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PostPosted: Mon Feb 23, 2015 11:36 am 
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I found this article by Paul Lew from Reynolds slightly alarming...http://www.reynoldscycling.com/reynolds ... rim-wheels

In it he suggests that running Open Tubulars on clincher rims that are 24mm or wider is potentially dangerous if the tyre is NOT wider than the brake track.
For the past couple months Ive been running Veloflex Corsa 25 on Pacenti sl23 rims (24mm wide). When measured with callipers the tyres are exactly 25mm while the brake tacks are 24.4mm wide. Just 0.6mm difference, which seems a rather fine safety margin if this theory is indeed true.

Also, would it not be the internal width that determines how well the tyre is held in place as opposed to the width at the outside of the brake track? he suggests the other way around but i don't understand how the outside width of the brake track can effect the tyre at all.


Should i be concerned?

Has anyone else heard of this before? or had open tubular tyres roll off rims?


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Posted: Mon Feb 23, 2015 11:36 am 


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PostPosted: Mon Feb 23, 2015 11:46 am 
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From Lew's perspective what is the difference between an "open tubular" and a clincher?

Note, I do not meant what is the difference generally, but rather specifically from the safety perspective Lew is looking at this from.


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PostPosted: Mon Feb 23, 2015 12:51 pm 
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...the key differentiating factor between molded bead and open tubular tires is the section shape. Molded bead tires are molded as a “half- round” shape, whereas open tubular tires are molded as a “lay-flat” shape...

...Narrow rim channel width also creates a condition where the beads lodge at the base of it. When the channel is wide, not only does the open tubular tire not assume the correct round shape, but the beads cannot lodge at the base of the rim. They’re left floating in space. This bead position is dangerous and can lead to tires decoupling from rims without warning and under conditions that can injure a cyclist.

On the other hand, molded bead clinchers have been molded into a half round shape and they have a molded hook bead. This type of tire does not rely on a narrow channel width in order for the bead to lodge securely at the base of the internal channel.


And Mr4Fox - you've read it wrong. It is the internal width that he suggests is the problem, but obviously in the majority of cases internal width follows external.


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PostPosted: Mon Feb 23, 2015 1:39 pm 
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That seems to be a very narrow definition of "Open Tubular" to me. I'm fairly convinced Vittoria (any numerous others) are offering "clincher" type tyres based on the same casing as their tubular ones, but with the treads vulcanised into shape. Compass tyres for sure are made like this.

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PostPosted: Mon Feb 23, 2015 2:31 pm 
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I had a hell of a time with Veloflex open tubs on Reynolds carbon rims. They worked fine on alu rims, but would not stay put on the carbon rims. There was also a red sticker warning on the tire box itself saying not to use on carbon clinchers. I think it may have been a case of the bead getting too worked while installing, it was a very tight fit, and could have stretched the bead a tad. I gave up on those tires and put them on my wife's training wheels. I think if you are super careful with the bead they are fine, but be careful not to stretch it. Not sure about the width issue.


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PostPosted: Mon Feb 23, 2015 5:07 pm 
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Thanks - I can see the point

Perhaps if this concern of Mr Lew's is supported by empirical evidence we can change from calling them "open tubulars" to "flawed clinchers"?


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PostPosted: Mon Feb 23, 2015 11:01 pm 
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I run vittoria open pave tyres on archetype rims on these are wide and no issues but I do run 23mm open corsa tyres on 25mm carbon rims. The tyres measure 25mm exactly and have given me no problems and I don't see how they could. I think the article is another scare story without too much basis in reality. Sure if you run a tyre that ends up being narrower than rim you might encounter some problems but I would wager that rim damage would be one of those issues. Also why would you run a tyre that is narrower than the rim that is a stupid idea.

I would not worry.

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PostPosted: Tue Feb 24, 2015 5:46 am 
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Quote:
When the channel is wide, not only does the open tubular tire not assume the correct round shape, but the beads cannot lodge at the base of the rim.

I really get the impression Lew is referring to rims with a much wider internal bead width thaan what is being discussed here in which case, Pacenti, Enve, and Zipp probably do not meet the criteria as all have relatively narrow internal bead widths of 20 mm or less. I run vittoria Open Corsa Evo CX in 700x25 on Zipp 303 Firecrest with latex tubes, which when inflated to 100 psi, measure ~27.1mm wide and work great but I will be the first to admit, that an explosive puncture at speed as a result of a pinch flat or debris in the road could make for an exciting times due to the supple nature of the casing of those tires.

