Why so few spokes?

Jim Price wrote:
dvt wrote:

Right, but is traction a limit to acceleration at speeds where a
spoiler is significant? At those speeds, I'd think you'd be limited by
available power rather than traction.

On a race track, the answer would be a yes, but not quite the way you
might think. You want to come out of a corner accelerating hard, and
there is a balance to be struck between available acceleration and the
overall traction the tyre can cope with. This overall traction is
actually a vector which is the sum of the effects of both acceleration
and cornering, so at absolute maximum cornering speed, you could break
traction with the accelerator even with a low powered car.

I hadn't thought of combining the two cases. As you probably surmised,
I'm not a motor sports nut. Thanks for the enlightenment.

To the original point, I would think that a front-drive car could
conceivably use a spoiler to enhance cornering traction at high speed.
Am I wrong?

--
Dave
dvt at psu dot edu

Dave Vt writes:

That is like the spoilers on the backs of cars that emulate but do
not function as those on 150mph racing cars, will improve commute
times as well as road holding at speeds one might attain on a
deserted public road.

I always enjoy seeing spoilers on front wheel drive cars.

OT, but you got my interest. Why does front wheel drive invalidate a
spoiler? Sure, spoilers on most cars are non functional, but I don't
know why spoilers would affect front and rear wheel drive cars
differently.

I think the use of wings on drag racers, where they are used to add
downward pressure to the drive wheels may be the issue. On most race
cars they are used mainly for cornering traction. Therefore, whether
front or rear drive has little bearing on whether to use the device.
Unfortunately the term "spoiler" became popular in the Kamm Effect
days when they were put on the rear of cars to get rid of lift from
eddies behind GT cars.

Jobst Brandt

That is like the spoilers on the backs of cars that emulate but do not
function as those on 150mph racing cars, will improve commute times as
well as road holding at speeds one might attain on a deserted public
road.

wrote:
I always enjoy seeing spoilers on front wheel drive cars.

dvt wrote:
OT, but you got my interest. Why does front wheel drive invalidate a
spoiler? Sure, spoilers on most cars are non functional, but I don't
know why spoilers would affect front and rear wheel drive cars differently.

I also find them hysterical. He meant not the air dam just
ahead of the front wheels but rather the wing over
the rear deck. At speeds over roughly 200K those wings are
supposed to press the back of the car down for traction

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Dans le message de
oups.com,
a réfléchi, et puis a déclaré :

Keep in mind, we're talking about measures marketed to a clientele
that believes that they can feel a two ounce difference in the weight
of a frame. "Negligible" is poorly understood.

For those who do not compete, feel free to use "negligible" or
"insignificant".
For those who compete, half a wheel's difference over 150 km may be
significant.
Your context and mine are not the same.
Thus, your opinion has a negligible effect.
Offered amicably.
--
Sandy
--
C'est le contraire du vélo, la bicyclette.
Une silhouette profilée mauve fluo dévale
à soixante-dix à l'heure : c'est du vélo.
Deux lycéennes côte à côte traversent
un pont à Bruges : c'est de la bicyclette.
-Delerm, P.

On Fri, 06 Jan 2006 19:21:56 +0000, jobst.brandt wrote:

Dave Vt writes:

That is like the spoilers on the backs of cars that emulate but do not
function as those on 150mph racing cars, will improve commute times as
well as road holding at speeds one might attain on a deserted public
road.

I always enjoy seeing spoilers on front wheel drive cars.

OT, but you got my interest. Why does front wheel drive invalidate a
spoiler? Sure, spoilers on most cars are non functional, but I don't
know why spoilers would affect front and rear wheel drive cars
differently.

I think the use of wings on drag racers, where they are used to add
downward pressure to the drive wheels may be the issue. On most race cars
they are used mainly for cornering traction. Therefore, whether front or
rear drive has little bearing on whether to use the device. Unfortunately
the term "spoiler" became popular in the Kamm Effect days when they were
put on the rear of cars to get rid of lift from eddies behind GT cars.

They're still used for that purpose, and to reduce total drag. FWD race
cars do sometimes have handling problems from rear end lift at high
speeds. And drag's effect on straightaway speed can be very much an
issue.

These days however you can't use a spoiler in a non-modified class
(unless it's standard equipment), and in modified classes the whole body
can be completely redesigned anyway. But aerodynamic aids can still be
used to good effect, as Ernie Rogers has done with his Volkswagen Beetle:

http://www.max-mpg.com/default.htm

Ernie shows exactly how wings can be used to reduce drag.

