Is there less rolling resistance on wet roads?



Roadie_scum wrote:
> Peter Wrote:
>> For many years I have noticed that cycling on wet roads appears easier
>> than on the same roads when they are dry. I suppose there must be some
>> reduction in friction between the tyre and the wet road when
>> travelling
>> in a straight line, just as there is when travelling around a corner.
>> Anyone know if this is true?
>>
>> Peter

>
>

Any rider (racer) who has ridden behind a bike knows that you get mighty
wet from the water thrown up by the tires in front - this takes energy.
There may be less friction, but in a straight line it would be
negligible I think, and certainly much less than our great bogey of air
resistance (friction).
Halcyon
 
On 2007-08-22, John Pitts (aka Bruce)
was almost, but not quite, entirely unlike tea:
> On 2007-08-22, TimC <[email protected]> wrote:
>> I'm super happy about my commute home these days (in the rare event
>> when I ride it). Away from the sun, and almost always a tailwind with
>> the prevailing westerlys.

>
> ...and downhill. Don't you work on top of a mountain, Tim?


Only obviously works for 6 or so of the 29 kilometers, although it
could be said the rest are a downward trend, and I certainly do feel
like I'm going faster home than there. It's a ***** of a commute
there. 1:15+10min shower time when I was fit. I'm not longer fit.

Euan could probably do it after a few months training :)

--
TimC
double value; /* or your money back! */
short changed; /* so triple your money back! */
-- Larry Wall in cons.c from the perl source code
 
Roadie_scum wrote:
>
> Peter Wrote:
> > For many years I have noticed that cycling on wet roads appears easier
> > than on the same roads when they are dry. I suppose there must be some
> > reduction in friction between the tyre and the wet road when
> > travelling
> > in a straight line, just as there is when travelling around a corner.
> > Anyone know if this is true?
> >
> > Peter

>
> It's unlikely to come from the tire, but what you are feeling is a
> recognised effect. When it's raining, there is a lower air density.
> This reduces your aerodynamic drag, meaning you go faster at a given
> power.


Its the first time I've heard someone say that cycling in the rain is
faster,
and because of reduced air drag.
I think I always go slower in the rain.

I would have thought dry air is less dense than humid air,
and that banging into rain drops slows you down.

Maybe records for time trials would show the differences.

Ask Lance Armstrong, now there's a guy who'd know.

Patrick Turner.
>
> --
> Roadie_scum
 
Roadie_scum wrote:
>
> TimC Wrote:
> > On 2007-08-22, Roadie_scum (aka Bruce)
> > was almost, but not quite, entirely unlike tea:
> > > Peter Wrote:
> > >> For many years I have noticed that cycling on wet roads appears

> > easier
> > >> than on the same roads when they are dry. I suppose there must be

> > some
> > >> reduction in friction between the tyre and the wet road when
> > >> travelling
> > >> in a straight line, just as there is when travelling around a

> > corner.
> > >> Anyone know if this is true?
> > >
> > > It's unlikely to come from the tire, but what you are feeling is a
> > > recognised effect. When it's raining, there is a lower air density.
> > > This reduces your aerodynamic drag, meaning you go faster at a given
> > > power.

> >
> > I wouldn't think that would be noticable -- in .au, most rain seems to
> > be associated with lows of 995-1000hPa vs 1013hPa -- a 1% effect.
> >
> > But what if, where you live, rain tends to be associated with weather
> > events that lead to a higher chance of having a tail wind?
> >
> >
> > I'm super happy about my commute home these days (in the rare event
> > when I ride it). Away from the sun, and almost always a tailwind with
> > the prevailing westerlys.
> >
> > --
> > TimC
> > The universe was strange after we had beauty and truth replaced

>
> You are mixing up pressure and density.
>
> Pressure = force per unit area
>
> Density = mass per unit volume
>
> Similar, but not the same. For a gas at a given temperature and
> pressure, the number of molecules in a given space is constant. As the
> molecular mass of water is less than the molecular mass of other
> constituents of air (18 vs 29), this leads to a drop in air density
> when there is higher humidity at a given air pressure and temperature.
>
> This is a noticeable effect.


Dazzling scientific explanations!

What about the surface tension of the water acting on the tyres and
chain et all?

And what about the human factor?

Its the "Its F$#@^! raining again and I hate it.." factor.

Definately slows most ppl by several %.

Oh, and a wet body + reduced temperature = slower metabolism.

Are time trials done in wet conditions faster than dry weather TTs?

Patrick Turner.


