Warning: Actual bike tech. Jan Heine's latest rolling resistance claim.

[James]

I received the Rene Herse email this morning. Something about tyre
pressure and rolling resistance, so I followed the link to read the
website blog post.

https://www.renehersecycles.com/the-science-behind-the-tire-pressure-calculator/

Part way down the page there is a bar chart of tyre pressure versus
rolling power for a real world test, not on a drum. And the quote that
follows:

"Here is a typical racing tire, a top-of-the-line 25 mm Vittoria Open CX
Corsa. We measured the power it takes to ride at a speed of 27.9 km/h.
(The test was done a few years ago, but there’s nothing to suggest that
the latest models behave differently.) What you see is that the tires
are fastest at either a relatively soft 5.5-6.0 bar (80-87 psi) or a
very firm 7.3-8.2 bar (106-120 psi). At ‘medium’ pressures, they are
actually slower than at lower or higher pressures. Those differences are
statistically significant. The differences aren’t huge, but 10 watts is
worth thinking about if you’re trying to win a race or complete a
randonneur brevet within the time limit."


In whole numbers, the graph shows a decrease of 7 watts from 147 watts
at 60 psi to 140 watts at 80 psi, then a 10 watt increase at 99 psi and
then a decrease of 6 watts to 120 psi.

Below that there is a similarly shaped graph of a wider tyre, though the
hump is less clearly defined.

Next there is a hand drawn graph that tries to explain the hump. I
think it is incorrect.

The hysteresis losses (those measured on a steel drum and characterised
by the calculated Crr), in the region of the pressures tested is almost
linear. (Actually exponential with a negative exponent.)

The only way that the total power, the sum of hysteresis and suspension
losses, can be shaped as measured is if the suspension losses contain a
resonant hump over a range of tyre pressure of about 1 - 1.5 bar.

This is simple to prove, by subtracting the measured rolling resistance
losses from the measured total power. It is all at the same speed so
aerodynamic losses are constant. The only variable being tyre pressure.


Of course Jan has comments turned off and for the life of me I can not
find a way to contact him.

--
JS.

[Frank Krygowski]

Since the mass absorbing energy is mostly the body of the rider, I
suppose a resonant "hump" at a certain frequency is a possibility. I
dimly recall reading about the response of the body to input frequencies
of bumps, perhaps in tests done by the military. (I guess battle tanks
have pretty lousy suspension.) IIRC, some frequencies were far worse
than others. That may correlate with energy absorption.

But I'd also expect that the input frequency would be very dependent on
conditions like riding surface details, and maybe some characteristics
of the bike itself. As an extreme case, our tandem's response to the
vertical component of bumps is way different than that of any of my
single bikes. Actually, that's true for both me in the captain seat and
my wife in the stoker seat.

Honestly, I don't think a truly optimum tire pressure can be chosen by
any online calculator. I think it's got to be done by the rider in his
individual riding conditions.

But I think Jan Heine has helped, by at least convincing many people
that rock hard tires are not necessarily (or usually) the best.


--
- Frank Krygowski

[Axel Reichert]

James <james.e...@gmail.com> writes:

> The only way that the total power, the sum of hysteresis and
> suspension losses, can be shaped as measured is if the suspension
> losses contain a resonant hump over a range of tyre pressure of about
> 1 - 1.5 bar.

Yes, sure, why not. This reminds me on an experiment I did as a student:
Think of two rulers with a couple of holes. The rulers can be connected
by bolting them together (4 bolts shown):

F
|
| V
|-----|-----|-----|-----|-----
|-----|-----|-----|-----|-----
|

As you can see, they are fixed on the left end. Now if you apply a
sudden force F on the free end, the system will start to vibrate. So
far, so easy. But both the frequency of the free vibration and the
damping characteric will depend strongly on the bolt pre-tension: If it
is close to zero, the two rulers will oscillate individually, albeit in
sync. This results in a low frequency and almost zero damping. If you
tighten the bolts close to the point of tear-off, the two rules can only
oscillate together, with a much higher frequency (because the stiffness
of the system is higher by a factor of 8) and also almost zero
damping. If you tighten the bolts just somewhat (the German expression
would be "luke warm") you will get an oscillation period in between and
very strong damping (due to the frictional sliding between the still
individually moving rulers).

So the phenomenon here is frequency-dependent damping. And like the
pre-tension in my example, tire pressure affects the frequencies.

