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Discussion Starter · #1 · (Edited)
Going through my misc. bin in the bike garage, I stumbled across an article from a few years ago, "Optimizing Your Tire Pressure for Your Weight," by Jan Heine (http://www.vintagebicyclepress.com/images/TireDrop.pdf). Applying the 60/40 rear/front wheel weight distribution assumption for a road bike, and adding 20 lbs bike weight to my 230 lbs, I calculated that I need over 140 lbs. pressure in my rear wheel to achieve the near-ideal 15% deflection recommended in the article (which contains a convenient chart).

Now I never have run my tires that high, and only recently (this year) switched to religiously using 25c tires on the rear wheel. I also vaguely remember thinking that the chart in the article seemed to "overdo" the rear/front variable in recommended tire pressure that I have gleaned over the years from personal experience and browsing forums like this one. But hey, maybe I'm wrong . . . .

I'm running almost new Vredestein Fortezza Tricomps in 25c (great tire), with a maximum pressure rating of 160 psi. (11 bar). So I figured 'dI give 140 lbs a try. Pumped up the rear tire and took the bike for a spin around the block for a test. A few houses down from the end of my circuit, KABLAAM! The rear tire blew dramatically, and dislodged a section of the rear tire bead from my Easton Orion II (fantastic wheel; wish they still made it....).

Question: Could the Vittoria Ultralight tube have been the culprit? The sizing on these is 18c-23c, so I was stretching it a bit to use them in 25c tires (though I've done it successfully for years at lower pressures). This is one of my two favorite tubes, the other being the Micheline AirComp Ultralight A1. While "ultralights," they are quality tubes that have peformed better for me over the years than cheaper, heavier non-ultrights (e.g., Peformance Bike stock tubes). And, importantly, they have smooth valve bodies, so they don't tear up the rubber sealing grommet in my Blackburn AirTower 4 pump, and do not require a herculean struggle to remove the nozzle after inflation.

I doubt it was the tube, but now I'm nervous. Flats, in my experience, are almost always a result of (i) poor tire quality; (ii) underinflation; (iii) road hazard; or (iv) poor rim strip. The rim strip on this wheel is my favorite in the world: Continental high pressure rimstrips (rated to 200lbs psi). None of these factors apply here.

It could be that I was sloppy the last time I installed the tire, and that the bead was not properly seated. I'm generally pretty careful about this, however. I replaced the tube with a Maxxis I had laying around that says its sized up to 25C, carefully inflated the tire initially to 20 lbs psi, worked my way around the tire on both sides, bending the tire back and forth perpendicular to the rim sidewall to seat the bead properly, visually checked to see that no section of the bead/sidewall was higher off the rim than the rest, and proceeded to re-inflate to 140 lbs. It is holding for now (ride around the block).

It is possible that 140 lbs exceeds the maximum tire pressure rating of the Easton Orion II rims. I cannot find reliable information about any such maximum, and will try to contact Easton (not holding my breath for a reliable answer from them, either.). The Vittoria tubes have no maximum pressure recommendation.

So the real question remains: Can the blowout be the result of a (slightly) undersized, "ultralight" tube, or not? I don't want to switch tubes if thats not the problem. If it is the problem, then at least there is a certain amount of peace of mind knowing that. . . .
 

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It could be that I was sloppy the last time I installed the tire, and that the bead was not properly seated.
I think you have it there. A dramatic blowout can only happen if part of the tube somehow escapes the confinement of the tire, either through a gash in the tire casing, or out the side where the bead dislodges. The tire being partly off the rim is a clue, too. Most likely that happened before the blowout, and in fact caused the blowout.

Have you been using these tires on these rims for a while? Some matches have a looser fit, and are hard to get seated adequately.
 

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Discussion Starter · #3 ·
yes

I bought 3 Fortezza Tricomps, used the first one on the rear wheel for months without incident (albeit at lower pressure, circa 120 lbs psi), and replaced it (worn out) a couple of weeks ago with a new one, that has run w/o incident for several hundred miles at the lower pressure.

The tires fit snuggly--not too loose, not absurdly tight.
 

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Discussion Starter · #4 ·
... More info:

Easton wheels customer service (she did not sound like she had any real clue, however) said that their wheels have a 125 psi maximum recommended tire pressure rating. This is disappointing, and a bit dubious. The operator admitted that she had no information on Orion II's, and was giving me information on their current lineup. Even that seems dubious, though.

I've seen Easton press releases re. their carbon wheels that say 135 maximum psi. So their aluminum rims are less?

I don't understand why a modern aluminum clincher would not handle at least 145 lbs psi.

I saw a random post from a couple of years ago where somebody reported that Easton rep told him that Orion II's have maximum recommended pressure of 130 psi. This is not posted on there web site, however (nor is the 125 lbs).

Looks like my options are: (i) to run at higher psi and risk blowout; (ii) run at lower psi and risk sub-optimal handling/rolling resistance; or (iii) switch to different rims (Campy?).

