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Tire Pressure For 27 x 1 1/4 hookless rim

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Tire Pressure For 27 x 1 1/4 hookless rim

Old 08-24-20, 01:43 PM
  #1  
SwimmerMike 
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Tire Pressure For 27 x 1 1/4 hookless rim

First of all I've learned a ton from this forum and want to thank everybody that shares their knowledge.

I just picked up a bike with 27 x 1 1/4" Weinmann hookless rims. It had some really bad tires on it so I bought some 27 x 1 1/4 wired Gatorskins (learned I needed wired beaded tires from the forum, thanks). Hadn't done much research besides which tires to buy, promptly starting pumping them up to 95 PSI and then had to replace both tubes. Started doing more research and it sounded like 80 - 85 PSI would be a good target. I was smarter this time and only blew off 1 tire. Backed it off to 75 on the next try and all seemed good. Let them sit for a day, no issues. Took them out on a test spin today. Checked them out after a coupe of miles, no issues. They seemed to be seated really well. At 13 miles, boom. replaced the tube and limped home.

It's in the garage now with 60 PSI in the tires.

What pressure are people running on their 27 x 1 1/4 hookless tires?
What size tubes do you run? The LBS only had 700c 32-50's. It felt like a lot of tube for the tire. I have some Conti 25-32's and 32-47's showing up tomorrow, so I some choices and my next iteration.
Any other advice on how to eliminate this problem?

Mike
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Old 08-24-20, 01:52 PM
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I run mine at around 70. Check the rim for any sharp spots, and make sure your rim strip covers the spoke nipples. Are the punctures all in the same spot on the tube?

I use 700c 28/32 tubes.
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Old 08-24-20, 02:04 PM
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70 psi used to be the magic number when I started riding in the early '70s. I listened to all the bike magazines and went with tubulars, then with skinny high-pressure tires on hooked-bead rims. A few years back I started riding 27 x 1 1/4-in tires again as part of a clunker challenge and discovered that with decently supple tires at 70 psi, I really don't lose all that much, speed wise. I've run Panaracer Paselas, IRC gumwall, Bell Streetster and CST blackwall 27 x 1 1/4-in tires on Weinmann, Araya and Ambrosio straight-walled rims without hook beads for several years now without incident. I suppose I could go up to 90 psi on the Rigida rims with the hooked beads - but why? I'd get a harsher, but no faster ride.

At 75 psi, I would think you would be okay, however, so I'll echo @BFisher's suggestion to check for sharp spots and rim tape coverage. But 70 was what those rims were designed for.
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Old 08-24-20, 02:14 PM
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Originally Posted by BFisher View Post
I run mine at around 70. Check the rim for any sharp spots, and make sure your rim strip covers the spoke nipples. Are the punctures all in the same spot on the tube?

I use 700c 28/32 tubes.
Thanks for the advice. The blowouts have been in different spots. I've kept all the tubes to "line them up" and confirm.

I did check the rim tape, but I didn't confirm the rim doest have any sharp spots. I assume I should just sand/polish anything I find. I'll try 70 for the next test.

Mike
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Old 08-24-20, 02:23 PM
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Originally Posted by rustystrings61 View Post
70 psi used to be the magic number when I started riding in the early '70s. I listened to all the bike magazines and went with tubulars, then with skinny high-pressure tires on hooked-bead rims. A few years back I started riding 27 x 1 1/4-in tires again as part of a clunker challenge and discovered that with decently supple tires at 70 psi, I really don't lose all that much, speed wise. I've run Panaracer Paselas, IRC gumwall, Bell Streetster and CST blackwall 27 x 1 1/4-in tires on Weinmann, Araya and Ambrosio straight-walled rims without hook beads for several years now without incident. I suppose I could go up to 90 psi on the Rigida rims with the hooked beads - but why? I'd get a harsher, but no faster ride.

At 75 psi, I would think you would be okay, however, so I'll echo @BFisher's suggestion to check for sharp spots and rim tape coverage. But 70 was what those rims were designed for.
Thanks @ruststring61. I'm sure I had hookless rims back in the 70's also. I'm surprised at how much I a remembering on working on vintage bikes from that time. This is one that is just eluding me, and more critically, having a blowout a couple miles from home is a PITA. I see you also have a '71 Gitane. I'm new to the Gitane club with my Grand Tourisme.

