Tire testing

[Frank Krygowski]

http://velonews.competitor.com/where-the-rubber-meets-the-road-what-makes-cycling-tires-fast

Interesting - for example, the "wider=faster" claim, and the data
showing that tire pressure really doesn't matter much, at least over a
reasonable range. I think those ideas are still not widely accepted.

The article alludes to the suspension effect, i.e. that one important
function of the tire is to reduce energy losses due to upward
acceleration of the bike+rider. But I don't see that their steel drum
test (even with a diamond tread) really replicates that effect.

Jobst would say that they are correct in measuring only energy loss
within the tire. But ISTM that if the question is "what makes a tire
fast?" (the article's lead sentence) it needs to account for the fact
that energy is lost within the body of the rider.

IOW, this test may show what makes a tire "fast" on an unloaded bike (or
a steel drum). But it may be different if the tire is supporting an
actual human being on an actual road.


--
- Frank Krygowski

[cycl...@yahoo.com]

We had an argument in our riding group with everyone on one side and me on the other about these tests.

This is basically because the tests are not run under real-world conditions.

While you would normally run a wider tire so that you could reduce your tire pressure slightly to give a more comfortable ride this test gives all tires the same pressure.

But let us assume that this is the way people would in fact use these tires.

The wider tires under real-world conditions would still give higher friction than the narrower tires.

Why is this? Let us assume a 200 lb rider and a 25 lb bike. Also let us assume that more or less normal 40/60 front/rear weight distribution. (This is why Specialized makes tire sets with the front and rear tires different from one another.)

At a slow speed (balance speed on smooth road) the front tire would require a support of some 90 lbs or .77 square inches of contact area while the rear 135 lbs and 1.16 square inch contact patch.

Now the testing machine assumes a smooth ride or an acceleration on a smooth surface. Something that sure isn't available on most of the world's roads. But nevertheless let's carry on.

A tire has a finite diameter. And this means that the wider the tire the less for and aft compression the tire requires to achieve it's contact patch. This is also the reason that tire compound makes such a difference. The softer the compound the more "smush" it will have to achieve the required contact patch with the least deflection of the tire cord. Or in another way of looking at it, you are effecting the roundness of the tire less.

But in the real world you aren't on a smooth surface. You are on a continuously undulating and even a potholed surface.

In these conditions what you have is the wider tires that contain a larger air volume "crush" more - that is - in order to counter the loads on the tires by increasing their air pressure they have to compress and change shape much more than the narrower smaller volume tires. So if your one purpose is a lower rolling resistance the narrower tires will actually work better in the real world riding that we do.

But, you say, every year the grand tour riders switch back and forth between narrower and wider tires without ever seeming to decide what to do.

And this is because each year the courses of the grand tours change and what becomes more important is whether you want lower rolling resistance or better rough road comfort and braking. And these are not a matter of road surface but rider preference.

For ordinary everyday riders like us on the group, we use more comfortable longer wheelbase bikes and lower rolling resistance 23 mm tires for descending faster.

[Doug Landau]

23 mm as opposed to what?

[cycl...@yahoo.com]

25 mm or 28 mm. As the test said they thought that a 26 cotton Specialized would test better than their 24 and theoretically a 28 would test even better.

[James]

I am more comfortable and seemingly just as fast using a 27mm rear tyre
(advertised as 25mm) inflated to between 80-90psi, compared to when I
used a 23mm tyre inflated to about 105psi. A 23mm front tyre is fine at
up to 100psi for me, but I usually let it run a bit softer.

--
JS

[Doug Landau]

cuz the rear doesn't take as much wind resistance behind the seat tube. swap them.

[James]

> cuz the rear doesn't take as much wind resistance behind the seat tube. swap them.
>

While you might be correct about wind resistance, swapping the front and
back tyres would make no sense at all. The back tyre carries more load
and my arse and back need more cushioning. My hands and arms are happy
with the 23 on the front.

--
JS

[Doug Landau]

What I am saying, and I am just regurgitating what I think I've learned here, not speaking from experience, is that there is a point of diminishing return on the rolling resistance curve, beyond which skinnier tires do have more RR than wider ones, and the reason for their use is their lower wind resistance. 20mm tires fall into this category. Whether said point occurs between 25s and 20s or between 28s and 25s or on the far side of 28s is the topic of much discussion.

At the same time, whether that point is at 25 or at 28 is academic, because all agree that a)the difference in RR is negligible..as you say 28s (and even 30s) at 90psi feel about as fast as 25s, and b)any difference is far overshadowed by the difference in effort required to spin them up.

[Frank Krygowski]

On 11/19/2015 3:28 PM, Doug Landau wrote:
> On Thursday, November 19, 2015 at 11:35:55 AM UTC-8, James wrote:
>> On 19/11/15 12:15, Doug Landau wrote:
>>> On Wednesday, November 18, 2015 at 5:58:17 PM UTC-8, James wrote:
>>>>
>>>> I am more comfortable and seemingly just as fast using a 27mm rear tyre
>>>> (advertised as 25mm) inflated to between 80-90psi, compared to when I
>>>> used a 23mm tyre inflated to about 105psi. A 23mm front tyre is fine at
>>>> up to 100psi for me, but I usually let it run a bit softer.
>>>>
>>
>>>
>>> cuz the rear doesn't take as much wind resistance behind the seat tube. swap them.
>>>
>>
>> While you might be correct about wind resistance, swapping the front and
>> back tyres would make no sense at all. The back tyre carries more load
>> and my arse and back need more cushioning. My hands and arms are happy
>> with the 23 on the front.
>>
>> --
>> JS
>
> What I am saying, and I am just regurgitating what I think I've learned here, not speaking from experience, is that there is a point of diminishing return on the rolling resistance curve, beyond which skinnier tires do have more RR than wider ones, and the reason for their use is their lower wind resistance. 20mm tires fall into this category. Whether said point occurs between 25s and 20s or between 28s and 25s or on the far side of 28s is the topic of much discussion.

