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Author Topic: Goodyear metro milers  (Read 3694 times)
scotty_vince
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« on: July 03, 2010, 09:34:01 AM »

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?
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« Reply #1 on: July 03, 2010, 09:53:24 AM »

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.
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scotty_vince
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« Reply #2 on: July 03, 2010, 12:08:22 PM »

How long is sustained. More than a few hours?
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Sean
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« Reply #3 on: July 03, 2010, 06:02:14 PM »

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
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belfert
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« Reply #4 on: July 03, 2010, 06:20:21 PM »

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.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #5 on: July 03, 2010, 06:34:50 PM »

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)
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Jeremy
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« Reply #6 on: July 04, 2010, 12:48:44 AM »

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
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« Reply #7 on: July 04, 2010, 03:45:14 AM »

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
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« Reply #8 on: July 04, 2010, 06:51:33 AM »

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
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Sean
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« Reply #9 on: July 04, 2010, 07:08:37 AM »

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
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bevans6
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« Reply #10 on: July 04, 2010, 07:19:05 AM »

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
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« Reply #11 on: July 04, 2010, 07:36:17 AM »

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
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« Reply #12 on: July 04, 2010, 07:39:40 AM »

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
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Sean
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« Reply #13 on: July 04, 2010, 10:31:34 AM »

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
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« Reply #14 on: July 04, 2010, 01:24:20 PM »

I say we flip for it.
Dennis
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« Reply #15 on: July 04, 2010, 03:20:25 PM »

Call it a draw? Grin
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« Reply #16 on: July 04, 2010, 03:35:51 PM »

It's yin and yang, two sides of the same coin.  No reason to have a fuss, in my view.

Sean, I wasn't intending to correct you with malice aforethought, I was trying to have a little fun with what was, in my school days, a lively topic of kind of fun debate and horseplay.  Picture a physics lab, tennis balls on strings, measuring centripetal force and oops, lookit that, Johny in the corner just got a tennis ball in the head, better tie the string tighter next time.  We also did scientific experiments documenting how big a wire the big capacitors in Electric Circuits lab could explode if you charged them up and put a short circuit on them.  I felt your correction of my light-hearted point was a tad heavy-handed and took some small offence from it, particularly because my position did seem to have some points on it's side.  You don't have to always win by killing the other guy.

And I do sincerely thank you for your advice that you have tendered to me from time to time.  Helps me a lot.  I was actually planning to ask you what you would use for a Xantrex Path-maker these days, since they don't seem to make them any longer.

Brian
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« Reply #17 on: July 04, 2010, 05:19:46 PM »

We stowed our satellite dish right after my last post, and then drove for four hours and I've been ruminating about this the whole time.  So let me just apologize for (1) not being clear in my first answer to Brian, and (2) getting all touchy about the whole issue.  Should not post when I am under a time constraint.

It's yin and yang, two sides of the same coin.  No reason to have a fuss, in my view.

Sean, I wasn't intending to correct you with malice aforethought, I was trying to have a little fun with what was, in my school days, a lively topic of kind of fun debate and horseplay.  Picture a physics lab, tennis balls on strings, measuring centripetal force and oops, lookit that, Johny in the corner just got a tennis ball in the head, better tie the string tighter next time.  We also did scientific experiments documenting how big a wire the big capacitors in Electric Circuits lab could explode if you charged them up and put a short circuit on them.  I felt your correction of my light-hearted point was a tad heavy-handed and took some small offence from it, particularly because my position did seem to have some points on it's side.  You don't have to always win by killing the other guy.


You're absolutely right and on re-reading and reflection, I should have said it a very different way.  I don't always "hear" how my words are coming across; a fault of mine for which I have had to apologize more than once on this board.

Let me just say it was not intended to be heavy-handed (although I see that now) but strictly factual.  I fondly remember many of the same physics lab experiments (we had air tables, which can take both lessons and pranks to a whole other level).  I also remember being sternly lectured in both high school and college by more than one physics professor on the "non-existence" of centrifugal force.  As a consequence, I (and probably hundreds of other engineering freshmen) excised it from my vocabulary.  Which is why I chose the word "centripetal" instead, and I probably should have just explained it that way.

Quote
And I do sincerely thank you for your advice that you have tendered to me from time to time.  Helps me a lot.  I was actually planning to ask you what you would use for a Xantrex Path-maker these days, since they don't seem to make them any longer.


As you may know, I have a PathMaker on my bus, and after trying unsuccessfully to brow-beat it into doing what I wanted it to, I finally gave up and now just use the high-current solenoid inside it.

What I recommend instead is a 200-amp, continuous-duty solenoid with the coil driven by a signal from a center-off, double-throw switch.  Connect the common lead to the coil, one side to +24v (or +12v as the case may be) and the other side to the "blower" circuit on the coach (driven by the alternator Relay signal).  Optionally, put a ~30 second time delay in this latter signal.

