Max air pressure for carbon clinchers

[steveoz]

Was in my LBS talking carbon rims and the proprietor said that the carbon clincher rims are rated only to 125-135 psi - is it just me or does that seem a little to close for comfort when regarding the max tire pressure - a tire at 115psi only leaves 10 or 15 lbs left before potential rim failure :eek: ...you'd think there would be a little more strength engineered in there for a safety margin..

[Dead Man]

theres no justification for getting anywhere near those kinds of pressures anyway

[steveoz]

theres no justification for getting anywhere near those kinds of pressures anyway

absolutely true - but I can see someone (like myself) not paying as close attention to the small pressure gauge on my floor pump as I should and going over by a few to many...

[Dead Man]

absolutely true - but I can see someone (like myself) not paying as close attention to the small pressure gauge on my floor pump as I should and going over by a few to many...

Well... My dump trailer is only rated for 8,000lbs... But I've put almost twice that in it on several occasions. "Limits" are suggestions sometimes :-D

[dustyrider]

Was in my LBS talking carbon rims and the proprietor said that the carbon clincher rims are rated only to 125-135 psi - is it just me or does that seem a little to close for comfort when regarding the max tire pressure - a tire at 115psi only leaves 10 or 15 lbs left before potential rim failure :eek: ...you'd think there would be a little more strength engineered in there for a safety margin..

Are aluminum clincher limits that much higher than carbon?

[makoti]

Well... My dump trailer is only rated for 8,000lbs... But I've put almost twice that in it on several occasions. "Limits" are suggestions sometimes :-D

Suggestions from lawyers, at that. Can't imagine running my tires that high, any more.

[FlashUNC]

You know the expiration dates on your food are BS too right?

[Cicli]

You know the expiration dates on your food are BS too right?

Yeah, but if the bread needs a shave?

[FlashUNC]

Eh, just go from the other end of the loaf.

[Mark McM]

Was in my LBS talking carbon rims and the proprietor said that the carbon clincher rims are rated only to 125-135 psi - is it just me or does that seem a little to close for comfort when regarding the max tire pressure - a tire at 115psi only leaves 10 or 15 lbs left before potential rim failure :eek: ...you'd think there would be a little more strength engineered in there for a safety margin..

Two things:

1) 115 psi is not the failure point for the rim - it is the failure point plus some margin of safety. I don't know about rim manufacturers, but tire manufactures typically rate maximum pressure at half the test failure point. Under normal conditions a brand new carbon rim rated at 115 psi will actually fail at much higher than 115 psi. But we can't always count on the rim being in as-manufactured state or to be operated under normal conditions, so the manufacturer (should) apply a factor of safety to the ratings.

2) The actual load on the rim depends on both the pressure and the tire width - at a given pressure, a wider tire generates larger forces on the rim (force = pressure x area). So a manufacturer should determine the maximum pressure rating based on the widest tire that is apt to be used on the rim. If a narrower tire is used, then the actual rim force is less, and therefore at a given pressure the rim is actually working with a larger factor of safety.

[quauhnahuac]

I have seen tires pop from being in the sun. any danger of filling to 110 and then pv=nrt'ing your way to a cracked carbon clincher on a sunny day?

[carpediemracing]

Although my information is a bit dated, I spoke with someone that was doing destruction testing of carbon clincher rims in 2004 or so. He was absolutely appalled by some of the rims (rated at 112 psi max, give or take) because they blew apart in the realm of real tire pressures (meaning in some range that some people might actually put in a clincher; I want to say 140 or 150 psi). Other rims he tested (made by the company he worked for) blew off the tires at well over 200 psi, I want to say 270 psi but I don't remember and I don't know how to verify this. Also I have no idea what size tires etc other than they were 700c/road/rim-brake. I got to tour the facility so I saw some of the stuff there, made me very sad to see new broken stuff.

Ended up buying two sets of wheels by that company as well as a fork.

[Dead Man]

Yeah, but if the bread needs a shave?

Use a corded Wahl.

[Dead Man]

I have seen tires pop from being in the sun. any danger of filling to 110 and then pv=nrt'ing your way to a cracked carbon clincher on a sunny day?

the sun?

[quauhnahuac]

the sun?

