Bicycle Quarterly Rolling Resistance Tests: No Surprises

On Mar 24, 11:43 am, Tim McNamara wrote:
I suspect ...
yeah but the idea was to stiffen the bottom bulge reducing bulge
friction induced by load then flex the sidewalls with the reduction of
friction from the stiffer contact area bottom. sensitive sidewalls
joined with stiff bottoms produce fast moments.
you get sensitive sdiewalls in part by reducing air pressure.
the beef with the conti TT seemed to be the TT had weak sidewalls with
low recommended pressure producing quick light touring tires-cafe-but
not haul beans down the road touring tires or sidewalls that could
take touring abuse with the recommended pressures. variable to needed
spec or cheating? positions varied...

i bring that forward as what i understand is a valid primitve and
probabbbly obsolete understanding of auto tires but how do or do not
cycle tires differ from auto tire design?

hahaha welcome to vegas...

wrote:
"It's stiff and inelastic, i.e. an energy sucker."
metal tires/wheels are energy suckers because metal wheels are
inelastic?

Metal is elastic, that's why springs are made of it and why a bell or
a tuning fork resonates for a long time after you ring it. However,
the spring constant is very high. Stiff and inelastic together means
an energy sucker: everything does have to deform when squeezed, but if
it is stiff it will take a lot of force to do that appreciably and if
it is inelastic you won't recover the energy.


elastic tires are not energy suckers?

Pretty much.

In article
. com,
"Ron Ruff" wrote:

I've looked at the BQ test and results and they seem to be seriously
flawed.

I modeled their setup and got the following results:

..............................V1 (mph)..V2 (mph)...t (sec)...dt (sec)

Baseline .................18.17..........13.82......26.29
CdA= .36 vs .35.......18.14..........13.65......26.50......0.2 1
Bar. =29.9 vs 30.1...18.18 .........13.86......26.25.....-0.05
Head wind =0.5 vs 0..17.96........12.93......27.39 ......1.10
Temp= 60 vs 50........18.20.........13.93......26.16......-0.14
Crr=.006 vs .005.......18.03.........13.32......26.89.......0. 60
Weight = 162 vs 160..18.19.........13.88 .....26.22......-0.08

Tiny amounts of wind will really throw off the results, as will small
changes in rider position. Plus a change in Crr from .006 to .005 is
only going to give them a .6 sec time difference. Obviously, this sort
of test is not capable of discerning small Crr differences unless
*many* tests are done for each tire, and great care is taken to
minimize the effects of the many random variables.

On Mar 23, 1:30 pm, "41" wrote:
the values given for these tires from some
other test that has been oft-quoted in this group (I think done by Le
Cycle, on steel rollers as well) are as follows:

Tire Prr Crr Speed*
Vittoria Open Corsa Evo CX 27.1 W .00334 23.22
Michelin Pro2 Race 29.2 W .00360 23.14
Michelin Carbon 34.7 W .00428 22.94
Panaracer Stradius Pro 35.4 W .00436 22.91
Hutchinson Fusion 39.6 W .00488 22.76
Continenta l Ultra GatorSkin 40.3 W .00497 22.73
Continental Grand Prix 3000 46.6 W .00575 22.50
*185lb rider + bike 250W rider output CdA = .32m^2 (racing crouch,
normal road bike) Transmission efficiency = 96%


That looks like writing, but something is off. This is the correct
comparison. BTW, this is from Tour's Crr test.


Tire Crr Speed* Delta

Deda Tre Giro d'Italia 0.0038 23.08
Vittoria Open Corsa Evo CX 0.0039 23.05 0.03
Michelin Pro 2 Race 0.0042 22.96 0.12
Vittoria Diamante Pro Rain 0.0044 22.90 0.18
Michelin Megamium 2 0.0047 22.81 0.27
Pariba Revolution 0.0048 22.78 0.30
Michelin Carbon 0.0050 22.72 0.36
Panaracer Stradius Pro 0.0051 22.69 0.39
Schwalbe Stelvio Plus 0.0052 22.66 0.42
Schwalbe Stelvio Evolution Front 0.0056 22.54 0.54
Continental GP Force (rear) 0.0057 22.51 0.57
Hutchinson Fusion 0.0057 22.51 0.57
Schwalbe Stelvio Evolution Rear 0.0057 22.51 0.57
Continental Ultra GatorSkin 0.0058 22.48 0.60
Ritchey Pro Race Slick WCS 0.0058 22.48 0.60
Schwalbe Stelvio 0.0059 22.45 0.63
Specialized S-Works Mondo 0.0061 22.39 0.69
Continental GP 3000 0.0067 22.21 0.87
Hutchinson Top Speed 0.0069 22.15 0.93
Continental GP Attack (front) 0.0073 22.04 1.04

When offering table data,
please format and post the tables with a monospace font.
--
Michael Press

(In case you wonder whether the author is qualified, check out his
credentials at http://www.vintagebicyclepress.com/contributors.html.
He had a minor in statistics in his Ph.D. studies.)

