A Tire Pressure Thread
 

I just put Continental Gatorskin 700x28 tires on. Their web site says the tire pressure range is 95-116psi.

What relationship is there between tire pressure, weight carrying and comfort?

Note: Some folks run some really low pressures. But, finally pinned down they confess to weighing very little.

Comparatively, I weigh very little (135 lbs) and run 120 PSI.

How is the ride? I weigh about 140 lbs and run about 100 psi on 700x25s. The ride is fairly comfortable.

I weight 220 lbs and use 90 psi in the front and 105 psi inflation at the rear with a tire that size. A tire should deflect 10 to 15%. Less than this reduces traction and more than this increases rolling resistance.

Remember to split the Front/Rear wheel load 45%/55% for Road Bikes

http://bikeforums.net/attachment.php...hmentid=380056

I was going to post a similar chart to FlatSix911. I might add that it is my experience that inflating a tire close to the maximum rated pressure will lead to significantly more flat tires. Of course under-inflating will lead to pinch flats and you risk damaging the rim.

135lb/140lb, 23mm tire at 120psi

A very hard, responsive ride.

205lb rider plus 17lb bike puts me at around 100 kilos all in. 85 psi rear 75 psi front when riding Challenge Parigi-Roubaix. 100/85 when riding Schwab One 700x25 and 95/80 when running Vittoria CX EVO iii 700x25. Latex tubes.

Life is too short to run cheap rubber. Never had a pinch flat.

190 lbs, 85/90 front/rear when running my Hutchinson Sector 28mm tubeless. Not pinch flats of course:)

At 143 pounds, I ride 25s at 115. Max pressure rating. I prefer a firm ride.

I weight 385 pounds and inflate the tires to 250 psi.

I'm 224lbs and I pump my tires to 115psi front & rear but some escapes when I take the chuck off, so maybe 110 or 105psi is left in the tires?

Hand pump or co2?

I too read the article that produced FlatSix's chart several years ago and reduced my pressure. My wife and I both ride at about 60 PSI on 28mm tires and haven't had flats in more than a year. The ride is also a bit more comfortable than would occur at higher pressure.

I pump mine up to the max, which is only 100 psi on the 25mm I have now, so that I have longer before having to pump them up again.

If I had to choose a set pressure it would be 80/90 front/back. Total weight is about 175.

The chart says 70/85 psi but that just seems weird. It might be right though for all I know.

I am 215lbs and ride on 100lbs 700x23. No problems and comfy ride.

High pressure more speed - Lower pressure more comfort
 

There certainly is a relationship between tire pressure, speed, and comfort. The relationship between pressure and speed is direct and between pressure and comfort is indirect. I bought a recumbent racing trike that came with Schwalbe Ultremo ZX 406 tires. The rated pressure is 85 to 160 PSI. If you run them at the highest pressure, you might as well be running solid rubber tires. The ride is incredibly harsh. The ride is faster though. I dumped them almost immediately for a set of Tioga PowerBlock tires rated at 35 to 80 psi. Much more comfortable at the rated pressure but slower. I don't like running Schwalbe tires much below the maximum pressure because of bad experience with premature sidewall failure. The sidewalls flex more at the lower end of the rated pressure range. It may mean a shorter life for the tire.

I don't think so. I think a speed/pressure curve has a maximum well before the highest pressure, other things held equal, and that the other variables complicate that even further.

It makes a difference, try it and decide for you.

I like to go as low as I can without risking pinch flats. I run about 70f and 80r in the Pasela TG 28s on my Casseroll and about 85f and 95r on the Turbo Pro 23s on my Roubaix. Sometimes lower. EDIT - I weigh about 170 lbs.

Another factor to consider is whether you ride light or heavy. Riders who stand up over RR crossings and rough spots, who know how to make a bike float over bumps, can go with lower pressure than those who keep their butts planted on the saddle in all situations.

I run my Marathon Supremes at 92 PSI, (35s and 40s) because, for me, that's where they roll the best. Not 85, and not 95, but 92. Everyone is different in their wants and needs.