Yes

[Dead Man]

Yes

I don't think the sun pops tires, man

Googling this, I'm reading that triathletes seem to think their tires pop from the sun at transition.. I'd think maybe triathletes not really being bike people and not fully seating the bead on their clinchers and pumping em up to 140, or other user errors would way more betterer explain that.

How many PsSI will a tire increase from radiant sun heat? Maybe a handful? Why don't they pop from riding on super hot asphalt pavement? That's gotta be way hotter than just radiant sun head on a tire. I'd bet rims get way hotter from hard braking than they ever do from sun.. And though tires have popped on hard technical descents it's still extremely rare

[Bwana]

My brother had a tube pop during RAGBRAI this year. His bike was leaning against a tent pole and all of a sudden BANG!

He pumps his tires up to 90ish psi and they were pretty much brand new tires/tubes (maybe a couple weeks old).

[PaulE]

I think the carbon clincher maximum air pressure limit is heat absorption from rim brakes, and the carbon rim/wheel manufacturers figure out what the safe maximum pressure is assuming an alpine descent with excessively heavy braking. The carbon is not a good material for absorbing the heat, so more goes into the tire and tube and the bead hook of the rim ends up getting deformed and letting the tire go off the rim. I bet you could pump up a clincher carbon rim to 145 lbs or whatever the tire's maximum pressure rating is and let it sit in the hot sun all day and it would be fine, just don't try riding and braking with that much air in the tire.

I have a set of Lightweight clincher wheels from 2010 or so. Not sure what model but they have 60 mm rims, 16 spokes front and 20 spokes rear. The maximum air pressure is 8 bar and the maximum tire width is 24 mm. I've done some heavy braking and not had any issues.

Does anyone know what the maximum pressures are for carbon clincher wheels that use disc brakes? I bet they are higher than for the rim brake versions of the same wheels.

[quauhnahuac]

I don't think the sun pops tires, man

Googling this, I'm reading that triathletes seem to think their tires pop from the sun at transition.. I'd think maybe triathletes not really being bike people and not fully seating the bead on their clinchers and pumping em up to 140, or other user errors would way more betterer explain that.

How many PsSI will a tire increase from radiant sun heat? Maybe a handful? Why don't they pop from riding on super hot asphalt pavement? That's gotta be way hotter than just radiant sun head on a tire. I'd bet rims get way hotter from hard braking than they ever do from sun.. And though tires have popped on hard technical descents it's still extremely rare

Not directly, but it heats the air in the tubes causing it to expand, hence the mention of the ideal gas law. i have had it happen while the bike was sitting in the back of my car on a sunny day.

how many psi? idk. say it's 75 degrees out when you pump your tire to 110psi, that's a volume of about 3250cm^3. Say it sits in the hot sun of a car or whatever, black tires compounding the temp rise. a quick google search says that hot cars can hit internal temps of 175. plugging in the data and solving for pressure, that's about 165psi. At the low end of 130 degrees, the pressure rises from 110 to 121psi.

just back of the envelope of course, but I def see how this could be an issue.

[benb]

My brother had a tube pop during RAGBRAI this year. His bike was leaning against a tent pole and all of a sudden BANG!

He pumps his tires up to 90ish psi and they were pretty much brand new tires/tubes (maybe a couple weeks old).

It is possible for the tire to blow off from heat, I've had it happen once or twice on a very hot day when the bike was in my old car (black on black with no tint).

But just sitting against a tent pole was probably something else.

I used to have a set of Easton rims. I got some Vredstein Fortezza tri-comp tires in a sale.. I got about 3 sets since they were so cheap.

Those tires if left to sit even in the cool house would blow off the rim if you left the bike sitting. It was absolutely freaky. Those were 23s, I would have been running about 110psi.

They never blew off riding, it would always happen within 1 hour after a ride, but needless to say I took those tires off and didn't take any chances after wasting a couple tubes. My understanding at the time was that the tires were at the large end of the range of tolerances for bead circumference and the Easton rims might have been at the small end of the tolerance range... heat definitely wasn't the culprit.

