need help picking out a bike

[David Martin]

On 1/10/04 10:21 am, in article
[email protected], "Mark Thompson"
<[email protected]> wrote:

>> So now I can ride up hills faster than my colleagues (who are much
>> lighter)
>
> ITYM "My colleagues are unaware that I'm racing them"

No, my colleague was quite aware that there was an element of competition in
the offing..

...d

 

[David Martin]

On 1/10/04 10:40 am, in article [email protected], "Peter
Clinch" <[email protected]> wrote:

>
> Given that that's the same as Jon's best and he is young, fit, fast and
> actively trains to go faster, I am doubtful.

Wheras my best in recent times without particular emphasis on training to go
harder was 70km/h freewheeling. Had I tried, I could have added a bit to
that as I wasn't expecting to really go that fast.

Fastest ever was 75km/h. I weigh considerably more than jon and am shorter
and rounder. So I have a faster aspect ration and a better sa/volume ratio
as well.

I don't think 48 on a slick tyred MTB is unreasonable given the right hill
and enough weight.

...d

 

[David Martin]

On 1/10/04 10:50 am, in article
[email protected], "Mark Thompson"
<[email protected]> wrote:

>> Given that that's the same as Jon's best and he is young, fit, fast and
>> actively trains to go faster, I am doubtful.
>
> I thought it had more to do with the size of the hill rather than the
> fitness of the rider - you don't need to be fit to tuck up into a small
> ball and start screaming as you approach 50mph... (although 48 does sound
> awfully high for an upright position - do the hill again!)

I've topped 70km/h on the MTB with semi-slick tyres (vredestein spider) on.
Scary thing was that it was a shared use path.

...d

 

[Gawnsoft]

On Thu, 30 Sep 2004 17:48:20 +0100, David Martin
<[email protected]> wrote (more or less):
....
>The resistance to motion through the air is related to the cross sectional
>area and the speed.

And the shape.

(I was originally going to add this to Jon's earlier post, but I'm
still crawling down the thread...)


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[Gawnsoft]

On Thu, 30 Sep 2004 22:45:31 +0900, James Annan
<[email protected]> wrote (more or less):

>Gawnsoft wrote:
>
>> Intuitively, the amount of work done to provide the angular
>> acceleration
>
>What work done to provide the angular acceleration?

From Dave's quote from the BHPC newsletter:
"the additional effort required to turn bike and rider through 180
degrees .... [calculated to knock] your average speed down from 63
km/h to 56"


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[Peter Clinch]

David Martin wrote:

> I don't think 48 on a slick tyred MTB is unreasonable given the right hill
> and enough weight.

The more I think about this the more I'm prepared to agree with that
aspect, but my doubts over 30 mph on near flat for an overweight chap on
a gaspipe bike remain and there's little I can do to shake them. And I
doubt the speed is misreading on one and not the other.

Beyond that, we don't actually know if Babylon Hill is the "right hill".
The only one of the name Streetmap turns up in the UK is good, but but
not good enough IMHO (70m descent over a kilometre) on the A30 just
outside Yeovil). Martin, is that the one, or am I looking in the wrong
place?

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email protected] http://www.dundee.ac.uk/~pjclinch/

 

[Gawnsoft]

On Fri, 01 Oct 2004 06:26:40 +0900, James Annan
<[email protected]> wrote (more or less):

>Dave Larrington wrote:
>
>> Moreover, the additional effort required to turn bike and rider through 180
>> degrees has a significant effect; Robert calculates the extra effort
>> required knocks your average speed down from 63 km/h to 56.
>
>I don't believe that. What is the basis for that calculation? It sounds
>to me that some people don't realise that a centripetal acceleration
>does no work, being perpendicular to the direction of motion.

The fact that a force is applied normal to the direction of travel to
achieve a component of travel normal to the previous direction of
travel does not mean there is no work done, surely?

An ice-skater can change from spinning slowly or quickly in place,
without additional motive effort, but that's with constant angular
momentum. But to go from a straight line into a turn, involves enough
energy to cut ice with a steel blade.

In a car, turning a corner causes a significant amount of tyrewall
flex, with energy losses as heat (and if you try too hard, loud
squealing noises)

Thinking about a body on a 2D frictionless surface, (or a hovercraft)
to effect changes in direction (say with a jet or a propellor)
requires substantial effort to be expended, or diverted from the
previous straight line effort, say by turning the propellor to face a
new direction.