I'm just the opposite.

Over the years I've slowly gravitated to using wider tires and less air pressure. The big "Aha" for me was when I went from using 120 psi to 100/110 psi with 28 mm tires on our tandem. We never pinch flatted, seemed to go about the same speed, but felt a lot smoother. I used to top up my tire pressure before every ride. Today I can't remember for sure the last time I pumped up my tires. I just squeeze them with my fingers and, if they don't feel "too" soft, I just ride. Subjectively I don't feel slower or that I'm having to work harder but, honestly, I don't fret about those things anymore.

I weigh 193 lbs. and am 71. I recently changed tire size of my GP4000s from 700x23 to 700x25. I used to run 110 rear and 100 fronts. I now run 105 rear and 95 fronts. I have never had a pinch flat on either size and have used these tires for better than 30,000 miles. They are ridden pretty hard with yesterdays ride hitting 45 mph. Some of the roads are fairly rough, especially on some mountain descents.

Don't know how this might fit in but I weigh 182 lbs and my bike weighs 18 lbs. I run 700X25 at 100 psi front and 110 psi rear. Rolls well and is comfortable.

I have bought into the 15% tire drop line of thinking (http://www.bikequarterly.com/images/TireDrop.pdf) and currently run my long wheelbase 'bent (30/70 Front/Rear weight) at 50/80 psi with 32 mm tires. Looking at the chart again, I could probably go lower at both ends. (225 lbs me+bike)

On my MTB I run 30-37 pounds because gripping in the turns is important.

I run 23's (Vitts Evo Courso) on the road bike. they recommend 125-145. I run 140 and weigh 225. It is a smooth and nice rolling tire. They claim to be the lowest rolling resistance out there. I really like them.

There are charts, fomulas and "science". Then there's reality.

Charts and formulas provide a rough guideline or starting place, but you need to use the pressure that's right for not only the wight nd section, but the flex properties of your tires and the rod conditions.

As a rule, more pressure means lower rolling resistance on smooth pavements, but can actually increase rolling resistance on rough pavement and over bumps because of the rear vector of the tire impact. Higher pressure also means lower traction, and less comfort. OTOH overly low pressure will mean high drag and pinch flats or dented rims.

Experiment and find the best balance for your needs. Start any place on the low side based on the charts, and increase pressure incrementally by 5#s or so over time, until you feel the effects of excess pressure -- harsh ride, skittish handling, serious rebound on bumps -- then drop back 5#s to where you feel the balance was right. BTW- don't forget to keep front tire pressure lower than rear.

Lower pressures with latex tubes is faster than higher pressures with butyl tubes and more flat resistent.

On smooth pavement, the harder you pump, the faster you go. There's no question. On less than smooth pavement it's more complicated. Nothing to do with the rearward force from bumps because for every rearward force there's a forward force from the other side of a random bump. Rough roller test show that resistance decreases with increasing pressure just the same as it does on smooth rollers. It's the upward movement of the bike that uses energy, so to get an increase in resistance there has to be enough upward movement to counteract the inherent lower resistance of higher pressure. That's going to be different with every tire and rider. The other thing that happens is that some tire/wheel/frame combination damp or eliminate lesser bumps before they reach the rider, preventing vibration from contributing to tiredness. Other combinations don't. So that's going to vary with the equipment, too.

The only way to sort it is to experiment with power and speed instruments with your bike on various courses. Otherwise it's all just internet noise. FWIW, I've done all my fastest long distance events on a carbon frame running light 23mm tires at 140 lbs., some smooth pavement, some chipseal. 150-160 lbs. TT riders and long distance racers report similar results. Frame makes a big difference. I run <100 lbs. on my aluminum CAAD9.

I bolded the main part of your error. There's no return of energy lost to the rear vector of the force needed to raise the bike over the bump because the bicycle is moving too fast and "ski jumps" off the other end of the bump and free falls back to earth.

You are right that the energy lost on bumpy roads relates to what's needed to raise the bike, but it's not the vertical movement that's an issue, it's the rear vector of that lifting force generated at the point of contact.