27" tire PSI limits
 

Howdy all. I'm a clydesdale rider (I weigh 225-230) and sometimes ride with a 20lb backpack to school or around town.

I have a ~1976 Peugeuot UO-8 and I love it. It's got a modern drivetrain on it, and modern tires, but the max pressure they list is 87psi. I used a university bike pump friday and inflated my tires up to 85, allowing for a little error, and had a wonderful ride home on nice hard tires that didn't flatten under my weight.

However, both of my tubes blew out while my bike was sitting on the back porch of my apartment and both tires have separated from the rims - one of them appears damaged. So I'm guessing the gauge wasn't good. I am, however riding on an original rigida front chrome wheel and a no-name 27" steel rear with a thread-on freewheel (8-speed 34-13T).

I've thought of getting a used 700c wheelset, but I want to wait until I graduate (very soon) and have a job (hopefully soon after graduation).
Buuuut, given that these tires looked pretty nice (michelin world-tour gumwall 27x1-1/4 I think) and now they're damaged, and I am having a heck of a time finding anything rated over 90psi (found some at 100 or 105), I'm thinking of going to 700c sooner.

So my questions are:
Are there any 27-inch tires (that aren't slicks) that can actually handle 120psi?
Are there any 700c tires (that aren't slicks) that can handle 120psi or more?
(It's important to me to not have slicks because I ride over rough terrain sometimes and don't like laying my bike down over a few grams of sand spilled on the road)
Does anybody sell 700c wheelsets for not-ridiculous prices (as in selling heavily used wheels for $150)?

Read the sidewall of the tire , what does it say?
RIM? you, likely need a Hook bead, straight sided interior ones wont hold the tire on,well,
at more than a modest PSI.

Just because the tire is rated for 87 PSI, doesn't mean the rim can handle it. Older rims lack a hook that better holds the tire's bead. These rims may coincide with the 27"-tire era, but they are mutually exclusive specifications.

If your rims are indeed hook-less, then forget about getting higher-pressure rated tires until you get new rims that can handle those pressures.

What damage did you notice on one of the tires? We may be able to help assess whether it needs replacing. Better yet, post a picture.

The problem is not the tires, and probably not the pressure gauge you mention. The problem is that you're using straight-wall rims. Generally around 70-75 psi is the max pressure that's safe with those. If you want to run higher pressure, you're going to need more modern, hook-edge rims. The outer edge of modern clincher rims has a hooked-edge that allow the use of higher pressures with clincher tires.

So the max pressure that's listed on the tires is irrelevant, the overriding factor is the straight-wall rims that will not typically hold a tire safely above about 70-75 psi. The reason I'm confident the rims are straight walled is that you say they are chromed steel, and I don't think I've ever seen a hook-edged steel rim. Maybe they exist, but they're typically straight-walled. You can check to be sure. :)

Meh, they're both straightwalls. I assumed they were hook/clincher beads. This explains why I was getting a bulge around my valve-stem.

The blowout on the rear is about 5" long.

I think my old bike (GTX 1000 dept. store bike from the mid-80's) had clincher steel wheels. Not chrome though.


How about 27" tires that (with an appropriate wheel) can handle over 100psi?

Not true!

IRC was making 27x1-1/4" HP 90psi tires long before hook edge rims came to market. They worked flawlessly on straight side steel and aluminum rims of the era. As of 3 years ago they were still in production and available for sale in the USA at very low prices, and still working fine on straight side rims.

These were not the only HP 27" tires that worked on straight side rims.

However it is true that tires designed around hook edge rims, may not hold their full rated pressure with straight rims. The hook design provides a mechanical interlock allowing the tire maker to use a lighter (stretchier) bead wire.

Sine tires have a large reserve for over inflation, most cases of blowoff are not because of a misfit on the rims, but because of user error in the form of poor seating when mounted.

And Jive Turkey makes a good point....the blowouts may have damaged the tires.

1. Yes there are some 27" tires that are rated for 120 psi looks like semi slicks
2. Yes, there are some 700c tires that are rated for 120 psi
3. you can get some new wheelsets for reasonable prices, look for online sales

Now why the magical 120 psi number? wider tires use lower pressures.
I weigh 235 lbs. and only fill my tires to about 105 psi for 23mm widths (I haven't gotten any pinch flats a that pressure) but if you us 28 or 32 mm tires the pressure may be as low as 80 psi. The advantage of the lower pressure is a more comfortable ride.

Also as fietsbob said the hook bead on the rim makes a big difference on the max pressure of the tire.

Are these wire bead tires?

When i got back into riding around 10-12? years ago, I was using a 70's Takara 10 speed with steel 27" straight wall rims and had no problems pumping the cheap Cheng Shin gumwalls up to 90 PSI. I do recall the tires being a severe PITA to mount though, so maybe the rim had a higher "wall".
I guess YMMV.
Remembered I still had the rims out in the garage-
They are ARAYA w/0? HP, so maybe they are "high pressure"?
The bike is now a 27 speed "hybrid/flat bar road bike" with CR-18's BTW.

These aren't wire-bead tires, though I thought they were when I bought them. I think wire-beads would be better.

I'm thinking these pasela panaracer tires look good. Wire bead and the 27x1-1/8 says 105psi rated. the 27x1 says 115, but as long as I can get to 90-100, I'm happy.

