# What improves the efficiency of a bicycle?

Discussion in 'Cycling Equipment' started by Neil, Jun 6, 2003.

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1. ### Peter Cole Guest

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

Thanks for the primer, but I think it's reasonable to talk about forces on the rider or power the
rider must supply to maintain a given speed. Total work doesn't make much sense, unless you're
counting calories.

2. ### Joakim Majander Guest

"Peter Cole" <[email protected]> wrote in message
news:<[email protected]>...
> "Ron Hardin" <[email protected]> wrote in message news:[email protected]...
> >
>
> Thanks for the primer, but I think it's reasonable to talk about forces on the rider or power the
> rider must supply to maintain a given speed. Total work doesn't make much sense, unless you're
> counting calories.

I think you missed the main point in Ron's reply.

If you calculate the drag _forces_ the aerodynamic drag increases to the square of speed, but
rolling resistance is _constant_ it _does_ not_ "go up with speed directly".

If you calculate _power_ loses the aerodynamic loses increase to cube of speed and RR does "go up
with speed directly".

If you ride with MTB-tires, rolling resistance is very significant even at higher speeds. Even with
good quality road tires RR is 20-50% of the total drag at the speeds of recreational cyclists
(15-35 km/h).

Changing from MTB-tires to good quality road tires will make you ~3-5 km/h faster at the speeds of
15-50 km/h depending on speed an riding position. Try this:
http://w3.iac.net/~curta/bp/velocityMetric/velocity.html.

Joakim

3. ### Jeff Wills Guest

[email protected] (Chris Zacho "The Wheelman") wrote in message
news:<[email protected]>... <snip>
> Here is where the benefits of a recumbent would defiitely start outweighing any downfalls.
>

Switching to a recumbent takes dedication- muscles and riding technique require a few months of
adaptation. Even then, I've known a couple people who have gone back to upright riding.

That being said, I know several 60-to-70 year olds who completed the last Cycle Oregon on
recumbents. Some were slow, some were fast- but back-to-back 90 mile days will string out any group.
Here's a bunch of them: http://www.geocities.com/e_r_r_c/COXV.jpeg Note preponderance of gray hair
and Aerobellys (tm). Jeff

4. ### Peter Cole Guest

"Joakim Majander" <[email protected]> wrote in message
news:[email protected]...
> "Peter Cole" <[email protected]> wrote in message
news:<[email protected]>...
> > "Ron Hardin" <[email protected]> wrote in message news:[email protected]...
> > >
> > > A loss is in additional work, not additional power.
> >
> > Thanks for the primer, but I think it's reasonable to talk about forces on
the
> > rider or power the rider must supply to maintain a given speed. Total work doesn't make much
> > sense, unless you're counting calories.
>
> I think you missed the main point in Ron's reply.
>
> If you calculate the drag _forces_ the aerodynamic drag increases to the square of speed, but
> rolling resistance is _constant_ it _does_ not_ "go up with speed directly".
>
> If you calculate _power_ loses the aerodynamic loses increase to cube of speed and RR does "go up
> with speed directly".

I think that's what I said, if you find what I said ambiguous, it's what I meant, hence my comments
about power, not work or force, being the important thing to consider.

> If you ride with MTB-tires, rolling resistance is very significant even at higher speeds. Even
> with good quality road tires RR is 20-50% of the total drag at the speeds of recreational cyclists
> (15-35 km/h).
>
> Changing from MTB-tires to good quality road tires will make you ~3-5 km/h faster at the speeds of
> 15-50 km/h depending on speed an riding position. Try this:
http://w3.iac.net/~curta/bp/velocityMetric/velocity.html.

That's a pretty crude site compared to the one I listed: www.analyticcycling.com.

According to the (your) site:

"The "Tire" menu choice also sets somewhat arbitrary rolling resistance coefficients. Actual
measurements for these values are hard to come by"

This doesn't fill me with confidence. I think hard RR numbers are out there. Where did you
get yours?

5. ### Joakim Majander Guest

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

> I think that's what I said, if you find what I said ambiguous, it's what I meant, hence my
> comments about power, not work or force, being the important thing to consider.

>
> > If you ride with MTB-tires, rolling resistance is very significant even at higher speeds. Even
> > with good quality road tires RR is 20-50% of the total drag at the speeds of recreational
> > cyclists (15-35 km/h).
> >
> > Changing from MTB-tires to good quality road tires will make you ~3-5 km/h faster at the speeds
> > of 15-50 km/h depending on speed an riding position. Try this:
> http://w3.iac.net/~curta/bp/velocityMetric/velocity.html.
>
> That's a pretty crude site compared to the one I listed: www.analyticcycling.com.
>
> According to the (your) site:
>
> "The "Tire" menu choice also sets somewhat arbitrary rolling resistance coefficients. Actual
> measurements for these values are hard to come by"
>
> This doesn't fill me with confidence. I think hard RR numbers are out there. Where did you
> get yours?

The site I mentioned is not mine. It uses RR coefficients of 0.012 for MTB, 0.005 for clincher and
0.004 for tubular. They are quite close to the truth, if MTB is a knobby tire, clincher a "normal"
road racing tire and tubular close to a track tire. The differenses between different makes, models
and pressure are quite large (http://www.terrymorse.com/bike/rolres.html road:RR coef 0.004-0.008,
MTB: RR 0.01-0.02)

I like the calculator, since it gives quite a good clue how fast you can go with different bikes,
positions and tires at a specific power. I'm familiar with www.analyticcycling.com. It also has a
power calculator, but you need to know much more in order to use it. It is quite hard to know
frontal areas and drag coefficients unless you have been in a wind tunnel test.

Joakim

6. ### Joakim Majander Guest

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

> I didn't see where the coefficients were listed on that site, so I was judging the accuracy from
> the annotations, which seemed pretty tentative.

I once looked trough the actual java code.

Joakim

7. ### Peter Cole Guest

"Joakim Majander" <[email protected]> wrote in message
news:[email protected]...
> "Peter Cole" <[email protected]> wrote in message
news:<[email protected]>...
>
> > I didn't see where the coefficients were listed on that site, so I was
judging
> > the accuracy from the annotations, which seemed pretty tentative.
>
> I once looked trough the actual java code.

Oh well, shame on me for not being that thorough.