So I don't see how the cyclist can do it without effort. Unless he's
on a wall of death. Or off the flat section at the inner track of the
velodrome, and up on the banking.



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[Gawnsoft]

On Fri, 01 Oct 2004 10:06:14 +0100, Martin Wilson
<[email protected]> wrote (more or less):

>On Thu, 30 Sep 2004 22:40:28 +0100, Jon Senior
>>> One other point is the tyres are pumped up to high pressures. I think
>>> its about 63psi on the back and about 55 psi on the front. Not sure if
>>> I've set them correctly but it seems that I need slightly higher
>>> pressure at the back. I was thinking of lowering the pressure at the
>>> front a little more perhaps to 50psi.
>>
>>Sorry. Had to laugh. The tyres on my fixer are both at 110psi, the Giant
>>runs at 125psi, and the recumbent at 80/100 front/rear.
>>
>
>Well I did think I had them at high pressure as people at work have
>commented on how solid and high pressure they are. I mean its a big
>tyre 26x1.50. Of course I didn't consider them high pressure compared
>to a racing bike tyre.
>
>>And pressure is not so relevant except by comparison to the same tyre at
>>a lower pressure. Both road bikes are running on 23mm tyres. If your's
>>is an MTB then even with slicks they're likely to be at least 28mm and
>>possibly wider.
>>
>>From my own experience I'd echo Peter's comments that it seems likely
>>that your speedo is miscalibrated. I'm reasonably fit, and an above
>>average sprinter and I top out on the flat at 35mph if I'm fresh and I
>>_really_ push it hard. The fastest I've ever done was 48mph and that was
>>on a very heavy fully laden recumbent on a 12% gradient (Going down...
>>obviously!).
>>
>>If we are wrong however, I seriously suggest you start planning which
>>races you are going to enter in 2005.
>>
>
>I've not checked the wheel settings yet but did notice on the computer
>that my maximum speed ever on the bike is 48.1mph. Not sure when this
>was but its most likely going down Babylon Hill. My overall average
>speed is 7.7mph :-(
>
>Seems a low average considering people seem to think I've set the
>computer wrong. The Lidl cycle computer I use has two settings near my
>tyre size and they are 26x1.25=1980mm circumference and 26x1.75=2040
>circumference so I set my 26x1.50 to 2010 circumference which wasn't
>listed but seems the logical setting. Perhaps I ought to measure the
>tyre around to see how accurate this is. Ok I've just measured the
>circumference and it came to 202cm so 2020mm. However resting the tape
>measure on the tyre after selotaping the start may have added a few mm
>so I suspect the 2010 setting is pretty much spot on.

Go down to a path/pavement/road with your bike, a tyre pump, a tape
measure and a bottle of washing up liquid.

Pump your tyres to the pressure you intend to keep in your tyres.

Drop a splodge of washing up liquid on the path

Ride your bike over the splodge for at least one full revolution of
the front wheel.

Measure the distance between the two rearward edges of the two splodge
marks. (The original one, and the one your bike made one rev after it
ran through the original one).

....


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[Clive George]

"Gawnsoft" <[email protected]> wrote in
message news:[email protected]...

> So I don't see how the cyclist can do it without effort. Unless he's
> on a wall of death. Or off the flat section at the inner track of the
> velodrome, and up on the banking.

We are already talking about velodromes, and being on the banking

Mr Obree said the banks were harder work, but that was in holding his body
up.

cheers,
clive

 

[Gawnsoft]

On Fri, 01 Oct 2004 10:27:20 +0100, Martin Wilson
<[email protected]> wrote (more or less):

>
>>> As I say I'm pretty sure I'm capable of more than 60, possibly
>>> somewhere near 80 or beyond.
>>
>>Measure it to be sure though. But also note there's more to applying
>>the necessary power than just ramping up the cadence. To go at 30 mph
>>you'll need to supply ~4 times the total power you supply to go at 15,
>>and that can come in either faster cadence in the same gear or pushing
>>harder, but cadence increases alone would have to maintain the power
>>through the pedal stroke. Pushing down with the same power at 80 rpm as
>>40 rpm, especially with platform pedals where you're not formally
>>attached to them, is easier said than done, and you're probably looking
>>at needing more power for any stroke, not less, to get to 30 mph.
>>
>
>I don't know the theory of how peddling works but I have found that if
>I peddle faster the bike goes faster and if I'm on a very slight
>gradiant in my favour I can go upto about 30mph. My thick tree trunk
>type legs are able to do a cadence beyond 60 that much I'm sure of as
>I can gauge a second in my head and I know I'm beating it. I've
>checked so far;
>
>a)the speedo is set at mph
>b)the wheel size is right

I think you've checked the unladen wheel size.

