Touring tyre - 35 or 38

Michael Tissington said:

For a long distance tour (with some rough road) how do I decide between

700 C x 35 or 700 C x 38 in the same tyre, the rims and frame can take up to
45.

Get the biggest tire you're willing to push. You'll give up a tiny
bit of rolling resistance in return for (potentially) better ride and
(certainly) better pinch flat resistance. You'll also get a bit more
"float" out of a fatter tire if you find yourself in loose dirt or
rocks.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Michael Tissington said:

For a long distance tour (with some rough road) how do I decide between

700 C x 35 or 700 C x 38 in the same tyre, the rims and frame can take up to
45.

For touring, in general, the larger tyre will be the better choice.
At some point, you will encounter loose sand and gravel surfaces, and
the wider tyre will handle these more gracefully. In addition,
there's more tread surface to absorb wear, and more crush depth to
provide cushioning and prevent pinch flats on bumps.

--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Michael Tissington said:

For a long distance tour (with some rough road) how do I decide between

700 C x 35 or 700 C x 38 in the same tyre, the rims and frame can take up to
45.

I did 1200 miles on 35's.

Ken

Messengers and mountain bikers share a common chromosome. ~James Bethea

"Michael Tissington" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

For a long distance tour (with some rough road) how do I decide between

700 C x 35 or 700 C x 38 in the same tyre, the rims and frame can take up
to 45.

--
Michael Tissington
http://www.sqlview.net

All else being equal, fatter tires will give a less harsh ride on paved
roads.
Fatter tires will help you "float" when the road surface is soft (mud, sand,
gravel, etc.)
They have higher rolling resistance and greater weight. I don't know how
to quantitate this.

Does anyone know the magnitude of the effect of various tire widths on
rolling resistance when compared to other forces acting on a touring
bicycle when riding on flat hard pavement. My guess is that the rolling
resistance is insignificant compared to weight when climbing any sort of
grade on a loaded touring bike.

What's the power required to propel a loaded touring bike with front and
rear panniers (bike about 30 lbs, gear about 50 lbs, rider 150 lbs) on flat
hard pavement with 700 x 21 tires?, 28? 38?

BobT

"BobT" <[email hidden]> wrote in message
news:5u8Sg.1402$Rp3.7@dukeread12...

Quoted message said:

What's the power required to propel a loaded touring bike with front and
rear panniers (bike about 30 lbs, gear about 50 lbs, rider 150 lbs) on

flat

Quoted message said:

hard pavement with 700 x 21 tires?, 28? 38?

You forgot to mention the most important parameter: speed.

Lou

On Tue, 26 Sep 2006 06:51:52 -0500, "BobT"
<[email hidden]> wrote:

[snip]

Quoted message said:

Does anyone know the magnitude of the effect of various tire widths on
rolling resistance when compared to other forces acting on a touring
bicycle when riding on flat hard pavement. My guess is that the rolling
resistance is insignificant compared to weight when climbing any sort of
grade on a loaded touring bike.

What's the power required to propel a loaded touring bike with front and
rear panniers (bike about 30 lbs, gear about 50 lbs, rider 150 lbs) on flat
hard pavement with 700 x 21 tires?, 28? 38?

BobT

Dear Bob,

Try this calculator:

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

If you plug in 80-lb bike and 150-lb rider, hands on tops, and 50
miles into the distance at the bottom, it predicts a speed of 17.5 mph
and a time of 2:51:25.7. (Wind drag would increase with panniers, but
we'll ignore that.)

Change from "narrow racing" tires to the hideous "robust touring"
tires and try again. The calculator predicts 15.8 mph and 3:09:52.4,
about 18 minutes longer on a 3-hour trip.

To check if the calculator notices the weight effect on rolling
resistance, lower the bike weight from 80-lbs to 30-lbs. Yes, the
speed and time improve: 16.3 mph and 3:04:02.9.

