uhm, no. Lower tire pressure = larger contact patch = more grip. This is why you lower pressure for a crit in the rain.

Admittedly, you can lower the pressure too far to the point the sidewalls flex and become squirrely. That said, all else equal, lower pressure equals more grip.

He said "too" low...

Best for what? Some conditions warrant lower pressure than others, some days I want a firmer tire. Plus, unless I'm racing, I'm not concerned about performance, and there's no discernible difference in ride feel across a very broad range. The reason I pump 25mm tires to 100-105 is because it's plenty firm, but allows me to keep riding for a long time without worrying about needing to re-inflate; I'm comfortable down to about 75 psi. I don't pump any closer to the rated max. because I'm lazy, and I don't want to get big arms.
However, there's the psychological aspect, too. Regardless of the science, I feel better starting a race or a gran fondo with firmer tires, so I may pump the same tires to 110, and the tubulars over 120, which, by the end of the day, won't be at 120 any more.

Exactly. psit instead of psig.

Best based on your personal preference and application. My only point is that tire pressure is something you should be making a decision on, and trying to keep the pressure within a reasonable variation of that. Pumping to 105, and then not putting anymore air in until the tires get to 75psi means you're 30psi away from your chosen pressure, which is a pretty drastic difference.

Now, maybe you're equally happy with 105, 75, and everything in between for all of your cycling applications, in which case your strategy would make sense. I'm a bit more picky about it though...

Pretty much: I'm not as picky as often.

"too low" will make the tire flex, and feel squirmy, decreasing control ,and making the handling sloppy.

However, you will still have a bigger contact patch and more traction.

So too low air pressure will negatively affect handling, but not by decreasing traction.

To the op - did you use the gauge on a floor pump to read that lower pressure?

If you did, the pressure reading on the pump’s gauge will be up to 20 psi lower than was really in the tire. This is because the tire’s air has leave the tire and fill the pump chamber, which lowers the overall pressure, giving a false low reading.

That's why I never use the pump as a gauge without first pumping a stroke or more of air into the tire.

I’d have thought it pretty damn obvious how you test for too low. Gets my nomination for the « most pointless thread of the year » award

It is not a false reading at the time of the reading. It is just false compared to the pressure that was in the tire before the hose was attached. But what difference does it make. You just want to ride tires that are properly pressurized. Once you attach the pump, you are essentially committed to adding air as you should do before every ride. No biggie. But it is valuable to understand that the tire didn't actually "lose" that air that goes to pressurizing the hose by permeation or leakage.

Not necessarily. Only if you want to maintain a certain high pressure. What matters is that if you don't trust your thumb gauge, the gauge on a pump is probably not what you want to use just to check, and if you do hook up a pump it would be pretty silly not to bring the pressure up to the higher end of your preferred range. Yes, it's important to check your tires before getting underway, but adding air just to be sure they have 105 psi and not just 100 (or heave forbid 85 - OMG! you're gonna get a pinch flat!)? That's hardly necessary, and if your friends are waiting on you, it's just annoying.

Back to the original question:
Depending on how you ride, that, and wear, are about it. You can ride with NO pressure if you ride slowly and carefully enough, and don't mind the ride feel or beating up your rims or throwing your money away on rubber. Speaking of which; get some tubulars so you can go a little faster with no air.

No one mentioned rolling resistance. As your tires get too soft you are wasting energy getting them to roll, as if your brakes are dragging or you're towing a parachute.

Never a shortage of ideas around here... hey - look - here comes another one!
1. At 155lbs, I ride 23's and 25's quite happily between 80 and 85 psi for standard suburban and country riding. Noticeably smoother and just as "fast" as higher pressures (lots of rsch on net reg that).
2. Racing, track or higher personal weight, adjust up. Notice strange handling in the turns? adjust up.
3. Then, if you're not getting pinch-flats, you're not too low.

Research suggests that is not true at all for good, fast tires. Lowest pressure possible the better. Any increase in drag due to deformation losses through rolling seems to be more than made up for by reduced suspension losses going over small irregularities in even a very smooth asphalt road.

I can attest that the above does not apply to 1000 gram+ winter studded tires

That is not the way it works. For every tire volume there is an ideal pressure for the bike/rider weight which reflects a balance between rolling resistance and conforming to the road. Below that point the rolling resistance goes up without an increase in useful road conformation.

Generally, a large volume tire at the correct lower pressure will have similar rolling resistance to a lower volume tire at its higher, correct pressure. So if you want more cushion without increased drag, you'll only find it by increasing the volume on your tires, not by lowering just the pressure.