I have no concerns about the statistical acumen or int egrity of the
authors. That is why I take it to be worthwhile to argue the points:

questions regarding our data:

1) Are we measuring actual differences between tires (explained
variance), or just random variations due to wind, rider position, etc.
(unexplained variance). We looked into that (see the current issue of
Bicycle Quarterly, Vol. 5, No. 3, p. 20). An analysis of variance
(ANOVA) showed that the ratio of explained to unexplained variance in
our initial test was more than 151 to 1. F(18, 36) = 151.9. The
resulting p is smaller than 0.0001, or in other words, there is less
than a 1 in 10,000 chance that we are just measuring random scatter in
the data.

It would be amazing if the null hypothesis were found to hold, i.e. if
it were found that all the tires were the same- look at the wide
variety of them you are testing. But you want to know much more than
that.

You want to know things like, "If I inflate my tires 10-20psi higher,
will I finish Paris-Brest-Paris faster than I would have otherwise?",
"If I choose tire x instead of tire y, or inflate it higher or lower,
would I set a course or age group record that I otherwise would have
missed?", and the like.

So, consider for example the effect of inflat ion pressure. According
to your tests, the effect in the relevant ranges was no greater than
the noise of your methods. But that certainly does not tell you what
you want to know:

The fact that the run time changes only very
little with increasing pressure above a certain point indicates that
the overall resistance of the tire also changes very little with
increasing pressure.

To re-emphasize, this is not a new result but just confirms the IRC
drum tests. As I quoted in my original post, by the IRC numbers, going
from 100 to 120 psi results in about a 13 second improvement over 40
km at 25mph, an amount corresponding to about 0.05-0.1s on your test
course, which is below the level of the noise in your procedures. This
difference is not s tatistically significant for your tests, but it is
athletically very significant for someone going for a course or age
group record, or to win at Paris-Brest-Paris.


somebody [I believe you mean me] said that our tests just confirmed what was known
already. That is true - with the original tests in Vol. 5, No. 1,
there was an article on 1930s handmade French clinchers that seemed to
incorporate all the design features we found make a tire fast at
moderate speeds: great width, supple casing, soft rubber compound, and
as a result low pressure rating. Unfortunately, without real-world
testing, many, if not most people, including tire manufacturers, since
have lost that knowledge.

Don't forget that since the 1930s, the roads got paved, and carbon
black rubber was invented. Still, I don't get this: what you say above
is none other than the conventional wisdom for all tire manufacturers
today, and what Jobst has been saying all these years. The difference
is that you are neglecting two other factors that they keep uppermost
in mind, namely intended application and durability. (One might also
add, wet grip, except that Jobst considers that more than most
manufacturers.)

Intended application: if your goal is to go fast then you have to
think about aerodynamics, and when going fast on even half-well paved
roads the aerodynamic advantage of narrower tires dwarfs the rolling
resistance and suspension loss advantages of wider tires. That is why
you find today's Tour de France riders using 20-23mmm tires at high
pressures, Jobst using 25mm at moderate pressures, and the world's
fastest racers at Paris-Roubaix using 25-30mm tires at pressures lower
still. I might add that all of them arrived at these choices through
evolution and refi nement, not rolling resistance tests of any kind.

So if you can't use wide tires to be the fastest on well-paved roads,
what would you want them for, and therefore, how should the
manufacturers design them?
One good use would be for carrying hea vy loads, either in the
form of yourself, or baggage. For that, the casing must be heavier
duty because you will still need to keep them well inflated, and
likely you want something more durable anyway. Likewise, another good
reason is for riding poorly p aved roads. Wider tires will give you
not just better suspension, but also keep your exposed sidewalls
further away from the debris. Correspondingly, you would want them to
have thicker rubber and stronger casings. The 66tpi casings and
probably 2 - 2.5mm of hard tread rubber of my Avocet Duro Pluses
(which I run at around maybe 50-70psi) make a lot of sense, but the
same size tire in 127tpi with 1mm of soft tread rubber would be a
highly specialized item: made for short races in dry weather on well-
swept roads, for out of shape riders who are not fat enough to need
high pressures, yet who cannot go fast enough for aerodynamics to be a
factor. Who on earth is that?

Remember, soft rubber without a lot of carbon black, while it does
have a lower rolling re sistance for the same thickness, is not
durable; a 66tpi casing is still very flexible; and carbon black is
the most effective means for giving safe wet grip. How many miles is a
Deda Tre good for, and what's the wet grip like?

I think durability must be a reasonably important factor for you as
well. You wouldn't want to be wearing through a tire 80% of the way
through P-B-P. And hard rubber is more puncture resistant too. Get
them to make those Grand Bois tires with 1.5mm (at 25mm, 127tpi) to
1.75 - 2.5mm (at 28 - 32mm, 66tpi) of hard, durable, wet-safe high
carbon rubber, with completely smooth tread (no file pattern), and you
will get some new customers- one of them likely being Jobst, and
myself another.
µ7

second!

