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Is tyre pressure on a 700Cx40 tyre critical?

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Is tyre pressure on a 700Cx40 tyre critical?

Old 11-19-18, 02:09 AM
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nios2
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Is tyre pressure on a 700Cx40 tyre critical?

I am quite new to riding and have a low end hybrid bike with aluminium frame and carbon forks. I have been pumping the tyres up to 60 PSI at the local petrol/gas station as 60 PSI is high as their pump goes. I recently bought a cycle foot pump with pressure gauge and pumped up to 80 PSI as the tyre rim states 85 PSI as max pressure (and 55 as min).
I do not notice any difference at all in the ride in terms of handling or bumps through the forks. I ride on paved/concrete paths and just at a slow pace.

Is tyre pressure on wider tyres as important as on narrow racing wheels?

Last edited by nios2; 11-19-18 at 02:11 AM. Reason: typo error
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Old 11-19-18, 03:08 AM
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Yes, it is.

All tires have a minimum pressure and maximum pressure. Exceeding the max could lead to blowouts or other damage, and at the least will result in a harsh ride. Exceeding the minimum could lead to side wall damage and pinch flats. These statements are true no matter what the tire width is.
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Old 11-19-18, 04:37 AM
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Tire pressure is a so-so thing.
There are two immediately ride-stopping values you need to steer clear of:
- so low that normal ride conditions can cause a pinch flat
- so high that the tire blows off or damages the rim, or burst, or pops the rim strip

Anything inbetween these two is pretty much optional.

Higher pressure generally gives lower rolling resistance until the tires become too bouncy. At some point, a pressure that allows a small pebble to sink into the tire instead of launching it skywards becomes a better option.
There's also a fatigue factor. Not much point in having the rolling resistance of your dreams if the ride is about to shake the fillings out of your teeth when you're looking at an all-day outing.

Lower pressure is generally more comfortable and may offer better performance on soft surfaces. If you have too much squish, tire sidewall life may be reduced and cornering may become vague and unpleasant.

Wider tires have more air to lose, and less pressure driving the loss. So you can usually get away with checking tire pressure less frequently on a hybrid than on a (drop bar) road bike.

And as always, YMMV.

Some riders always want their rides to be just right, and will tinker and experiment until they're satisfied or bored with the procedures.
Others have more of a "good enough" or, "ain't broke, don't fix" attitude.
It's your ride, your time that's on the line if you get it wrong.
Unless you're doing group rides, you're "free" to spend as little time/effort as you wish on chasing the optimum IMO.
If you're not inconvenienced by higher pressures, I suggest you stay at the higher end of the range. It offers more protection against pinch flats. And it'll be more forgiving if you should forget to check pressure before a ride.
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Old 11-19-18, 05:13 AM
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Originally Posted by dabac View Post
Tire pressure is a so-so thing.
There are two immediately ride-stopping values you need to steer clear of:
- so low that normal ride conditions can cause a pinch flat
- so high that the tire blows off or damages the rim, or burst, or pops the rim strip

Anything inbetween these two is pretty much optional.
Thanks for that; I might stick with the 60 PSI then as pass the gas station air pump at the start of my ride.
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Old 11-19-18, 07:19 AM
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If you don't notice a difference between 60 psi and 80 psi, then 60 psi is probably too high already...or at least higher than you might desire. I'd go DOWN in pressure to see if you find an increase in comfort. You won't be losing too much in terms of rolling resistance, but you might find a big increase in compliance. I'm 240 pounds and I ride my 40mm tires about 35 psi in the front and 50 psi in the rear. On my larger tires (50mm or larger), I'm down to about 25-30 psi in the front and about 40-45 psi in the rear.

Just find what you like best. Air pressure modifications are about as "free" as it gets in the biking world, and you can adjust all day long to find what suits you and your riding conditions. I typically prefer less air vs. more air, but it's certainly all personal preference.
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Old 11-19-18, 09:06 AM
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Originally Posted by hokiefyd View Post
If you don't notice a difference between 60 psi and 80 psi, then 60 psi is probably too high already.
100% agree. Either this, or one (both?) pumps don't measure pressure correctly (which is not unusual), so your real change was much less than 20 psi. IMHO it is difficult to not notice 20 psi change unless it is way, way out of optimal pressure range already.
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Old 11-26-18, 03:03 AM
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Tire pressure isn't critical on 700x32 or wider tires. Just needs to be enough to avoid pinch flatting from under-inflation, feeling too sluggish, or feeling splashy on fast curves. Depends on rider weight and road conditions too.

Maximum pressure has less rolling resistance under lab conditions, but real world conditions tend to work out better with somewhat lower pressure. I find maximum pressure way too harsh and over the course of several rides on the same routes, no faster than with lower, more comfortable pressure.

Hard tires also tend to overreact to bad roads, and rebound sharply from creases and ledges in bad pavement. Lowering the pressure can often be safer. Almost everyone I know who rides the local multi-use path has stories of nicking the edge of the paved path and losing control, often from re-entering the pavement at a bad angle. Ditto, railroad tracks at angles to the road. Lowering the pressure a bit may help minimize the risk of a fall.

