Effects of aero bars and disk wheel?

Hi everyone,

I've been trying to figure out the virtual penalty I pay in TT's by not
using aero bars and a disk wheel. I'm sort of comparing apples to
oranges when I gauge myself against some local riders who use this type
of equipment.

Obviously aerobars will have a wide variation based on position, etc,
but can anyone give me some pointers? I've checked analyticcyling for
aero bars, but can't really determine what the abrs and disk would do.

Thanks!

Joseph

On 17 Jul 2005 01:12:08 -0700,
wrote:

Hi everyone,

I've been trying to figure out the virtual penalty I pay in TT's by not
using aero bars and a disk wheel. I'm sort of comparing apples to
oranges when I gauge myself against some local riders who use this type
of equipment.

Obviously aerobars will have a wide variation based on position, etc,
but can anyone give me some pointers? I've checked analyticcyling for
aero bars, but can't really determine what the abrs and disk would do.

Thanks!

Joseph

Dear Joseph,

You can get some idea of the advantage of aero/triathlon
bars over riding on the drops of ordinary bars with this
calculator:

http://www.kreuzotter.de/english/espeed.htm

Using the defaults, the triathlon bars are predicted to
reach 20.5 mph, while the hands-on-drops position is
expected to reach only 19.4 mph.

Raise the watts from the default 160 watts to 300 watts, and
the hands on drops speed rises to 24.8 mph, while the aero
bars reach 26.3 mph.

If you page down on this site's calculator:

http://www.recumbents.com/wisil/simul/HPV_Simul.asp

There's a list of expected drag coefficients. The explicit
aero bar and disk rear wheel is expected to have a CDA of
0.23, while a diamond-frame racing position (drops) is
expected to have a CDA of 0.38.

Confusingly, this seems to contradict the note below the
table that says that "all bike CDA's assume the use of a
rear wheel disk"--which seems unlikely for the mountain bike
in the table, if not several of the others.

If you look again at Analytic Cycling, click on "wheels and
aero and weight" he

http://www.analyticcycling.com

And then click on "drag coefficients."

This leads to a table of disk and spoked wheel coefficients
of drag.

You can also go to this page:

http://www.analyticcycling.com/DiffE...urse_Page.html

Here, you can select different front and rear wheels for
comparison, including disk wheels.

For the defaults, the calculator predicts a 7.72 second
speed improvement in 4km with a disk rear wheel replacing a
36-spoke rear wheel.

Carl Fogel

wrote:

Hi everyone,

I've been trying to figure out the virtual penalty I pay in TT's by not
using aero bars and a disk wheel. I'm sort of comparing apples to
oranges when I gauge myself against some local riders who use this type
of equipment.

Obviously aerobars will have a wide variation based on position, etc,
but can anyone give me some pointers? I've checked analyticcyling for
aero bars, but can't really determine what the abrs and disk would do.

As a quick point, in case you are thinking of getting the equipment
yourself: my experience is that the aero bars make a much greater
difference than a rear disk.

Mark

wrote:

I've been trying to figure out the virtual penalty I pay in TT's by not
using aero bars and a disk wheel. I'm sort of comparing apples to
oranges when I gauge myself against some local riders who use this type
of equipment.

Obviously aerobars will have a wide variation based on position, etc,
but can anyone give me some pointers? I've checked analyticcyling for
aero bars, but can't really determine what the abrs and disk would do.

1) Cost money.

2) Save @ 2-1/2 minutes in 40k if you are already at or below the one
hour mark for that distance. --TP

wrote:
Hi everyone,

I've been trying to figure out the virtual penalty I pay in TT's by not
using aero bars and a disk wheel. I'm sort of comparing apples to
oranges when I gauge myself against some local riders who use this type
of equipment.

Obviously aerobars will have a wide variation based on position, etc,
but can anyone give me some pointers? I've checked analyticcyling for
aero bars, but can't really determine what the abrs and disk would do.


Carl's given you some good pointers. While I haven't done a _lot_ of
time trialing, I can give my impressions.

At various times, I've had either or both on a couple bikes. (Well,
actually I had disk spoke covers on my spoked rear wheels.) My
impression is that the rear disk may help a little, but it's not
readily perceptible.

OTOH, the aero bar has an immediately noticeable effect. So much so
that I now have an aero bar on my touring bike - which is a bit of a
trick with a handlebar bag!