My overall experience--up until now--with Easton wheels has been very, very good. Strong, light wheels; never broke a spoke; handbuilt; stay true; etc. But this is a potential bummer. Wish I could get solid info on max air pressure from them, and understand why it is so low if the information I received is correct.
 

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drewmcg said:
Going through my misc. bin in the bike garage, I stumbled across an article from a few years ago, "Optimizing Your Tire Pressure for Your Weight," by Jan Heine (http://www.vintagebicyclepress.com/images/TireDrop.pdf). Applying the 60/40 rear/front wheel weight distribution assumption for a road bike, and adding 20 lbs bike weight to my 230 lbs, I calculated that I need over 140 lbs. pressure in my rear wheel to achieve the near-ideal 15% deflection recommended in the article (which contains a convenient chart).
You're in an interesting situation. I've used the Jan Heine tire pressure chart to suggest that friends, who often weigh less than 160 pounds, need not inflate their tires to the max pressure limits of their tires. In your case, your weight and 25mm tire size suggest an exceptionally high pressure, but your tire can cover that pressure. Since you were well within the tire pressure limit and your tube was undersized for the tire, and an ultralight tube too boot, I'd think that the tube size was the culprit. An undersized standard tube might have survived, but the thin walls of the ultralight left little margin for error (air) at that hugh pressure.
 

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drewmcg said:
Easton wheels customer service (she did not sound like she had any real clue, however) said that their wheels have a 125 psi maximum recommended tire pressure rating. This is disappointing, and a bit dubious. The operator admitted that she had no information on Orion II's, and was giving me information on their current lineup. Even that seems dubious, though.

I've seen Easton press releases re. their carbon wheels that say 135 maximum psi. So their aluminum rims are less?
This could change my thought about the reason for your blow-out. The max pressures for their rims seem likely to relate to the lateral load that the rims can take where they contact the tire bead. Your blow-out could have occurred because there was enough lateral flex in the edge of the rim at 140 psi that the tire bead slipped, the tube poked out and blew.

As with other dicussions here, it's not the material al/carbon that matters, so much as how it's used. Easton may build more lateral strength into the edge of the rims of one set of wheels than in another.

There aren't alot of clinchers now that are rated much above 120psi. Building rims to accommodate the max rating of most tires doesn't seem unreasonable.

Of course, another option would be to run 28mm tires, if they'd fit on your bike. however, in view of you're using ultralight tubes, I suspect your bike wouldn't accommodate them or you might not like the weight.
 

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why would you ever want to put so much pressure into a clincher? Extremely high pressure can cause the blowouts - it can happen on carbon rims due to braking heat (which effectively adds 20-30 psi). Most clincher rims have a maximum pressure rating - if you don't know it, I wouldn't go above 120. Mavic, Zipp, Hed have it at 125psi. Beside, higher tire pressures can actually increase rolling resistance..
 

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Not likely

PdxMark said:
Your blow-out could have occurred because there was enough lateral flex in the edge of the rim at 140 psi that the tire bead slipped, the tube poked out and blew.
An aluminum rim would deform and stay deformed. It would not release the tire unless the sidewall had seriously deflected, and that would mean the rim taking a permanent set. I'm with everyone else that the OP flubbed the installation of the tire and left a little bit of tube caught under the tire bead.
 

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Discussion Starter · #9 ·
PdxMark said:
This could change my thought about the reason for your blow-out. The max pressures for their rims seem likely to relate to the lateral load that the rims can take where they contact the tire bead. Your blow-out could have occurred because there was enough lateral flex in the edge of the rim at 140 psi that the tire bead slipped, the tube poked out and blew.

As with other dicussions here, it's not the material al/carbon that matters, so much as how it's used. Easton may build more lateral strength into the edge of the rims of one set of wheels than in another.

There aren't alot of clinchers now that are rated much above 120psi. Building rims to accommodate the max rating of most tires doesn't seem unreasonable.

Of course, another option would be to run 28mm tires, if they'd fit on your bike. however, in view of you're using ultralight tubes, I suspect your bike wouldn't accommodate them or you might not like the weight.
28c's won't fit in the rear chainstay fork. Vittoria Evo Corsa's, Vredelstein, and Maxxis all make clinchers rated over 125 psi--130 psi (maxxis); 145 psi (Vittoria and some Vredelstein's); and 160 psi (Vredelstein Fortezza Tricomp). Some even actively promote higher pressures as providing better ride. True that Conti and Micheleins have lower pressure ratings.

Easton famously bills its wheels as NOT having a rider weight limit. Given this fact, and that they build wheel sets like the Orion II and (now) EA90 SL's that have more spokes for heavier riders, why would they not want to support higher psi? Higher psi, after all, protects the rims more under heavier riders. Conti and Michelein's lower psi max probably sacrifices the rims a bit to make life easier for the tires (don't have to meet as high a quality control to stay on rims at higher pressures).
 

