see the forest for the trees, eh?

Carl Sundquist says...

Quoted message said:

Quoted message said:

No, no no! I was using a resolution of 4 nanometers when we failed to
detect your brain!

Quoted message said:

Can't see the forest for the trees, eh?

No one taught you that you shouldn't think with your wood?

William Asher said:

I vaguely recall that h2 lives in Seattle and if that is so, I also
strongly suspect I have actually seen her in person on the BGT. Not that
has anything to do with anything here, I just wanted to point that out.

i haven't been on the bgt for at least a year (just fyi). now i spend
most of my time riding around beautiful (cough) tukwila. did you know
that tukwila is an american indian word meaning "place where the
hazelnuts grow"? finding that fact out depressed me. now it's the "land
of shopping malls and office parks". but i haven't been out at all
recently, i need to buy new tires (yes, still). the old ones are too
scary to ride on.

i love how people from rbr see me but never say "hi" (hmm). if it wasn't
for suz weldon recognizing my existence, i'd be a total rbr reject...
heather
ps. when bill talks about sex, he isn't trolling for me, he talks about
sex all the time, even when he thinks i'm not listening.

Michael Press said:

Quoted message said:

Now I bunny hop off the rollers and onto the floor. Assume that
I stop pedaling, but my tires instantly grab the floor with perfect
traction, meaning no skidding, and convert that angular momentum
into linear momentum. This is unrealistic (there would surely be
skidding) but gives the maximum possible forward velocity.

Quoted message said:

Angular momentum is not the quantity to consider.
Kinetic energy is.

I'm not so sure. Because the tires instantly grab the floor
with perfect traction, it's effectively an inelastic collision
(like colliding bodies sticking together). KE is not conserved in
inelastic collisions. Linear momentum is always conserved
in the absence of an external force. One could argue about the
idea that the wheels' angular momentum is instantly converted
into linear momentum, but I thought that captured the putative
process we are talking about reasonably well. For there to be
no skidding, the tires have to grab the floor with a fair amount
of friction.

What I did omit to say was that the original linear momentum
of the total system (rider, bike and floor) was zero, so the
post-hop momentum is positive for the rider moving forward and
negative for the floor moving backward. Of course the earth is
very heavy, so unless I have grossly underestimated Mad Dog's
spin, it doesn't make a difference for the relative velocity.

Mad Dog said:

7' skid mark story goes
like this (bikees drinking after-ride beers circa early 80s):

MadDog, I know you wouldn't BS me, so I'm sincerely interested in knowing
what kind of cluster you had in the early 80s that had an 11-tooth cog.
Thanks!

Mark
ps. I just couldn't resist so, like a dumbass, I went out in the garage and
hopped off the rollers at ~15 mph and went absolutely nowhere. It's not easy
to bunny hop off the rollers btw. I'm trying to decide if it is worth the
risk to my wheels and frame to do it at higher speed. Plus, if I don't get
much lift, the little notches that the drum axles sit in will shred my
tires. We do the craziest things in the name of science, eh?

h squared said:

i love how people from rbr see me but never say "hi" (hmm). if it
wasn't for suz weldon recognizing my existence, i'd be a total rbr
reject... heather

It was a while back, you don't know me from Adam, or Eve for that matter,
so it was more like: "I wonder if that skater chick is h2? Looks kinda
like her picture but why is she beating the [censored] out of that guy wearing
the 'All Mad Dogs Go to Heaven' t-shirt? Best not get involved."

Besides, the light changed and I had to get around a recumbent, two
moms pushing double-wide strollers, a brace of nuns in wheelchairs, the
homeless man with all the cleaning supplies on his balloon-tire cruiser,
and five guys in local team colors stopped in the middle of the path to
discuss what gear to use for the upcoming hill before the guy with the
katana in the back scabbard caught up with me.

--
Bill Asher

h squared says...

Quoted message said:

ps. when bill talks about sex, he isn't trolling for me, he talks about
sex all the time, even when he thinks i'm not listening.

Well, hopefully you didn't take my question seriously but if you have a story
about rollers, I'm sure some of the guys around here could use another cold
shower. I never understood that cold shower thing myself - seems like the
possibility of permanent damage is too real. Anyway, it was like an obvious
lead by Bill and somehow, I couldn't let it go by.