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There's a question for mountain bike tyres but I can't seem to find anything on here for road bikes. At the moment I'm running at around 90psi. Is that too much? too little? Also, am I more likely to get punctures running at higher pressure? I seem to be getting a lot lately.

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Also, one thing nobody's said: go with the manufacturer recommendation listed on the sidewall. –  Stephen Touset Apr 9 '12 at 22:29
    
The mountain bike tire pressure question referred to here is: bicycles.stackexchange.com/questions/471/… –  amcnabb Aug 19 '12 at 3:17

12 Answers 12

up vote 23 down vote accepted

All other things being equal, run them as high as the tyre manufacturer recommends (there will be an advisory notice on the tyre wall). For most tyres of even medium quality, this should be at least 100psi, if not 110; higher end tyres might go up to 130+. (I generally inflate both tyres to similar pressures, but I think that there are some theories that if either were to be higher, that should be the rear, because it carries the majority of the weight.)

Indeed, the higher the pressure and the harder the tyre, the fewer punctures you should expect as the surface should be better at repelling objects.

You should keep tyres topped up, natural leakage occurs and at the higher pressures you might expect 10-20 psi drift within a week.

When re-inflating, you should also take the opportunity to inspect the tyres. Any deformity or wear will be sure to be far more obvious and damaging when the tyre is inflated to the limits of its recommended pressure.

The only caveat is in poor weather, where a reduction in pressure increases the contact area and introduces give, which should make for enhanced traction.

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+1 -- I'll add that the maximum not only varies with tire quality, but also width. 28mm tires are not likely to go up to 130psi. –  darkcanuck Feb 8 '11 at 16:48
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+1 -- I'd add the second caveat that reducing pressure can make the ride more comfortable over slightly rough asphalt. –  freiheit Feb 8 '11 at 21:32
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+1 -- I'll add that for most purposes, 100psi is a decent pressure to ride at. The increased performance of any higher pressures is likely negligible, and will have a noticeable decline on ride quality. –  Stephen Touset Jun 23 '11 at 11:34
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I'll counter the advice to reduce pressure in wet weather. On a bike tire, pressure is what displaces surface water instead of it lifting the tire off the surface (hydroplaning). With more pressure, the tire will roll at a higher speed before hydroplaning. This may not matter at normal riding speeds and pressures, but at low pressure it could make a difference. –  JRobert Apr 7 '12 at 23:20
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Interesting fact - hydroplaning on a bike is effectively impossible. See Sheldon Brown's page for details: sheldonbrown.com/tires.html#hydroplaning –  Smashd Aug 8 '12 at 17:21

I always run mine around the recommended 120psi (recommended on the tire wall). You can let a little air out for some "old skool" suspension or add a touch for a firmer ride.

Not sure of your weight, but this may be a cause for your punctures, which is why you get a better response around 90psi.

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Without knowing what type of tire you are running, that question is hard to answer. For instanct, a 700x23 will be higher (like 120psi) than a 700x28 which will be lower (like 90psi). Generally tires give a range, the lower number will have more cushion but run slower and pinch-flat easier. Higher end will roll better and resist pinch-flats, but can cause a harsh ride.

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Michelin says this for road bikes:

Air guide

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Of course, rider weight is an important variable –  Mike T Jun 26 '11 at 0:11
    
At what web site/address did you find that chart? –  ChrisW Aug 19 '11 at 13:35
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Michelin says this is for comfort and handling as well as speed. If I am only concerned about speed, is higher pressure always better? –  xpda Apr 4 '12 at 19:08
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@xpda. The short answer is: Only on a perfectly smooth road or tire testing drum. On real-world roads slightly lower pressure is faster as it avoiding "suspension losses" - jiggling the rider about. See BQ article for details. Also maintaining constant contact with the road can only be good for power transfer. –  James Bradbury Feb 8 '13 at 16:28
    

Yep, generally run them at the sidewall rated pressure, or maybe 5psi under. If you want a softer ride (at the expense of higher rolling resistance) you can drop the pressure maybe 20% from it's sidewall rating -- no more (unless you're a fairly small person). Running 30-40% below rated pressure on road tires greatly increases the chance of "snake bite".

