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Non hook-edge rims: how much pressure is too much?

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Non hook-edge rims: how much pressure is too much?

Old 10-21-06, 04:49 PM
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Non hook-edge rims: how much pressure is too much?

On rims without a hook-edge, I've always run something like 27 x 1 1/4" tires with about 75psi, without problems. But I'm working on a bike right now that has Araya 27's on it, and although the rims have a small lip at the edge, I don't believe they could be called hook-edge rims. So anyway, on this particular bike, I'd like to run Panaracer Pasela Tourguards, in 27 x 1 1/4". The tires have a max pressure rating of 95 psi, but I'm sure that assumes the use of a hook edge rim. I've used these same tires in 700 x 32 on a different bike that has modern rims, and I really like them best at about 90 psi. The 700 x 32's and 27 x 1 1/4's both are rated at 95 psi, and they appear to be about the same width. So my question is, based on your experience with wheels and tires similar to this, how much pressure can you run without a significant risk of the tire blowing off the rim?

Another thing I should mention is that the tires in question have a kevlar bead. It seems like I've heard that wire bead tires are best for non-hook-edge rims, but that really doesn't make sense to me. If it's true, could someone explain why? Also, the amount of pressure, or stress, that's put on a tire's bead is the result of a combination of the tire's air volume and air pressure. So is there a general rule of thumb that says you can put a certain percentage of a modern tire's max pressure in a non-hook-edge rim, without problems? Obviously a 27 x 1 tire would almost always have a higher pressure rating than a 27 x 1 1/4 for example, so can you just work off of a percentage?

Thanks for any help on this-
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Old 10-21-06, 05:24 PM
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Originally Posted by well biked
On rims without a hook-edge, I've always run something like 27 x 1 1/4" tires with about 75psi, without problems. But I'm working on a bike right now that has Araya 27's on it, and although the rims have a small lip at the edge, I don't believe they could be called hook-edge rims. So anyway, on this particular bike, I'd like to run Panaracer Pasela Tourguards, in 27 x 1 1/4". The tires have a max pressure rating of 95 psi, but I'm sure that assumes the use of a hook edge rim. I've used these same tires in 700 x 32 on a different bike that has modern rims, and I really like them best at about 90 psi. The 700 x 32's and 27 x 1 1/4's both are rated at 95 psi, and they appear to be about the same width. So my question is, based on your experience with wheels and tires similar to this, how much pressure can you run without a significant risk of the tire blowing off the rim?

Another thing I should mention is that the tires in question have a kevlar bead. It seems like I've heard that wire bead tires are best for non-hook-edge rims, but that really doesn't make sense to me. If it's true, could someone explain why? Also, the amount of pressure, or stress, that's put on a tire's bead is the result of a combination of the tire's air volume and air pressure. So is there a general rule of thumb that says you can put a certain percentage of a modern tire's max pressure in a non-hook-edge rim, without problems? Obviously a 27 x 1 tire would almost always have a higher pressure rating than a 27 x 1 1/4 for example, so can you just work off of a percentage?

Thanks for any help on this-
As a general rule when working with 27X1-1/4" tires:

Anything over 75 PSI on a smooth-bead 27" rim is usually inviting trouble. Aluminum straight-side might take 80 PSI, but doing so would be dicey.

I have never experimented with Kevlar bead tires, although as you say, I doubt if there will be much difference between Kevlar and wire bead - but don't quote me on that.

-Kurt
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Old 10-21-06, 05:35 PM
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I inflate my 27 x 1-3/8" Schwinn knobbies, officially rated at 70PSI, to 75 or 80 PSI, tops, on smooth-sided aluminum Rigida or Araya rims. The only time I ever had problems with a tire threatening to lift off a rim was with a 27 x 1" Specialized tire on a smooth-sided Weinmann rim; no real problem, but it was a little scary to see it lifting while I was riding.
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Old 10-21-06, 05:53 PM
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Originally Posted by John E
The only time I ever had problems with a tire threatening to lift off a rim was with a 27 x 1" Specialized tire on a smooth-sided Weinmann rim; no real problem, but it was a little scary to see it lifting while I was riding.
Tell me about that. I remember when the rear IRC 28C tyre on my Paramount came off the bead on the first ride. Hooked bead rims too, guess it wasn't seated right. Was able to stop, unscrew the Presta valve and deflate the tube before it exploded. I defy anyone to succeed doing the same with a Schrader valve.

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Old 10-21-06, 08:25 PM
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Originally Posted by cudak888
Tell me about that. I remember when the rear IRC 28C tyre on my Paramount came off the bead on the first ride. Hooked bead rims too, guess it wasn't seated right. Was able to stop, unscrew the Presta valve and deflate the tube before it exploded. I defy anyone to succeed doing the same with a Schrader valve.