I think the aero bar is the single biggest performance enhancer you can
install on the bike.

- Frank Krygowski

wrote:
wrote:
Hi everyone,

I've been trying to figure out the virtual penalty I pay in TT's by not
using aero bars and a disk wheel. I'm sort of comparing apples to
oranges when I gauge myself against some local riders who use this type
of equipment.

Obviously aerobars will have a wide variation based on position, etc,
but can anyone give me some pointers? I've checked analyticcyling for
aero bars, but can't really determine what the abrs and disk would do.


Carl's given you some good pointers. While I haven't done a _lot_ of
time trialing, I can give my impressions.

At various times, I've had either or both on a couple bikes. (Well,
actually I had disk spoke covers on my spoked rear wheels.) My
impression is that the rear disk may help a little, but it's not
readily perceptible.

OTOH, the aero bar has an immediately noticeable effect. So much so
that I now have an aero bar on my touring bike - which is a bit of a
trick with a handlebar bag!

I think the aero bar is the single biggest performance enhancer you can
install on the bike.

- Frank Krygowski

Must be careful here. I see people all over that have had tri bars
slapped onto their bike and they end up riding around with their hands
on the pads. Why? Because the bike is not fit or set up for these. Most
tribars have a reach MUCH longer than the hoods or drops and many
cannot really reach the tribar hand positions as designed. If you can
put on tri bars and easily reach them, I will say the fit on the normal
dropbars is not proper. In addtion, if you shove your saddle forward to
be able to reach them, then it compromises your position in relation to
the knee and the BB/pedal spindles.

Comfort and power out trumps aero position all the time. If ya can have
both, fine but many complained of Indurain's position when he did the
hour record but it was the best compromise in terms of comfort,
aero-ness and power out.

Tri bars are not a panacea for faster riding.

On 18 Jul 2005 22:11:30 -0700, wrote:



wrote:
Hi everyone,

I've been trying to figure out the virtual penalty I pay in TT's by not
using aero bars and a disk wheel. I'm sort of comparing apples to
oranges when I gauge myself against some local riders who use this type
of equipment.

Obviously aerobars will have a wide variation based on position, etc,
but can anyone give me some pointers? I've checked analyticcyling for
aero bars, but can't really determine what the abrs and disk would do.


Carl's given you some good pointers. While I haven't done a _lot_ of
time trialing, I can give my impressions.

At various times, I've had either or both on a couple bikes. (Well,
actually I had disk spoke covers on my spoked rear wheels.) My
impression is that the rear disk may help a little, but it's not
readily perceptible.

OTOH, the aero bar has an immediately noticeable effect. So much so
that I now have an aero bar on my touring bike - which is a bit of a
trick with a handlebar bag!

I think the aero bar is the single biggest performance enhancer you can
install on the bike.

- Frank Krygowski

Do you have a photo somewhere we could look at of the bar with the
handlebar bag installation? I'd love to have a setup like this on
mine.

Geezer Boy

Geezer Boy wrote:


Do you have a photo somewhere we could look at of the bar with the
handlebar bag installation? I'd love to have a setup like this on
mine.

I don't think I do. (I do analog, not digital photography, and little
of that.)

But it's nothing you'd like to emulate. The aero bar is a first
generation Scott. The handlebar bag is an old canvas one, dating from
about 1974. It hangs on one of those 1/4" diameter steel rod racks,
the under-the-stem-over-the-bars type, bent way out of shape for this
application. And the aero bar interferes badly with access to the bag
contents. I was cussing at it last night for the thousandth time.

I keep thinking about brazing up something better, but so far I've
accomplished only the cussing.

- Frank Krygowski

If you page down on this site's calculator:

http://www.recumbents.com/wisil/simul/HPV_Simul.asp

There's a list of expected drag coefficients. The explicit
aero bar and disk rear wheel is expected to have a CDA of
0.23, while a diamond-frame racing position (drops) is
expected to have a CDA of 0.38.

Is .38 to .23 really realistic? That's a huge difference. Using Cd's
even close to .23 on the various calculators on anatyticcycling
indicates massive savings.


http://www.analyticcycling.com

And then click on "drag coefficients."

This leads to a table of disk and spoked wheel coefficients
of drag.

If the drag savings of wheels is at most 3% of total drag, but the aero
bar disk combo above is 40%, this indicates that an aero bar is hugely
more important than wheels.

Guess I'll go buy a bar now!

Joseph