You can set the power and solve for speed and change other variables.

If you have specific rolling resistances for particular tires, try
this calculator:

http://w3.iac.net/~curta/bp/velocityN/velocity.html

In addition to offering more variables and oodles of decimals, the
Austin calculator gives convenient side-by-side comparisons.

Cheers,

Carl Fogel

BobT said:

"Michael Tissington" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

For a long distance tour (with some rough road) how do I decide between

700 C x 35 or 700 C x 38 in the same tyre, the rims and frame can take up
to 45.

Quoted message said:

All else being equal, fatter tires...have higher rolling resistance

No, no, no! All else being equal, wider bicycle tyres have lower
rolling resistance than their narrow brethren. Schwalbe explain why
this is so on their web page for the Big Apple

http://www.schwalbe.com/gbl/en/bicycle/on_tour/produktgruppe/?gesamt=276&ID_Produktgruppe=24

And it's been mentioned here many times before. The widely believed
fallacy that narrow tyres have lower rolling resistance is making
hundreds of cyclists ride uncomfortable, puncture prone tyres for
nothing. At touring speeds, the lower rolling resistance of a 38 more
than makes up for the tiny increase in aerodynamic drag and all up
weight compared with a 23

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

Kinky Cowboy said:

BobT said:

"Michael Tissington" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

For a long distance tour (with some rough road) how do I decide between

700 C x 35 or 700 C x 38 in the same tyre, the rims and frame can take up
to 45.

Quoted message said:

All else being equal, fatter tires...have higher rolling resistance

No, no, no! All else being equal, wider bicycle tyres have lower
rolling resistance than their narrow brethren. Schwalbe explain why
this is so on their web page for the Big Apple

http://www.schwalbe.com/gbl/en/bicycle/on_tour/produktgruppe/?gesamt=276&ID_Produktgruppe=24

And it's been mentioned here many times before. The widely believed
fallacy that narrow tyres have lower rolling resistance is making
hundreds of cyclists ride uncomfortable, puncture prone tyres for
nothing. At touring speeds, the lower rolling resistance of a 38 more
than makes up for the tiny increase in aerodynamic drag and all up
weight compared with a 23

Interesting article. Thanks for that, but I've two questions:
1) The article states, "It is amazing that wide tires roll more easily,
but that is because a broader tire has a smaller footprint in the
driving direction. So the tire bounces less and the flattening of the
footprint on the road is smaller."
--Seems like this wouldn't be true with narrow tires inflated to full or
as-near-to-full-as-appropriate pressures. To be clear, my experience is
limited to 32 mm, 25 mm, and 23 mm tires.

2) "With an air pressure of 30psi (2 Bar) the rolling resistance is
about 30 per cent lower than a 1.3/8 (37mm) wide tire."
--Assuming that's the gospel truth, does a valid comparison of a
'balloon' tire to one that's 37 mm wide validate your comparison of a 38
mm to a 23 mm wide tire?

In article <[email hidden]>,

Paul Hobson said:

Kinky Cowboy said:

BobT said:

"Michael Tissington" <[email hidden]> wrote in message
news:[email hidden]...
> For a long distance tour (with some rough road) how do I decide between
>
> 700 C x 35 or 700 C x 38 in the same tyre, the rims and frame can take up
> to 45.

Quoted message said:

All else being equal, fatter tires...have higher rolling resistance

No, no, no! All else being equal, wider bicycle tyres have lower
rolling resistance than their narrow brethren. Schwalbe explain why
this is so on their web page for the Big Apple

http://www.schwalbe.com/gbl/en/bicycle/on_tour/produktgruppe/?gesamt=276&ID_Produktgruppe=24

And it's been mentioned here many times before. The widely believed
fallacy that narrow tyres have lower rolling resistance is making
hundreds of cyclists ride uncomfortable, puncture prone tyres for
nothing. At touring speeds, the lower rolling resistance of a 38 more
than makes up for the tiny increase in aerodynamic drag and all up
weight compared with a 23

Interesting article. Thanks for that, but I've two questions:
1) The article states, "It is amazing that wide tires roll more easily,
but that is because a broader tire has a smaller footprint in the
driving direction. So the tire bounces less and the flattening of the
footprint on the road is smaller."
--Seems like this wouldn't be true with narrow tires inflated to full or
as-near-to-full-as-appropriate pressures. To be clear, my experience is
limited to 32 mm, 25 mm, and 23 mm tires.