The wider the tire the lower the rated pressure, generally.

If you're worried about puncture resistance, buy Kevlar belted tires -- they're just about bullet-proof in normal road use. (I haven't had a puncture in maybe 5000 miles riding Kevlar tires.)

I run my 35mm tires at 95-100 psi -- they're rated 100.

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I tend to inflate 10% shy of max because I'm light (150lbs) and I like my ride to not be jarring yet roll fast. For me its a compromise.There is a sweet spot you find after riding a particular tire for a while. Also if its wet or rough or sandy you may wish to run lower pressure resulting in a larger contact patch=more grip but also more rolling resistance. Ultimately, with experience you will feel whats best for you. It just takes a little time.We all start out not knowing!

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I do not agree that running at the max pressure is a good idea. Most manufacturers express the recommended pressure as a range and there is a reason for that (as has been pointed out in various answers above). There is a "sweet spot" that tends to be affected by a variety of factors such as your weight, bike weight and road conditions. You'll probably need to experiment to find what feels comfortable without feeling "squirmy" or squishy.

There are some arguments that running full pressure actually wastes more energy than the increased rolling resistance from running at slightly lower pressures. At full pressure, the tires tend to "bounce" off road imperfections rather than absorb/conform to them. And of course the increased road shock will add fatigue.

One trick I'll add is to run your front tire about 5-10 psi lower than your rear. The rear tire has more weight over it and so it needs the higher pressure. The front tire has more bearing on perceived handling and comfort IMO, so running lower pressure there has more benefit.

As an example, I use Gatorskins on my road bike (23c) and my commuter bikes (28c). I run the rear tire 10 psi below the max and the front tire 15-20 psi below the max. When I made that transition (from running at max) I noticed a lot more comfort and no loss of speed or efficiency; that includes fairly objective measurements with a power meter. I also have not had any increase in the rate I flat--which is incredibly low by the way, I highly recommend Gatorskins! I am 160 lbs FWIW.

Most of the above observations are discussed in a Bicycle Quarterly article.

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"One trick I'll add is to run your front tire about 5-10 psi lower than your rear." That's a good point. Additionally, using a 2mm bigger tire in the rear than in the front has a similar effect (with both tires at the same pressure). –  amcnabb Aug 19 '12 at 3:15
    
Spot on. bikequarterly.com/images/TireDrop.pdf –  James Bradbury Feb 8 '13 at 16:24

On tires with tubes (which is what most of us have) you should always ride with the maximum recommended pressure but be sure to check both the tires and tubes max PSI. This is mainly to avoid pinch flats but also to decrease rolling resistance. It also will kick debris out from under the tire quicker to help avoid punctures. If you are on tubulars its less of a factor. If you are on nice roads on tubular tires i would always want to max them out as the are usually able to inflate to higher pressue thus reducing rolling resistance. On the other side with tubulars it is still safe to run them lower for nastier surfaces. For more information on tubulars and low pressure google Paris Roubaix + tires and you'll see why.

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There's always a safety factor built in to the engineering design. I'm fat and out of shape, and I've had pretty good luck running about 20% over the sidewall spec. Yes, you'll run a risk that the manufacturer never intended. Yes, you'll be more likely to pop your tires and cause injury to yourself and to others. (Yes, I have a BSME Mechanical Engineering with a fluid mechanics specialization and happen to have been doing this for years on old, worn-out bicycles without a problem.) I do want to warn you that a harsh ride is hard on your bicycle, especially the bearings. It's also going to be more important that the rim itself is free of burrs and that the backs of your spoke nuts aren't exposed (if applicable).

Within a minimum and maximum pressure range, bicycle tire pressure is largely subjective. If you want a smoother ride or are worried about dry grip, go low. If you want a harsher ride that's easier to pedal or are worried about wet grip, go high.

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All things are not equal.

