Ken C. M. said:Tim McNamara said:In article <[email hidden]>,
Ken C. M. said:I have read that a slick or semi-slick tire will have less r.r. than
a tire of the same size and pressure that is of a treaded design. Is
this true or a myth?
Oh good grief. PLEASE use Google and search for this. There are
hundreds and hundreds of posts in the Usenet archives about this, plus
Web sites as well. We really don't need another monthly thread on
rolling resistance- we just finished one, fer pity's sake.
I'm sorry to pollute the NG. I guess I am not worthy.
Quoted message said:
Quoted message said:Second whick type of tire is better for mixed riding a slick or
treaded. By mixed riding I am refering to town / urban commuting and
recreation fitness rides.
Slicks. Slicks are better for all riding on hard surfaces from asphalt
to slickrock. Tread on a tire used on such surfaces is not only
useless, it is actually detrimental as it creates voids which in turn
increase tread squirm and thus rolling resistance, as well as being able
to entrap sharp bits of stuff that can lead to a puncture. The
decorative tread on some tires like the Continental Ultra 2000 is
probably harmless as well as useless.
Quoted message said:Third I have read that 26 or 28 is about the optimal balance between
ride comfort and performance. What is the opinion on this?
26 or 28 what? Wheel diameter? Tire width? If tire width, I have
found that 700 x 28 is the best compromise size for me. These tires are
usually 25-26 mm wide in actual measurement. But I am 6'4" and 216 lbs.
If you're 5'9" and 135 lbs or you're 6'9" and 300 lbs, your best
compromise might be different.
26 or 28 inches. Of course it's mm. 700c rim.
Quoted message said:If you're racing, then 700 x 23 might be the best choice because it'll
be interchangeable should you need a spare wheel- almost everyone else
will be using 700 x 23s.
Well I'm not racing, mostly riding in town. On streets that are okay,
not great, but not bad.
Ken
Dear Ken,
Don't worry, you're perfectly worthy.
Almost every bicycling topic has been discussed previously
on RBT.
Tim just went through the ritual complaint that your first
question has already been addressed on RBT (quelle
surprise!) and then enjoyed himself addressing your next two
questions--which have also been addressed on RBT.
The ritual this-has-already-been-discussed is just a way of
telling you how well-informed we are and how terribly hard
it is for us to take the time to explain things.
(It's also often used to pretend that a controversial topic
has been settled in the poster's favor, but that's an
advanced debating tactic not commonly used for innocent
queries.)
The bad manners involved in this-has-already-been-discussed
are justified by the fact that it's easier than actually
answering the question (notice that Tim's self-pitying reply
about tread and rolling resistance was so knowledgeable that
it gave no hint of an answer) or even just providing a link
to an explanation.
Despite all the ritual complaints that topics have been
beaten to death, that's pretty much what most of the poster
who complain love to do. Regulars like Tim (who's a pretty
good fellow, incidentally, and probably just cracked for a
moment under the strain) would have scarcely anything to say
if they didn't post about the dead horses that haunt RBT.
(Notice that after pulling his hair out about rolling
resistance and tread, Tim proceeded to address your other
questions, which are just as familiar and easily googled in
the archives of RBT.)
Concerning tread blocks or grooves and rolling resistance,
the problem is that rubber is basically incompressible, so
it must bulge out in another direction when compressed
instead of acting as a spring and returning the force. When
there are voids in the tire rubber, it can bulge even more
uselessly than usual, wasting energy in all directions.
Knobby tread can even raise wind drag noticeably, since all
those wretched knobs are busy stirring up turbulence. Put a
pair of bikes upside-down, crank their rear tires up, and
notice how much more fan-action you get off to one side of
the knobby.
On dry pavement, tread patterns don't help traction for
cornering, acceleration, or braking. Dragsters, race cars,
and racing motorcycles all use smooth tread tires for
maximum traction.
The grooves on car tires are for rain. Without grooves, the
flat, wide slicks on race cars turn rain-flooded race tracks
into bumper car follies.
This groove-for-water trick is pointless for narrow, rounded
bicycle tires. To the water, a bicycle tire looks like an
oncoming U instead of a car's \_____/ tire. The bicycle tire
has a long, narrow contact patch whose ability to cut down
through water isn't improved by tiny tread patterns.
If you want to see a practical calculation of the effects of
rolling resistance, you can use this online speed calculator
to compare the same bicycle and rider using several kinds of
tires:
http://www.kreuzotter.de/english/espeed.htm
For the default settings and hands-on-tops, the calculator
predicts these speeds:
17.3 mph narrow racing tires
17.2 mph medium-wide high-pressure slicks
17.0 mph wide high-pressure slicks
16.2 mph robust wide touring tire
17.5 mph Rinkowsky radial wide slick
16.2 mph offroad 1.75" (presumably a knobby)
Fiddling with calculators like this can help put things in
perspective. Notice that the narrow tires do indeed go
faster than the knobbies, but that the rolling resistance
advantage is around 1.1 mph at a moderate cruising speed.
This is why we see so many people happily riding around on
pavement on knobby tires--the difference is not really quite
as large as we'd like to think.
Similarly, the difference between narrow and medium tires is
discouragingly small. Despite claims often seen here for
dramatic, easily-felt improvements in how a new tire rolls,
it's unlikely that most riders can notice the tiny actual
speed increase under practical conditions.
The Rinkowsky radial tire's superior performance reminds us
that once the tread is smooth, it's the nature and design of
the casing material that governs the rolling resistance.
Embarrassingly, the sturdy, comfortable, robust touring
tires with smooth tread are expected to be just as sluggish
as a typical off-road tire. It takes a lot of effort to
deform all that heavy casing and thick tread on a wide
touring tire.
Whether long-winded replies like this are better than
briefer this-has-already-been-discussed dismissals is a
separate topic.
Cheers,
Carl Fogel