2) "With an air pressure of 30psi (2 Bar) the rolling resistance is
about 30 per cent lower than a 1.3/8 (37mm) wide tire."
--Assuming that's the gospel truth, does a valid comparison of a
'balloon' tire to one that's 37 mm wide validate your comparison of a 38
mm to a 23 mm wide tire?

We need good laboratory data. I run 28 mm slicks at
90-115 psi on my town bike, and whenever I coast along
with another town bike, I coast farther.

--
Michael Press

Quoted message said:

If you plug in 80-lb bike and 150-lb rider, hands on tops, and 50
miles into the distance at the bottom, it predicts a speed of 17.5 mph
and a time of 2:51:25.7. (Wind drag would increase with panniers, but
we'll ignore that.)

Change from "narrow racing" tires to the hideous "robust touring"
tires and try again. The calculator predicts 15.8 mph and 3:09:52.4,
about 18 minutes longer on a 3-hour trip.

That seems like an awful lot of penalty just for going with fatter
tires - what are the specs on those "hideous robust touring" tires?
Inflation?

For example, I ride typical 23 or 25mm high-pressure (110-120psi)
tires on my road bike, and 35mm semi-slicks (85-90psi) on my 'cross
bike, and would be surprised if there's a 1mph delta, even with the
more upright position on the 'cross bike.

OTOH, I've never actually measured the relative speed (don't bother
with a computer on anything other than the tandem, and then only to
make sure the wife is working hard enough). ;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

On Tue, 26 Sep 2006 21:17:00 -0700, Mark Hickey <[email hidden]>

Quoted message said:

Quoted message said:

If you plug in 80-lb bike and 150-lb rider, hands on tops, and 50
miles into the distance at the bottom, it predicts a speed of 17.5 mph
and a time of 2:51:25.7. (Wind drag would increase with panniers, but
we'll ignore that.)

Change from "narrow racing" tires to the hideous "robust touring"
tires and try again. The calculator predicts 15.8 mph and 3:09:52.4,
about 18 minutes longer on a 3-hour trip.

That seems like an awful lot of penalty just for going with fatter
tires - what are the specs on those "hideous robust touring" tires?
Inflation?

For example, I ride typical 23 or 25mm high-pressure (110-120psi)
tires on my road bike, and 35mm semi-slicks (85-90psi) on my 'cross
bike, and would be surprised if there's a 1mph delta, even with the
more upright position on the 'cross bike.

OTOH, I've never actually measured the relative speed (don't bother
with a computer on anything other than the tandem, and then only to
make sure the wife is working hard enough). ;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Dear Mark,

Consider your sincere but extremely dubious theory that a 1 mph
difference between "more upright" and presumably "on the drops"
positions would be surprising.

Take the defaults here:

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

Choose on-the-drops, and the prediction is 19.4 mph.

Choose hands-on-tops, and the prediction drops to 17.3 mph, 2.1 mph
slower.

That's without the wider, squashier cyclocross tires.

Go to 1.75" off-road tire, and the predicted speed drops to 16.2 mph.

For a cross-check, try this calculator, which is the MPH version that
suggests tire types instead of allowing specific RR values:

http://w3.iac.net/~curta/bp/velocity/velocity.html

Reduce the 300 watt default to 160 watts, choose clincher tires, and
use "drops"--the prediction is 19.46 mph.