I'm just guessing, but I expect the tyre will compress when you seat
your 20-odd stone on your bike.

That's why I suggest the washing-up liquid method - it measures what
the effective circumference is when you're on the bike.

Having said that, I'm sure it won't make a huge difference, but it
will bring the speed /down/ the way, and I'd expect by about 3% at
most, (i.e. the bike settles by at most ~9mm when you sit on it).



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[Jon Senior]

In article <[email protected]>,
[email protected] says...
> And the shape.
>
> (I was originally going to add this to Jon's earlier post, but I'm
> still crawling down the thread...)

Indeed. Drag from turbulence is significant, as demonstrated by the
(anecdotal and unscientific) observation that my recumbent with wicker
basket is faster than the same bike without the basket.

Jon

 

[Jon Senior]

In article <[email protected]>, Ged.1dfz7y@no-
mx.forums.cyclingforums.com says...
> But he also has a lower mass in the first place and hence will need
> less energy to obtain the same acceleration.

All other factors being equal, two bodies subject to a gravitional pull
will accelerate at the same rate.

> Fat people aren't large flat objects.

You noticed?

> Air resistance is related
> to volume as the cross section of an object may alter along its length
> (hence wind tunnels)

Air resistance is related to volume, but in a non-proportional manner
(Expect in the case of the spherical cow!). The reason for mentioning a
long flat object is that you can change its air resistance by changing
its angle relative to its velocity without changing its volume.

Air resistance is actually a factor of the full 3D shape as drag occurs
from turbulence caused by the breakup of laminar flow as well as due to
the displacement of air. In a simplified analysis however, you are
better talking of cross-sectional area than volume since the former is
more likely to have an effect on air resistance than the latter.

Which brings us back to:

A fat man has a higher mass for a non-proportionally higher cross-
sectional area. Thus the energy imposed on him due to wind resistance
will not increase propotionally with his mass and will have a lesser
proportional impact on his velocity than it does on the lighter man.

Simple really!

Jon

 

[David Martin]

On 1/10/04 12:54 pm, in article [email protected], "Peter
Clinch" <[email protected]> wrote:

> David Martin wrote:
>
>> I don't think 48 on a slick tyred MTB is unreasonable given the right hill
>> and enough weight.
>
> The more I think about this the more I'm prepared to agree with that
> aspect, but my doubts over 30 mph on near flat for an overweight chap on
> a gaspipe bike remain and there's little I can do to shake them. And I
> doubt the speed is misreading on one and not the other.

You are assuming that all the acceleration was on the flat..
Having said that, getting to 30 on anything less than a reasonably
noticeable hill (definitely not flat) is not easy.

...d

>
> Beyond that, we don't actually know if Babylon Hill is the "right hill".
> The only one of the name Streetmap turns up in the UK is good, but but
> not good enough IMHO (70m descent over a kilometre) on the A30 just
> outside Yeovil). Martin, is that the one, or am I looking in the wrong
> place?
>
> Pete.

 

[Peter Clinch]

David Martin wrote:

> You are assuming that all the acceleration was on the flat..

Indeed I am. It seems odd to cite a peak speed for the flat having just
run down a hill, however...

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email protected] http://www.dundee.ac.uk/~pjclinch/

 

[Jon Senior]

In article <[email protected]>,
[email protected] says...
> Pray tell where I claimed that it would? It would be better if you
> disagreed with what I said rather than something I doid not say.

You said: "At least, with similar wind-resisting properties they get to
the bottom faster, though they may initially accelerate at the same
rate."

Initially accelerate at the same rate implies that this acceleration
would change as they got faster.

> The lighter one will certainly be accelrating more slowly as soon as
> either have any speed, since it will have less accelerating force
> (gravity) and teh same retarding force (wind resistance).

Although as you may have noticed (No doubt with a wry grin) I'm
currently arguing that very point elsewhere. Thankfully no formal
agreement re trips to the moon or carbon fibre bicycles took place so i
shouldn't have to reciprocate my demands on you.