I'm sure that where that point occurs depends heavily on the road
surface roughness. And I don't mean only macro roughness, like pothole
patches. The difference in roughness between a well-paved asphalt road
and a "chip-seal" road is pretty extreme, as seen by a bike tire.

--
- Frank Krygowski

[James]

On 20/11/15 12:16, Phil W Lee wrote:
> Frank Krygowski <frkr...@sbcglobal.net> considered Thu, 19 Nov 2015

> Indeed.
> It takes quite a lot of power to keep a 200lb bag of jelly vibrating
> in the way that is experienced by any rider on 23mm tyres on coarse
> chip-seal roads.
> Fit 28 or 32 mm tyres, and drop the pressures accordingly, and much
> less power will be lost in that way.
> The problem is that you can't generally change tyres for every change
> in the road surface, so you just have to figure out what works on the
> roads you ride.
> It's quite possible that a slightly narrower tyre on the front may
> make sense, as it does typically carry less weight.
>

That was my conclusion also. My hands and arms make pretty good shock
absorbers without wasting lots of energy jiggling all about - compared
to the rest of me that could be jiggled about more by a narrow and hard
back tyre.

--
JS

[cycl...@yahoo.com]

On Wednesday, November 18, 2015 at 5:58:17 PM UTC-8, James wrote:

And I find it more comfortable to ride alone rather than with a group that is keeping the pace do high for no reason than to complete a ride 10 minutes earlier.

On a couple of occasions I've let the greyhounds get far ahead and then run them down on their favorite hard climbs so that they realize that I can ride faster than them and don't because I don't like to ride fast all the time everywhere. But it never seems to sink in. And so every ride there they are again jack-rabbiting off. So I'm spending more and more time just going on lone rides.

[Duane]

<cycl...@yahoo.com> wrote:
> On Wednesday, November 18, 2015 at 5:58:17 PM UTC-8, James wrote:
>> On 19/11/15 09:11, cycl...@yahoo.com wrote:
>>> On Saturday, November 14, 2015 at 9:01:15 AM UTC-8, Frank Krygowski
>>> wrote:
>>>> http://velonews.competitor.com/where-the-rubber-meets-the-road-what-makes-cycling-tires-fast
>>>>
>>>>
>>>>

>> Interesting - for example, the "widerúster" claim, and the data

That's the nice thing about cycling. Lots of options.

> On a couple of occasions I've let the greyhounds get far ahead and then
> run them down on their favorite hard climbs so that they realize that I
> can ride faster than them and don't because I don't like to ride fast all
> the time everywhere. But it never seems to sink in. And so every ride
> there they are again jack-rabbiting off. So I'm spending more and more
> time just going on lone rides.
>

Why does it bother you?


--
duane

[cycl...@yahoo.com]

Because I expect group rides to be GROUP rides. We have lost many members over the years precisely because of this stupid practice. There's rides that you go fast on and 3000 of mostly 8% climbing and 45 miles is not the time or place for senior citizens.

Last year the group broke completely up into small groups going their own speed in what turned out to be a rainy day on a 72 mile day and the ride leader swore she'd never lead another group ride and hasn't.

Plus when you do that there are always people that try to keep up and burn themselves completely out and have a completely miserable time.

This might be your idea of a group ride but it isn't mine.

[Frank Krygowski]

A married couple who were avid members of our bike club had to move to
another state for his job. They had such excellent experiences with our
club that they immediately joined the club in their area.

They showed up for their first club ride and were handed route maps -
something that almost never happens with our club. Then all the others
took off at various high speeds, leaving my friends behind. In that
club, the idea seemed to be "ride as fast as you can, and maybe we'll
have lunch at the finish."

(At one time, some young guys in our club did do "Survival of the
Fittest" rides. They were advertised as "no stops, no wimps," which is
fine if that's what you want to do. But my friends had expected a more
sociable, less lonely riding experience.)

--
- Frank Krygowski

[Sir Ridesalot]

A lot of clubs will host "No Drops" rides which means that no rider will be left behind. Also, with some clubs it depends on what they feel like doing on any particular ride. Thus what's supposed to be a nice recovery ride can end up being a real workout if that's what they feel like that day.

Once again it's a question of knowing what any particular club is like and asking questions BEFORE joining the ride.

Cheers

[Duane]

Ah. I misunderstood you. I didn't see that you were talking about the
group you were with.

What we do is limit the group size and break the groups up by average
speeds. This doesn't always work but it helps.

Still people climb at different rates so we typically regroup at the tops
of hills. Rides like you're describing 8% for 45 miles usually break into
smaller groups just like you say.


--
duane

[Duane]

Yeah rules are different for different clubs. Find a club that rides like
you like. We have several in our area.

Even so, some of our faster groups train for races and they tend to drop
slower riders. Most of us don't drop people though. This doesn't mean
that a slower rider won't get the suggestion to find a different group if
they can't keep up.

We have riding clinics and group leader rides at the beginning of the
season to try to help people to acclimate as well as to teach new riders
how to ride safely. Not everyone likes this.

--
duane

[Lou Holtman]

Totally agree. If you are stronger take longer turns in front or take care
of the stretches with headwind.

--
Lou

[Clive George]

On 21/11/2015 22:23, Frank Krygowski wrote:

> (At one time, some young guys in our club did do "Survival of the
> Fittest" rides. They were advertised as "no stops, no wimps," which is
> fine if that's what you want to do.

Isn't that what a chain gang is about?