Switch to "hoods"--the predicted speed drops to 17.98 mph.

Put on a pair of MTB tires--the predicted speed drops to 16.05 mph.

This is why Tour riders aren't using 38 mm tires--the extra rolling
resistance of the heavier construction and the increased wind drag of
the wider tires is subject to the laws of physics. To reduce sidewall
flexing enough to improve the RR of the wider tires would require an
unreasonably harsh ride.

If you're interested in the details of the calculations and the RR
values used, here's the source code for the mph version of the Austin
calculator:

String words[] = {"hoods", "bartops", "bar ends", "drops", "aerobars",
"drafting"};
double values[] = {0.388, 0.445, 0.420, 0.300, 0.233, 0.200};

String words[] = {"clincher", "tubular", "MTB"};
double values[] = {0.005, 0.004, 0.012};

http://w3.iac.net/~curta/bp/velocity/Velocity.java

Obviously, individual riders will have different actual wind drag
coefficents, just as individual tires will vary (as will inflation and
road surface). Plenty of clinchers are over 0.0060, and lots of mtb
tires are under 0.0120. Heavy touring tires tend to be around 0.0100.
Here's a table that suggests such averages, but remember that it's
mostly for small versions of the named tires:

http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm

And here's the IHPVA's calculator, harder to use, but with some tire
RR and drag coefficient values for comparison:

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

These raw differences are very small--19 vs 17 mph.

And we're bad at noticing them--try guessing your speed for a while
and then comparing it to the cyclocomputer--can you reliably
distinguish 17 from 18 mph?

It takes a cyclocomputer, a stopwatch, and a lot of rides around the
same route to find out that we were averaging 10% slower. Indeed,
that's why the calculators and computers are useful--they take out the
variables of traffic, how lively you felt that day, and what the
almost imperceptible wind was doing.

Three mph is a gentle walk down a long hallway. The wind on your face
is practically imperceptible. But plug a 3 mph headwind into one of
those calculators and see what happens:

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

Take the defaults, choose hands-on-tops, and it predicts. 19.4 mph.

Add an almost unnoticeable 3 mph headwind, and the predicted speed
drops almost 9% to 17.7 mph.

Turn it around to a -3 mph tailwind. Predicted speed rises to 21.2
mph, a little more than a 9% increase.

Cheers,

Carl Fogel

On Tue, 26 Sep 2006 23:05:29 -0600, [email hidden] wrote:

[snip]

Quoted message said:

Three mph is a gentle walk down a long hallway. The wind on your face
is practically imperceptible. But plug a 3 mph headwind into one of
those calculators and see what happens:

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

Take the defaults, choose hands-on-tops, and it predicts. 19.4 mph.

^^^^^ er, drops

Quoted message said:

Add an almost unnoticeable 3 mph headwind, and the predicted speed
drops almost 9% to 17.7 mph.

Turn it around to a -3 mph tailwind. Predicted speed rises to 21.2
mph, a little more than a 9% increase.

Cheers,

Carl Fogel

Curses! Hands-on-drops just above here, for 19.4 mph, not
hands-on-tops.

CF

On Wed, 27 Sep 2006 01:27:16 +0100, Kinky Cowboy <[email hidden]>

Quoted message said:

No, no, no! All else being equal, wider bicycle tyres have lower
rolling resistance than their narrow brethren. Schwalbe explain why
this is so on their web page for the Big Apple

http://www.schwalbe.com/gbl/en/bicycle/on_tour/produktgruppe/?gesamt=276&ID_Produktgruppe=24

And it's been mentioned here many times before. The widely believed
fallacy that narrow tyres have lower rolling resistance is making
hundreds of cyclists ride uncomfortable, puncture prone tyres for
nothing. At touring speeds, the lower rolling resistance of a 38 more
than makes up for the tiny increase in aerodynamic drag and all up
weight compared with a 23

There are no two tires of 38 and 23 where "all else is equal" and I
doubt a 38 exists that has as low rolling resistance as a good 23 at
the proper pressure for each tire.
--
JT
****************************
Remove "remove" to reply
Visit http://www.jt10000.com
****************************

Quoted message said:

Mark Hickey <[email hidden]>wrote:

Quoted message said:

Quoted message said:

That seems like an awful lot of penalty just for going with fatter
tires - what are the specs on those "hideous robust touring" tires?
Inflation?

