Marketing parlance ?

SKCOLLAB

"Jim" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

We have known for years that tire pressures over 120 psi can actually increase rolling resistance
as the tire treads are pushed past their

elastic

Quoted message said:

limit and high local input stresses can lead to higher than allowable strains which begin to
actually fail the rubber in shear....

Surely tyre manufacturers must do exhaustive tests on their tyres to work out an ideal recommended
pressure for each tyre, and that if a tyre is rated at 120psi then they would have tested it and
found this gives best performance including rolling restistance.

On Wed, 2 Apr 2003 18:27:44 +0100, "Jim" <[email hidden]> wrote:

[SNIP]

Quoted message said:

Any opinions out there ?

A very inexpert one, Jim. I pump my road bike's tyres up to around 100psi. This works okay for me.

FWIW, I have no idea what make or model the tyres are and I can't be bothered to wobble through
my house to look. My back muscles have just started to go into spasm. (Old skiing injury -
another one.)

James

--
A credit limit is NOT a target.

Adrian Boliston said:

Surely tyre manufacturers must do exhaustive tests on their tyres to work out an ideal recommended
pressure for each tyre, and that if a tyre is rated at 120psi then they would have tested it and
found this gives best performance including rolling restistance.

There can be no universal ideal pressure because performance depends on the weight load and
conditions. The recommended pressure should only be used as a rough guide. For a start, front tyres
should be softer than rears.

See the comments on marketing and legal departments in this article:
www.sheldonbrown.com/tyres.html#pressure

~PB

Quoted message said:

Any opinions out there ?

Any tests out there? Good up-to-date ones with popular tyres?

~PB

Jim said:

From the zipp website...

We have known for years that tire pressures over 120 psi can actually increase rolling resistance
as the tire treads are pushed past their elastic limit and high local input stresses can lead to
higher than allowable strains which begin to actually fail the rubber in shear. High tire
pressures only feels fast, as an increase in pressure will increase the frequency at which the
tire vibrates, and in turn transfers more vibration into the hub and rider. This results not only
in increased rolling resistance as the rubber begins to build heat, but also to increased tire
degradation and wear, not to mention wear and tear on the rider

Any opinions out there ?

I believe higher pressures _can_ lead to higher rolling resistance. It can certainly lead to less
comfort, and that alone may be sufficient not to always pump as hard as you can go.

Most of the market-speak sounds like drivel, however.

regards, Ian SMith
--
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Jim <[email hidden]> wrote:
: From the zipp website...

: We have known for years that tire pressures over 120 psi can actually increase rolling resistance
: as the tire treads are pushed past their elastic

Actually, while it's marketing, I think that as general advice it's not bad. Most riders, most of
the time, will be faster with tyres not pumped over 120psi - roads aren't perfectly smooth.

On a velodrome (at one extreme), riders use tubs with very, very high pressure. Time trialists often
use higher pressures than road racers as well. I'm not sure that there is any good reason why TT
riders do this, but there is a good reason why road racers don't - most tyres handle very badly in
corners when over-inflated.

110-115 PSI works for me anyway. Not that it stopped me getting a instant pinch flat when I hit a
stone a 30mph on Tuesday [1]

Arthur

[1] Unfortunately I wasn't doing 30mph on the flat due to decent fitness but due to a large
tailwind....

--
Arthur Clune clune.orgclune.orgOpen ↗ Power is delightful. Absolute power is absolutely delightful -
Lord Lester

Jim posted the same question to rec.bicycles.tech. The following is Jobst Brandt's reply:

----------------------------------------------------------

Jim who? quotes:

Quoted message said:

"We have known for years that tire pressures over 120 psi can actually increase rolling resistance
as the tire treads are pushed past their elastic limit and high local input stresses can lead to
higher than allowable strains which begin to actually fail the rubber in shear. High tire
pressures only feels fast, as an increase in pressure will increase the frequency at which the
tire vibrates, and in turn transfers more vibration into the hub and rider. This results not only
in increased rolling resistance as the rubber begins to build heat, but also to increased tire
degradation and wear, not to mention wear and tear on the rider."

Quoted message said:

Really ?

No! Not the part about an increase in RR. That is pure fiction as the curves at:

terrymorse.comrolres.htmlOpen ↗

show. That is because, as often, manufacturers don't understand their products, the engineering
skills for that having sought more rewarding positions. Rolling resistance is not caused by road
scrubbing as myth and lore tells us, but rather through losses in elastic materials used in tires.
Old-timers may recall when the first durable clincher was offered by Specialized, it had a 1/4"
raised center ridge that was claimed to reduce RR by minimizing scrub (road contact). In fact the
tire had its highest RR when new and after the ridge was flush with the rest of the surface, was
lower. Elastomer losses include the inter-cord matrix that holds the casing together, and the tread.
The tube also becomes an integral part of the tire when inflated. The higher the pressure the less
the tire flexes, and therefore, the lower the RR. That's pretty simple but beyond the scope of the
folks in charge of the product who are, no doubt, in charge of the hype in the PR texts.

As to wear, they should show some wear curves to support their claim. That is to say, where is the
optimum. We don't want to ride flat tires and too high a pressure endangers the rider with tire
blow-off and greater wear.

Jobst Brandt [email hidden] Palo Alto CA

"Jim" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

From the zipp website...

We have known for years that tire pressures over 120 psi can actually increase rolling resistance
as the tire treads are pushed past their elastic limit and high local input stresses can lead to
higher than allowable strains which begin to actually fail the rubber in shear. High tire
pressures only feels fast, as an increase in pressure will increase the frequency at which the
tire vibrates, and in turn transfers more vibration into the hub and rider. This results not only
in increased rolling resistance as the rubber begins to build heat, but also to increased tire
degradation and wear, not to mention wear and tear on the rider

Any opinions out there ?

It sounds like marketing gobbledegook to me. From a table of test results published by Jobst Brandt
in rec.bicycles.tech it appears that rolling resistance decreased for every tyre tested as pressure
increased. From the FAQ at draco.acs.uci.edu8b.14.htmlOpen ↗ :

"These comparative values were measured on various tires over a range of inflation pressures that
were used to determine the response to inflation. Cheap heavy tires gave the greatest improvement in
rolling resistance with increased pressure but were never as low as high performance tires. High
performance tires with thin sidewalls and high TPI (threads per inch) were low in rolling resistance
and improved little with increasing inflation pressure."

--
Dave...

Arthur Clune said:

Jim <[email hidden]> wrote:
: From the zipp website...

: We have known for years that tire pressures over 120 psi can actually increase rolling resistance
: as the tire treads are pushed past their elastic

Actually, while it's marketing, I think that as general advice it's not bad. Most riders, most of
the time, will be faster with tyres not pumped over 120psi - roads aren't perfectly smooth.

On a velodrome (at one extreme), riders use tubs with very, very high pressure. Time trialists
often use higher pressures than road racers as well. I'm not sure that there is any good reason why
TT riders do this,

TTs are usually on better surfaced roads and the rider has no obstruction to his vision, so can miss
any potholes, stones etc.

Stephen

"Arthur Clune" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

Jim <[email hidden]> wrote:
: From the zipp website...

: We have known for years that tire pressures over 120 psi can actually increase rolling
: resistance as the tire treads are pushed past their elastic

Actually, while it's marketing, I think that as general advice it's not bad. Most riders, most of
the time, will be faster with tyres not pumped over 120psi - roads aren't perfectly smooth.

It may be good advice but the technical explanation is gibberish and it's simply not true that
rolling resistance increases beyond 120 psi.

--
Dave...