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PostPosted: Tue Feb 24, 2015 12:49 pm 
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I guess I got hung up on the paragraph further down where he says "As a general rule, if you use an open tubular tire, the tire diameter must be larger than the rim width at the brake track. The aerodynamic advantage that’s gained from the wider rim will be lost"

Furthermore I just received an email back from veloflex saying that the do not recommend the corsa 25's on rims with an internal diameter greater than 15-17mm and hence I should stop using them.

These tyres were a nightmare to get on the PAC anti rims...especially with 50g condom thin latex tubes lol! Broke one tyre lever in the process but luckily didn't damage any tubes. The fit is so tight I really struggle to believe that they could slip off the rims.


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PostPosted: Tue Feb 24, 2015 1:06 pm 
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Thanks for the input peoples. I feel more confident knowing that others are running similar rim widths with similar tyres with t problems.


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PostPosted: Wed Feb 25, 2015 12:01 am 
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Just one word of caution.

I use ENVE XC rims on my gravel bike. I tried using 30mm Challenge Strada Bianca open tubulars. Possibly the tightest tyres ever made, or possibly just a bad combination with these particular rims.

Because of the tight fit, even when fully inflated to 110psi the reinforced part of the tyre around the bead was not forced firmly into the hook of the rim. The hook is quite deep since it is designed for the thicker bead of a mountain bike tyre. A looser fitting tyre would have been fine since it would have allowed the bead to sit snugly up against the underside of the hook.

As a result the softer sidewall was the only part of the tyre in contact with the hook of the rim. I have now been through 4 tyres as a result of sidewall cuts where the rim has sliced through the weaker sidewall where it should have been in contact with the stronger bead. Because of the wide rim/tight tyre combo, and the flat nature of the open tubular vs a normal clincher, the combination just did not work, and was actually dangerous. Effectively the tyre sidewall was able to move up and down the hook as the tyre moved around during compression and rebound, causing enough movement under 110psi of pressure to cut through.

I have subsequently had great success running these tyres on a narrow Open Pro rim, and have had equal success running 25mm Open Corsa CX tyres on the ENVE rims because they are a little larger in diameter.

Whilst this is more a factor of this particular combination, it is worth bearing in mind that as well as the perils of loose fittting tyres, a very tight fit on a wide rim can also create problems. I always thought that a tight tyre was inherently safer despite the hassle of fitting and removing it, but this has proven that there is such a thing as too tight a tyre and too wide a rim.


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PostPosted: Wed Feb 25, 2015 1:33 am 
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solarider wrote:
Because of the tight fit, even when fully inflated to 110psi the reinforced part of the tyre around the bead was not forced firmly into the hook of the rim. The hook is quite deep since it is designed for the thicker bead of a mountain bike tyre. A looser fitting tyre would have been fine since it would have allowed the bead to sit snugly up against the underside of the hook.


I have also had this issue mounting Veloflex Master 23s on a WTB i19 Freq Team MTB rim. I was using my cross bike as a roadie/commuter for a while. When re-inflating with the Veloflex which are an open tubular it was necessary to inflate part way, ensure the bead was evenly distributed and then keep pumping. I put it down to the tubeless interface in the rim.

FWIW, i run Master 23s on my pacentis and haven't had any issues to speak of so far. I ran them on my XC279s for about a year with no issues either.


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PostPosted: Wed Feb 25, 2015 1:44 am 
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Just a heads up, it looks like at 30c the Enve XC rim is only rated to a max of 90psi.

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PostPosted: Wed Feb 25, 2015 3:04 am 
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i have this problem with my boyd altamont and vittoria open corsa 23. its very hard to make the bead sit into the hook of the rim. i have to slowly inflate, then massage the tire and roll it to make sure the bead sits. i do this every stroke pump till i reach my desired psi. i have veloflex corsa 25 on the way and see if they will fit better.


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PostPosted: Wed Feb 25, 2015 3:17 am 
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The issue with Veloflex's and Challenge tires is an unreinforced tire casing along the bead. The hook on carbon rims tends to be sharper than on aluminum rims and cuts the cloth. Vitoria's have a little bit heavier material along the bead.


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Posted: Wed Feb 25, 2015 3:17 am 


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