For example, I ride typical 23 or 25mm high-pressure (110-120psi)
tires on my road bike, and 35mm semi-slicks (85-90psi) on my 'cross
bike, and would be surprised if there's a 1mph delta, even with the
more upright position on the 'cross bike.

OTOH, I've never actually measured the relative speed (don't bother
with a computer on anything other than the tandem, and then only to
make sure the wife is working hard enough). ;-)

Quoted message said:

Consider your sincere but extremely dubious theory that a 1 mph
difference between "more upright" and presumably "on the drops"
positions would be surprising.

That's quite an assumption - why would you assume that I'd ride the
bike with lower bars "on the drops" and the bike with the higher bars
"on the hoods"? If anything, the tendency is the opposite.

<snip>

Quoted message said:

Reduce the 300 watt default to 160 watts, choose clincher tires, and
use "drops"--the prediction is 19.46 mph.

Switch to "hoods"--the predicted speed drops to 17.98 mph.

Put on a pair of MTB tires--the predicted speed drops to 16.05 mph.

Here's where I think your example starts divorcing itself from my
experience - we were looking at a 1.5mph penalty for "touring tires",
yet "MTB tires" exhibit "only" about 1.9mph of penalty. Based on the
calculation variables you include below, I'd conclude that "MTB
(tires)" are knobbies (since they have 3X the (presumed rolling
resistance) value of a tubular.

Quoted message said:

This is why Tour riders aren't using 38 mm tires--the extra rolling
resistance of the heavier construction and the increased wind drag of
the wider tires is subject to the laws of physics. To reduce sidewall
flexing enough to improve the RR of the wider tires would require an
unreasonably harsh ride.

If you're interested in the details of the calculations and the RR
values used, here's the source code for the mph version of the Austin
calculator:

String words[] = {"hoods", "bartops", "bar ends", "drops", "aerobars",
"drafting"};
double values[] = {0.388, 0.445, 0.420, 0.300, 0.233, 0.200};

String words[] = {"clincher", "tubular", "MTB"};
double values[] = {0.005, 0.004, 0.012};

http://w3.iac.net/~curta/bp/velocity/Velocity.java

Obviously, individual riders will have different actual wind drag
coefficents, just as individual tires will vary (as will inflation and
road surface). Plenty of clinchers are over 0.0060, and lots of mtb
tires are under 0.0120. Heavy touring tires tend to be around 0.0100.
Here's a table that suggests such averages, but remember that it's
mostly for small versions of the named tires:

http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm

Great chart - though I think it reinforces my belief that the 1.5mph
penalty is vastly overstated. The RR value tends to be within .001 or
..002 of a smallish road slick, and the wattage penalty in the 10-20
watt range. There are exceptions of course, but generally for tires
I'd never consider for touring.

Quoted message said:

And here's the IHPVA's calculator, harder to use, but with some tire
RR and drag coefficient values for comparison:

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

These raw differences are very small--19 vs 17 mph.

And we're bad at noticing them--try guessing your speed for a while
and then comparing it to the cyclocomputer--can you reliably
distinguish 17 from 18 mph?

Probably not.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

On Tue, 26 Sep 2006 21:17:00 -0700, Mark Hickey <[email hidden]>

Quoted message said:

Quoted message said:

If you plug in 80-lb bike and 150-lb rider, hands on tops, and 50
miles into the distance at the bottom, it predicts a speed of 17.5 mph
and a time of 2:51:25.7. (Wind drag would increase with panniers, but
we'll ignore that.)