Now you have a system that bridges the banks either never (center off), always (+24v) or only when the alternator is charging (relay signal).  Leave it in this final position normally; the other positions are useful for troubleshooting or emergency jump-start of the coach.

That will get you charging of both banks from the alternator, but not the 120-VAC charger.  IMO, this is a good thing, but if that's a problem for you I can follow up with further.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #18 on: July 04, 2010, 06:24:48 PM »

Sean, thanks for the advice, I have such a solenoid and a manual system is fine for me, i don't trust automatic systems much anyway, and I have such switches around as well.  Trust you had a nice drive on your Independence Day, we went for a nice drive on our day on Thursday (although we never committed independence, so to speak, we do seem to be sneaking up on it).  Also, I do hope your cat is feeling better.

Sorry for the misunderstanding.  I leave you with this, that I found quite appropriate and very funny, in today's context...   I hope you do too.  I might have been able to "construct Newton's laws in a rotating system" for about 6 minutes in 1977, if at all...

http://www-istp.gsfc.nasa.gov/stargaze/Sfigs/centrifA.png

Brian
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scotty_vince
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« Reply #19 on: July 04, 2010, 06:41:41 PM »

Anyone want to trade some highway rated 22.5 tires for my metro milers, there in excellent condition with plenty of tread. I am moving and need six tires to put on my 4104 to make it the 500 miles to Virginia condition is not super important. Just need enough tread for the trip.

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« Reply #20 on: July 04, 2010, 07:27:14 PM »

Scotty, I would just drive and not worry about changing I have a friend that has that tire on his RTS and he goes all over the desert southwest 112 here today he drives at 62 mph his top speed with no problems and the only thing he doesn't like about the tire is the ride



good luck
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Sean
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« Reply #21 on: July 04, 2010, 09:19:03 PM »

..  I leave you with this, that I found quite appropriate and very funny, in today's context...   I hope you do too.  I might have been able to "construct Newton's laws in a rotating system" for about 6 minutes in 1977, if at all...

http://www-istp.gsfc.nasa.gov/stargaze/Sfigs/centrifA.png


I thought of that comic during our discussion... it's actually from one of my favorite comic strips, XKCD.  Original is here:
http://xkcd.com/123/

I especially like the Goldfinger quote at the end, one of my all-time Bond-villain favorite quotes.  As an amusing side note, Gert Fröbe, who played Auric Goldfinger, did not speak a word of English, and so that (and all his lines) ended up being overdubbed by Michael Collins.

It was not in Goldfinger but rather in Moonraker where Bond does end up in a centrifuge, and like seemingly every villainous sci-fi movie centrifuge set, the seat is mounted in the wrong orientation, a detail that I could not overlook.  Later in the same film we are supposed to believe the space station has centripetally generated artificial gravity, also going in the wrong direction.  Considering the Kubrick classic 2001: A Space Odyssey got this (and nearly every other technical detail) 100% correct more than a full decade earlier, I found it inexcusable.  Rolex wrist-watches with metal-cutting lasers or 100' long, 300lb-test grappling lines inside (or anything else Q Branch invented, for that matter) I had no problem with.  Go figure.

Anyone want to trade some highway rated 22.5 tires for my metro milers, there in excellent condition with plenty of tread. I am moving and need six tires to put on my 4104 to make it the 500 miles to Virginia condition is not super important. Just need enough tread for the trip.


I'm with Clifford on this.  If you only need to make it 500 miles, keep what you've got, and just watch your speed.  The trip at 55 will take you about an hour and a half longer than at 65, no big deal.  If you have qualms about driving 55 on the freeway (something we do all the time, with no ill effects so far), I can help you with planning alternative 55mph roads that are bus friendly.  Lots of ways to work around this without spending money on a set of shoes.

All that being said, I personally would not run those tires much above 55mph longer than a few minutes at a time, such as making a pass, or taking advantage of some downhill momentum.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com
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RJ
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« Reply #22 on: July 06, 2010, 01:58:40 AM »

Sean -

All that being said, I personally would not run those tires much above 55mph longer than a few minutes at a time, such as making a pass, or taking advantage of some downhill momentum.


Just an FYI - The transit agencies I'm familiar with have their coaches driven to the property (i.e. running down the Interstate) on these tires.  Very, very rarely does one fail.

Granted, a lot of transit coaches are geared so that 57 - 62 is "flat out", but the point is that the tires do hold up to sustained freeway speeds.  Drivers take a few minute break every two hours or so (highly recommended), and that gives the tires some breathing room.

I do agree with you, tho, that for long-term Interstate travel, Scotty should invest in tires rated for 65 or 75 mph.  But I think, for this trip anyway, that if he weighs his coach fully loaded, ready to go, and adjusts his tire pressures accordingly, he should be fine.

FWIW & HTH. . .

 Wink
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