Mike
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Old 08-24-20, 02:38 PM
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Originally Posted by SwimmerMike View Post
I'm new to the Gitane club with my Grand Tourisme.

Mike
Hushed silence. A Grand Tourisme is one of the very few bikes I would seriously pursue. My Gitane is a basic TdF converted to fixed-gear, something it excels at, but a Grand Tourisme is well into randonneur/federale coolness. Someday perhaps I'll find one in my size at a price I can pay at that moment!
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Old 08-24-20, 02:39 PM
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30 and 40 years ago on my old Schwinn and Weinmann rims I always ran 80 and even 85 not knowing any better on the old Schwinn approved and Kenda 27 x11/4s. Just dumb luck. Now I run 60-70 and still have no problems but have a better ride.
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Old 08-24-20, 02:57 PM
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Originally Posted by rustystrings61 View Post
Hushed silence. A Grand Tourisme is one of the very few bikes I would seriously pursue. My Gitane is a basic TdF converted to fixed-gear, something it excels at, but a Grand Tourisme is well into randonneur/federale coolness. Someday perhaps I'll find one in my size at a price I can pay at that moment!
@rustrystrings61 to tell the truth I didn't know what I was buying. I saw a CL add for a Old Italian Gigante (Set up as a "townie"). I looked at it on line and saw it was a Gitane, so I knew it wasn't Italian. I also saw it had a Campy NR Triple. Living near the hills, I figures I could pick it up, strip the parts, have the triple for my Colnago for Eroica and for rides around here. I got it home, determined it was my size, did my research, and now I have a second Vintage bike to rebuild.

I am planning on doing a write up with pictures after I get to 10 posts.

Mike
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Old 08-24-20, 02:59 PM
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It is a rare and lovely bike, and I look forward to seeing the write-up! Somewhere on this forum are some posts about a "Gitane with a weird fork." That's another GT, and I hope more surface!
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Old 08-24-20, 05:13 PM
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I go up to 80-85 on my Weinmann concave, running Panaracer Pasela wire bead. I've NEVER had a problem
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Old 08-24-20, 05:19 PM
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Originally Posted by rustystrings61 View Post
Hushed silence. A Grand Tourisme is one of the very few bikes I would seriously pursue. My Gitane is a basic TdF converted to fixed-gear, something it excels at, but a Grand Tourisme is well into randonneur/federale coolness. Someday perhaps I'll find one in my size at a price I can pay at that moment!
Are you talking about a Gitane federale? Those are pretty rare birds in the US; so was the Grand tourisme.
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Old 08-24-20, 05:20 PM
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I've never had an issue at 70-75 PSI with a wired clincher on a hookless rim. But there are variations in tires and rims so maybe 70 is the safe spot for your combination of tire and rim.

One thing I do--especially when dealing with a tire/rim combo that might be a bit dodgy--is to take a lot of care in seating the tire on the rim. I'll inflate and then deflate it to check how it is seated by going all around the wheel and making sure the tire is inserted as deeply as possible. Once I'm satifisfied I'll pump it up to pressure.

Last edited by bikemig; 08-24-20 at 05:23 PM.
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Old 08-24-20, 05:27 PM
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Before I knew what I was doing, I would run new Kenda 27 x 1 1/4 tires and always pumped them up to the max pressure - 90 psi. Still do, however, for a lighter rider, lower pressures might be just fine.
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Old 08-25-20, 12:39 AM
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The Weinmann 27" rims from the early 70's, not the Concave model but the plain OEM model has a troublesome quality control record in terms of having inaccurate diameter needed to retain a tire at high pressures.
I've had to add layers of tape that reaches the inner sidewalls of those rims on my Schwinn Supersport, not easy to do when the inside of the rim has anything but a flat shape. I had to trim down some very wide Velox tape to help the tires not blow off above 75psi.

I remember lots of other 27" rims having no problem at all with tires inflated to 90 or even 100psi, that's what the tires on new bikes had printed on them as mounted to hookless 27" aluminum rims.
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Old 08-25-20, 09:26 AM
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Originally Posted by SwimmerMike View Post
What pressure are people running on their 27 x 1 1/4 hookless tires?
I run 70-80psi with wire bead Panaracer Paselas on Weinmann concave hookless rims. No problems.
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Old 08-25-20, 02:13 PM
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Originally Posted by dddd View Post
The Weinmann 27" rims from the early 70's, not the Concave model but the plain OEM model has a troublesome quality control record in terms of having inaccurate diameter needed to retain a tire at high pressures.
I've had to add layers of tape that reaches the inner sidewalls of those rims on my Schwinn Supersport, not easy to do when the inside of the rim has anything but a flat shape. I had to trim down some very wide Velox tape to help the tires not blow off above 75psi.

