Help with upgrades for speed?

On Tue, 19 Apr 2005 17:47:08 -0600,
wrote:

On Tue, 19 Apr 2005 00:37:47 -0400, "David L. Johnson"
wrote:

On Mon, 18 Apr 2005 20:54:58 -0600, carlfogel wrote:

As for the results, they surprised me, too, but that's why I
posted them.

First, remember that the imaginary tires are mounted on the
same imaginary frame, which is not exactly something that
most of us have experimented with.

Yeah, but I can't imagine that that would make up for the difference in
speed capabilities I notice between a mountain bike and a road bike. If
the position is the same, the frame type would have no effect.

The coefficient of rolling resistance is given for both tires--do they
seem out of line to you?

ugly 1.75" mtb tires 0.0070 crr
narrow racing tires 0.0060 crr

Yeah, this seems questionable. I noticed that inflation pressure was not
mentioned on the calculator. Odd. It certainly has a large effect, as we
all know. We often first recognize that a tire is going flat by the fact
that we are having trouble keeping our speed up. These tires cannot be
assumed to be inflated to the same pressure. If I inflated my mountain
bike tires to the 110psi I use for road tires, they would blow off the
rims, or even (see other threads) burst the rims themselves.

Is there some other significant factor involved that the calculator
skips?

Like I said, tire pressure.


Hands-on-tops 300 watts, default the rest:

ugly 1.75" mtb tires 20.7 mph
narrow racing tires 22.0 mph, 1.3 mph faster

Hands-on-drops 300 watts, default the rest:

ugly 1.75" mtb tires 22.8 mph
narrow racing tires 24.8 mph, 2.0 mph faster

I'm not questioning whether or not you read the output correctly, but the
assumptions that went into it.

Dear David,

Here's Tom Compton's calculator for rolling resistance and
pressure, partly based on Jobst's test data:

http://www.analyticcycling.com/ForcesTires_Page.html

While it doesn't do mtb tires, you can see some of the
effects of air pressure by choosing a kind of tire (premium,
utility, touring in apparent order of squashiness) clincher
or tubular, and road or track glue for the tubulars.

You can vary air pressure from 50 to 150 psi (one of the few
non-metric variables I've seen on the site).

Run the model and "Crr, adjusted for tire ratio" changes.

***

Clincher tires, crr x 0.0001

psi 50 60 70 80 90 100 110 120 130 140 150
Premium 68 60 54 50 47 44 42 40 39 38 37
Utility 87 77 71 66 61 57 54 51 49 47 45
Touring 105 95 87 81 75 70 66 62 59 56 53

***

Tubular tires, road glue, crr x 0.0001
(need 14 to 22 extra psi to roll as well as clinchers)

psi 50 60 70 80 90 100 110 120 130 140 150
Premium 82 75 71 67 64 62 60 60 59 59 59
Utility 101 93 87 83 79 75 73 71 69 68 67
Touring 120 111 104 98 93 89 85 82 79 77 75

***

Tubular tires, track glue, crr x 0.0001
(slightly better Crr compared to clinchers from 50 to 110
psi, slightly worse Crr compared to clinchers from 120 to
150 psi)

psi 50 60 70 80 90 100 110 120 130 140 150
Premium 63 56 51 48 45 43 41 40 40 40 40
Utility 82 74 68 63 59 56 53 51 50 49 48
Touring 100 91 84 79 74 69 66 63 60 58 56

Carl Fogel


Aaargh!

Ignore foolish comment about 14 to 22 psi--I subtracted
crr's, not psi. It's actually even worse for tubulars.

To match a premium clincher's lower crr at 50 psi, a premium
tubular with road glue needs about 80 psi.

After that it gets much worse--a premium clincher at 60 psi
rolls as well or better than tubulars with road glue at 110
psi to 150 psi.

(The track glue clinchers comment was correct.)

