Road Fan

I don't think it's based on 20-somethings. Frank Berto put it in Bicycling Magazine somewhere around 1977. He got it by measuring how much the tire was compressed from holding up the weight stated. I think Frank was maybe 40 when he did that work, he certainly had a day job as an engineer. He was not in a racing career.

As far as the validity of the results, that's up to you. There is no absolute correct perspective, nor an ISO standard reflecting a global agreement with all "member nations" having signed it. Frank Berto's chart is simple and quick. For your bikes, how much difference is there between Berto, Heine, Silca, and SRAM rules and calculators? Considering that on light road tires you could lose 10 psi from clumsy valve handling combined with seepage as your ride reaches 20 miles? If you think it really matters, why does it really matter? Do you have a TdF coach breathing down you neck? Can you feel a 2 psi difference with 21 mm tubulars? Do you really want the feel of finer gravel to be absorbed, or is there some benefit to having feel of when a road surface might be loose or get loose?

Also, if it feels loose in some small way, is it your tire pressure or are your spokes under tension, just to give you all some more to think about, especially, at what point do you stop worrying and think, "25 miles to home, and I don't have my pump with me anyway - better just keep going!"

LarrySellerz

OP rides in the wet and should go with “low” pressure. I disagree with the calculator suggestion, it really doesn’t matter that much. So many people ride around with like half or less of the adequate pressure. Depending on the bike I like around 100 in 25s, but normally go to ~125 and often don’t fill up again until it’s 70 or less. I go higher because it doesn’t matter, and I wait until it’s too low because it also doesn’t matter.

just press on the tire to gauge if you need more air. If you can’t tell, its probably fine lol. If it’s wet, take some out and if you get a pinch flat (snakebites on tire) then you know it was too low for next time.

shelbyfv

And it's a wrap, folks. Pick your authority, Larry or Frank Berto.

prj71

At what rider weight? I'm about 200 kitted up.

tomato coupe

Good point. At your weight, it would be almost 1.1 W difference.

pdlamb

Exactly, back when I was a 20-something.

LarrySellerz

Checking the tire with a pump before each ride isn't "not complicated." It's a hassle and unnecessary. Not knocking anyone who does it, but its certainly not required or recommended for someone questioning how much to pump their tires up.

PDKL45

OP's running Schwalbe Marathons which I find instantly turn your bike into a dumptruck. They're tough and incredibly rigid with that fat rubber band in them and IMO, need to be rock hard for decent rolling properties. I run my Marathon & Lifeline marathon clone combo (both 700x32c) at 70 psi, but I have some new tires arriving this week and they weigh about half what the present tires do. With the more supple tires I plan to go down to about 50-55 psi, even though they're also 700x32c.

Someone posted a Rene Herse chart above and it's completely off for Schwalbe Marathons. Just thinking about Schwalbe Marathons can induce a dark teutonic existential crisis in Jan Heine, where he lies awake muttering grimly about casing rigidity, angry with the excesses of Germanic urban utility cycling. For Rene Herse tires, lower pressures are more appropriate, especially when set up tubeless, as they are more supple, so their pressures will not translate exactly to Marathons.

shelbyfv

And yet, if you survey the riding group you have forced yourself upon, I'll wager there are few who don't pump before each ride. You should at least try to stay in your lane.

PeteHski

Yeah I didn't spend a load of cash on Conti GP5000S TR tyres to not make a bit of an effort to find out what optimal pressures to run and actually check them before a ride. But I realise from reading this thread that, for a lot of people, tyre pressure on their bicycle doesn't really matter very much.

The OP asking the question suggested that they do care at least a little bit and the info is out there and easily accessible - even if those who don't care, or believe they have super-natural pressure/rolling resistance sensing powers turn their noses up at it.

prj71

Tire pressure matters. It just depends how anal retentive people want to be about it. Most of us aren't. In the end, it's a personal thing that no online calculator or chart will be able to help you with.

Unfortunately there are people that overthink this stuff and think there is some perfect number that they should use all the time. But the reality is between tire casing, rider weight, terrain, rider speed, etc. there is a wide range of possible pressure combinations that no online calculator or chart will be able to give you.

