Hi,

I'm sorry for asking very basic questions. I'm trying to break my dependence on the bike shop and I've vowed to do as much maintenance as I can by myself. But I'm very new to this.
I have had a Fuji Touring series III for a few weeks and the tube in my front wheel just blew up. I'd just bought and tried a foot pump on it and had gone for a ride. It exploded as I was parking the bike : not riding and no weight on it, so I'm assuming I put too much pressure.

1st question : my tire says 85psi, which is exactly where I stopped pumping, according to the gauge on the pump. What should I make of this : is the gauge possibly faulty and I put too much without realizing (it's a cheap ccm foot pump...), or is the 85psi mark on the tire an absolute maximum and I should actually keep the pressure under that?

2nd question : the size on the tire is 37-630 (27 x 1-3/8). I'm trying to determine if a spare tube that I have here will do. I've been reading self-help pages and I don't think so, but I thought I'd ask here to make sure. My spare tube is a «700 x 28/32C (27x1-1/8x1-1/4 a/v)»
If I get this right, the last bit (1-1/8x1-1/4) is a range, and thus it won't fit in a 1-3/8 tire... Am I right ?

Thanks greatly in advance for any input.

Your gauge might be faulty. No way for us to check it.
Typically, you can exceed max tire pressure by a "bit", but obviously we can't recommend that.
Your tube will work. Not ideal to stretch it that much, but better than letting it sit on the shelf.

Tubes don't "explode" unless they escape the confines of the tire.
Was the tire flat when you pumped it up? It sounds like the bead seats weren't lined up properly.

Is this an OLD steel rim? Many of the OLD 27" rims are straight flange instead of "hooked bead".
Tires are much more likely to blow off those rims.
85 sounds a bit high for a 1-3/8x27" tire. The only ones I've seen in that size are the CHEAPLY made Bell folding tires at the dept. store.
Edit-
To quote St. Sheldon-
"Note on tire/rim compatibility:

Traditional 630 mm (27 inch) rims were straight side design, but in the late '70s they evolved to a "hook edge" design which would permit the use of higher pressures.

These days, many 630 mm (27 inch) tires are marked "For hook edge rims only" (some companies use the term "crochet type" instead of "hook edge"...this is the result of poor translation.)

The fact is that modern 630 mm (27 inch) tires will work on older straight-side rims, but they won't handle as much pressure as they are capable of with hook edge rims.

Generally, the "rule of thumb" for traditional 630 mm (27 inch) tires is that they should be inflated to 70-75 psi. This shouldn't be a problem with any tire, despite whatever disclaimer the manufacturer puts on the sidewall. However, if you're restricted to this pressure range, you probably shouldn't be running tires narrower than 1 1/8, or preferably 1 1/4, unless you're a very lightweight rider."

How old was the tire? Tire casings can degrade over time, and lead to blow-outs at lower than listed pressures.

Your 700 x 28-32 tube will fit in your 700 x 37 tire, but will be stretched a bit thinner than it should. This may make it more susceptible to puncture but is not necessarily a show-stopper.

Even if your gauge is faulty, max pressure ratings have a big safety margin, so a gauge error of even 25-30% wouldn't be an issue. In any case, over-inflation is a fairly instantaneous event.

I suspect it was a tire seating issue, so a question. Has this tire been on a long time and were you just topping off. Or it is it a recently installed tire, or a flat repair, or has the tire been empty sitting on the floor and you were pumping from zero. The odds of poor seating being the issue depend on your answer, since a tire that's been OK for a long time wouldn't suddenly get unseated.

As for the tube, odds are it'll be OK, since tubes are only balloons and have decent ability to stretch quite a bit (usually to double rated size). It might be more prone to splitting if punctured, but should be OK until then. The biggest issue with undersized tubes is that they're stretched thinner, and so the natural pressure loss that tires all undergo will be faster, so you'll need to top off more often.

When you install the tube, pump to enough pressure for he tire to take shape (15-25psi), then spin the wheel and make sure the tire is seated evenly all the way around by looking at the molded line just above the lip of the rim. You can sometimes also detect a poorly seated tire by wobble.

Sounds just like a bead seating issue to me too.

I highly recommend you read the thread from a couple days ago, because it's full of great info.

Regarding the tube stretching to fit, I think the main issue would be a tendency to lose air pressure faster than usual. If you pump regularly, it might not be an issue. And if you ever get a slow leak of a flat, you may not be able to limp home. On the plus side, you're probably saving 4 grams in using a lighter tube!!!1

By the way, 85 PSI sounds like a heck of a lot for a 37c tire. That's probably too much unless you are a truly huge guy. Overfilling tires is just going to make your ride uncomfy and possibly even slow you down or slightly reduce the life of the tire. I recommend the article on tire pressure and then check out the handy pressure calculator. 40%/60% should be OK weight distribution for a touring bike. You may want to overfill somewhat past those numbers to avoid pinch flats, but you'd be surprised how little air you need to achieve 15% tire drop with 37's.

Hi,

All the above posts are very informative, starting with Bill Kapaun's. All tell me what I have to be mindful of. Thanks.

To answer a few questions:
I am a fairly heavy rider because I often carry my son on the back. Altogether, we weight 250+ lbs. That weight is why I worried about the "right tube pressure" in the first place.
The wheels, I believe, date from the 80's and are probably steel. (The frame is chromoly, but I haven't checked for the wheels.)

I'll get a new tube tomorrow and install it. Thanks again for all the tips.

Clincher tires are required, I think, to be capable of sustaining twice their rated pressure before a blowout--and that isn't an unreasonable thing to be *able* to do.

Clincher rims, however, usually are another story. Lower end rims will blow out at around 100-130PSI, higher end clinchers at around 200 or so. That is all assuming perfect conditions. A defect in a rim could cause random blowouts at normal inflation pressures.