Carl Fogel

On Tue, 19 Apr 2005 17:47:08 -0600, carlfogel wrote:

Dear David,

Here's Tom Compton's calculator for rolling resistance and
pressure, partly based on Jobst's test data:

http://www.analyticcycling.com/ForcesTires_Page.html

While it doesn't do mtb tires, you can see some of the
effects of air pressure by choosing a kind of tire (premium,
utility, touring in apparent order of squashiness) clincher
or tubular, and road or track glue for the tubulars.

And from the data it's clear that it matters. The fact that the other
calcluator does not take this into account is significant, since the
various tires being compared do not operate in the same pressure range.

psi 50 60 70 80 90 100 110 120 130 140 150
Premium 68 60 54 50 47 44 42 40 39 38 37 Utility 87 77 71
66 61 57 54 51 49 47 45 Touring 105 95 87 81 75 70 66 62
59 56 53

So, you notice a factor of two difference here, and those "radial" tires
with the out-of-bounds rr numbers might not fare so well when compared
with, say, the max rated pressure on each tire.

--

David L. Johnson

__o | Enron's slogan: Respect, Communication, Integrity, and
_`\(,_ | Excellence.
(_)/ (_) |

On Tue, 19 Apr 2005 00:37:47 -0400, "David L. Johnson"
wrote:

On Mon, 18 Apr 2005 20:54:58 -0600, carlfogel wrote:

As for the results, they surprised me, too, but that's why I
posted them.

First, remember that the imaginary tires are mounted on the
same imaginary frame, which is not exactly something that
most of us have experimented with.

Yeah, but I can't imagine that that would make up for the difference in
speed capabilities I notice between a mountain bike and a road bike. If
the position is the same, the frame type would have no effect.

The coefficient of rolling resistance is given for both tires--do they
seem out of line to you?

ugly 1.75" mtb tires 0.0070 crr
narrow racing tires 0.0060 crr

Yeah, this seems questionable. I noticed that inflation pressure was not
mentioned on the calculator. Odd. It certainly has a large effect, as we
all know. We often first recognize that a tire is going flat by the fact
that we are having trouble keeping our speed up. These tires cannot be
assumed to be inflated to the same pressure. If I inflated my mountain
bike tires to the 110psi I use for road tires, they would blow off the
rims, or even (see other threads) burst the rims themselves.

Is there some other significant factor involved that the calculator
skips?

Like I said, tire pressure.


Hands-on-tops 300 watts, default the rest:

ugly 1.75" mtb tires 20.7 mph
narrow racing tires 22.0 mph, 1.3 mph faster

Hands-on-drops 300 watts, default the rest:

ugly 1.75" mtb tires 22.8 mph
narrow racing tires 24.8 mph, 2.0 mph faster

I'm not questioning whether or not you read the output correctly, but the
assumptions that went into it.

Dear David,

Here's a good page from Terry Morse, showing three sets of
tires graphed for rolling resistance and inflation:

http://www.terrymorse.com/bike/imgs/rolres.gif

Of course, since the tests were done by different people,
it's hard to compare them directly. Jobst's upper left-hand
test used a 50 kg load on 700c road tubulars and clinchers,
while the lower left mountain bike tests were done at 30 kg
by Ian Simms, but Terry's note suggests multiplying the
values by 1.67 on the theory that rolling resistance should
increase linearly.

If so, the middle of the 80 psi mtb tire pack looks to be
around 450 grams, which multiplied by 1.67 would be 751
grams.

The middle of the touring pack on the left at 5.5 bar (80
psi) looks to be around 370 grams. That's about 380 grams
less than the mountain bike tires at the same pressure.

Of course, there are two tires, so double it to 720 grams.

One way to visualize this 800 gram resistance is to imagine
pedalling down a level road away from the Grand Canyon, with
a half-mile weightless string looped over a pulley and a
3/4ths full liter Coke bottle dangling on the far end.
That's why rolling resistance doesn't make as much
difference as we expect when bikes are going 20 mph.

Carl Fogel

On Tue, 19 Apr 2005 20:26:41 -0600,
wrote:

On Tue, 19 Apr 2005 00:37:47 -0400, "David L. Johnson"
wrote:

On Mon, 18 Apr 2005 20:54:58 -0600, carlfogel wrote:

As for the results, they surprised me, too, but that's why I
posted them.

