Tire Rotation

new tires are always faster than old tires!!
why? well, why not no seriuosly when new and scribbed in and or beaten
with larch,
soaked in boredoe the intended designed capacity is correct
when worn the intended designed capacity was flogged to death and no
longer holds true.

the flabby worn gives better grip is a special application as 28 inch
rims for stoned cobbled highways

new tires, once "scrubbed in" or beaten with larch
are always faster than
old worn tires.

why. well, why not no seriously becaws the design is right on the money
when new
the design capacity fades with wear.

In article t,
zen says...

Question: even if a flat profile on the rear tire isn't a safety issue, at
what point does it become a performance issue, if at all, in terms of
cornering ability, rolling resistance, etc.?

When there is no more rubber and all you see is casing. I usually end up
replacing the rear when it starts to get flats on a regular basis.
-----------
Alex

wrote a typical post.
^^^^^^^^^^^^^^^^
I love challenges. Trying to understand what you are saying is one of
life's pleasures.

If you did not recalibrate your cyclometer for the worn and new tyre
circumferences, and all else being equaI, I would expect to see a
slower reading for the new tyres. No?

Pete

On Thu, 11 Aug 2005 11:38:51 -0400, Sheldon Brown
wrote:

"Kovie" wrote in message

Question: even if a flat profile on the rear tire isn't a safety issue, at
what point does it become a performance issue, if at all, in terms of
cornering ability, rolling resistance, etc.?

Tom Nakashima wrote:

After pilling on the miles, my tires had developed a square profile from the
original round radius, which is slightly more pronounced on the rear. I've
heard when this happens, it's time to change tires, as it could be
dangerous to ride on this profile on the front....and there is also a slight
performance loss, which the experts call "rolling resistance".

I'm not convinced of this. I would expect worn tires to have _less_
rolling resistance, because as they get thinner they get more flexible.

The reason for replacing worn tires is that the thinnest part becomes so
thin that it takes a smaller and smaller sliver of glass or whatever to
poke through to the tube, so you start getting more flats.

I've been riding the same weekday training ride just about everyday for the
last 9 years, so I know the road well and speed checks along the whole
route. There's one section on the descent that I gauge as my maximum speed
of 33-35mph before the tire change. When I put on the new tires (yes I
purchased 2 and the same size and brand, same air pressure) with the
rounded profile my speed increased to 39-41 mph on the descent....averaged
checked over 10 rides as I reset my cyclometer before I begin each ride.
On the flats my speeds have increased 1 to 2 mph, but on the climbs I see no
difference in speed.

I can't believe that this is due to the use of new vs old tires.

Rolling resistance is such a small percentage of total retarding force,
especially at high speeds like that that even if you installed totally
frictionless tires I don't believe it would give you half a mph of speed
improvement. I think there's some placebo effect involved here.

Sheldon "Skeptic" Brown
+-----------------------------------------+
| Well, the truth is usually just |
| an excuse for a lack of imagination... |
| --Garak, DS-9 |
+-----------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Dear Tom and Sheldon,

Do I hear a calculator calling my name?

http://w3.iac.net/~curta/bp/velocityN/velocity.html

First, just take the defaults. The calculator predicts 37.2
km/h with 0.0050 rolling resistance.

Now wave the magic wand and use zero rolling resistance. The
calculator predicts 39.4 km/h.

That's a whopping 2.2 km/h faster, about 1.4 mph difference
at 23.1 mph.

So Sheldon must face the horrifying possibility that he
could gain 1.4 mph if he sold tires without adding the
rolling resistance in the back of his shop.

But let's be a bit more realistic. It's unlikely that a worn
tire can achieve even a 50% reduction in rolling resistance,
since much of the loss occurs not in the tread, but in the
flexing of the side casing--which doesn't wear.

Here's a site tested rolling resistance before and after the
tread was ground off--recumbent riders are fond of this
trick for creating tiny street tires:

http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm

Page down once to the Primo 37-349 tire, which was tested
before and after its tread was ground off at four pressures:

New, the Primo's rolling resistance was 0.0070 to 0.0078.

Worn down with a grinder, it dropped to 0.0060 to 0.0066.

(At 140 psi, a faint difference appeared between a normal
and a latex inner tube on the ground-off Primo--0.0060
dropped to 0.0058)

However, even this modest improvement from 0.0070 to 0.0060
may not work in real life.

Page down further to the Continental Grand Prix 28-406 tire
and compare the new and used data--at 120 psi, the used tire
actually increased in rolling resistance, from 0.0067 to
0.0082!

Drat! A real-life worn tire got worse instead of better!

Further down, a used Haro at 85 psi was a tiny bit worse
than a new Haro at 85 psi--reistance rose from 0.0067 to
0.0068. (But that's getting into the realm where the
accuracy of the air gauge may be involved.)

The Schwalbe City Jet 32-406 improved with wear, dropping
from a range of 0.0087 to 0.0082 down to 0.0065 to 0.0063.

The Vredstein Monte Carlo got worse with wear, rising from a
range of 0.0064 to 0.0069 when new to a range of 0.0069 to
0.0077 when worn.

So some tires seem to get worse when worn, some better, and
some stay the same--and the accuracy of the air gauge may
make a considerable difference, not to mention the testing
technique.

Anyway, let's imagine a standard Nakashima rolling down a 7%
grade on tires with 0.0070 and 0.0050 rolling resistance:

http://w3.iac.net/~curta/bp/velocityN/velocity.html

I'll use 0 watts and an 80 kg Nakashima on a 10 kg bike (I
favor fattening riders to default values and putting them on
default bikes).