Probably, your brake rubbed a hole in the sidewall of the tire, or the tire wasn't properly seated with the tube and there was a pinch.

By the '80s, any bike decent enough to have a cromoly frame probably had aluminium rims, and even some steel rims had hook edges on them. If you can actually stop the bike properly in the wet, it hasn't got steel rims.

I just double-checked and you're right. (This goes to show how little I know about bikes, about my own bike and about metals...)
Thanks for pointing that out.

I don't notice any special wear on the tire... I'm about to go change the tube : I'll inspect it closer, as well as the inside of the rim for anything sharp.

Woulda linked you to the same place. And as for inner tube fit, one size bigger or smaller won't hurt you, just a smaller is gonna be thinner and a bigger you'll have to avoid wrinkles with. But at least until you order a right size inner tube, use the one you got.

You may want to put larger tires and tubes on if the rims are big enough and you have clearance all around.

there are very few options
if any
for 27 inch tires larger than 1 3/8 inches

Agreed but he has to do something other than upping the tire pressure. There may be some bigger tires left somewhere. Another thought. A sudden unloaded blowout could mean the rim tape has shifted or worn through.

It could also have been caused by a sudden change in temperature.
If you inflated your tire to max pressure indoors which may have been air conditioned,
then ride for a while on a fairly hot day, it is possible for a blowout to occur.

No, even assuming 65 degree inside and 105 outside that would mean only about 8 pounds extra pressure - not nearly enough to cause a problem. Most tires can easily take 20-25% overpressure.

A problem with rim tape or sharp object is extremely unlikely - no good explanation why that could blow off a tire and in 20 years of working on bikes I did not see a blowout traceable to rim tape, spoke end, etc.

I ride on roads that have temps of 120*F...No Blow Outs.

I did change the tube.
Nothing wrong with the tire, the rim or rim tape that I could see.
The valve's stem was torn to shreds though : that's where it seems to have burst... Maybe just defective ? It was one of those tubes filled with green sealant, and some of it had gone into the valve the last time I put air in it... I don't know if that changes anything. Also, before that, I'd had trouble with the valve which seemed stuck : I'd press with the pump nozzle and it wouldn't let air in or out.


Anyways, I inflated the new tube back to near 85psi and went for a ride with the kid. No explosion so far. I'll report back if it ever does again.

Reading the posts above, I take it that I have an unusual tire size ?..
What'd be the advantage of getting a bigger wheel, as Delmarva suggests ?

he suggested getting a bigger tire
and the problem with that suggestion
is that nobody makes a bigger tire for 27 inch rims
as far as a i know

27 inch wheels are fairly common on older bikes
almost all 10 speeds from the 60s 70s and 80s had them
but they have been almost entirely replaces by 700c wheels
which have a slightly smaller diameter
but have many many many options for tire sizes

wider tires can carry the same load as a narrower tire
but with less pressure

this generally gives a smoother ride
and more traction

the 1 3/8 wide tires you have
are very similar in size to 700 x 35c
which is a very very common size for city riding
and people are able to do all sorts of riding
carrying all sorts of loads

if you wanted to change the wheels intirely

I'd misread Delmarva's post.

Thanks for the info on wheels and tires. There is a forum member, Ciufalon, who owns Fuji Touring bikes and who'd also told me these wheels would be good for lugging weight. I don't know how much of a difference they make, but the bike in general handles super well when it's fully loaded with the kid and luggage.

I was wondering because the spokes are pretty rusty. So I was wondering if I'll change them or if I better buy new wheels. But I guess the latter option would mean getting 700c's.

I don't know if you meant a new tube Before or after it exploded, or both.

If the failure happened within a fairly short interval after the installation of a new tube, it's classic for poor seating.

The tube is thicker near the valve, plus the valve itself gets in the way, so the tire near the valve often ends up with some tube trapped under the bead rather than seating properly. Eventually the trapped part of the tube jacks the tire over the edge of the rim and blows it off.

Whne you finish mounting, and before inflating, push the valve up into the tire so it drags the tube clear, then pull it back down to locate the tube above the inside of the tire. If you haven't done that with the new installation, spin the wheel watching the reference line molded just beyond the rim to make sure it's the same distance all the way around. If not you're primed for a repeat trip down blowout lane.

The tube that exploded was on the bike when I bought it. That's the one with the blocked valve and with the sealant that had leaked into the valve. From what I know of the previous owner, that tube must have been in there for the last decade as the bike was rusting on his balcony...

I'll have a look at that reference line.

Hi,

85 psi is still a hell of a lot for a 35mm front tyre. A kiddy on
the back over the rear wheel won't change the front much.

My rule of thumb is get the rear tyre pressure right and then
seek little bumps, rumble strips, grates etc and adjust the
front pressure so the jolts etc seem about the same.

rgds, sreten.

85psi is what's written on the tyres... But I didn't quite inflate the front one that much this time.

Hi,

Just using numbers is not an intelligent approach to tyres pressures.

Same tyres your rear may be near max for you and a rear passenger
but your front should be less, quite a bit to get the same sort of
contact patch size as the rear, giving better front grip/suspension.

rgds, sreten.

There's no reason to suspect a tire cannot hold 85psi if it's rated for that, but it's possible an old tire is no longer in good shape. As almost all blowouts are related to either poor seating or damage/defect in tire those possibilties should be explored. The guidance FB posted above should help. Just mount a new tube, inflate to about 40 psi, then about 10 lbs at a time, making sure that the tire is well seated with no tube underneath. If the tire's raised rubber bead line next to the rim starts to pull away from the rim in some areas, deflate and recheck for tube or rim strip under the bead in that area, as well as making sure the tire casing is in good shape in that area. If it keeps occuring you may have a bad tire.