> Think very very carefully - you are honestly claiming that if you drop
> a bowling ball from head height it will strike the ground at teh same
> instant as an inflated childs balloon dropped from teh same height at
> the same time?
>
> Forget physics (since it's obviosly misleading you), just try it -
> bowling balls fall quite fast, but inflated balloons float slowly
> downwards - taking a second or two to drop that sort of distance.

Ooops!

Jon

 

[Gawnsoft]

On Fri, 1 Oct 2004 13:13:50 +0100, "Clive George"
<[email protected]> wrote (more or less):

>"Gawnsoft" <[email protected]> wrote in
>message news:[email protected]...
>
>> So I don't see how the cyclist can do it without effort. Unless he's
>> on a wall of death. Or off the flat section at the inner track of the
>> velodrome, and up on the banking.
>
>We are already talking about velodromes, and being on the banking

Actually, we were talking about being at velodromes, and being right
down at the inmost cyclable track - i.e. down off the banking.

>Mr Obree said the banks were harder work, but that was in holding his body
>up.

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[Clive George]

"Gawnsoft" <[email protected]> wrote in
message news:[email protected]...
> On Fri, 1 Oct 2004 13:13:50 +0100, "Clive George"
> <[email protected]> wrote (more or less):
>
> >"Gawnsoft" <[email protected]> wrote in
> >message news:[email protected]...
> >
> >> So I don't see how the cyclist can do it without effort. Unless he's
> >> on a wall of death. Or off the flat section at the inner track of the
> >> velodrome, and up on the banking.
> >
> >We are already talking about velodromes, and being on the banking
>
> Actually, we were talking about being at velodromes, and being right
> down at the inmost cyclable track - i.e. down off the banking.

The black line is on the banking. If you're trying for a record, you can't
help but be on the banking, as they put bits of foam below it.

cheers,
clive

 

[Dave Larrington]

Gawnsoft wrote:

> Actually, we were talking about being at velodromes, and being right
> down at the inmost cyclable track - i.e. down off the banking.

For certain values of "we" only. I wasn't.

--

Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
===========================================================
Editor - British Human Power Club Newsletter
http://www.bhpc.org.uk/
===========================================================

 

[James Annan]

Gawnsoft wrote:

> On Thu, 30 Sep 2004 22:45:31 +0900, James Annan
> <[email protected]> wrote (more or less):
>
>
>>Gawnsoft wrote:
>>
>>
>>>Intuitively, the amount of work done to provide the angular
>>>acceleration
>>
>>What work done to provide the angular acceleration?
>
>
> From Dave's quote from the BHPC newsletter:
> "the additional effort required to turn bike and rider through 180
> degrees .... [calculated to knock] your average speed down from 63
> km/h to 56"

yebbut that is just restating the same nonsense a second time...what is
this "additional effort" and why doe it arise?

As I said before, the centripetal component of acceleration does no
work...this is very trivial school level mechanics (at least, it was
when I was at school).

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

 

[Ian Smith]

On Fri, 1 Oct, Jon Senior <jon@restlesslemon_DOT_co_DOT_uk.remove> wrote:
> In article <[email protected]>,
> [email protected] says...
>
> > Pray tell where I claimed that it would? It would be better if you
> > disagreed with what I said rather than something I doid not say.
>
> You said: "At least, with similar wind-resisting properties they get to
> the bottom faster, though they may initially accelerate at the same
> rate."
>
> Initially accelerate at the same rate implies that this acceleration
> would change as they got faster.

Indeed, and it does - both objects acceleration reduces the faster
they get. This is fact. Are you still disputing it?

In teh particular case in question (balloon v bowling-ball falling 2m)
teh balloon acceleration probably reduces to zero during teh drop,
since it will reach terminal velocity very quickly.

> > Think very very carefully - you are honestly claiming that if you drop
> > a bowling ball from head height it will strike the ground at teh same
> > instant as an inflated childs balloon dropped from teh same height at
> > the same time?
> >
> > Forget physics (since it's obviosly misleading you), just try it -
> > bowling balls fall quite fast, but inflated balloons float slowly
> > downwards - taking a second or two to drop that sort of distance.
>
> Ooops!

Hmm. Does that mean you did try it and broke something?
Do I get my flashy bicycle now?

regards, Ian SMith
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