are 32mm panaracer ribmos actually 32mm?

General cycling advice ( NOT technical ! )
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hubgearfreak
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are 32mm panaracer ribmos actually 32mm?

Postby hubgearfreak » 16 Jun 2014, 9:27pm

are 32mm panaracer ribmos actually 32mm?

that's it really, i know some manufacturers aren't true to size

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RickH
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Re: are 32mm panaracer ribmos actually 32mm?

Postby RickH » 16 Jun 2014, 9:37pm

Don't forget that the actual size of any given tyre will vary depending on the rim it is fitted to. The same size tyre will be smaller on, say, a 15mm wide rim than it will be on a 19mm one (by a mm or two in my guesstimation).

Rick.

reohn2
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Re: are 32mm panaracer ribmos actually 32mm?

Postby reohn2 » 16 Jun 2014, 10:11pm

hubgearfreak wrote:are 32mm panaracer ribmos actually 32mm?

that's it really, i know some manufacturers aren't true to size


On a Mavic 719 rim yes 32mm.
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SimonCelsa
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Re: are 32mm panaracer ribmos actually 32mm?

Postby SimonCelsa » 16 Jun 2014, 10:46pm

I'd say a little bit less than 32mm on a Sputnik rim..... in the region of 31.5mm (measured a few times for increased accuracy!!).

Hope that helps, all the best,

Simon

reohn2
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Re: are 32mm panaracer ribmos actually 32mm?

Postby reohn2 » 17 Jun 2014, 10:51am

Make me a liar for 0.5mm :shock:
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iandriver
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Re: are 32mm panaracer ribmos actually 32mm?

Postby iandriver » 17 Jun 2014, 11:25am

Where is this measurement taken from? Is it supposed to be measured from the edge of the rim to the highest point?
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beardy
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Re: are 32mm panaracer ribmos actually 32mm?

Postby beardy » 17 Jun 2014, 11:29am

I always assumed it was the width (using callipers).

Some people kindly give both.

iandriver
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Re: are 32mm panaracer ribmos actually 32mm?

Postby iandriver » 17 Jun 2014, 11:59am

Of course it's width, dumb moment there. I just don't think of width as that important. It's the depth that avoids the pinch punctures and gives the cushion (I've always assumed). Would probably rather see overall air volume.
Supporter of the A10 corridor cycling campaign serving Royston to Cambridge http://a10corridorcycle.com. Never knew gardening secateurs were an essential part of the on bike tool kit until I took up campaigning.....

reohn2
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Re: are 32mm panaracer ribmos actually 32mm?

Postby reohn2 » 17 Jun 2014, 4:45pm

iandriver wrote:Of course it's width, dumb moment there. I just don't think of width as that important. It's the depth that avoids the pinch punctures and gives the cushion (I've always assumed). Would probably rather see overall air volume.


I always measure both,32mm Ribmos are 32x32mm,give or take 0.5mm :wink:
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Brucey
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Re: are 32mm panaracer ribmos actually 32mm?

Postby Brucey » 17 Jun 2014, 6:06pm

reohn2 wrote:
iandriver wrote:Of course it's width, dumb moment there. I just don't think of width as that important. It's the depth that avoids the pinch punctures and gives the cushion (I've always assumed). Would probably rather see overall air volume.


I always measure both, 32mm Ribmos are 32x32mm, give or take 0.5mm :wink:


The unsupported part of the inside of a simple bias-ply carcass (like a bike tyre) always assumes a near-toroidal shape. (NB all this will change when we -finally- get radial bike tyres, C'mon Michelin, extractez le doigt... :roll: ).

But anyway assuming that your sidewalls are not lathered in rubber the apparent height of the tyre off the rim is equal to measured width of the tyre, plus the tread thickness, minus the height of the segment of the imaginary toroid that lies below the rim lips.

Since you can easily estimate the last of these, and measure the tyre width, the width of the tyre less the segment height is a good way of estimating the amount of 'squash' available in a tyre. The tyre height is not so useful; tread thicknesses vary from ~2mm to about 5mm.

Whilst fatter tyres roll nicely, strictly speaking the volume of a tyre only greatly affects the rate at which any given leakage rate lowers the pressure in the tyre. It doesn't alter the spring rate of the tyre much, not on bicycle sized wheels.

cheers
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hubgearfreak
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Re: are 32mm panaracer ribmos actually 32mm?

Postby hubgearfreak » 17 Jun 2014, 6:25pm

thanks for all the swift responses. :D

Brucey wrote: (NB all this will change when we -finally- get radial bike tyres, C'mon Michelin, extractez le doigt... :roll: ).


it seems that it's already been tried and dismissed.. quote below from from sheldon brown

"Radial-ply tires for bicycles have been tried -- Panasonic made them for a short time in the 1980s -- but they proved to have an odd feel due to their reduced lateral stability. "

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Re: are 32mm panaracer ribmos actually 32mm?

Postby Brucey » 17 Jun 2014, 10:13pm

I believe that Michelin presently make radial ply tyres for things like eco-racers and that they have about half or two thirds the Crr of other (otherwise similar) tyres.

If there are problems with lateral stability I'm sure they can be solved, just as they have been with motorcycle tyres.

I'd far sooner have decent radial ply cycle tyres than (say) tubeless ones, if it brings such Crr reductions, even if it means new rims etc, I'd go for it like a shot.

cheers
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