Change from "narrow racing" tires to the hideous "robust touring"
tires and try again. The calculator predicts 15.8 mph and 3:09:52.4,
about 18 minutes longer on a 3-hour trip.

That seems like an awful lot of penalty just for going with fatter
tires - what are the specs on those "hideous robust touring" tires?
Inflation?

For example, I ride typical 23 or 25mm high-pressure (110-120psi)
tires on my road bike, and 35mm semi-slicks (85-90psi) on my 'cross
bike, and would be surprised if there's a 1mph delta, even with the
more upright position on the 'cross bike.

OTOH, I've never actually measured the relative speed (don't bother
with a computer on anything other than the tandem, and then only to
make sure the wife is working hard enough). ;-)

I have measured the speed difference; on a 10 mile course, my TT bike
with Conti GP Supersonic 23mm at 110psi is about 1 minute faster than
my cross bike on 37mm Conti SportContact at 80psi. Putting the best
gloss on the narrow tires, I've done a timed training run on the cross
bike, early season, in 28:20 and my best time later in the year on the
TT bike was 25:56. But...the TT bike has tribars and weighs about 3kg
less than my cross bike, and the TT race time was on the course as
raced (it's a 9.5mile loop+1/2 mile overlap) and the training ride had
the start/finish point moved nearer to home so there was a net
altitude gain rather than the net drop which using the proper course
gives you. Only about 20ft either way, but still worth a few seconds.

Another test; I did a standing start kilo on the cross bike in 1:26
and a week later did 1:21 on the TT bike. That's a 1.6mph difference
in a test which should substantially favour the TT bike

So, whatever difference the tyres are making is so small that it's
totally masked by other factors, at my modest racing speed. On the fat
tyres, I can ride in comfort for 5 hours, take in some off road
sections if I want to and have a huge peace of mind about punctures.

If I were the OP, I'd be skipping straight past the 38 and looking for
a suitable 42 or 45. Based on my experience with the 37mm tyres, I'll
be replacing them with the CityContact 42 when they wear out

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

On Thu, 28 Sep 2006 00:38:53 +0100, Kinky Cowboy <[email hidden]>

Quoted message said:

On Tue, 26 Sep 2006 21:17:00 -0700, Mark Hickey <[email hidden]>

Quoted message said:

Quoted message said:

If you plug in 80-lb bike and 150-lb rider, hands on tops, and 50
miles into the distance at the bottom, it predicts a speed of 17.5 mph
and a time of 2:51:25.7. (Wind drag would increase with panniers, but
we'll ignore that.)

Change from "narrow racing" tires to the hideous "robust touring"
tires and try again. The calculator predicts 15.8 mph and 3:09:52.4,
about 18 minutes longer on a 3-hour trip.

That seems like an awful lot of penalty just for going with fatter
tires - what are the specs on those "hideous robust touring" tires?
Inflation?

For example, I ride typical 23 or 25mm high-pressure (110-120psi)
tires on my road bike, and 35mm semi-slicks (85-90psi) on my 'cross
bike, and would be surprised if there's a 1mph delta, even with the
more upright position on the 'cross bike.

OTOH, I've never actually measured the relative speed (don't bother
with a computer on anything other than the tandem, and then only to
make sure the wife is working hard enough). ;-)

I have measured the speed difference; on a 10 mile course, my TT bike
with Conti GP Supersonic 23mm at 110psi is about 1 minute faster than
my cross bike on 37mm Conti SportContact at 80psi. Putting the best
gloss on the narrow tires, I've done a timed training run on the cross
bike, early season, in 28:20 and my best time later in the year on the
TT bike was 25:56. But...the TT bike has tribars and weighs about 3kg
less than my cross bike, and the TT race time was on the course as
raced (it's a 9.5mile loop+1/2 mile overlap) and the training ride had
the start/finish point moved nearer to home so there was a net
altitude gain rather than the net drop which using the proper course
gives you. Only about 20ft either way, but still worth a few seconds.