"lowest possible pressure" probably wasn't the best way to describe it...as sure, if your rim is sitting a millimeter off the road, or you're getting pinch flats once a day, you're probably giving up too much drag as well. But still - from everything I've read on the subject, the ideal 'fastest' pressure is much less than what was previous conventional wisdom. I'll see if I can dig up some of the research I read on it.

Take a look at these charts:

Find the Rolling Resistance chart on this page:
https://www.bicyclerollingresistance...0s-ii-23-25-28

Then plug in weights using this chart (keeping in mind to divide for each tire):




Using the 23c and 28c tires to compare, let's use 88 lbs for our weight on wheel. That gives us recommended pressures of 91 psi and 65 psi respectively. When you apply those to the rolling resistance graph you'll see that gives us rolling resistance numbers of 13.5 Watts for the 23c at 91 psi and 13.7 Watts for the 28c at 65 psi. Pretty darn close. And both of those pressures are optimal for conforming to pavement for optimal real world rolling resistance while high enough to prevent pinch flats.

That optimal number is usually thought to be around 15% compression of the tire, static. And while you ride and hit bumps that compression number will go up and down. The reason the big tire is more cushy is that when either tire compresses an extra 10% for a bump, the bigger tire has more travel (10% of 28mm vs 10% of 23mm). The larger volume tire has greater "travel" in suspension terms, even though it is offering about the same rolling resistance of the short travel 23c tire.

But if you just lower your pressure, your rolling resistance climbs and your bump compression starts to overlap where you'd get a pinch flat. So if you were to lower your 23c tire's pressure under optimal to 75 psi, you're now at a rolling resistance of 14.7 Watts. Why ride a smaller tire with greater rolling resistance when you could get similar rolling resistance by using a larger volume tire?


(I used 23c and 28c to illustrate the problem. The same fundamentals apply to any two tire sizes of the same construction. 28 and 32, 1.5 and 2.0, etc.)


The reason someone might choose a narrower tire like a 23c is that it will have the least rolling resistance at optimal pressure and have the lowest total weight while still conforming to the road optimally. But it will transmit more large bumps than the large volume tire because of its limited "travel".

Not entirely accurate. Lowering pressure reduces suspension losses independent of tire size. And, at a given pressure, a larger tire will always have the lower rolling resistance. So you can't say the 23mm tire has the lower rolling resistance at optimal pressure.

Also, an important bit of data from the bicyclerollingresistance site is the ~3 watt difference in the tire between 120 psi and 60 psi.

So, the real question is: Do suspension loss differences account for more than ~3 watts on a normal road between 60 and 120 psi. If so, then 60psi is faster at all tire sizes. Ignoring aerodynamics, of course, which is opening up a whole different can of worms...

edit: and 'travel' as a percentage of tire drop/etc really doesn't play into things. When a tire compresses, it creates a larger contact patch, which creates a larger total force pressing against the pavement, which will force the bike(and rider) up and over the obstacle.

How hard is it to "get the pump out"? Mine is always out, right next to the bike. I pump up the tires before every ride, and they always need at least a little air. I keep the front around 100psi and the back around 110psi (lower when it's wet). If I go more than a couple of days without adding air they drop into the 80s.

I got used to pumping up before every ride. It's like putting my bike shoes on, just part of getting ready. You don't really need a helmet every time, either, but you do it anyway. That's what topping them up is.

A guy on the local hiking forum was giving me hell for the 1.5 watt I lose using wider, lower pressure tires. For context, most of us in here probably have an FTP somewhere from 200 to 300 watts.

Lowering pressure to something optimal reduces rolling resistance, which is why the different surfaces in this chart show a point of minimum rolling resistance (43W on the Green, 48W Yellow):


https://janheine.wordpress.com/2016/...ses-confirmed/

For the course asphalt (Yellow line), when you go below OR above 100 psi with that tire your resistance goes up. 100 psi with that tire on that surface is optimal. As your tires get softer they aren't providing any additional "roll over" efficiency, but they are becoming inefficient due to sidewall flex.


You can't create a larger contact patch without compressing the tire vertically. They are two ways of measuring exactly the same thing.

But the goal of the tire changing shape is not to lift the rider over the bump but to conform to the bump so the rider does not move up and down at all. That's where the efficiency comes from - the bike is traveling in a more horizontal line, rather than moving up and down with the pavement irregularities. Very high pressure tires are going to "force the bike(and rider) up and over the obstacle", and we don't want that.

Haha, and I'm sure your wider tires are faster on the gravel roads you ride anyway. Probably by a lot.

Not very hard, but it's extra work that isn't necessary. When I commuted I rode at least twice each day and frequently 4 or more times if I needed to get groceries or something. Absolutely no need to pump up the tires before each of those rides.