-Kurt
Yup, Prestas rule! I stopped, let out the air, and reinflated the tire. I asked a nearby LBS to inspect it, but they couldn't find anything wrong. (I am sure Fred at my favorite LBS would have said, "You cannot safely use a 95PSI tire on a non-hooked rim!")
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Old 10-22-06, 08:25 AM
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I am using Araya 27 inch not hooked aluminum rims with Specialized Tri sport tires on My 79 Trek SS and run 80lbs pressure for a couple months now and have had no trouble at all. I don't run higher pressure because I like a smoother ride than 95lbs gives me.
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Old 10-22-06, 08:50 AM
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everyone seems to deny it, but I have had consistent problems with kevlar beads with non-hooked rims. It really makes no sense to me, since one would think that either the wire or the kevlar cord will not stretch. But nevertheless, with several brands of kevlar tires and several different rims, I have had the problem. j
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Old 10-22-06, 12:54 PM
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Thanks for the responses, guys. I'm thinking I may reconsider running the Panaracer Pasela Tourguards with the non-hooked rims. Because they appear to be more or less the same size tire as the 700 x 32's I've been running at 90 psi, I just don't think I'll be happy with them at 75 psi (and since jgedwa says he's had trouble with kevlar bead tires on non-hooked rims, that's another reason not to use them)...........It's not that I like my tires rock-hard, it's just that on the rear tire in particular I prefer to air it up to the point that it doesn't "sag" too much, if you know what I mean............So, does anyone have any recommendations for a good 27 x 1 1/4" wire bead tire that rides nicely (without much "sag") at about 75 psi? The bike will be used for city riding mostly, but will see some longer distance open road type of riding as well-

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Old 10-22-06, 03:48 PM
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Take a look at the Specialized Tri Sports, good looking tire and ride very well at 80lbs.
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Old 03-31-16, 05:42 PM
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Good thread. I have a really nice set of wheels with campy hi flange hubs (dated from 1972) and milremo rims but no hook. I did bring the tires up to around 80 psi but I'm thinking of letting some air out after reading this thread.

The first time I pumped it up though that tire came right off the rim, though. Really nice wheels but I'm having some second thoughts about them.
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Old 03-31-16, 06:58 PM
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I put a Schwalbe 27" wire bead gumwall on a less than perfect steel rim and it worked it's way out after an hour. Didn't have a tyre gauge at the time but the pressure wasn't over the top. I rode that until I got some Weinmann straight sided alloy rims. Now I have a tyre gauge, I've been incrementally increasing the pressure which is at 80psi now and all seems fine.
The tyres don't feel maxed out and I weigh around 68kg.

On the other hand 80psi with 27" Wolber Gentleman box section eyeleted rims and the wire bead Paselas feel like they're at their limit but I don't weigh much so all good so far.
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Old 03-31-16, 07:59 PM
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Timely thread as I just realized that the Fiame rims on my 1972 Bottecchia is not hooked. The tires are very old and very heavy. I was wondering about this very subject and was thinking of starting a thread. Done! Thanks!
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Old 03-31-16, 08:08 PM
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Originally Posted by SJX426 View Post
Timely thread as I just realized that the Fiame rims on my 1972 Bottecchia is not hooked. The tires are very old and very heavy. I was wondering about this very subject and was thinking of starting a thread. Done! Thanks!
Yeah same problem with a pair of wheels I was thinking of using on my 1960 Olmo; I guess if you have an old bike, you'd better stick to tubulars, .
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Old 03-31-16, 08:51 PM
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My general rule with non-hooked rims is to use a larger tire (32mm, 1-1/4" or more) at lower pressure, like 75psi. That's kind of the point of having larger tires anyway, isn't it? I am under the impression that wire beads are stiffer and less likely to get popped off the rim. If you want high pressure tires then get another set of rims.
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Old 03-31-16, 09:10 PM
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Originally Posted by Vintage Raleigh View Post
I put a Schwalbe 27" wire bead gumwall on a less than perfect steel rim and it worked it's way out after an hour. Didn't have a tyre gauge at the time but the pressure wasn't over the top. I rode that until I got some Weinmann straight sided alloy rims. Now I have a tyre gauge, I've been incrementally increasing the pressure which is at 80psi now and all seems fine.
I was blowing 1 1/4 Schwalbe Marathons off my Weinmann straight sided concave alloy rims at 80 psi so I went to 70 psi with no problems and no noticeable difference in firmness. I've since switched to the same size wire bead Paselas and those seem Ok so far at 75 psi.
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Old 03-31-16, 10:19 PM
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Now the physics of the matter [it seems to me] are, looking at the axis of the tire (i.e. tangential to the rim), the tension trying to enlarge the circumference of the tire/tube in this axis is proportional to the pressure x the cross-sectional diameter. I suppose this tension can be integrated around the circumference of the rim to arrive at a net tension trying to enlarge the tire bead diameter, in which case, you end up with the same relationship of the tension being proportional to the pressure x the cross-sectional diameter. So on that basis, replacing a 25mm tire inflated to 120 psi with a 30mm tire inflated to 100psi would impose the same hoop stress on the tire looking at the tangential axis, and therefore the same hoop stress on the tire as a whole [and hence the bead], looking at the axis of the wheel itself [but it's late, and maybe I've missed something important, geometrically or aSSumption-wise]. Any Stressmen /women/persons around to shed light on the subject?
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Old 03-31-16, 11:13 PM
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Since it's my experience that Paselas fit "tight" I would think they'd be better than some others on on a non-hooked rim. I had a set of Kenda K35s I put on some Araya unhooked rims - without noticing they were unhooked rims. I'm filling up the tires for the lady who's buying the bike for me and at 85psi - BLAMMO!