>
> --
> Roadie_scum
 
DeF, > wrote:
>
> Roadie_scum wrote:
> > TimC Wrote:
> >> On 2007-08-22, Roadie_scum (aka Bruce)
> >> was almost, but not quite, entirely unlike tea:
> >>> Peter Wrote:
> >>>> For many years I have noticed that cycling on wet roads appears
> >> easier
> >>>> than on the same roads when they are dry. I suppose there must be
> >> some
> >>>> reduction in friction between the tyre and the wet road when
> >>>> travelling
> >>>> in a straight line, just as there is when travelling around a
> >> corner.
> >>>> Anyone know if this is true?
> >>> It's unlikely to come from the tire, but what you are feeling is a
> >>> recognised effect. When it's raining, there is a lower air density.
> >>> This reduces your aerodynamic drag, meaning you go faster at a given
> >>> power.
> >> I wouldn't think that would be noticable -- in .au, most rain seems to
> >> be associated with lows of 995-1000hPa vs 1013hPa -- a 1% effect.
> >>
> >> But what if, where you live, rain tends to be associated with weather
> >> events that lead to a higher chance of having a tail wind?
> >>
> >>
> >> I'm super happy about my commute home these days (in the rare event
> >> when I ride it). Away from the sun, and almost always a tailwind with
> >> the prevailing westerlys.
> >>
> >> --
> >> TimC
> >> The universe was strange after we had beauty and truth replaced

> >
> > You are mixing up pressure and density.
> >
> > Pressure = force per unit area
> >
> > Density = mass per unit volume
> >
> > Similar, but not the same. For a gas at a given temperature and
> > pressure, the number of molecules in a given space is constant. As the
> > molecular mass of water is less than the molecular mass of other
> > constituents of air (18 vs 29), this leads to a drop in air density
> > when there is higher humidity at a given air pressure and temperature.
> >
> > This is a noticeable effect.
> >
> >

>
> With all due respect to Mr(s) Scum, I think this is cobblers.
>
> From engineeringtoolbox.com, the density effect of humidity on
> air is captured by the formula
> air density = (dry air density) x ( 1 + R)/(1+1.609 R)
> where R is the humidity ratio or weight to weight ratio of
> water vapor to air in the mixture. So, increasing R from zero
> *does* decrease density but by a small and I would suggest negligible
> amount.
>
> For air at 20C, the maximum R can be is 0.01466 (100% humidity)
> which reduces dry air density by less than 1% - the same order
> of effect that TimC was talking about.
>
> DeF
>


Perhaps those of you who have studied a basic flying course
would know more of the effects of rainny conditions on air drag
on aircraft.

I can only ride.

Patrick Turner.
> --
> e-mail: d.farrow@your finger.murdoch.edu.au
> To reply, you'll have to remove your finger.
 
On Wed, 22 Aug 2007 12:03:06 +1000, Roadie_scum wrote:

> It's unlikely to come from the tire, but what you are feeling is a
> recognised effect. When it's raining, there is a lower air density.


Rain may usually come with slightly lower air pressure, but since
humidity is nearly 100%, surely the air is more dense, and more effort
is needed to push molecules of water out of the way, not to mention
raindrops.

Picking up water from the road and flinging it around uses energy, too.
 
Michael Warner wrote:
> On Wed, 22 Aug 2007 12:03:06 +1000, Roadie_scum wrote:
>
>> It's unlikely to come from the tire, but what you are feeling is a
>> recognised effect. When it's raining, there is a lower air density.

>
> Rain may usually come with slightly lower air pressure, but since
> humidity is nearly 100%, surely the air is more dense, and more effort
> is needed to push molecules of water out of the way, not to mention
> raindrops.
>
> Picking up water from the road and flinging it around uses energy, too.


Try learning some science. Banging on about how humid air MUST be more
dense isn't a valid argument, find out the reason and post it here so we
can all be enlightened.

Dorfus
 
On Thu, 23 Aug 2007 08:33:37 +0800, Dorfus Dippintush wrote:

> Try learning some science. Banging on about how humid air MUST be more
> dense isn't a valid argument, find out the reason and post it here so we
> can all be enlightened.


I checked, and it's because I said so :)
 
Roadie_scum wrote:
> Peter Wrote:
>> For many years I have noticed that cycling on wet roads appears easier
>> than on the same roads when they are dry. I suppose there must be some
>> reduction in friction between the tyre and the wet road when
>> travelling
>> in a straight line, just as there is when travelling around a corner.
>> Anyone know if this is true?
>>
>> Peter

>
> It's unlikely to come from the tire, but what you are feeling is a
> recognised effect. When it's raining, there is a lower air density.
> This reduces your aerodynamic drag, meaning you go faster at a given
> power.
>
>

More thoughts here http://www.velonews.com/tech/report/articles/13136.0.htm
and here http://www.velonews.com/tech/report/articles/12493.0.html

Halcyon
 

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