On Friday, November 20, 2015 at 7:50:44 PM UTC-8, Duane wrote:
wrote:
On Wednesday, November 18, 2015 at 5:58:17 PM UTC-8, James wrote:
On 19/11/15 09:11, wrote:
On Saturday, November 14, 2015 at 9:01:15 AM UTC-8, Frank Krygowski
wrote:
http://velonews.competitor.com/where...ing-tires-fast



Interesting - for example, the "widerúster" 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

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.


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.

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.


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?

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.