Of course the wings and things we see on kids' cars these days are all for
looks.

Matt O.

Sandy wrote:
Dans le message de
oups.com,
a réfléchi, et puis a déclaré :

Keep in mind, we're talking about measures marketed to a clientele
that believes that they can feel a two ounce difference in the weight
of a frame. "Negligible" is poorly understood.

For those who do not compete, feel free to use "negligible" or
"insignificant".
For those who compete, half a wheel's difference over 150 km may be
significant.
Your context and mine are not the same.
Thus, your opinion has a negligible effect.
Offered amicably.

Thanks for the amicable response. But even for most racers, these
supposed advantages are usually negligible.

Some racers seem to think that a 0.05% reduction in drag coefficient of
the wheels, or of the bike, will lead to a 0.05% reduction in their
race time. There are several reasons it won't.

One is, of course, that the aero drag of the rider's body is much
greater than that of the bike, so any improvement in the bike yields a
smaller percentage improvement overall.

Another reason is that drag force increases greatly with velocity. The
increase in speed would be much less than the above thinking predicts.

A third reason is that, except for time trials, most of the mileage of
most races is spent in the slipstream of at least one rider.
Aerodynamics of the bike and rider are much less important there.

But the biggest reason is that such small advantages are routinely
overwhelmed by one's physical and psychological variation from day to
day.

However, I certainly don't want to dissuade anyone from spending their
money on anything they choose, including a "faster" paint job. It may
give you that psychological boost you need to gain half a wheel.

- Frank Krygowski

Sandy wrote:
Dans le message de
oups.com,
a réfléchi, et puis a déclaré :

Keep in mind, we're talking about measures marketed to a clientele
that believes that they can feel a two ounce difference in the weight
of a frame. "Negligible" is poorly understood.

For those who do not compete, feel free to use "negligible" or
"insignificant".
For those who compete, half a wheel's difference over 150 km may be
significant.
Your context and mine are not the same.
Thus, your opinion has a negligible effect.
Offered amicably.

Thanks for the amicable response. But even for most racers, these
supposed advantages are usually negligible.

Some racers seem to think that a 0.05% reduction in drag coefficient of
the wheels, or of the bike, will lead to a 0.05% reduction in their
race time. There are several reasons it won't.

One is, of course, that the aero drag of the rider's body is much
greater than that of the bike, so any improvement in the bike yields a
smaller percentage improvement overall.

Another reason is that drag force increases greatly with velocity. The
increase in speed would be much less than the above thinking predicts.

A third reason is that, except for time trials, most of the mileage of
most races is spent in the slipstream of at least one rider.
Aerodynamics of the bike and rider are much less important there.

But the biggest reason is that such small advantages are routinely
overwhelmed by one's physical and psychological variation from day to
day.

However, I certainly don't want to dissuade anyone from spending their
money on anything they choose, including a "faster" paint job. It may
give you that psychological boost you need to gain half a wheel.

- Frank Krygowski

Dans le message de
oups.com,
a réfléchi, et puis a déclaré :
Sandy wrote:
Dans le message de
oups.com,
a réfléchi, et puis a
déclaré :

Keep in mind, we're talking about measures marketed to a clientele
that believes that they can feel a two ounce difference in the
weight of a frame. "Negligible" is poorly understood.

For those who do not compete, feel free to use "negligible" or
"insignificant".
For those who compete, half a wheel's difference over 150 km may be
significant.
Your context and mine are not the same.
Thus, your opinion has a negligible effect.
Offered amicably.

Thanks for the amicable response. But even for most racers, these
supposed advantages are usually negligible.

Some racers seem to think that a 0.05% reduction in drag coefficient
of the wheels, or of the bike, will lead to a 0.05% reduction in their
race time. There are several reasons it won't.

One is, of course, that the aero drag of the rider's body is much
greater than that of the bike, so any improvement in the bike yields a
smaller percentage improvement overall.

Another reason is that drag force increases greatly with velocity.
The increase in speed would be much less than the above thinking
predicts.

A third reason is that, except for time trials, most of the mileage of
most races is spent in the slipstream of at least one rider.
Aerodynamics of the bike and rider are much less important there.

But the biggest reason is that such small advantages are routinely
overwhelmed by one's physical and psychological variation from day to
day.

However, I certainly don't want to dissuade anyone from spending their
money on anything they choose, including a "faster" paint job. It may
give you that psychological boost you need to gain half a wheel.

- Frank Krygowski

You're happy and you're wrong, but that's OK by me.
--
Bonne route !

Sandy
Verneuil-sur-Seine FR