"Uh, let me get out a new tube for you, and you'll be on your way..." She rode off pumped up to about 70psi.
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Old 03-31-16, 11:24 PM
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Back when Rigidas and Weinmanns were the norm, we typically pumped up everything to 90 psi. Obviously this is going to depend on the tire and the tire/rim interface, but if it couldn't take 90 lbs pressure, it would have been considered defective for a road tire. IIRC Michelin elan tires were the worst for blowing off a rim if pumped to the rated pressure.

RE the Paselas, I'd try them at 90 instead of 95 since you don't have a hook rim. It is typically pretty obvious if a tire is going to hold pressure or not. I've got the PT kevlar version, and they are quite tight.

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Old 03-31-16, 11:30 PM
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Originally Posted by cudak888 View Post
As a general rule when working with 27X1-1/4" tires:

Anything over 75 PSI on a smooth-bead 27" rim is usually inviting trouble. Aluminum straight-side might take 80 PSI, but doing so would be dicey.
Going back 30+ years and until fairly recently IRC produced 27x1-1/4 95psi rated tires designed for straight side rims. These were full sized tires, and extremely reliable.

The issue isn't that you can't make a straight side tire that will hold high pressure on a straight side rim. The issue is that most of today's tires are designed for hook edged rims, and require the hook for proper resistance to blow off.
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Old 04-01-16, 12:30 AM
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^I don't think I've seen an IRD 27" tire. Were they labeled as such or made for another company?

Fwiw, I've been commuting nearly 5 days a week for the past couple years on wire-bead 27x1-1/4 Paselas on straight edge Wolber Mod. 58s. Rated for 95psi, I usually inflate the front tire to 75-80psi and the rear around 80-85psi depending on conditions. Often hauling two full panniers and a trailer bike. Never once a blowout.
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Old 04-01-16, 06:26 AM
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Originally Posted by bikemig View Post
Yeah same problem with a pair of wheels I was thinking of using on my 1960 Olmo; I guess if you have an old bike, you'd better stick to tubulars, .
My thoughts exactly. My thinking is that the clinchers will be replaced with Tubulars.
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Old 04-01-16, 06:33 AM
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Originally Posted by FBinNY View Post
Going back 30+ years and until fairly recently IRC produced 27x1-1/4 95psi rated tires designed for straight side rims. These were full sized tires, and extremely reliable.

The issue isn't that you can't make a straight side tire that will hold high pressure on a straight side rim. The issue is that most of today's tires are designed for hook edged rims, and require the hook for proper resistance to blow off.
What's the difference between a tire designed for a hook edged rim and one designed for straight side rims?
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Old 04-01-16, 08:06 AM
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[QUOTE=gaucho777;18654193]^I don't think I've seen an IRD 27" tire. Were they labeled as such or made for another company?

I don't know that IRD ever marketed tires. IRC, on the other hand was a dominant manufacturer and brand name of bicycle tires for decades . They are still big players in the market with factories in Japan, Indonesia, and China. However, they don't seem highly focused on marketing their brand in the USA these days.
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Old 04-01-16, 08:19 AM
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So, other than wire bead Paselas, any suggestions for 700c tires? Those would be ok but I would like to know if there are other good options for a reasonably light and fast tire. My rims are Weinmann concave (16mm ID).
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Old 04-01-16, 10:31 AM
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As I posted in @SJX426 's Bottechia thread, for a few years I ran Pasela TG's on Fiamme Yellow Label clincher rims at 120psi (rated at 115psi). When you mount the tire it helps if you examine the tire bead carefully with just a bit of pressure before you pump it all the way up. I've seen tires that don't like to seat themselves evenly around the rim, hooked bead or not. FWIW, the Fiamme YL had no hook or lip at all.

I finally had one blow off. I rode for an hour, returned home and tried using alcohol to clean some brake pad gunk off the rim, then left the bike in the sun for an hour while I did other stuff. The failure was at the same point on the rim where I'd been applying alcohol, so maybe some seeped under the bead. Now that I think about it, I recall it was a hot (90+F) day and I probably pumped up the tires in the cool my the basement. PV=nRT may have intervened, even though many people, including one semi-famous guy with a big forehead, don't believe it really works. I think I'll call that tire episode Inflategate.
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