Best regards

Axel

P. S. for the theory gurus out here: In the "luke warm" case from above
there are nonlinear effects involved (friction) and so the concept of
harmonic oscillation (which is linear) becomes somewhat shaky. But this
affects only the math, not the outcome. In fact, the real oscillation
observed was quite weird and impressive (for large deflections it also
depends on the "pattern" of bolt pre-tensions), as was the very quick
decay of the oscillation to a stand-still.

[AMuzi]

Would you say then that tire casing material affects
frequency and amplitude of that vibration?

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

[Roger Merriman]

I’d be cynical to be honest, with drum testing.

Essentially I’m not sure that as a model/method of testing that it matches
riding on the road/gravel/trails it’s particularly poor with MTB tires
which seems way off.

Roger Merriman

[funkma...@hotmail.com]

That would make sense in as much as the material affects sidewall flex

[Sepp Ruf]

James missed the first thread on this topic:

2442 NW Market St # 426
Seattle, WA 98107-4137
LEFTCOSTIA
;-)

--
"The sort of geopolitical discussions in regards to Ukraine that you
have on Twitter with some anonymous dude with a Roman statue avatar
exceed the quality of discussion held in the White House. Kamala Harris
has dispelled any doubt you could have about this." (rintrah.nl)

[Tom Kunich]

This is very particular to the road surface he is running his test on. The lower pressures have lower rolling resistance because the surface is either very rough or has potholes and such on it. While I haven't run tests using a power meter, my legs are now such that I can feel the difference in rolling resistance.

[Tom Kunich]

I'm quite sure that there are harmonic effects but again they are substantially effected by the weight and weight distribution of the rider. I have a lot of winter weight on right now. When I was first recovering from my concussion I had a lot of extra weight on then as well. I was the last one on the road on group rides. Then as my weight fell below a certain point I went from the front to the back. I am not convinced that this was merely from the weight but the response of my C40 that I was riding at the time.

[Tom Kunich]

I would say most definitely. But it also is effected by your own weight and the way your own weight is distributed and the way you move it about on the bike. Vittoria Corsa supposedly has the lowest rolling resistance but I can instantly tell when I am on Michelin Pro4's since they feel so much faster.

[Axel Reichert]

Yes.

The key idea is to decouple the rider (the big energy dissipator) from
the vibrations. For this you need a soft spring (a low pressure
tire). In order to allow for low pressure, the tire has to be wide. The
flexible casing (the small energy dissipator) diminishes the hysteric
losses in the tire.

Even a +/- 0.5 mm vibration at 10 Hz that comes through to the rider
instead of being evened out by the tire amounts roughly to 12 Watts
loss in the rider. Few roads are that smooth ...

Best regards

Axel

[Joerg]

On 3/29/22 6:08 PM, James wrote:
> I received the Rene Herse email this morning.  Something about tyre
> pressure and rolling resistance, so I followed the link to read the
> website blog post.
>
> https://www.renehersecycles.com/the-science-behind-the-tire-pressure-calculator/
>
>
> Part way down the page there is a bar chart of tyre pressure versus
> rolling power for a real world test, not on a drum.  And the quote that
> follows:
>
> "Here is a typical racing tire, a top-of-the-line 25 mm Vittoria Open CX
> Corsa. We measured the power it takes to ride at a speed of 27.9 km/h.
> (The test was done a few years ago, but there’s nothing to suggest that
> the latest models behave differently.) What you see is that the tires
> are fastest at either a relatively soft 5.5-6.0 bar (80-87 psi) or a
> very firm 7.3-8.2 bar (106-120 psi). At ‘medium’ pressures, they are
> actually slower than at lower or higher pressures. Those differences are
> statistically significant. The differences aren’t huge, but 10 watts is
> worth thinking about if you’re trying to win a race or complete a
> randonneur brevet within the time limit."
>

This study does not include the time it takes to fix the pinch flat that
resulted from running 80psi and hitting a pothole :-)

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

[AMuzi]

On 3/30/2022 2:06 PM, Joerg wrote:
> On 3/29/22 6:08 PM, James wrote:

>> I received the Rene Herse email this morning. Something

>> about tyre pressure and rolling resistance, so I followed
>> the link to read the website blog post.
>>
>> https://www.renehersecycles.com/the-science-behind-the-tire-pressure-calculator/
>>
>>
>> Part way down the page there is a bar chart of tyre
>> pressure versus rolling power for a real world test, not

>> on a drum. And the quote that follows:

>>
>> "Here is a typical racing tire, a top-of-the-line 25 mm
>> Vittoria Open CX Corsa. We measured the power it takes to
>> ride at a speed of 27.9 km/h. (The test was done a few

>> years ago, but there’s nothing to suggest that the

>> latest models behave differently.) What you see is that
>> the tires are fastest at either a relatively soft 5.5-6.0
>> bar (80-87 psi) or a very firm 7.3-8.2 bar (106-120 psi).

