Leebo

Acugage works well for me. 4-10 psi depending on the season and tire. 26 x 3.8 - 4-8.

Gresp15C

Indeed, the gauges probably all contain the same mechanism.

I once went to a public lecture given by Normal Ramsey, who got the Nobel Prize for his work leading to the atomic clock. He told a story about how he wanted to own the world's most accurate watch, so he researched how watches worked, etc. At the end of the story, he pulled back his sleeve to reveal a cheap Casio digital watch, since he found out that all watches used the same grade of oscillator crystal from the same factory.

ZHVelo

Oh that is interesting, when I pumped it up yesterday, so the day after, the front was indeed at 7.5 and the back at 7. So indeed there was such an imbalance you describe that I was not used to.

Darth Lefty 

If you think your gauge is inaccurate at 8 bar look at how well it does at the <1 bar level for us plus and fat tire riders

Drew Eckhardt 

It's common.

That's enough to make you slower on a lot of pavement, and regardless you're compromising comfort. Use a wider tire if your weight dictates that with narrow ones. Most road bikes made in the last 20 years will clear 25mm tires, and contemporary disc brake bikes fit 32mm which is the widest size the fastest tires are sold in.

Get a pump with a built in gauge and note how long it takes your tires to deflate to an unacceptable level.

With 25mm wide tires I start Monday at 80-85 front/90-95 rear, and add air the next week at 70-75/80-85. Less is sufficient to prevent pinch flats but the front feels squishy riding.

kenshireen

Drew, I don't have your level of expertise so help me understand the first chart. Is wheel load the weight of the rider and I don't understand the "pressure for a 15% wheel drop.. what is this chart actuality showing in laymans' terms

DomaneS5

Same PSI on tires here, but I have the 5000's.

himespau 

Heisenberg's uncertainty principle, right?

Rides4Beer

I could, but the process is pretty easy, just pump it up fast without paying attention to where it hits so long as it's over where I want to be, then bleed it down with the Topeak gauge. Since I do it for every ride, I've gotten pretty quick at it. Probably takes me longer to put on my shoes.

Gresp15C

Good question. Wheel load is how much weight is on each wheel. It's not exactly half your weight, because you normally have more weight on the rear wheel.

The 15% wheel drop is how far the tire deflects under that load, i.e., 15% of the tire diameter, so a 25 mm tire would be compressed by just under 4 mm. This is also enough to visually confirm that the tire is pooching out under your weight by maybe a couple mm on each side. In fact, I inflate my tires by gauge when at home because my pump happens to have one. But for quick confirmation or if fixing a flat while on a ride, I just check how much the tire is pooching out.

One useful thing about that graph is it shows that the effects of tire pressure are gradual, and forgiving of minor variations.

Drew Eckhardt 

Wheel load is the amount of weight on a wheel, which is total rider + bike weight multiplied by the fraction on that end. Road bikes typically have a 45%/55% front/rear split; so given a 160 pound rider on a 20 pound bike you'd have 180 * .45 = 81 pounds front and 180 * .55 = 99 pounds rear.

Frank Berto observed that a 15% drop in tire height was optimal - not hard enough to create unpleasant vibration, not soft enough to feel squishy and slow. E.g. the ideal pressure for a 25mm tire produces a 25 * .15 = 3.75mm drop.

The chart has curves for various tire widths mapping from weight on a wheel to the desired inflation pressure.

A layman should figure out how much weight they have on each wheel. find their tire width, and use the corresponding inflation pressure.

E.g. with a 25mm tire, the hypothetical 160 pound rider on a 20 pound bike with an 81 pound / 99 pound weight distribution would run about 75 psi front and 87 rear.

It's a good starting point which you can adjust to taste.

Pratt

Quantum mechanics, or a Zen koan.
You can never know what the pressure is, just what it was

Viich

BicycleRollingResistance.com results seem to indicate that wider is better as far as rolling resistance at the same pressure, that at the 15% drop value narrower was slightly better, and it was exactly the same if he adjusted for the same 'comfort' (4.5mm drop for each)

This was his GP5000 comparison: Continental Grand Prix 5000 Comparison: 23, 25, 28, and 32 mm Compared Published: 2019-02-19 by Jarno Bierman

I pasted in the first table, the raw psi numbers:



Rolling Resistance with Michelin Latex Inner Tube
Tire GP 5000 GP 5000 GP 5000 GP 5000
Tire size 23-622 25-622 28-622 32-622
Tube Latex 80g Latex 80g Latex 80g Latex 80g
120 psi 8.5 Watts 8.4 Watts 8.0 Watts 7.8 Watts
100 psi 8.9 Watts 8.9 Watts 8.4 Watts 8.2 Watts
80 psi 10.2 Watts 10.0 Watts 9.2 Watts 9.0 Watts
60 psi 12.3 Watts 11.8 Watts 10.9 Watts 10.3 Watts

Metieval

I changed a tire tube for a neighbor. A day later he tells me the tube I bought and put in for him was Sh**!

I am like why, he says it was already flat. Then he proceeds to tell me that it was losing air so fast. Every time he checked the pressure, it was lower.

I asked him how many time he checked it, and he said like 10... I went down to his house pumped it up and told him to quit checking the tire pressure with a gauge. hahha

Sy Reene

All true, but realize that handling, grip, weight and aerodynamics aren't part of their evaluation.

