Is that equation correct? It will indicate a lower pressure for a narrower tire, and vice-versa.

whoops. Just did it for different weights, forgot to use different widths. Thanks for the catch:thumb:

I never mentioned 23mm tires in this thread.

I ride with 25mm tires because I weigh too much for most 23mm tires.

I stand by my original statements on this subject, and I note that Sheldon Brown supports my posts.

I apologize for misreading and thinking you were on 23's, but the fact remains that the SB page does indicate a higher pressure than what you're running, even for 25's (which I did include in the #'s I extrapolated from SB's page on tires & pressure).

Anyhow, if you're happy with how your bike rides and you're not getting pinch flats, then enjoy it.

Your original one did use different widths, it just had the width # in the numerator, instead of the denominator where it belongs. :)

I suspect Syscrush has not actually read what Sheldon has to say on the subject.

And, no, the SB page does not "indicate" a higher pressure.

From SB's site:

"Pressure Recommendations

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

The legal department wants the number kept conservatively low, in case the tire 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 tire purchasers make the (unreliable) assumption that the higher the pressure rating, the better the quality of the tire.

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 tire 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 tires.

Since most bicycles have substantially more weight on the rear wheel than on the front, the rear tire 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/tire sizes.

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

http://sheldonbrown.com/tires.html

Wow, just you people make a simple task as hard as possible.

Just inflate to max recommended PSI using a floor pump with a gauge. They cost a bit more, but they are well worth it as you will never pump them up enough without a gauge. I am always surprised how the gauge tells me MORE! MORE!!!

here is Sheldon's chart. I weigh 70kg, which means 35kg per tire, so I should put 100psi in. (oh shnizzle, i alreadly do that!)

Wheel load ____50mm ____ 37mm _____32mm ____28mm ____ 25mm ___23mm____ 20mm
100 lbs/50 kg __45________ 60 ________75 ______100 _______110 _____120 ______130
70 lbs/35 kg ___35 ________50 ________65 ______80 ________90 ______100 ______110

Read the side of your tires. Inflate accordingly. Re-check frequently.

anybody recommend a good pump with gauge for a reasonable price? i've went the cheap route twice now and regret it.

I picked up a Silca Pista at Bikeisland, so far so good, gauge works. Says it will hit 240 psi in the specs.

http://bikeisland.com/cgi-bin/BKTK_S...ils&ProdID=640
http://www.silcapompe.it/pista_en.htm

get the joe blow sport. the base joe blow sucks.

I check mine once per week or so, and I ride maybe 4 times per week or so. I run mine about 28-30 psi or so. Max is 33-34 or so psi, but there is this section of broken up pavement where I have to go to get on the trail, so I run a little low because of the bumps there.

Read the rec pressure on the side wall, and then experiment in that ballpark for what works for your ride. I find I vary the pressure right down to what road I'll be on regularly.

I use this pump from MEC - never seems to fail, and the gauge works out nicely.

I tend to feel when the tyres get low, so I go by that - depends how heavy I've hit weird things (sometimes I notice hard pothole bangs squeeze air out) or how far/often I've ridden - I ride to work everyday but only usually need a refill every fortnight or so.

I inflate to around 100-110psi, I've had some weird blowouts with Conti Ultrasports (max. rec. is 100psi I think) so I try to err on the side of caution with that tyre, my front is apparently able to deal with 120 (Vredestein Fortezza SE) but 100/110 seems to work well for me(tm).

It's not rocket science, and you ought to feel when the bike is sagging as low pressure can give you speed/effort differences if they're getting fairly low or feeling more bumps than it should.

Yes, I try to look at the bright side of being smaller in stature also!

don't worry about it and if you get a flat throw your bike out.

that weight/psi table is only applicable up to a certain weight. if you're more than ~175lbs the best you can do is inflate to max rated psi as stated by your tire manufacturer.

as for checking air pressure, i hate to do it so frequently, but it beats getting a pinch flat in BFE or the hoodz during a night ride. usually i pump up once a week but if there's an interesting group ride or whatever i'll top off just for that. kinda sucks because i rotate between 3 bikes (roadie, fixie, foldie) and i don't put enough saddle time across all 3 so i'm doing pressure checks/top offs more frequently.

thanks for the input, guys. i went with the serfas fp200 for $40 at the lbs. no problem getting the pressure high and the shop covers it with a lifetime warranty!

no.

no.

no.

there is considerable evidence that lower pressures provide better wear, comfort, and grip. i am 175-180 and routinely run 100/110 f/r in 23c open corsas, 90/100 in 25c. the sidewall says 115-145. yes, i am under the minimum. i have never pinch flatted.

i used to be a pump-it-to-the-max kinda guy until somebody clued me in. the improvements are astonishing, and no, i am not any slower. as i understand it, the difference is essentially that the contact patch can give a bit to conform to the pavement rather than skitter over it.

i suggest you try it for a bit. what harm could it do? if you don't appreciate the difference, you can always jack 'em up again...

Wrong.

100% of everyone will fare just fine by following the manufcturer's recommendations.

I did not offer incorrect advice.

i suppose not. only incomplete.

when it says only 'max pressure 130psi', what is 'accordingly'?

It isn't rocket surgery to read and follow directions. If you can't figure out what to do after you read the side of the tire then I cannot help you further. I'm not here to play the nit picking game and I don't appreciate being accused of telling an untruth to someone when I have not. If you want to offer advice on your supposed "evidence" based practices then offer it. Don't act like a child by telling everyone else they're wrong and only your input is sagacious.

i don't recall asking for your help and i absolutely did not claim my opinion as the sole truth. my point is only that the sidewall markings are hardly gospel and fail to take a lot of things into consideration. will they 'work' for everyone? sure. so does the abacus, but it's not optimal.

the research i mention is out there (if i had a link handy, i'd provide it) and convinced me to experiment and develop an opinion. my opinion is merely anecdotal evidence.

so what pressure do you ride? tire size? weight? road conditions? and most importantly, what does your sidewall say?

But you sure didn't hesitate to knock everyone else while promoting your own opinion, didn't you?

Grow up.