Michael Press wrote:

When offering table data,
please format and post the tables with a monospace font.

I already do that. But what does the font I post with have to do with
the font you read with?e

In article .com,
"41" wrote:

(In case you wonder whether the author is qualified, check out his
credentials at
http://www.vintagebicyclepress.com/contributors.html. He had a
minor in statistics in his Ph.D. studies.)

I have no concerns about the statistical acumen or int egrity of the
authors. That is why I take it to be worthwhile to argue the points:

questions regarding our data:

1) Are we measuring actual differences between tires (explained
variance), or just random variations due to wind, rider position,
etc. (unexplained variance). We looked into that (see the current
issue of Bicycle Quarterly, Vol. 5, No. 3, p. 20). An analysis of
variance (ANOVA) showed that the ratio of explained to unexplained
variance in our initial test was more than 151 to 1. F(18, 36) =
151.9. The resulting p is smaller than 0.0001, or in other words,
there is less than a 1 in 10,000 chance that we are just measuring
random scatter in the data.

It would be amazing if the null hypothesis were found to hold, i.e.
if it were found that all the tires were the same- look at the wide
variety of them you are testing. But you want to know much more than
that.

You want to know things like, "If I inflate my tires 10-20psi higher,
will I finish Paris-Brest-Paris faster than I would have otherwise?",
"If I choose tire x instead of tire y, or inflate it higher or lower,
would I set a course or age group record that I otherwise would have
missed?", and the like.

If you read that issue of BQ you will see that those extrapolations were
made using the calculators at the www.analyticcycling.com Web site. I
don't remember that differences in tire pressure were calculated, since
the differences were felt to be below the threshold of statistical
significance by Jan and crew, I doubt it. I'd have to walk all the way
upstairs to double check and I'm currently too lazy. But I do recall a
discussion of the impact on PBP finishing times that would result from
tire choice and they were really quite large. Differences of several
hours, in fact, over the 1200 km in 90 hours at the same rider output.

I was, and remain, skeptical of the BQ test results. However, I have
not yet read the more recent data analysis and will keep an open mind
until then.

So, consider for example the effect of inflat ion pressure. According
to your tests, the effect in the relevant ranges was no greater than
the noise of your methods. But that certainly does not tell you what
you want to know:

The fact that the run time changes only very little with
increasing pressure above a certain point indicates that the
overall resistance of the tire also changes very little with
increasing pressure.

To re-emphasize, this is not a new result but just confirms the IRC
drum tests. As I quoted in my original post, by the IRC numbers,
going from 100 to 120 psi results in about a 13 second improvement
over 40 km at 25mph, an amount corresponding to about 0.05-0.1s on
your test course, which is below the level of the noise in your
procedures. This difference is not s tatistically significant for
your tests, but it is athletically very significant for someone going
for a course or age group record, or to win at Paris-Brest-Paris.

You're making that assumption and taking it as fact, which is a logical
error, but that was one of the main assumptions that Jan's test
challenged. I don't know with certainty one way or the other, but it
may be that the differences in rolling resistance resulting from higher
or lower inflation pressures may be of far smaller magnitude than smooth
drum tests would suggest.

You are making an apparent second error when you say that Jan's test
results "confirm" the IRC results or the Tour Magazine results, for that
matter. Jan's test suggests that the effect of tire pressure is either
lost in the noise of other factors such as road surface grain, or simply
of much lesser magnitude than tire construction, tread design, etc.

snip

Remember, soft rubber without a lot of carbon black, while it does
have a lower rolling re sistance for the same thickness, is not
durable; a 66tpi casing is still very flexible; and carbon black is
the most effective means for giving safe wet grip. How many miles is
a Deda Tre good for, and what's the wet grip like?

Jan described using the Deda Tre tires on a brevet in that issue of BQ.
While it is largely an anecdotal report (e.g, about how the tires felt),
he also set course record times while using those tires.

I think durability must be a reasonably important factor for you as
well. You wouldn't want to be wearing through a tire 80% of the way
through P-B-P. And hard rubber is more puncture resistant too. Get
them to make those Grand Bois tires with 1.5mm (at 25mm, 127tpi) to
1.75 - 2.5mm (at 28 - 32mm, 66tpi) of hard, durable, wet-safe high
carbon rubber, with completely smooth tread (no file pattern), and
you will get some new customers- one of them likely being Jobst, and
myself another. ?7

You of course just described the classic Avocet Road tire. Since that
already exists (albeit with black sidewalls, unfortunately), there's not
much need to duplicate it.

everything goes in here comes out a second
some days are worse than others needing word wrap
oogle realy ubtchers my prose
some inject the word over nuisance
butt yes coping into WORD then straightening the emss tou is btes
like if ure gonna read that bs ya miteswell blow it up and color it.