[steveoz]

Not directly, but it heats the air in the tubes causing it to expand, hence the mention of the ideal gas law. i have had it happen while the bike was sitting in the back of my car on a sunny day.

how many psi? idk. say it's 75 degrees out when you pump your tire to 110psi, that's a volume of about 3250cm^3. Say it sits in the hot sun of a car or whatever, black tires compounding the temp rise. a quick google search says that hot cars can hit internal temps of 175. plugging in the data and solving for pressure, that's about 165psi. At the low end of 130 degrees, the pressure rises from 110 to 121psi.

just back of the envelope of course, but I def see how this could be an issue.

So in relating this information to my original concerns about there not being a very large margin of error in carbon rims for max air pressure - I live in S.Fla - there's no chance of over heating brake pads causing rim sidewall delamination -cause it's flaaaat - but it's hot...really frikn hot - and the asphalt is even hotter -what you propose is that the increased air volume due to heat could raise the pressure to the point of rim delamination failure...

[steveoz]

You know the expiration dates on your food are BS too right?

yes -but the one on the package of raw chicken is definitely not the one to mess with

[Hermes_Alex]

Most of the time, the typical failure mode of too much pressure, whether or not it's a carbon rim, is the tire bead popping off and the tube exploding, like some people have observed. In the case of worn aluminum rims, the beads can rip off at the point where the material is thinnest, but I've never observed this happening on carbon.

As a general rule, aluminum and carbon rims designed for road use can safely handle road pressures, plus with an allowance for greater pressure due to heat, etc.

Like any bike part, don't do anything crazy, and it will most likely take good care of you :)

[carpediemracing]

Hm local shop had an article about carbon clinchers and overinflating. Someone went in with a carbon rim where the rim's sidewall split open. I think the rider was putting 150 psi or something in the tires. Unfortunately shop is closed now and FB stuff doesn't seem to have the picture from that shop blog post.

Goes to show my memory isn't that great. I had downloaded the picture and posted on my blog. It was an aluminum rim. 150 psi is right.

http://4.bp.blogspot.com/_TbmplkIYLx8/SpqvrIYnDFI/AAAAAAAACGA/Py24y7dWWIE/s800/rim.jpg

[Waldo]

Eh, just go from the other end of the loaf.

Go from inside the loaf.....

[Mark McM]

Hm local shop had an article about carbon clinchers and overinflating. Someone went in with a carbon rim where the rim's sidewall split open. I think the rider was putting 150 psi or something in the tires. Unfortunately shop is closed now and FB stuff doesn't seem to have the picture from that shop blog post.

Goes to show my memory isn't that great. I had downloaded the picture and posted on my blog. It was an aluminum rim. 150 psi is right.

http://4.bp.blogspot.com/_TbmplkIYLx8/SpqvrIYnDFI/AAAAAAAACGA/Py24y7dWWIE/s800/rim.jpg

I suspect that it wasn't the high pressure alone. This failure mode is quite common on MTBs with rim brakes, even at low pressure (30 psi or less). MTB conditions tend to be gritty, and braking wears down the sidewalls, until they become so thin they can't take the pressure anymore.

If you were to look at the pictured rim closely, I'll bet that you'll find that the sidewalls had been well worn, and only a thin cross section remained.

[eric01]

Who's running more than 110 psi in their tires these day anyhow? Isn't the new conventional wisdom wider rims / wider tires at lower psi?

[carpediemracing]

I run 120 psi in my 23mm tubulars. I tried as low as 90 psi in them and found myself doing weird stuff in corners. I'll readily admit that I'm looking for a certain feel in corners and in sprints, and lower pressures make me feel uneasy. I read a review about radial clinchers (by definition most all bike tires are bias ply construction) and the reviewer said that it took a huge leap of faith to get over the squishy-sliding-out feeling. One fellow tester said they just could not get used to the tires. I've crashed due to slow leaking or flat tires and I get sort of clenchy when I ride low psi.

On my clinchers I run 95/105 in 23c, HED Ardennes 23mm wide rims. There's one acute turn half mile away from the house at the bottom of a descent. Good run off (big field) but when I tried it at 85 psi I thought I'd end up in the field. On another rider, at 65 psi or so, I ran wide on the only two left turns I took. So, there, too, I run higher pressures than what I'm supposed to run.

[FlashUNC]

Just saw a carbon clincher blow on the one lane descent of Hawk Hill today. Guy got stuck behind a car and had to drag the brakes down. Pulled the tube and it was most definitely warm to the touch.

Carbon clinchers everyone.