In particular, the load on the rear tire of a road bike is about 60% and on the front it is about 40%. Nor do all riders+bikes weigh the same amount. A 250 lb ultra-Clydesdale might not even want to ride on 21mm tire, let alone ride on it and inflate it up to the sidewall maximum.

If you do overinflate, you will get a rock hard ride with uneven tread wear and be more susceptible to flats. An overinflated tire will also have less cornering ability and greater rolling resistance (at least according to Sheldon Brown and he's smart).

http://sheldonbrown.com/tires.html

If on the other hand you underinflate, you will get a mushy ride, again with more rolling resistance and with snake bite flats. Cornering will also suffer. Even going straight, your bike can shimmy uncontrollably if it hits something.

Getting the pressure RIGHT is worth the effort. Fast, more control and longer life, both yours and your tires'.

This chart is a good starting point:

a chart

Take this and add about 10% for the rear and subtract about 10% for the front. You have less load in the front and you DON'T want a rock hard ride working up through your bars.

Don't go over the sidewall maximum. If the number you get is considerably over the sidewall maximum then take that as a hint that you need a tire which can sustain a greater load.

A wider tire is going to have a lower rolling resistance and will last longer. It's going to weigh a leetle more (matters for acceleration and not climbing) and it's going to have a leetle more drag (not significantly until much faster).

You can stagger tires and ride a beefier tire on the rear for that 60% load. Its increased drag will be insignificant in the frame turbulence. It's also easier to fit that tire within the chainstays than in the fork, say 23 front, 25 rear or 25 front or 28 rear. What's important is that the PSI you calculate for front+rear is within their sidewall maximums.

Your floor pump is not to be trusted. Its gauge will have you progressively overinflating with time. That's another reason to go with Schrader tubes since you can use a better gauge with your car as well.

In summary, before you even contemplate inflation pressure for your tires, make sure you have the right tires. Just so you know, pro tour riders are riding wider tires these days than they did even 10 years ago.

Thin and rock hard to the sidewall maximum is NOT the right answer.

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Welcome to Bicycles Olsonist. You've clearly put some effort into this answer, but it it would be greatly improved with some links to sources. I also strongly disagree that hard tires give reduced cornering ability - the opposite is the case: low pressure tires give dangerously low cornering ability. –  andy256 Nov 3 at 23:47
    
Yeah, I question several things stated above. In particular, increased tire pressure above the above chart values does not increase rolling resistance, but continues to decrease it, and higher pressure also tends to reduce punctures. –  Daniel R Hicks Nov 4 at 2:04
    
(Your chart is in considerable conflict with the Michelin chart in Svinto's answer above.) –  Daniel R Hicks Nov 4 at 2:06
    
For cornering, imagine your tire as an infinitely hard torus. Then in a turn it will contact the ground at one point. All of the friction holding you in that turn would depend on that one point. Let a little air out; now the tire will deform a little and you have more grip in the turn. But let too much out and you've got other problems. Same argument holds for tire wear; over inflating is bad for tread wear; proper inflation distributes the load. –  Olsonist Nov 4 at 6:12
    
As for punctures, the choice is not between high and low pressure. The choices are high, proper and low. High pressure and low pressure can both be the cause of flats. Proper depends on load and tire. –  Olsonist Nov 4 at 6:20

Be careful with overinflation, as while rolling resistance drops with increasing pressure, there comes a point when further increasing tyre pressure begins to dramatically increase rolling resistance.

Often this is around the point of the tyre's maximum rated pressure, although it can be less than that depending on a few factors.

Here is an article that discusses some of the physics of tyres and demonstrates a methodology to assess where the sweet spot for lowest rolling resistance is: http://www.slowtwitch.com/Tech/What_s_in_a_tube__1034.html

Tyres that are overinflated become more skittish when cornering, and are more likely to slip in wet road surface cornering.

Also many modern carbon rims have maximum pressure ratings that can be less than the tyres themselves, so be careful with that.

In general, it's better to be a little under inflated than over inflated.

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