Tyre Pressure...how much?

[Cycling Naturalist]

My tyres are rated to 120, but I use 100. If the pressure drops, then the handling suffers.

 

[andy_wrx]

The holy words of Sheldon Brown
http://www.sheldonbrown.com/tyres.html

Pressure Recommendations

Most tyres have a "maximum" pressure, or a recommended pressure range marked on the side of the tyre. These pressure ratings are established by the tyre manufacturers after consultation with the legal and marketing departments.

The legal department wants the number kept conservatively low, in case the tyre gets mounted on a defective or otherwise loose fitting rim. They commonly shoot for half of the real blow-off pressure.

The marketing department wants the number high, because many tyre purchasers make the (unreliable) assumption that the higher the pressure rating, the better the quality of the tyre.

Newbies often take these arbitrary ratings as if they had some scientific basis. While you'll rarely get in trouble with this approach, you will usually not be getting the best possible performance with this rote approach.

Savvy cyclists experiment with different pressures, and often even vary the pressure for different surface conditions.

Optimal pressure for any given tyre will depend on the load it is being asked to support. Thus, a heavier rider needs a higher pressure than a lighter rider, for identical tyres.

Since most bicycles have substantially more weight on the rear wheel than on the front, the rear tyre should almost always be inflated to a higher pressure than the front, typically by about 10%.

Rough surfaces generally call for a reduction in pressure to improve ride comfort and traction, but there is a risk of pinch flats if you go too far.
Rider skill also enters into this: more experienced cyclists learn to "get light" for a fraction of a second while going over rough patches; newbies tend to sit harder on the saddle, increasing the risk of pinch flats.

The table below is based on my experience and a certain amount of guesswork, and should only be used as a very rough guide to a starting point. Interpolate/extrapolate for your own weight/tyre sizes.

Tyre widths are in millimeters, pressure recommendations in pounds per square inch. (Divide by 15 if your gauge reads in bars/atmospheres.)

Wheel load 50 mm 37 mm 32 mm 28 mm 25 mm 23 mm 20 mm
100 lbs/50 kg 45 60 75 100 110 120 130
70 lbs/35 kg 35 50 65 80 90 100 110

Note that these recommendations are based on the actual tyre width. Many tyres are marked wider than they actually are

So ignore what's written on the side of the tyre.

 

[beckc]

Hi
I have had tyres very similar to those mentioned come off a reputable rim at 115psi.

I have had no pinch flats to report at 90psi.

Generally I run at 100psi

Recent info in the press suggested some top pros run at this in practice.

I suppose one imponderable is just how accurate all our gauges are !

I think above 100psi feels very slippery in the wet.

 

[andy_wrx]

I do generally run mine at 100psi front, 110 rear (700-23's : Michelin Pro Race 2, Conti GP4Season, Vittoria Rubino Pro)
or a bit higher on TT/tri bike for flat surfaces, race conditions (Vittoria Open Corsa)

But if it's wet I'll let them down 10-15psi

Never had a pinch flat, in fact have never had a flat in competition or when doing a sportive (that's done it ! desperately looks for wood to touch) but have gone past quite a few others at the roadside of sportives
- did wonder whether they were using superlight race tyres without any puncture protection (in 100m+ sportive ?), but I guess they could just be terribly-prepared and running underinflated tyres (or just unlucky !).

I generally check my tyres pretty regularly to see there's nothing stuck into them - thorns, bits of glass, wire, etc.
Once a week in High Summer, after every ride at this time of the year when leaves are coming down or in Winter when rain washes stuff into the road, after any ride when they've been hedge cutting, etc.
I've pulled a few bits of debris out of the tread, which whilst they hadn't caused a p*nct*re, would have worked their way in until they did...

I learnt this after getting a p*nct*re on the rollers - it was a thorn I could hardly have picked-up on the rollers, it must have been stuck in from the ride the day before !

 

[Tynan]

'a p*nct*re on the rollers'

excellent

and a point well illustrated

 

[Fab Foodie]

As usual, Sheldon's advice is good.
My Michelins go to 115psi, and I'm sure they are great at that pressure if on a billiard-table smooth surface. Fact is that most roads are relatively rough and very hard tyres can roll slower on rough tarmac than a slightly softer one. So it pays to experiment on finding what suits you.
I run 95 on the fron at 105 rear and I get a fast comfortable ride on the average tarmac surface, full pressure is harsher and less comfortable for no percieved increae in speed or reduced effort...in fact the extra vibes seem to make it hard work.
Below 90, things do start to feel a bit sluggish.
Experiment!