For my 700x32 to 700x42 tires, the manufacturer may recommend a maximum pressure of 85-90 psi, and around 75 psi for my weight (160), but I usually prefer around 50-60 psi, even lower for longer rides on gravel. No problems, and my average speeds and times are the same. At maximum pressure a lot of energy goes into using the body to offset road vibration. After 30 miles or so the difference in comfort translates to more energy to ride more.
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Old 11-26-18, 09:03 AM
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I've got 700 x 45's on mine, top pressure is 75 PSI with a low of 35. I found anything about 50 was too harsh. As long as you put in enough to keep the tires full while riding for your weight then you should be OK.
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Old 12-01-18, 12:33 PM
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On 700x23 tires if you are a 200 pound rider, you have a very narrow range of acceptable tire pressure. Odds are, your tire will be marked with 120 as the max. If you are going for comfort and less abuse on chip-seal roads, you may be tempted to run them at lower pressures, and you really should. But if you go much below the max, particularly in back where more weight sits, you may start getting pinch flats.

A 150 pound rider on the same tires has a wider margin of safety -- it's not necessary to put in as much pressure to avoid pinch flats.

As tires go wider, the air volume increases. As air volume increases, less pressure is needed to avoid pinch flats. As riders become lighter, less risk of pinch flats exists as well.

A 32mm or 35mm or 40mm tire will have a lower max pressure than a 23mm tire. And it will have a lower minimum pressure too. The most versatile ones will have a wide range between the max and the min, to accommodate a wide range of bike and rider weights, and riding conditions.

Generally speaking, you can ride closer to the minimum pressure if you are on surfaces that are less likely to cause pinch flats, or if you are a lighter weight rider. A heavier rider, or someone riding up curbs or hitting 1.25" steel plates in the road is going to want higher pressure to avoid pinches. A rider on rough surfaces, or in the rain, or in the snow is going to want lower pressures.

So do this: Find an online calculator that estimates optimum tire pressure for a given tire width, bike weight, and rider weight. Use that as your baseline. Ride at that pressure (which will be different in front and in back) most of the time. But then when you plan a longer ride, on a smooth surface, add 5 pounds or 10 pounds, as long as you stay below the tire's max. This will help you favor rolling resistance efficiency for your long rides. And the next time you head out in the rain, or onto gravel, or other harsh conditions where comfort or traction are more important than efficiency, drop 5 to 10 pounds below that baseline. ...maybe 5 until you're confident that you won't get pinch flats.

Lower pressure will improve comfort and traction. Higher pressure (within reason) will improve efficiency. Most people get tired because of discomfort and attribute it to being tired due to reduced efficiency. ...so in general favor that baseline number or a little below it.
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Old 12-01-18, 12:45 PM
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I'm 170 pounds. I use 38 psi front and 45 psi rear on my 39mm tires. It's fast and plush. About 15% less pressure on a front tire is good, since the front carries less weight than the rear tire.
It's quite common to use pressures below the recommended minimums on the tire sidewall. Those are quite conservative, to handle heavy riders and big bumps or potholes.

These are expensive (Compass) tires, with thin, flexible sidewalls. The tire flexes to roll over rough road efficiently, at the expense of being somewhat more prone to punctures. So this low air pressure is both fast on smooth roads and extremely comfortable on very rough roads.

You might want a little more air pressure on a stiffer hybrid tire that doesn't flex the sidewalls as efficiently. Perhaps 45 to 50 psi front, and 55 to 60 psi rear. Then try lower pressures after a few more rides. If it's too low, it'll feel mushy and the steering will be slower. If you rarely go on bumpy roads, then these higher pressures are okay as is.

Pinch flats
Some of the posts mentioned pinch flats. That's where you hit a sharp edged rock or pothole at speed. The tire is momentarily flattened against the wheel rim, which squishes the tube between the tire tread and the rim edge. This causes one or a pair of small slits, a "pinch flat" or "snake bite".

These happen at high speeds with full pressure, or at lower speeds with too low pressure. They are rare when it's just a small rounded bump or hole, a larger object with a sharper edge is more likely to cause a pinch flat.

Last edited by rm -rf; 12-01-18 at 12:52 PM.
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Old 12-04-18, 06:49 AM
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Originally Posted by dabac View Post
Tire pressure is a so-so thing.
Anything inbetween these two is pretty much optional.

Others have more of a "good enough" or, "ain't broke, don't fix" attitude.
It's your ride, your time that's on the line if you get it wrong.
Unless you're doing group rides, you're "free" to spend as little time/effort as you wish on chasing the optimum IMO.
If you're not inconvenienced by higher pressures, I suggest you stay at the higher end of the range. It offers more protection against pinch flats. And it'll be more forgiving if you should forget to check pressure before a ride.

I've never been too bothered by the differences in air pressure. Right before I grab my bike and head out the door I'll grab the tire and squeeze it ,push down on it and watch what the tire does on the pavement beneath. Usually telling myself "Ahh perfect" Every so often I'll take the pump off the frame and give the valve a few pumps, squeeze the tire and push down on it. Might give it a few more pumps or might tell myself "Ahh perfect ".

It's my way of coping with OCD on most every other aspect of my life. I can enjoy my ride whether I have 45 psi or 65 psi in the tires .... But at the same time I can tell the difference in rides from the two, I just don't obsess over it.


I'll be riding along and think for just a second that that last crack in the road about knocked out my fillings. Then look out over the landscape and forget about my teeth and think "wow what a glorious day" . A bad day on a bike.... is still a pretty damn good day....
Just my two cents ....
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Old 12-05-18, 04:45 PM
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Cool Depends..

You Really notice it with heavy duty/thorn resistant tubes ,
though I did a 9 month bike tour without a puncture,
by using heavier tubes in the tires..
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