I remember lots of other 27" rims having no problem at all with tires inflated to 90 or even 100psi, that's what the tires on new bikes had printed on them as mounted to hookless 27" aluminum rims.
@dddd Thanks for the background on the Weinmann OEMs. I don't have the concave, so I think I have the OEMs. I'm pretty sure these came with the bike (The Bike was spec'd with Mavic rims, but based on the fact that the rims have Mavic stickers on them (Yes, Weinmann rims and Mavic Stickers) and the hubs (Campy Record with flat QR levers and the freewheel (ATOM)) seem period correct and original ('71 or '72 Gitane Grand Tourisme).

I'm trying to picture the process. Is the rim tape procedure to apply the rim tape just on the bottom of the rim and from sidewall to sidewall? When I originally read this I thought you were trying to use tape to create a "hook" on the sidewall by applying the tape there. What is you theory as to why this helps (I see you are an ME so you must have one). Do you think you can explain it to a EE, I assume you've had to try to explain things to EE's before.
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Old 09-01-20, 12:56 PM
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Thanks for the help on this. Re-did the rim tape, checked the rims for sharp spots, inflated the tires a bit and made sure everything was seated correctly, pumped up to 70 psi. I let it site for a couple of days and now completed 2 rides of 20 miles each w/o any problems.
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Old 09-01-20, 02:50 PM
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Thanks for the follow-up, and sorry I never replied to your last question.

Basically it's the ID of the rim where the tire's beads wrap around, nearest to the inside vertical wall where the thick tape needs to stay put.
Due to the irregular and concave "floor" of the inside of the rim, the tape tends to pull away from the walls when the tube is inflated.
I dealt with this while doing a lot of training miles in the late 90's and came up with the idea to paint on some epoxy glue to the OD of the inside floor of the rim adjacent to each rim sidewall.
I never actually followed through though, but if/when this next presents as an issue I will do that.
I was wedded to a few pairs of 27" wheels at the time and would have wanted to start my own 27" tire thread back then! --The ideas are still alive and well.

I do run over 75psi in 1-1/8" tires on my '71 Supersport with the afflicted rear Weinmann rim, after adding a layer of wall-to-wall Velox cut down from their widest 25mm cloth tape.

One little bit of Science that I read about explains tire blow-off as bead slack accumulating at one small region around the rim/tire, such that any initial local slack which exists quickly steals all of the bead slack and then some, leading to blow-off local to that location around the rim. This occurs because the one spot where any slack lifts above the rim shelf creates a larger cross-sectional area of the tire casing local to the slack. What this does is to create greater tire casing tension at the same spot, which is what strongly pulls the bead's slack tighter at that one spot, and further stretches the entire bead by that same % increase in casing fabric tension. So it feeds itself with a peak of tension and local slack which may grow exponentially (say to the 1.1st power?) enough to exceed the height of the rim sidewall.

But basically, it's a lack of bead hooks and the limited height of the rim's sidewall combined with ANY deficiency in the rim's meeting the full tensioned diameter of the tire beads which causes SOME old clincher rims to retain tires poorly.

Last edited by dddd; 09-01-20 at 02:54 PM.
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Old 09-01-20, 03:15 PM
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@dddd I see what you're trying to accomplish with the tape. Next time I have the tires off (or they blow off) I'll play around with the tape. With the 1-1/4" tires I have on now, the 70 psi feels pretty good.

I figured the blowouts were a positive feedback loop of some sort. Take a system in balance, add 180 lbs mass, rotate the spot where the force is applied, add in a lot of vibration, then create a bit of slip, with nothing applying an opposite force, the slack on the opposite side of the wheel being taken up, add more vibration and forces, thus allowing for more slip, then load noise, swearing (from me), and tube replacement. I figured an ME would have a more technical explanation.
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Old 09-01-20, 04:28 PM
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BITD, I had a bunch of blow outs riding down hills with Weinmann concave rims. If you are going to be in a hilly area, you may have to adjust your regular pressure downwards.
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