>> At ‘medium’ pressures, they are actually slower than

>> at lower or higher pressures. Those differences are

>> statistically significant. The differences aren’t huge,
>> but 10 watts is worth thinking about if you’re trying to

>> win a race or complete a randonneur brevet within the time
>> limit."
>>
>
> This study does not include the time it takes to fix the
> pinch flat that resulted from running 80psi and hitting a
> pothole :-)
>
> [...]
>

Nor running 28psi and slicing a tire with a pinch flat.

[Tom Kunich]

> http://.analogconsultants.com/
Joerg, I'm now 200 lbs and run 60 psi in 28 mm tires and they have never gotten even close to pinch flatting on a pothole. You have in the past talked about getting sidewall cuts on Gatorskins as well. I have to wonder just how hard you're riding to do these things. I might not be as fast as you up hills but I'm probably every bit as fast going downhills. And the roads around here are often VERY potholed. You must have smoke coming off of your cloths as you approach the sound barrier if you're doing things like that.

[Lou Holtman]

60psi (4.13 bar) is low for a 28 mm tire. I run them at 6 bar (rear) for my 76 kg. Regarding breaking stuff Joerg is in a league of his own. Don’t compare that with your world.

Lou

[ritzann...@gmail.com]

On Wednesday, March 30, 2022 at 11:17:01 AM UTC-5, cycl...@gmail.com wrote:
> This is very particular to the road surface he is running his test on. The lower pressures have lower rolling resistance because the surface is either very rough or has potholes and such on it. While I haven't run tests using a power meter, my legs are now such that I can feel the difference in rolling resistance.

Tommy says: "my legs are now such that I can feel the difference in rolling resistance."

???????????????
I do not have the numbers or engineering formulas like Frank and Jeff to dispute Tommy's saying. But I am pretty positive its utter nonsense.

[funkma...@hotmail.com]

Well, tommy is also the one who started a thread a while ago where he claimed he was training with power - without a power meter.

[Tom Kunich]

Lou, you are quite correct. After using the Silca Pressure Calculator, they recommended 176 lbs (12 bar) so I tried that with surprisingly little change in ride feel.

[Tom Kunich]

So you cannot feel the change in pedaling force when you go from a smooth surface to a rough one?

[Tom Kunich]

On Tuesday, March 29, 2022 at 6:09:08 PM UTC-7, James wrote:

By the way, just so we're on the same page - the rolling resistance is HIGHLY sensitive to weight of the bike and rider and the surface he is riding on. Super-hard tires on rough surfaces are VERY SLOW contrary to that chart. I suggest you go to the Silca Pressure calculator.

[funkma...@hotmail.com]

This is how I know tommy is reading the posts of people he claims to have killfiled.

[Andre Jute]

On Wednesday, March 30, 2022 at 4:59:50 PM UTC+1, Sepp Ruf wrote:
> --
> "The sort of geopolitical discussions in regards to Ukraine that you
> have on Twitter with some anonymous dude with a Roman statue avatar
> exceed the quality of discussion held in the White House. Kamala Harris
> has dispelled any doubt you could have about this." (rintrah.nl)
>

Love your sig file, Sepp. Not only witty, but the bonus of truth as well. -- AJ
>

[Andre Jute]

I know your question is aimed at Axel, but it seems pretty obvious to me, from my days developing automobile suspensions, that the softer sidewalls of (especially) touring bicycle tyres are analogous to a soft spring with firm damping from the air volume inside the tyre. Think of a Chapman strut, which he bought in from Renault, a notorious leaning car in those years, and then tamed for competition and fast road use with a firm damper.
>
Andre Jute
Sixty years on from when I found tyres the most frustrating part of developing racing suspensions, we've progressed only to the extent of narrowing the area of ignorance. That's progress!
>