Marketing parlance ?

Discussion in 'UK and Europe' started by Jim, Apr 2, 2003.

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  1. Jim

    Jim Guest

    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 ?
     
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  2. "Jim" <[email protected]> wrote in message news:[email protected]...

    > 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....

    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.
     
  3. James Hodson

    James Hodson Guest

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

    [SNIP]

    >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.
     
  4. Pete Biggs

    Pete Biggs Guest

    Adrian Boliston wrote:
    > 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
     
  5. Pete Biggs

    Pete Biggs Guest

    > Any opinions out there ?

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

    ~PB
     
  6. Ian Smith

    Ian Smith Guest

    On Wed, 2 Apr 2003 18:27:44 +0100, Jim <[email protected]> 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 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
    --
    |\ /| no .sig
    |o o|
    |/ \|
     
  7. Arthur Clune

    Arthur Clune Guest

    Jim <[email protected]> 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 http://www.clune.org Power is delightful. Absolute power is absolutely delightful -
    Lord Lester
     
  8. Pete Biggs

    Pete Biggs Guest

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

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

    Jim who? quotes:

    > "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."

    > Really ?

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

    http://www.terrymorse.com/bike/rolres.html

    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 protected] Palo Alto CA
     
  9. Dave Kahn

    Dave Kahn Guest

    "Jim" <[email protected]> wrote in message news:<[email protected]>...
    > 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 http://draco.acs.uci.edu/rbfaq/FAQ/8b.14.html :

    "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...
     
  10. On 3 Apr 2003 08:55:34 GMT, "Arthur Clune" <[email protected]> wrote:

    >Jim <[email protected]> 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
     
  11. Dave Kahn

    Dave Kahn Guest

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