Oneder

Just feel the sidewalls eventually you will know when it's ready by feel

DaveSSS 

25mm tires shouldn't need 100-110 psi. I have used that much in old 23mm tires, but one of the first things I picked up after an 8 year cycling hiatus was that 25-28mm tires are the new norm, with lower pressures. I only weigh 140, so I use 80 in the front and 90 in the back. Allegedly rides and rolls better.

I use a Silca pump with it's own gage that's at least 30 years old. I replaced the leather plunger once, but I have a spare that I bought 20 years ago, waiting to be used.

Hopefully the OP uses presta valve stems.

rydabent

At 82 years old, I try to ride every other day. My routine before a ride is to wipe down the chain, and attach my floor pump with its guage and check the tire pressure.
The tires almost always need a few stroke to put them at the pressure I want. The pressure guage on the pump is of reasonable quality, and I trust it.

The reason to check the pressure before every ride is to ensure I havent pick up some tiny object that is causing a slow leak. Anything below the usual expected drop in pressure is cause for investigation.

kenshireen

Help me understand this chart. I assume the lower the watts the less the rolling resistance. Wouldn't this mean that if I am running 25 that me rolling resistance will be less as I increase the psi.. although it appears that there is not a significant difference between 120 and 100.
Are these psi numbers on both front and back

kenshireen

This was his GP5000 comparison: Continental Grand Prix 5000 Comparison: 23, 25, 28, and 32 mm Compared Published: 2019-02-19 by Jarno Bierman

I just looked at the chart with a 15% drop and it appears that the rolling resistance between a 25 and 28 is almost identical when the 25 is at 100 psi and the 28 at 90 psi (even though the Butyl tubes weighs 30 grams more on the larger tire)
Is this true... to me this means that you can pump up a 28 at less psi and it will have a similar RR to a 25 which will be at a higher psi.

I always thought that a thinner tire with high pressure would have less RR than a wider tire with a similar psi

MadKaw

Try changing the balance and let me know how it feels.

WizardOfBoz

I'm up there at 108kg or so, and I used to run my Bontrager R3s tubeless at 116: the max rating. Finally figured out that I didn't need that high a pressure, at least in the front. So I run 116 psi rear, 95psi front. This gives me good performance and a pretty comfortable ride (I have a Trek Domane, which has the isocoupler, which also absorbs shocks).

To the OP's point, it seems to me that the goal is a comfortable, efficient ride that is reliably consistent. So the point isn't getting 110.000 psi in the tire, it's getting the right amount of air in the tire for a good ride. So if you test your tire with a gauge and it reads 113psi, and that gives you a great ride, why worry that testing with the gauge drops you to 110psi?

The gauge's value is in allowing you accurate repeatability, not in delivering an accurate arbitrary pressure.

WizardOfBoz

That was the theory back in the 1970s or so. There's been some learning since then. Higher pressure tires do transmit more vibration and this causes power loss. If you're a bigger guy (like me) it would be pretty impossible to get the tire pressure in a 21mm up high enough to avoid bottoming out on big bumps, and so the tire flexes, which is a major cause of power loss.

Here's something from Jobst Brandt: https://sheldonbrown.com/brandt/rolling-resistance.html

Jan Heine, another knowledgeable bicycle guy, weight in here. His take: inflation doesn't matter that much. Inflate your tires with enough pressure to keep you from bottoming out on bumps and to avoid the tires rolling in hard cornering, and ride. And don't worry about it.

Now I don't optimize stuff much. I probably would best like 28mm tires. I settled on 26mm because Bontrager R3s were on my wheels when I bought the bike, and I trust the previous owner's (Neko Mulally) judgement so I stayed with R3s, and R3s come in 26mm. Could I go to 28s and get a better ride? Maybe. Some cyclists being tech-wienies means we can't help but optimize. I've gotten better perspective as I've aged*. When I was a lad working in the bike shop, all these things mattered a lot. Now, more important to make a choice and go ride. Same with tire pressure. Signficantly more comfortable with 95psi in the front, and I think it vibrates less and is actually more comfortable.

But to the OPs point: I disagree: pressure gauges can give you a reliable, repeatable measurement. Figure out what that is for best performance and... get out and ride.

(looking at this as an optimist, if your tire pressure is a few psi low you'll have a more comfortable ride, AND you'll get more exercise!)

*Slower too. Shoot.

Viich

You've got it - less W, faster rolling tire. But, he's testing purely rolling resistance. There's also a suspension component, where tire deflection when you hit a bump stops the bike & rider from lifting (at least as far) - this is extremely variable depending on your surface. He discusses it as 'comfort' and tire drop - the wider tire is going to be able to absorb more at the same drop because of the greater air volume.

Yea, this isn't quite as far out there as the 'wider tires are actually faster' that Bicycle Quarterly went with a few years ago, but it isn't the way people thought it worked before powermeters were common enough to do a lot of testing and guys like this started doing component level quantitative testing.

The pro peleton has mostly switched to 25mm tires, in place of the 17-21mm they were on 10-15 years ago. I'm riding a mix of everything from 23 to 32 in road tires - there's not actually as much difference as we all thought..... lots of difference between tires, but there are now good road-style fast rolling tires available in wider sizes than they used to be.

fietsbob

BTW you can have a comfortable rolling efficient tire even if wider by buying premium tires ,

or so says Bike Quarterly, who has conducted tests and gets tires made to sell that offer this advantage..