First, remember that the imaginary tires are mounted on the
same imaginary frame, which is not exactly something that
most of us have experimented with.

Yeah, but I can't imagine that that would make up for the difference in
speed capabilities I notice between a mountain bike and a road bike. If
the position is the same, the frame type would have no effect.

The coefficient of rolling resistance is given for both tires--do they
seem out of line to you?

ugly 1.75" mtb tires 0.0070 crr
narrow racing tires 0.0060 crr

Yeah, this seems questionable. I noticed that inflation pressure was not
mentioned on the calculator. Odd. It certainly has a large effect, as we
all know. We often first recognize that a tire is going flat by the fact
that we are having trouble keeping our speed up. These tires cannot be
assumed to be inflated to the same pressure. If I inflated my mountain
bike tires to the 110psi I use for road tires, they would blow off the
rims, or even (see other threads) burst the rims themselves.

Is there some other significant factor involved that the calculator
skips?

Like I said, tire pressure.


Hands-on-tops 300 watts, default the rest:

ugly 1.75" mtb tires 20.7 mph
narrow racing tires 22.0 mph, 1.3 mph faster

Hands-on-drops 300 watts, default the rest:

ugly 1.75" mtb tires 22.8 mph
narrow racing tires 24.8 mph, 2.0 mph faster

I'm not questioning whether or not you read the output correctly, but the
assumptions that went into it.

Dear David,

Here's a good page from Terry Morse, showing three sets of
tires graphed for rolling resistance and inflation:

http://www.terrymorse.com/bike/imgs/rolres.gif

Of course, since the tests were done by different people,
it's hard to compare them directly. Jobst's upper left-hand
test used a 50 kg load on 700c road tubulars and clinchers,
while the lower left mountain bike tests were done at 30 kg
by Ian Simms, but Terry's note suggests multiplying the
values by 1.67 on the theory that rolling resistance should
increase linearly.

If so, the middle of the 80 psi mtb tire pack looks to be
around 450 grams, which multiplied by 1.67 would be 751
grams.

The middle of the touring pack on the left at 5.5 bar (80
psi) looks to be around 370 grams. That's about 380 grams
less than the mountain bike tires at the same pressure.

Of course, there are two tires, so double it to 720 grams.

One way to visualize this 800 gram resistance is to imagine
pedalling down a level road away from the Grand Canyon, with
a half-mile weightless string looped over a pulley and a
3/4ths full liter Coke bottle dangling on the far end.
That's why rolling resistance doesn't make as much
difference as we expect when bikes are going 20 mph.

Carl Fogel

Aaargh again! The link should be to the whole page, not just
one image:

http://www.terrymorse.com/bike/rolres.html

Carl Fogel

"Radial? Who makes a radial bike tire?"

Didn't Sheldon do some sort of blurb about radial tires once? ISTR
that they rolled very nicely, but squirmed like the dickens in corners.

SYJ

On 19 Apr 2005 19:30:49 -0700, "StaceyJ"
wrote:

"Radial? Who makes a radial bike tire?"

Didn't Sheldon do some sort of blurb about radial tires once? ISTR
that they rolled very nicely, but squirmed like the dickens in corners.

SYJ

Dear Stacey,

You're right:

http://groups.google.co.uk/groups?hl...donbrow n.com

Here's Sheldon's picture of a radial bike ti

http://sheldonbrown.org/4-leading-4-trailing01.jpg

Here's what Sheldon noticed:

Not super soft, but definitely weird.

The good news was the rolling resistance was quite low, also they seemed
to transmit torque possibly better than conventional tires. At least I
seemed to feel that in on-road climbing in very low gears. (I was
running these on my 63 speed bike for a while.)

Cornering traction was great.

The bad news is that they're a bit floppy from side to side. Riding
straight, you're never actually riding truly straight, always curving
very slightly to the right or left. These tires seem to have a bit of
lateral flop that is quite unnerving when you're riding straight. Feels
a bit like you've got a slow leak.