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Discussion Starter · #10 ·
stevesbike said:
why would you ever want to put so much pressure into a clincher? Extremely high pressure can cause the blowouts - it can happen on carbon rims due to braking heat (which effectively adds 20-30 psi). Most clincher rims have a maximum pressure rating - if you don't know it, I wouldn't go above 120. Mavic, Zipp, Hed have it at 125psi. Beside, higher tire pressures can actually increase rolling resistance..
Reasons for higher psi on rear wheel under heavier riders are articulated in the article. Hey, these guys are supposed to be the experts . . . .
 

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the maximum tire pressure Easton recommends for alloy clinchers is 130 psi. It's not about quality control - it's the design of the tire (and its tpi). At really high pressures the only additional thing you'll get is a backache and a tire that skips along the read. Worst case you get a rim that ends up like this:

http://bethelcycle.com/articles/warning-do-not-over-inflate-clincher-tires.-pg296.htm

the article is useless without some assumptions about tire construction - deformation will depend not only on psi but also details of tire construction.
 

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Discussion Starter · #12 ·
stevesbike said:
... It's not about quality control - it's the design of the tire (and its tpi). .... the article is useless without some assumptions about tire construction - deformation will depend not only on psi but also details of tire construction.
So Easton knows more about Vredestein's tires than Vredestein (who rates them to 160 psi)? How does this make sense?
 

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Discussion Starter · #13 · (Edited)
stevesbike said:
the maximum tire pressure Easton recommends for alloy clinchers is 130 psi. It's not about quality control - it's the design of the tire (and its tpi). At really high pressures the only additional thing you'll get is a backache and a tire that skips along the read. Worst case you get a rim that ends up like this:

http://bethelcycle.com/articles/warning-do-not-over-inflate-clincher-tires.-pg296.htm

the article is useless without some assumptions about tire construction - deformation will depend not only on psi but also details of tire construction.
Interesting article. I wish the links to Zipp's research links worked. I could not find any info on this issue at Zipp's website . . . .
 

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PdxMark said:
You're in an interesting situation. I've used the Jan Heine tire pressure chart to suggest that friends, who often weigh less than 160 pounds, need not inflate their tires to the max pressure limits of their tires. In your case, your weight and 25mm tire size suggest an exceptionally high pressure, but your tire can cover that pressure. Since you were well within the tire pressure limit and your tube was undersized for the tire, and an ultralight tube too boot, I'd think that the tube size was the culprit. An undersized standard tube might have survived, but the thin walls of the ultralight left little margin for error (air) at that hugh pressure.
i willing to bet that the tube had nothing at all...zero...to do w/ this blowout. any tube, even a lightweight, will handle 2mm larger tires no problem. the tube can only expand as far as the tire will allow. the OP said he might have been sloppy w/ the install, and the blowout blew the tire off the rim...it was a bad install.
 

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drewmcg said:
So Easton knows more about Vredestein's tires than Vredestein (who rates them to 160 psi)? How does this make sense?
this whole thread is a good example of over-thinking an issue; rim manufacturers try to make light rims because consumers are obsessed with grams. The only way to do that is to use less material and rate them with a maximum tire psi. Tire companies can put silly high maximum psi ratings on their tire, but there's absolutely nothing in a tire max psi that implies anything about whether a rim can withstand that pressure. So, if you want to put tubular track psi into a road clincher go ahead - it doesn't provide any benefit. But it might blow up the rim...
 

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FWIW, I had a bad batch of Vittoria Ultralight tubes last year that randomly blew out like that. 3 tubes: 1 front & 2 rear both with different new tires & rims. I returned them all including the extras not installed because of my newly lack of confidence in them.
 

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Discussion Starter · #18 ·
alright....

stevesbike said:
this whole thread is a good example of over-thinking an issue; rim manufacturers try to make light rims because consumers are obsessed with grams. The only way to do that is to use less material and rate them with a maximum tire psi. Tire companies can put silly high maximum psi ratings on their tire, but there's absolutely nothing in a tire max psi that implies anything about whether a rim can withstand that pressure. So, if you want to put tubular track psi into a road clincher go ahead - it doesn't provide any benefit. But it might blow up the rim...
This makes more sense to me that your prior response. BTW, where did you get the Easton aluminum rims = 130 psi max info?
 

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??

drewmcg said:
They blew the tires off the rim? At what pressures?
I'm seriously missing something here, and I'll acknowledge there's lots I don't know. But somebody explain to me what kind of a tube failure can "blow a tire off the rim." I don't see how it's possible. I don't see how a tube can explode violently when it's confined by the rim and tire. It has to get out first, An improperly-installed or ill-fitting tire can be forced off the rim by the pressure of the tube, but that's not a tube failure, and the tube only explodes after it gets out.

So 'splain it to me.
 
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