And what hasn't been discussed here is that the tire pressure guages on the pumps or a stand alone guage are rarely accurate and very few people (myself included) don't have them calibrated. I have a pump that reads ~10psi less than my pressure gauge, then I have another pump that reads ~5 psi more than my pressure guage...which one is right? And how are you suppose to reference an online calculator that tells you what pressure you are supposed to be at with a 15 psi spread between three different guages?!

Best to just go by feel and if you must use a guage...Pick one guage and use that number all the time.

shelbyfv

I'm convinced. From now on I'll straddle the wheel and squeeze the tire with my finely calibrated butt cheeks.

PeteHski

The good online calculators simplify all those variables you keep mentioning. That is the whole point. It's dead simple:-

1. Check with the calculator what pressure it recommends for your setup (maybe 20 secs effort)
2. Set your tyre pressure with a decent quality gauge (I have at least 3 gauges and they all read within a couple of psi. I do check them against each other occasionally)
3. Ride
4. Tweak the recommended pressure if you feel the need. (I very rarely do)
5. Make a note of your preferred pressures and check them regularly

My observation is that most people who don't bother to look up what pressures are recommended for modern wider tyres almost always set them way too high. Typical case is someone who has been using 23/25C tyres for years at 100+ psi buys a new bike with wider tyres and sets them at 80 psi because that seems like a reasonable drop - just a guess basically. It kind of works okay like that so they never even experiment with lower pressures and miss out on the potential benefits. Then there are those who don't even bother with pressure measurement at all and just use their super-sensitive thumb gauges. I'll do that at the side of the road if I get a flat, but it's a very low bar for anything else.

tFUnK

If you ride daily, then you should pump up once a week and do not need to reinflate before each ride only need to top off as needed between rides. Depending on your setup, you may not need to reinflate at all.

If you often go at least a few days between rides, then it's good practice to inflate before rides. A 15psi drop on a 23mm tire can be detrimental on the next ride.

Yes gauges are inaccurate, but it's all relative. If 80psi on your pump is too high, you can try 75psi on your pump, etc.

Yes different tires may be suited for different pressures, but for any one tire you can try to find what works best.

tFUnK

Back in the day when I did group rides, these are the guys who received no sympathy (or a spare tube from me) if they got a pinch flat during the ride.

Back then we didn't have these refined online calculators, and had to eyeball it from that tiny blurry chart and pray we got within 10psi. To know that such tools are available today but actively disregarded by many on this very forum is almost heresy.

terrymorse 

^ ^ ^ Written by people who do not ride latex tubes.

PeteHski

Stating that such tools are over-complicating it or even "dumb" is laughable.

PeteHski

or tubeless.

DaveSSS 

Tubeless tires and thin tubes both lose enough pressure that I feel justified in pumping up for my every other day rides. No way they would go for a week without attention, unless you started with as much as 10 psi too high to start with.

​​​​​Gauges don't have to be inaccurate. I made a manifold that allows comparing several gauges against a new and accurate gauge. My 30 year old Silca read 8 psi higher than actual. A new and much larger 0-100 psi gauge fixed that. No need for a 0-160 gauge anymore.

Eric F 

During a normal week, I ride multiple bikes, plus my trainer. It might be a week or more before I do consecutive rides on the same bike. Topping-off my tires with a pump before each ride is necessary for me, and not really a big deal at all....at least not since I ditched those pesky valve caps. Those things made pumping tires a real nightmare.

Eric F 

Riding every day means a tire loses less air than if you go a few days between rides? Please explain how that works.

For me, knowing that my tires are properly inflated for the performance I want/expect is worth the time and effort to check my tire pressures before each ride.

tFUnK

Good catch. I don't, but I have in the past. Definitely top off before each ride.

For tubeless, I've not found that level of attention necessary, but it's still good practice.

tFUnK

No, it just means that you'll have a more up to date understanding of its current pressure. Obviously (or perhaps not), one should top up as needed.

Eric F 

I was poking at the inconsistency of your previous advice.

tFUnK

Edited just for you.