Correct Tire Pressure.
 

I thought this would be the best forum to know the correct pressure for 700c tires.

I bought Panaracers 700-23c tires and put them on sun mz 14 rims. I put in salsa inner tubes.

I inflated them up to 140 and rode 5 miles. The next morning the tire was flat and wouldn't take any air.

I took it apart and the puncture is on the rim side of the tube, lining up exactly with a spoke, and the rim strip is cut.

Should I run these at a lower pressure? Max is 150, and IIRC rec. is 130.

Or should I just get rim tape?

I don't quite dare take them to 150, would it be o.k.?

Thanks for the assistance.

new rim tape is in order. get some velox.

Rim tape is a good idea.

You're going to ignite a huge debate as to what the proper tire inflation is. Check your tire and your rim max. inflation pressures, then the max you should ever go is to the lesser of those two. Correct inflation (albeit and inexact science) depends on your weight. For comparison, I'm 185 lbs, and I run my tires at 110/120 (front/rear).

New rim tape. Velox or cloth equivalent. Done.

Rim tape and maybe lower pressure. How much do you + bike weigh? That's a very high pressure.

You are dealing with two different issues, the flat and appropriate pressure. As for the first question, the flat was likely caused by the rim tape problem, so get new tape, as has already been suggested.

Second, there is no one "correct" pressure. For a start, look on the tire sidewall for the manufacturer's recommended maximum pressure. (Sometimes there will be a minimum and a maximum.) But tire pressure is affected by the kind of riding you do, your weight, a choice between comfort and rolling resistance. Consider experimenting--a little higher, a little lower (being careful not to underinflate too much and risk pinch flats). Sheldon Brown offers this: http://www.sheldonbrown.com/tires.html#pressure, then scroll down to the section entitled "Pressure Recommendations."

Incidentally, you are likely to find answers to most of your cycling questions on Mr. Brown's site.

132psi. Subtract 1lb for every 1000 feet above sea level.

It's been like almost a month since I last posted this so I guess I'll bring it out again:

http://www.bikeforums.net/showthread.php?t=229546

These equations are linear extrapolations of the recommendations that are on Sheldon's site. The real curves of recommended pressures would probably not be linear so keep that in mind. Basically I'm saying that these equations will get you into a good starting point. Adjust as needed for your specific tires, ride quality, weight, etc...

I ride a Kona Dew Deluxe, with a rack and fenders mounted. I believe it weighs about 19lbs.

I weigh about 180.

By psimets calcs, I should be about 113. Hmm...


Edit: Stock the 2006 is 26 lbs, I imagine the 07 is similar. I am probably closer to 28.

Get rim tape and maybe use the guide below as a starting point.


http://www.precisiontandems.com/phot.../tirechart.jpg

According to that chart, I should be using 80psi. Has tire technology changed that much since 1989?

I was discussing tire pressure with a racer recently & he claimed that high-end tires are supposedly designed to grip at higher psi's. So he could run his tires at 140psi, while a cheaper tire would have to run at 120 or less.

I don't use 70 dollar tires, so I can't confirm or deny this. Just another variable to consider.

That chart uses combined weight of rider and bike together. Ends up about the same as the equations I posted.

Not an engineer but that makes Zero sense to me. The available grip is a function of the coefficient of friction of the material on the road surface, and the size of the contact patch. More pressure = smaller contact patch = less grip.

At best, you might be able to argue that high end tires such as the Michelin Pro Grip for example (compared to Pro Race) have a higher coefficient of friction because of softer tread compound, and therefore you can still have good grip at a higher pressure.

The reason people lower pressure racing in the rain is to increase the contact patch size and increase the grip.

Bolo's tire pressure chart works very well, even though it provides PSI levels for riders who weigh 100 pounds to 150 pounds that are much lower than most lighter riders use. A 100 pound rider might be riding at 80 PSI on the same tire that a 250 pound rider uses at 120 PSI.

The PSI stamped on the tire is a MAXIMUM, based on a hypothical "average" rider and a hypothetical "average" rim. In real life, most riders will get the best performance from a tire at something far below the maximum PSI. But, a 250 pound rider will generally need to ride at, or even above, the maximum PSI to prevent the tire sagging beyond the ideal 15% deflection.

The chart is designed to provide a PSI that yields 15% deflection of the sidewalls under the weight of the rider. At 15% deflection, a tire provides the best balance between shock absorption, cornering ability, braking ability, and rolling resistance.

A puncture to the inside of the tube can be caused by the end of a spoke, or by a burr or sharp edge inside the rim. Find that defect, fix it, and then put in some fresh Velox tape. Using high quality inner tubes reduces the number of flats. I've had much better success with Continental tubes than with the "bargain" brands.

My bike and I are about 220, so I run 700X23 @ 120.

I think you meant 700X23, not 700x32.(?)

Its not an exact science, but in general, more air, less rolling resistance, but less traction going around corners. Less air, more grip around corners.

I keep my front kinda soft, 80-90 and the rear pretty high, 110-120. This way, the front, which tends to slide first, has good grip and the rear, which carries most of the weight, has less rolling resistance.

Typo. Corrected. Thank you.

I wrote to Kona on what the max pressure for the Sun MZ14 rims were. Here is their response:

Just follow the tire pressure noted on the sidewall and you’ll be fine. I’ve seen them run up to rock hard for commuting without a hitch.

If you really need to run high Psi all the time then go with a model that runs disc brakes. Rim brakes wear away the rim and cut grooves into it that will eventually fail. I’ve had tires run at under 50 Psi, and rims still disintegrated in a spectacular fashion.






I already have Disc brakes so this is not a problem for me.

I run my front around 115-120 and my rear at around 130-135 on Bontrager Race Lite's. I weigh 157 and my bike weighs about 18 pounds. Of course, I'm 17 and my body can handle road vibrations and such that would leave sometime 3x my age crippled for a week. I haven't had many grip issues, but I don't race either, I'm planning on racing some crits next spring, and imagine that I'd run a lower pressure there for better cornering.

I generally use the visual deflection rule more than actual pressure. If I get 2-4mm's of deflection when I lean on the tire, I roll out, unless its a recovery ride and I want a slower, more comfortable ride, then I let it slide down to 4-8mm's. It all depends on how much comfort you're willing to sacrifice for decreased rolling resistance. I know that at this point, I don't see myself running anything below around 110psi, front or rear, unless it's a rainy fall day with lots of leaves on the road.

Wrong, friction is independent of area of contact, in theory.

+1 It's usually a good idea to have the front 5%-10% lower than the rear anyway. This will give you a similar contact patch on both, giving you a neutral slide-out distribution. You can weigh yourself on the bike one tire at a time to figure out what your actual front/rear weight distribution is, and equate that to tire pressure.

Another factor to consider is the road surface. Really bad Texas chipseal is so rough that you might want to go with lower pressure just due to comfort. My Tour de Gruene partner goes much faster on the final 5 mi of the course with his tires running about 20psi lower. His Cannondale just beats the tar out of him otherwise.

I put in the velox, and mounted up the tires. I mounted the front tire in reverse rotation, whoops.

Aired front to 140, rear to 150.

Seems to work well so far.

Well, according to those forumla, I should be running my tires at about 90 psi .......... and guess what ............. I feel most comfortable when my tires are somewhere between about 90 and 100 psi!! :D Nice to have the confirmation that I'm running the correct tire pressure for me! :)