francis1

Question about vintage rims & tires. A number of times, I've found that with 70s 27" steel rims, modern tires will blow off the rim at 80/90 psi. I get that the older rims don't have much if any hook, but my question is how were tires different in 1975 from modern ones to prevent this from happening. Thicker wire bead? Are any modern tires suitable for these older rims?
Cheers

tricky 

Was the blowoff happening with rims that were completely hook-free? "Hookless" were common back in the day. They were never intended for high pressures. Hooked rims should be fine at high pressures with folding or wire beads. I don't recall if folding bead tires work with hookless rims. Someone will come along and give info on that.

Blowoffs at 80 seem a little weird. This thread has a few members claiming 80 is fine, but it definitely depends on the tire/rim combo. Some tires fit much tighter than others. https://www.bikeforums.net/classic-v...edge-rims.html

daverup 

I use Panaracer Pasela wire bead tires on my older 27" rims and they generally hold on at 80psi or so.

trailangel

70s steel 27 inch rims.. tires were 1 1/4 inch. 60-70 pounds was high pressure. Nobody had a Schrader pump that went that high.

Chombi1 

Yup, it was the wire beads that kept higher pressure tires on rims back then....

clubman 

Conti makes Super Sport wire beads that should stay on.

repechage

Steel rims will require steel bead tires.
Expectation that one can go above 65-70psi... Variable. 90? NO.

old's'cool

I found a specific tire and rim combination that did not work together. Unfortunately, it is a matter of trial and error, and the tube extrusion scenario can happen several hours or even days after initial inflation. After 3 occurrences, checking my work ever more carefully on each iteration, I concluded the tire and rim were incompatible and moved on. Have had no problems with other tires on that particular rim model. The rim is a mid-70s Araya aluminum 27x1-1/4 and the tire is a 2009 vintage Forte something or other 27x1-1/4. Both items going strong today with no issues, combined with alternative counterparts. I do believe the Forte tires are now mounted on rims with beads.
[edit]
In case there is any misunderstanding about the Forte tire, it is kevlar belted, but most definitely with a conventional steel bead.

pcb 

IIRC a lot of those tires back then had "75psi max" molded right into the rubber.

There can be some tire variability as well. I remember a very cheap Japanese tire on some lower-end Matsuris that would never blow off at 75psi, but almost always blow off at 76psi+. We made Matsuri take them all back and give us Panaracer replacements.

T-Mar

+1. Steel, non-hooked rims require tyres with rigid/steel beads. Even, then they could blow off if the tyres were not seated properly. Prior to hooked edge rims, checking for proper seating was a standard practice. Most tyres had a circumferential line molded into the tyre that would roughly align with the rim's outer edge, to aid in visual seating of the tyre. You would partially inflate the tyre, then check for proper seating. If it wasn't correct, you would deflate the tyre and re-seat it.

Tyres for 27" steel rims typically had a maximum pressure of 65-75 psi. Aluminum rims had a higher coefficient of friction with rubber and you could get away with higher pressure tyres on non-hooked versions of aluminum rims, though the tyres still had to be rigid bead versions. Using detergent when mounting tyres on steel rims decreased the co-efficient of friction and was typically a recipe for disaster, unless you were very careful with seating and waited for it to dry before inflating to full pressure.

randyjawa 

+1 I still do that to this day.

francis1

Thanks for all the feedback. Looks like it boils down to compatibility, aka trial and error. 27 x 1 & 1/4 tires seem to vary quite a bit in their width. The fatter tires hold fairly well on non hooked steel rims even at 90 psi, where a narrower tire with same nominal dimensions will blow off at 80 psi. Cheers

seedsbelize 

I still do that. Partially inflate and check for seating.
With hooked rims.

old's'cool

guess what I tried to put as a acronym meaning usual method starting with S

davester

For a 27 x 1 1/4" tire (nominal 32 mm width), unless you weigh 250 lbs or more you really don't need to inflate beyond 70 or 80 psi anyway.

Road Fan

I think this is not quite true. I have an old 27" Rudge with 27x1 ¼" Dunlop Special Lightweight rims with no hooks in the rims. "Old" here means 1952. The tires are modern Specialized RoadSport wire-bead, proper size. In installation, the wire bead fits tightly on the rim pressing the bead into the inner rim. With a good rim strip this creates a pretty seamless base for the tube. The tube, when inflated, presses the tire bead even tighter into the inner rim surface. I don't have a vintage tire to test it with, but with the modern Specialized, I filled it up to 90 psi (marked limit of the tire), rode it about 5 miles, put it away and left the wheels while I started the overhaul.. Several months late, still good pressure.

70 or 80 psi is not the limit for that tire technology on a hookless rim. It may be a valid limit for hooked tires on a hookless rim.. And the original Dunlop tires were marked as High Pressure good to 90 psi as well.

tricky 

Interesting data point. yeah, I was just quoting what I saw on that thread. It sounds like the "max" pressure for hookless rims is anywhere from 70-90 depending on the which rim and which tire you have.

alo

Where I am, they import container loads of used bikes from Japan. I believe many of them are the same size as the old 27 inch bikes. 27 inch tires and tubes are still readily available, and inexpensive, in S E Asia.

Road Fan

francis1 There is a thread, I think it's a sticky, on what is available in 27x1 ¼" tires, also known in modern times as 630 x 32 mm. If you have a non-hooked rim, you need to determine if the tire you are looking at is wire bead. It used to be that the tire and rim were both marked "27 x 1 ¼ inch," indicating they are designed to match. This is the case with my Dunlop rim and the Specialized tire. I'm looking for a set of wire bead 32 mm 630 mm Paselas for my old Rudge - I think that will be a pretty decent ride. I assume that if the Specialized engineers knew that these markings were supposed to indicate a match, then the Panaracer/Pasela engineers have the same understanding and competency. The Specialized Road Sport has ever appearance and feel of being a nice tire, but it weighs about 550 grams each where original Paselas and the Tserv variant are much less massive. I've only ridden about 5 miles on the original Rudge wheels, but I can feel the weight.

alo Where is your area, that all these used Japanese bikes are coming in? I think there are now so many new marketing designations of bike tire sizes in the USA that I tend to doubt tire designations any more. "630" is clear and specific as far as the bead seat diameter, but it doesn't say what the bead/inner rim design is.