Chainring

In article <[email hidden]>,
[email hidden] says...

Quoted message said:

I would like to know if changing from a 52 to a 53 would be a good idea?
Would it improve speed or just cause more drag peddling?

Are you spinning out your top gear? If not, it won't help.
--------------
Alex

Morg said:

I would like to know if changing from a 52 to a 53 would be a good idea?
Would it improve speed ?

Only if it's red.

"maxo" wrote: Only if it's red.
^^^^^^^^^^^^^^
That's if the bike is riding away from the observer. The shift is toward
the blue if it's coming toward you.

Morg said:

I would like to know if changing from a 52 to a 53 would be a good idea?
Would it improve speed

NO

Quoted message said:

or just cause more drag peddling?

NO

It will increase your gearing ratio by less than 2%... this is a
trivial amount. Unless you are spinning out in your biggest gear now
(unlikely unless you are a top pro, or regularly have a strong tailwind
or long, straight downhills), there is no reason to have bigger gears.

-Ron

Morg said:

I would like to know if changing from a 52 to a 53 would be a good idea?
Would it improve speed or just cause more drag peddling?

Dear Morg,

Short answer, no noticeable drag effect.

Long answer . . . calculators and spreadsheets increase the
amount of time that can be wasted on interesting questions.

Wind drag does increase as cadence rises, so a larger front
sprocket will reduce cadence at the same speed and therefore
reduce wind drag.

But the drag-change will be only around 2%, which is the
pedal speed difference between 52 and 53 teeth at the same
bicycle speed.

You can see an estimate of the effect here:

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

Set the bicycle to hands-on-drops, credit yourself with a
generous 400 watts, and use the defaults, but play with the
cadence.

If you use a cadence of 104 rpm (roughly correct for a 53x16
tooth), the prediction is 27.5 mph.

Now change the cadence to 106 rpm and imagine that you're
using a 52x16.

You still get 27.5 mph--the difference is predicted to be
less than a tenth of a mile per hour.

You need 101 rpm reach 27.6 mph, or 113 rpm to drop to 27.4
mph.

You can see the explanation for increased wind drag with
higher cadence here:

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

Some drag is just the extra effort needed to whirl two
badly-shaped 175mm fan blades faster--even sitting still on
a trainer, it's slightly harder to spin a crank at a higher
rpm.

More of the drag comes from the forward-speed difference
between the same foot-and-pedal at the top and at the bottom
of the stroke when the bike is moving rapidly.

Here's exaggerated example.

If you're zooming along at 70 mph on a 53x11 and a 175mm
crank on a 2124 mm 700c tire, your cadence is 183.5 rpm and
your feet are spinning at 7.5 mph.

Relative to the wind, your foot is going 77.5 mph at the top
of the pedal cycle (70 + 7.5), but is going only 62.5 mph at
the bottom of the cycle (70 - 7.5).

Although the raw mph gain and loss appear to match and
cancel out, the gain and loss in wind drag is actually
unbalanced because wind drag increases with the square of
velocity:

62.5^3 = 3906.25 lost 993.75 units of drag
70.0^3 = 4900.00 normal drag units
77.5^3 = 6006.25 gained 1106.25 units of drag

So the same idealized foot gains about 11% more drag at the
top of the cycle than it loses at the bottom.

(Again, changing this drag by only 2%, one tooth out of
about fifty, is going to be almost imperceptible.)

To see the difference, use this calculator again:

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

Use a triathlon bicycle, an impressive -19.1 slope to
provide the real power, a cadence of 106 rpm (for a
52-tooth) and a negligible 17 watts to support it, and the
prediction will be 70.0 mph.

Drop the cadence to 104 rpm (raising the sprocket to an
imaginary 53-teeth), and the prediction . . .

Stays at 70.0 mph. One tooth and 2 rpm just don't do much.

(In this case, the 70.0 mph range almost matches the two
examples--107 rpm predicts 69.9 mph, and 103 rpm predicts
70.1 mph.)

If you drop the cadence to 1 rpm (effectively 0, but needed
to support the 17 watts), then the prediction rises to 74.4
mph.

This 4.4 mph difference between coasting and flailing your
legs shows why it's often useless to pedal down steep hills.

To speed up from coasting down the 19.1% grade at 70.0 mph
to 74.4 mph by spinning the pedals at 106 rpm, you'd need to
put 668 watts into the pedals!

It's awfully hard to add 4.4 mph at such high speeds.

For a more plausible example, use hands-on-drops, set the
slope to -7, and coast down with a cadence and watts of 0.

The calculator predicts that you'll coast down the 7% grade
at 40.1 mph, which would require 105 rpm on a 53x11.

If you add 1 watt and 105 rpm, the speed drops to 37.8 mph
from the increased wind drag.

To regain the lost speed and go as fast as you were
coasting, you have to add 117 watts.

To return to the original question, there's only a 2%
difference in cadence between the 52 and 53 tooth sprockets
at the same speed, so there won't be much wind drag
difference.

The chain would also be more efficient because the larger
sprocket produces a slightly gentler chain rotation on entry
and exit from the sprocket.

But again, the chain is already rather efficient and the
tiny improvement from 52 to 53 teeth isn't enough to show up
in the real world.

With a 53-tooth front sprocket, an 11-tooth rear sprocket,
and a pair of 11-tooth idler sprockets, each link bends
through a total of 189.4940 degrees.

With a 52-tooth sprocket, this rises to 189.7752 degrees,
only about a quarter of a degree out of roughly half a
circle.

Carl Fogel

Morg said:

I would like to know if changing from a 52 to a 53 would be a good idea?
Would it improve speed or just cause more drag peddling?

Do you mean pedaling? Peddling is selling.

--
Ted Bennett