Another test; I did a standing start kilo on the cross bike in 1:26
and a week later did 1:21 on the TT bike. That's a 1.6mph difference
in a test which should substantially favour the TT bike

So, whatever difference the tyres are making is so small that it's
totally masked by other factors, at my modest racing speed. On the fat
tyres, I can ride in comfort for 5 hours, take in some off road
sections if I want to and have a huge peace of mind about punctures.

If I were the OP, I'd be skipping straight past the 38 and looking for
a suitable 42 or 45. Based on my experience with the 37mm tyres, I'll
be replacing them with the CityContact 42 when they wear out

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

Dear Kinky,

For fun, play with a calculator:

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

Let's bump you up to 250 watts, put in 10 miles, and test a triathlon
bike. The predicted speed and time are 24.5 mph and 24:29.4 in the
ballpark.

Now switch to hands-on-drops.

The predicted speed drops to 23.2 mph and the predicted time rises to
25:51.7, 1.3 mph and 82 seconds slower with the same tires.

Add a pair of "wide high-pressure slicks" to the hands-on-drops bike.

Predicted speed drops to 22.4 mph and time rises to 26:47.1.

Use the "robust wide touring" tires.

Speed goes down to 21.4 mph and time goes up to 28:02.2.

I agree that for riders who don't care about time, these differences
are insignificant--a bit more than 10% at most.

But it's worth emphasizing that "tests" of less than several hundred
rides year-round on the same loop aren't worth much. Fewer tests are
usually skewed by variables such as wind, temperature, humidity, and
what the rider ate for breakfast, as well as the psychological goad of
seeing how fast the different bike can go--just paying more attention
than usual is going to improve your times and give a false impression.

To illustrate such variation, here are my times on my daily 15.2 mile
ride for September 13-19:

46:09
43:51
48:13
46:08
46:40
45:48
48:35

I count off for the sole traffic light and for any cars that
inconvenience me, so it's basically a very sedate TT course. Note the
4:44 spread in times, about 10%, all for the same bike and rider in
only seven days.

(I blame the slow times on the wind and take full credit for whatever
the hell led to the unusually fast 43:51--probably the same wind
changing direction at just the right point on my ride.)

Even an average for a week is well-nigh useless.

(I really like that average of 46:29 for those seven recent rides
because it's so much better than my average for the year so far of
48:27.)

To illustrate the point again, here are my 7 rides from January 1st,
when it was so unusually warm, averaging over 60 degrees, that I was
riding in my shorts:

51:07
49:06
49:15
52:15
48:47
49:45
49:17

Same bike, same rider, same clothes, same 15.2 mile loop, but probably
windier. The average is an embarrassing 49:56. I was 3:36 slower and
would have been more than a mile behind my more recent average at the
finish line.

Cheers,

Carl Fogel

In article <[email hidden]>,

Kinky Cowboy said:

On Tue, 26 Sep 2006 21:17:00 -0700, Mark Hickey <[email hidden]>

Quoted message said:

Quoted message said:

If you plug in 80-lb bike and 150-lb rider, hands on tops, and 50
miles into the distance at the bottom, it predicts a speed of 17.5 mph
and a time of 2:51:25.7. (Wind drag would increase with panniers, but
we'll ignore that.)

Change from "narrow racing" tires to the hideous "robust touring"
tires and try again. The calculator predicts 15.8 mph and 3:09:52.4,
about 18 minutes longer on a 3-hour trip.

That seems like an awful lot of penalty just for going with fatter
tires - what are the specs on those "hideous robust touring" tires?
Inflation?

For example, I ride typical 23 or 25mm high-pressure (110-120psi)
tires on my road bike, and 35mm semi-slicks (85-90psi) on my 'cross
bike, and would be surprised if there's a 1mph delta, even with the
more upright position on the 'cross bike.