At 0.0070 rr, Tom hits 57.55 km/h.

At 0.0050 rr, Tom speeds up to 58.46 km/h.

The 0.9 km/h difference amounts to 0.56 mph at about 36.0
mph--well under 1 mph at the maximum speeds that Tom has in
mind.

One trouble with watching a speed on a familiar stretch of
road is that the stupid wind has a nasty habit of
overwhelming the tiny differences that we're looking for.

But the squaring might have some effect that the calculator
ignores, so I'll keep an open mind.

As a side note, the state of Colorado very nicely repaved my
long daily downhill recently. When the chip-seal turned into
smooth asphalt, the rolling resistance dropped quite
dramatically with the same tires. I now hit over 40 mph
about half the time on the long, gentle upper section, where
34-37 mph used to be my maximum. But the wind can knock me
right back to the old speeds without being very noticeable.

So like Tom, I seem to be seeing noticeably faster speeds
with reduced rolling resistance. But this calculator seems
to throw cold water on my notions:

http://www.analyticcycling.com/ForcesSpeed_Page.html

Using 0 watts and -0.07 slope, the default rider is
predicted to hit 17.25 m/s on the 0.0040 asphalt road.

His speed rises to only 17.80 m/s on the 0.0080 rough
asphalt road.

That's only a rise from 38.6 to 39.8 mph. Maybe my chip seal
was rougher than 0.0080 and my new pavement is smoother than
0.0040? Using 0.0090 and 0.0030, I still get only a
predicted difference of 40.1 mph versus 38.3 mph, less than
2 mph for an awfully generous estimate of best versus worst
rolling resistance.

Tom and I are right about going faster (of course!), but I
haven't figured out why yet. I'd go out and re-test things,
but a mysterious colorless liquid seems to be falling from
the sky right now and might confuse my results.

Carl Fogel

:
: wrote a typical post.
: ^^^^^^^^^^^^^^^^
: I love challenges. Trying to understand what you are saying is one of
: life's pleasures.

Not for me. When he starts on that drivel, I just tune out and go to a
different post. Life's too short to try and figure out gibberish....


:
:

Tom Nakashima wrote:
I recently purchased two new tires to replace my old tires which have
developed a flat profile after approximately 4000 miles. I also have been
rotating the tires from front to rear every 500 miles to prolong the profile
(keeping it round) as the rear wears faster than the front. I've also been
making sure the tires have been properly inflated. There have been
articles about rotating a tire from front to rear may not be a good idea for
safety reasons. It seems to me if you don't rotate the tires what you'll
have is a very flat profile on the rear and not getting best mileage out of
the tires.
-tom

Perhaps but the best tire should go onto the front, not the rear. As
the rear wears out, buy a new one, put it on the front, put the old
front on the rear.

"Sheldon Brown" wrote in message
...

Tom Nakashima wrote:

After pilling on the miles, my tires had developed a square profile from
the original round radius, which is slightly more pronounced on the rear.
I've heard when this happens, it's time to change tires, as it could be
dangerous to ride on this profile on the front....and there is also a
slight performance loss, which the experts call "rolling resistance".

I'm not convinced of this. I would expect worn tires to have _less_
rolling resistance, because as they get thinner they get more flexible.

The reason for replacing worn tires is that the thinnest part becomes so
thin that it takes a smaller and smaller sliver of glass or whatever to
poke through to the tube, so you start getting more flats.

I've been riding the same weekday training ride just about everyday for
the last 9 years, so I know the road well and speed checks along the
whole route. There's one section on the descent that I gauge as my
maximum speed of 33-35mph before the tire change. When I put on the new
tires (yes I purchased 2 and the same size and brand, same air pressure)
with the rounded profile my speed increased to 39-41 mph on the
descent....averaged checked over 10 rides as I reset my cyclometer before
I begin each ride.
On the flats my speeds have increased 1 to 2 mph, but on the climbs I see
no difference in speed.

I can't believe that this is due to the use of new vs old tires.

Rolling resistance is such a small percentage of total retarding force,
especially at high speeds like that that even if you installed totally
frictionless tires I don't believe it would give you half a mph of speed
improvement. I think there's some placebo effect involved here.

Sheldon "Skeptic" Brown
+-----------------------------------------+
| Well, the truth is usually just |
| an excuse for a lack of imagination... |
| --Garak, DS-9 |
+-----------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com


Sheldon, sounds strange, and I was just as surprised as you were,
the only thing I could say is; "try it". You probably ride and wear out
tires just as fast as I do.
Find yourself a straight 6-8% grade slope, 1/2 mile long. No pedaling, just
push off to get started.
Carl mentioned wind resistance, (could be) I'm thin, 147 lbs 5'8".
Bibs with cycling jersey, hands on top bar near the stem with arms tucked
into the side of my body, and chin touching the stem. Feet in the horizontal
position parallel to the ground. I'm riding the Avocet Fasgrip SL Carbon 12
700x23C, weight 200g, 127 tpi, 110psi rear, 100psi front.
Record the max speed and repeat at least 5x for each of the tire sets
between the worn and new, record the average max speed.
-tom

pore favor-
which tire flats most often?
which tire slides more?
which tire carries more weight?
which tire is more important heading into the corkscrew?
which tire is more important heading out of the corkscrew?