William,

Heavy rider almost always do better with more width rather than more pressure. Unfortunately the selection of tires for 27" i more limited than for 700c, but seek out the widest tires you can find.

For comparison look at the auto/truck world where heavier vehicles use bigger (fatter) tires. The pressure doesn't change so much, it's the size that does. Here's a guide to optimizing pressure and width for various weights. You'll see that you always have a choice between narrower/higher pressure or wider/lower pressure, but overall you'll do best wider rather than more pressure.

The tire's bulge (post #5 ) around the valve might be from poor tire mounting. If the tube/valve in not fully inside the tire beads, or if it is trapped under the tire's bead, then the tire will not fully sit down in the rim. The tube has a thicker portion around the valve that can easily be caught under the bead. When mounting the tire if the valve stem is pushed up and into the rim a bit the thick tube at the valve's base will fit up inside the tire and not be under the bead. The air pressure of the tire will push the valve back out as much as is needed. Andy.

Hmmm, I'd noticed that before. A 26x2.x" mountain bike carried me around at around 40-50psi no problem. And lower pressures mean slower pressure drop over time (I think).
I'll see if I can actually fit 1-3/8 tires on my bike. Thanks for the tip.

I resemble the OP's size and weight along with a Peugeot bike. I think I typically use 60# in my tires. They are original to the bike when I bought it over 20 years ago and I have never had a flat. (Yes, it sat around a while and I rode a lot on my mountain bikes but I brought it back out of semi retirement last fall.)

I do have original rims which might make a difference to the OP.

-SP

How did you get from

"...inflated my tires up to 85, allowing for a little error, and had a wonderful ride home on nice hard tires that didn't flatten under my weight."

to wanting to use 120 psi or more?

I'd suggest following FB's advice and the guidelines in the linked article. More is not always better.

A friend had a '71 Raleigh Super Course that came with 27" Weinmann straight side alloy rims. The tires we used in the mid-80's (27x1-1/8 but I don't remember the make or model) would stay put up safely to about 90 psi but would start to crawl over the bead above that.

Well, at the very least wear ear protection to protect your hearing from the inner tube explosions. :D Or get rims with a hooked edge. :)

I'd rather have narrower tires for less rolling resistance, which necessitates a higher pressure. The only time I've truly loved the ride on any bike with 27x1-_ is when the tires are over 90 psi. And I only didn't go higher than that because the tire sidewalls started to fail (some kenda club-roosts I rode) when I tried.

I think the wire-bead would work, but if I'm getting new tires, I'm tempted to get new wheels too and tires that fit them.

This is a very popular mythconception. The reality is that wider tires at lower pressures often have much lower rolling resistance. The benefits of wider tires are greatest on poor pavement, but even on glass smooth pavements, the lowest rolling resistance isn't with the narrowest tire.

I believe that's correct up to about 700-28 (27-1/1/8) or so and above that the resistance does increase. What it means is 700-18 tires are not the best for low rolling resistance.

The actual breakeven point varies with pavement condition, rider weight and speed. It'll shift toward with lighter riders and higher speeds where aerodynamic effects begin to factor. For heavier riders at lower speeds, the added air drag of wider tires is less, so the low shifts to the wide.

There's no perfect width for everyone, but the reality is that most Americans with road bikes are probably riding on narrower tires than they should. One reason is that the trend has been to very tight clearance frames and forks, which may be fine for Europeans, and conditioned athletes which weigh less on average, but restrict big people from going as wide as they might otherwise.

The club roost cross-terra tires I used to run were 27x1-3/8, which is the widest tire size I know of for a 27" tire. At the max inflation pressure for those of 65psi, I was always wanting firmer tires and more pressure. Even with the widest tires, I'm still going to want to be at or above 80-90psi.

Wow. Niagara Cycle has some super cheap 700c wheels. I'm going to go for it and get some ... just as soon as I figure out this rim-width specification.
Like this front wheel http://www.niagaracycle.com/categori...ub-14g-ucp-36h
What's the 25 in the 700x25? Is it the space between the bead seats inside to inside?


PS I had a WTB 700 and WTB 27" wheels ad up and scoured craigslist for months last summer trying to find them. No dice or people with no idea what they were selling.

Update: Ok, so it looks like I want a 700x19 wheel based on this: http://sheldonbrown.com/tire-sizing.html#width That'll let me go down or up within reason - there's no way I'd ever go beyond a 40 or 44.
A 700x21 would push me to 35 or larger, which seriously limits my choices of tires.

I hate it when they add the width this way to wheels and rims. The 25 probably refers to the width of the target size tire, ie. for 700x25c tires. In that case the inside rim width is probably 13-17mm, but you have to ask to confirm.

If you're using these to replace your 27" wheels, be aware that a 700c (622) rim is 8mm smaller in diameter, so you'll be lowering the brake shoes by 4mm to match. Take a look at your brakes and confirm that you have the room.

The bike will also be 4mm lower to the ground, (with the same width tire), but this won't be an issue either way.

Lastly, if you still weigh the same as you did in the OP, consider shopping for tires nearer to 28 or 32mm, and wheels to match, with inside rim width of 17-19mm.