OTOH, I've never actually measured the relative speed (don't bother
with a computer on anything other than the tandem, and then only to
make sure the wife is working hard enough). ;-)

I have measured the speed difference; on a 10 mile course, my TT bike
with Conti GP Supersonic 23mm at 110psi is about 1 minute faster than
my cross bike on 37mm Conti SportContact at 80psi. Putting the best
gloss on the narrow tires, I've done a timed training run on the cross
bike, early season, in 28:20 and my best time later in the year on the
TT bike was 25:56. But...the TT bike has tribars and weighs about 3kg
less than my cross bike, and the TT race time was on the course as
raced (it's a 9.5mile loop+1/2 mile overlap) and the training ride had
the start/finish point moved nearer to home so there was a net
altitude gain rather than the net drop which using the proper course
gives you. Only about 20ft either way, but still worth a few seconds.

Another test; I did a standing start kilo on the cross bike in 1:26
and a week later did 1:21 on the TT bike. That's a 1.6mph difference
in a test which should substantially favour the TT bike

So, whatever difference the tyres are making is so small that it's
totally masked by other factors, at my modest racing speed. On the fat
tyres, I can ride in comfort for 5 hours, take in some off road
sections if I want to and have a huge peace of mind about punctures.

If I were the OP, I'd be skipping straight past the 38 and looking for
a suitable 42 or 45. Based on my experience with the 37mm tyres, I'll
be replacing them with the CityContact 42 when they wear out

This can be settled. Get an assistant to ride one bike
while you ride the other. Match coasting on various
surfaces. Then switch mounts and match again. Try to
eliminate rider air resistance by starting at different
initial speeds; and by using different rider positions
where you vary only _one_ rider's position to check
differences in coasting. You get the idea. The effect of
the tires may be small to negligible for typical riding,
but it can be resolved.

--
Michael Press

Kinky Cowboy said:

So, whatever difference the tyres are making is so small that it's
totally masked by other factors, at my modest racing speed. On the fat
tyres, I can ride in comfort for 5 hours, take in some off road
sections if I want to and have a huge peace of mind about punctures.

If I were the OP, I'd be skipping straight past the 38 and looking for
a suitable 42 or 45. Based on my experience with the 37mm tyres, I'll
be replacing them with the CityContact 42 when they wear out

IIRC, the OP was talking about long distance touring, and the frame and
wheels would take up to 45. I'd look at the clearance with fenders
before I went up above 38. (Yeah, it's that important!) I suspect he
could get fenders and a 38 to work quite easily, but I'd want plenty of
clearance to change the flat when it's raining.

Pat

"Michael Press" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

In article <[email hidden]>,
Kinky Cowboy <[email hidden]> wrote:

<snip>

Quoted message said:

This can be settled. Get an assistant to ride one bike
while you ride the other. Match coasting on various
surfaces. Then switch mounts and match again. Try to
eliminate rider air resistance by starting at different
initial speeds; and by using different rider positions
where you vary only _one_ rider's position to check
differences in coasting. You get the idea. The effect of
the tires may be small to negligible for typical riding,
but it can be resolved.

--
Michael Press

This reminds me a lot of the old sewups vs. HP clincher debates.

Most of the people in my old cycling group rode sewups. We did a lot of
high speed "touring" with at least a 50-100 mile ride every weekend
during most of the year.

When the then new Michelin, Wolber and IRC 19-25mm high pressure
clinchers first came out a number people in our group switched to them
over sewups. They ran them at 90-100 PSI

I rode Clementi Paris-Roubaix 30mm cotton sewups most of the time. I
kept them pumped to 75-80 PSI and had very few problems with flats.

The riders in my group all weighed within 10 to 15 pounds of each other
and rode similarly equipped pro bikes of the era. When coasting down
hills, the sewup riders always out distanced the pack.

Chas.