When I was riding these regularly, I found myself stopping frequently to
pinch the tires to see if they were properly inflated. They always
were, but they always felt a bit underinflated.

They might work better on a wider rim.

Sheldon "Radial Spokes, Not Bad; Radial Tires, So-So" Brown

Carl Fogel

On Tue, 19 Apr 2005 22:21:13 -0400, "David L. Johnson"
wrote:

On Tue, 19 Apr 2005 17:47:08 -0600, carlfogel wrote:

Dear David,

Here's Tom Compton's calculator for rolling resistance and
pressure, partly based on Jobst's test data:

http://www.analyticcycling.com/ForcesTires_Page.html

While it doesn't do mtb tires, you can see some of the
effects of air pressure by choosing a kind of tire (premium,
utility, touring in apparent order of squashiness) clincher
or tubular, and road or track glue for the tubulars.

And from the data it's clear that it matters. The fact that the other
calcluator does not take this into account is significant, since the
various tires being compared do not operate in the same pressure range.

psi 50 60 70 80 90 100 110 120 130 140 150
Premium 68 60 54 50 47 44 42 40 39 38 37 Utility 87 77 71
66 61 57 54 51 49 47 45 Touring 105 95 87 81 75 70 66 62
59 56 53

So, you notice a factor of two difference here, and those "radial" tires
with the out-of-bounds rr numbers might not fare so well when compared
with, say, the max rated pressure on each tire.

Dear David,

I don't notice a factor of two difference unless I compare
50 psi to 150 psi on road tires. Here's the table again
(your quoting comes out wrapped on my screen, so this might
make it easier for people to see);

psi 50 60 70 80 90 100 110 120 130 140 150
Premium 68 60 54 50 47 44 42 40 39 38 37
Utility 87 77 71 66 61 57 54 51 49 47 45
Touring 105 95 87 81 75 70 66 62 59 56 53

Hope that comes out in table form.

At 80 psi, the crr is 50 for the Analytic Cycling idealized
premium clincher. At 120 psi, the crr drops to 40. That's a
20% reduction of one small factor in the overall forces
affecting the bicycle at 20 mph, not a factor of two.

The radial tires seem to out-do the narrow conventional
tires quite nicely, which should be expected--the radial
tire's significantly lower rolling resistance is why cars
use it almost exclusively.

Carl Fogel

wrote in message
...
On 19 Apr 2005 19:30:49 -0700, "StaceyJ"
wrote:

"Radial? Who makes a radial bike tire?"

Didn't Sheldon do some sort of blurb about radial tires once? ISTR
that they rolled very nicely, but squirmed like the dickens in corners.

SYJ

Dear Stacey,

You're right:


http://groups.google.co.uk/groups?hl...donbrow n.com

Here's Sheldon's picture of a radial bike ti

http://sheldonbrown.org/4-leading-4-trailing01.jpg

Here's what Sheldon noticed:

Not super soft, but definitely weird.

The good news was the rolling resistance was quite low, also they seemed
to transmit torque possibly better than conventional tires. At least I
seemed to feel that in on-road climbing in very low gears. (I was
running these on my 63 speed bike for a while.)

Cornering traction was great.

The bad news is that they're a bit floppy from side to side. Riding
straight, you're never actually riding truly straight, always curving
very slightly to the right or left. These tires seem to have a bit of
lateral flop that is quite unnerving when you're riding straight. Feels
a bit like you've got a slow leak.

When I was riding these regularly, I found myself stopping frequently to
pinch the tires to see if they were properly inflated. They always
were, but they always felt a bit underinflated.

They might work better on a wider rim.
.
Sheldon "Radial Spokes, Not Bad; Radial Tires, So-So" Brown

Carl Fogel

I have a pair of these tires in the basement. Came as OE on a Myata LT1000.
They are awful. The tread pattern squirms on the road and feels like it
simply absorbs all your energy as it deforms it's way down the highway.
Pretty good in gravel though.
Bill Brannon