Goodyear metro milers

[scotty_vince]

Anyone know about Goodyear metro milers. They have a max speed marking of 55mph.  Is that for safety or to get the longest life out of them?

[HighTechRedneck]

It would be for safety.  Those tires are designed for urban and short range driving at 55 or below.  They have thicker sidewalls to better tolerate side impacts from curbs and such and I think they have additional tread belts to resist puncture hazzards more (not positive on the latter).  But at sustained highway use they can overheat.

[scotty_vince]

How long is sustained. More than a few hours?

[Sean]

How long is sustained. More than a few hours?

No.  More than a few minutes.

The treads on these tires have a lot of mass.  At speeds above rated, the tread can literally fly apart from centripetal force.

None of these manufacturers advises (or will stand behind) exceeding the speed rating of this type of tire for any length of time at all.  Usually it is a non-issue, because the coaches they are installed on are already speed-limited.

By contrast, some tires are speed-limited strictly for heat reasons.  Usually, these are 65- or 68-mph tires.  Most manufacturers publish de-rating tables for these tires, where the maximum speed can be increased if the weight of the load is decreased.

Why mess around with a safety issue like this?  Get tires rated for the maximum speed your coach can attain.  The few dollars you can save are not worth your life, your loved ones, or those on the road around you.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[belfert]

The Metro Milers are used on the transit buses locally.  Many of them travel for more than more than a few minutes at speeds above 55 MPH.

I wouldn't advocate using these on a bus conversion regardless of how they work for the local transit company.

[HB of CJ]

Seems unreasonably high heat would de-rate any tire.  Who makes a tire that can tolerate 80 mph for hours on end during a mid August high speed run to Las Vegas NV in the late afternoon?  Anyone?  Do the same speed codes on passenger tires relate to Bus Conversion tires?  Dunno. HB of CJ (old coot)

[Jeremy]

The treads on these tires have a lot of mass.  At speeds above rated, the tread can literally fly apart from centripetal force.

Wow...I think that's the first time outside a physics class that I've ever heard another person say 'centripetal' rather than 'centrifugal'.

Jeremy

[bevans6]

Oddly, the correct term would probably have been centrifugal force.  Centripetal force is the acceleration in towards the center that keeps the tire together.  Centrifugal force is the reaction by the mass that tries to blow it apart.  I hated physics class but I liked the experiments in physics lab...

Brian

[Jeremy]

It's twenty years since I was taught physics, but as I remember it centrifugal forces don't technically exist - there is no force acting outwards, only a reaction to the acceleration inwards (ie. the centripetal). Therefore it is correct to say that it is the centripetal forces that cause the tyre to blow apart.

But it was twenty years ago, and I probably didn't understand it properly even then.

Jeremy

[Sean]

Oddly, the correct term would probably have been centrifugal force.  Centripetal force is the acceleration in towards the center that keeps the tire together.  Centrifugal force is the reaction by the mass that tries to blow it apart.  I hated physics class but I liked the experiments in physics lab...

Sorry, Brian, but  to a physicist, there is really no such thing as "centrifugal force".  What blows the tire apart is its inability to sustain the centripetal force attempting to accelerate the tread in a circular motion.

The term centrifugal force is a common shorthand to visualize centripetal acceleration from the reference point of the rotating object itself.  But it does not really exist.

http://www.regentsprep.org/Regents/physics/phys06/bcentrif/centrif.htm
http://regentsprep.org/regents/physics/phys06/bcentrif/default.htm
http://www.schoolforchampions.com/science/force_centrifugal.htm
http://www.mathpages.com/home/kmath633/kmath633.htm
...and dozens more.

The shorthand is so common, however, that you will find very authoritative "definitions" of it everywhere.  When you sit down with a slide rule to calculate the force, you'll find the formula under "centripetal" in Halliday and Resnick.

-Sean
http://OurOdyssey.BlogSpot.com

[bevans6]

http://en.wikipedia.org/wiki/Reactive_centrifugal_force

It's  basically the inertia of the mass being  spun, the opposite reactor to the centripetal force, as I was taught it in Physics 101 lo those many years ago.  Centripetal force is the inwards force holding the mass in towards the center, centrifugal force is the opposite reaction.  Semantics really.  There are as many authoritative arguments against as for, I would expect.  Two of your cites acknowledged the existence of centrifugal force per my definition.  More than willing for current usage to differ from what I was taught 30 years ago, but the force still exists no matter what you call it!

Oh, and because no one believes Wikipedia, here are the current (and some a little not so current) publications cites:

References

   1. ^ Delo E. Mook & Thomas Vargish (1987). Inside relativity. Princeton NJ: Princeton University Press. p. p. 47. ISBN 0691025207.
   2. ^ Acceleration and force in circular motion by Peter Signell §5b, p. 7
   3. ^ A. K. Mohanty (2004). Fluid Mechanics. PHI Learning Pvt. Ltd. p. p. 121. ISBN 8120308948. 
   4. ^ Roger Leslie Timings (2005). Newnes Mechanical Engineer's Pocket Book. Oxford: Elsevier/Newnes. p. p. 111. ISBN 0750665084. .
   5. ^ a b The Columbia Electronic Encyclopedia: Centripetal force and centrifugal force
   6. ^ For more detail see Hall: Artificial gravity and the architecture of orbital habitats.
   7. ^ Hall: Inhabiting artificial gravity
   8. ^ M. Alonso & E.J. Finn (1992). Fundamental university physics. , Addison-Wesley. ISBN 0201565188.

Brian

[luvrbus]

Good grief guys some one ask the time of day here and he gets told how to build a clock,back to my cave now 




good luck

[bevans6]

Think of it as guys sitting around a  campfire shooting the breeze, having a wide ranging conversation.  What's wrong with that?  It's how you learn things.

Brian

[Sean]

It's  basically the inertia of the mass being  spun, ...  Semantics really.

Precisely -- it is inertia, and not a different force.  All of your references will acknowledge that, and you are right, it is semantics.  As I said, the term is shorthand, and we all use it, myself included.  But you felt the need to correct me from centripetal to centrifugal, which is, by your own set of references, a pointless correction.

When a crane exerts 10,000 lbs of upward pull on a 5,000-lb test rope connected to a 20,000 lb weight, when the rope breaks, the force that broke it might be described as the pull of the crane, but it is equally well described as gravity.

When parts of the tread come loose from the tire, the force that ripped the rest of the tire from those parts is centripetal force.  If you (or anyone else) prefer instead to describe the opposing reaction, using the term "centrifugal force," I would not stop you or correct you.  Because it is, indeed, semantics, or a preference for a different frame of reference.  Apparently, though, you felt the need to "correct" me, and I am merely disputing that correction.

-Sean
http://OurOdyssey.BlogSpot.com

[Hi yo silver]

I say we flip for it.
Dennis