Tire pressure vs Speed Question
 

I've been riding for two years. I have a Giant Toughroad, which is not a fast bike. I am not that fast either.
My tire pressure was getting low and today I put some air in. Before, you could squeeze them and they were hard as maybe a beachball, 60 psi, but today I had them slightly less than rock hard, maybe 80 psi.
When I went out, it was raining like hell and windy and cold and starting to freeze . My feet were soaked then feeling funny and I got concerned so I jacked up my speedto get home fast.
With the higher pressure, I noticed I was moving pretty briskly and then I noticed was able to use the big ring and smallest cog the whole 30 miles and cut 20 minutes of my time.
That being said, what 32 to 35 mm inner tube can be pumped up to 100 psi like a road bike?
Next, at what psi does this effect wear off. I'm guessing 120 is the limit? Because after that, rock hard is rock hard?
Sure had some fun today...or was it my imagination? BTW my lower legs and feet were purple and my hands were too.

With all this talk about softer tire pressures, in circumstances where the roads are good, narrow tires with high pressures are really fast. But I don't think there are many 35mm tires that can be pumped to 100psi.

Physics being what it is you definitely don't want to pump a 35mm tire up to 100psi. That would be the rough equivalent of a 23mm tire at 140psi. It doesn't matter which inner tube you use, it will only expand as big as the tire...so you could theoretically inflate any tube to 200psi if the tire would stay on the rim. Guessing about your ideal pressure is useless unless we know how much you and your bike weigh AND what the road surface you ride on is like.

I got my wife some Vittoria Zaffiro pros 32s for the winter, which say they can be pumped up to a maximum of 100psi. Although normally I have hers at about 60/65psi for fall riding. Interestingly, as a side note, the Vittoria's measure 29.5mm on her bike, slightly less then the Continental GP4000iis 28s on my bike that measure 29.8mm.

I'm guessing you probably have tires with stiff casings on your bike like a puncture proof tire or similar? So increasing the tire pressure on them does make some sense, in theory some better tires will maybe run with lower rolling resistance at lower inflation than your tires.

https://www.roadbikerider.com/the-ti...-jan-heine-d1/

In the same road tire, higher pressure will run faster since the higher pressure will reduce the contact patch. But as roads aren't usually smooth, past a certain pressure the resulting road vibration can create greater fatigue slowing you down and make the bike less stable/more bouncy over rough patches requiring slower speeds. Optimal pressure is based on your weight, tire size, materials, rim size, and road conditions. Strictly road I don't have any tire under 35mm I run at under 80psi for myself or under 70psi for my wife.

I guess my fast ride today was half due to the 20 extra psi and half due to my imagination . Because its only 8 30 pm here and I need a monster nap.
But do you think those super heavy duty Schwalbe inner tubes could take 75 psi?

Any tube can "take" any riding pressure, as long as the pressure doesn't cause the tire to blow off the rim.

97 psi for everything. rain or shine. rim cuts will slow you down more than your lowered tire pressure will speed you up on bumpy roads.

note that in winter, your indoor bike will lose pressure if you go from 72 degrees to 38 F.

note that if you climb to 5000 feet that your tires will feel like teak wood from less atmospheric pressure.

note that if you brake constantly coming down the 5000 ft peak that your rims will heat up and your handling will feel weird due to hi pressure.

note that if you use wood rims, you will be the coolest cyclist on the block.

Size of contact patch doesn't actually have much to do with rolling resistance. Rolling resistance depends much more on frictional losses in other parts of the tire/tube system. It's sort of sleight-of-hand misdirection -- people looked at the tire and thought the losses were related to the contact patch, which they could see since it touches the road; however, most of the losses occur in the parts of the tire that they weren't looking at. That's why latex tubes reduce rolling resistance compared to butyl tubes, even though they don't affect contact patch; and why two tires with the same width and same contact patch but different sidewalls or rubber thicknesses can have different rolling resistance. It's also why knobbed tires can have higher rolling resistance than smooth tires even though their contact patch is smaller.

When you understand that it's not the contact patch per se that matters, it frees you up to look at other components of the system and why lower tire pressure can, in some but not all cases, reduce rolling resistance even though it can increase contact patch. That is, in the same tire, higher pressure will not always run faster.

This article explains why rock hard tires usually are not faster. The takeaway is rolling resistance decreases as tire pressure increases until a limit is reached where rolling resistance increases very, very quickly. This inflection depends on the road surface and tire construction.

https://www.velonews.com/gear/road-g...en-testing-it/

Most tires state their theoretical or rcommended limit. I wouldnt exceed what it says on the sidewall.

very interesting article, so my tubulars pumped up to 120 are are all a fantasy in my mind that I'm going much faster oh well I guess I'm just living in lala land haha

Don't feel bad, I used to crank mine to 150 back in the day.

That Zinn article isn't bad. Here's a link to Tom's original discussion of impedance (note how he "undertook an experiment 'on the road' armed with a PowerTap power meter and a method for determining the Crr").

Here's another...
 

I watched this well over a year ago, so I can't comment on specific content, but I recall this being a really good in-depth discussion on finding the right tire pressure. Ignore the clickbait-y title...

You can find out for your tires on your bike by brushing with a friend, thusly:
Start out together, coasting down a hill at the same speed, note who gains.
Now change something on your bike, more pressure, less pressure, what ever, and repeat. Keep everything else the same, same hill, same speed, same position, no changes to friend's bike. Now, did you get faster of slower? Your friend, with unchanged position and bike is presumably the same.
This evaluates the bike, not the terrain, your fitness, the phase of the moon, or any thing else, but it does a good job of that

The recent articles/studies saying that wider tires at lower pressures are just as fast as thin tires at high pressure is Big Gravel trying to n+1 roadies. Follow the money.

OP I'm 250 lbs and run my 33 mm tires at 100+ psi. They say 65 psi on them but they dont break.

Tailwind!

If you don't have data from multiple rides of the same route, then I'd say all you have is conjecture which is borderline on imagination.

What was that - the good ol' Chang Method?







:innocent:

Stop it Larry.

I suspect that's best you'll get out of those tires on that bike. but keep experimenting & report back. maybe w/ a pic next time

tailwind plus the desire to get home fast. I was soaked.
My legs and feet and hands were dark red / purple. I prepared a hot bath, but I couldn’t even feel the temperature so I didn’t get in, was afraid I might burn or scald myself.
My first priority is not hi pressure tires. It’s rain pants rain shoes and waterproof gloves. Rain is worse than snow.

The relevant piece is that he discovered it by doing field tests on the road, not in the lab. Until then, doing high-precision road tests was a huge PITA so no one did them (it's still kind of a PITA, just less than before). Actually, when he told me about the planned experiment I wasn't sure he'd be able to get the necessary precision and resolution, so when he said that he had some puzzling results my first thought was "I told you so" and that the finding was garbage. But we looked at his data, and we tried to figure out what he'd done wrong, and he re-ran some tests, and we re-analyzed the data. And the results replicated. I was agog. I think the two lessons are: 1) Tom is a really good experimentalist, much better than I am, damn him; and 2) when he found an unexpected result, he tried to figure out what he'd done wrong and to reject it. He didn't start with a hypothesis and then do experiments to prove it; he had data that showed something unexpected and odd and tried to figure out what went wrong. In the end, we have to go with the data, and in this case it forced us to change our minds and learn something we hadn't previously known. That's always cool.

barmitts are good for rain too, not just cold