seems like you have it figured out fine. There is no need for blowing tires off the rim and skittering around corners on rock hard tires.

Lower than you would think..

On Conti GP4000 S2 i have been gradually creeping downwards over the years to 83 PSI and this gives reasonable comfort over bumpy tarmac and awesome grip around crit corners.. (I'm 75Kg)

So my understanding is correct?

(I guess that's what I was asking, as my previous rule of thumb was 'old school' )

Smooth wood track, my tires are at their max. Every day riding 80-85 PSI. Just did a local crit with a few interesting corners at about 75 psi. Off the line, it felt like I had a flat but I didn’t. The conti tires were great and never struggled in the corners! Actually I lapped the field solo and I think a lot of the time that I gained was in some of the sharper corners.

makes sense to me. The whole "inflate the tires until they explode on the road" thing seems more popular in the triathlon world. For real life racing on real life roads, your 95-100 psi 25c tire plan seems a lot more sound.

Thanks for the replies. I shall have a crack with slightly lower pressure.

Check out the podcast by Josh from Silca (formerly Zipp) for a deep dive on individualized tire pressure.


https://podcasts.apple.com/us/podcast/ask-josh-anything-001/id1449434247?i=1000430660084

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Madison photographer Timothy Hughes | Instagram

New school: drop pressure to the point where you start pinch flatting and then add a few psi.

If you are pinch flatting you just need bigger tires!!

Seriously, we talk about it on the podcast and all the science and theory can be found in our blog: https://blog.silca.cc/page/7

In simple terms, tire pressure is the intersection point of road surface roughness, rider weight, weight distribution and tire volume. The surface roughness is the hardest to pinpoint, particularly as most surfaces are dominated by negative voids rather than positive protrusions, so even brand new 'perfect pavement' can vary pretty widely depending on the size of fill used in the paving process.. we're still working on how to best solve this piece of the equation in terms of creating a pressure algorithm.

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http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

Has anyone tried the TyreWiz app? For my weight (175 lbs) and a 20 lbs bike, riding 700cX23mm it is recommending 82 psi in front and 85 psi in back. I think I heard about the app from a youtube video from Global Cycling Network, maybe this one .

I can't wait to listen to the podcast that others have posted on this thread.

Everyone wants to reduce it to a simple "100 psi" rule, or the modern equivalent of it, but it's not that simple. It depends on your weight and the actual mounted width of the tire. Recommendations for tire pressure have been dropping not just because we understand that overinflating your tires also increases rolling resistance, but because rim widths have increased and people are tending to run wider tires. The actual mounted width is as much a function of your internal rim width as it is the marked width on the tire. The key factor in actual tire width is the inner width of the rim, not the outer width.

Here's an old school tire pressure chart from Michelin. I think the pressures for 23C tires and 32C tires are too high but this chart is a reasonable starting point if you have older narrow rims with an internal width of 12-15 mm or so.

Here's a new school tire pressure chart from Hed. It works if you have very wide road rims, with an internal width of around 21 mm or so. Notice how much lower the tire pressure is!

Many of us have rims with widths that are somewhere in between these two extremes, and you have to interpolate and find a happy medium somewhere between the recommendations of these two charts.

I've found this to be helpful as a guide: http://flocycling.blogspot.com/...g-tire-pressure.html

Pneumatic tires are a suspension system. Pumping them as hard as possible defeats their purpose.

Imagine a bicycle rolling along a perfectly-smooth surface, that suddenly comes upon a tiny 5mm bump. For the bike to get over the bump, something is going to have to move upwards by 5mm.
If the tire is pumped squishy, it can deform around the bump, and only the contact patch needs to be 5mm higher. If the tire and bike are all ultra-super-duper stiff, the entire bicycle is deflected upwards by 5mm, and the rider is pushed upwards as well.
It takes astronomically more energy to lift the entire bicycle and rider over the bump than it takes to deform the contact patch around the bump. That energy is stolen from your forward motion. So, the squishy tire is faster over the bump than the super-stiff tire (in addition to being more comfortable!).

How squishy do we want to pump it?

Well, we want it to be squishy enough that the bike doesn't get rattled by the small irregularities on our road surfaces. The rougher the roads, the squishier we want the tire to be.

BUT

If we pump it really squishy, the tire will constantly be highly deformed against the surface, even when it's smooth. It takes energy to deform the tire like this.
The energy penalty of this deformation tends to be less dramatic than the energy penalty of bouncing the bike+rider around, so it's usually better to "err low" with tire pressure. But that doesn't mean we should be running tires near-flat.

Both of these effects - how much the bike will get rattled over bumps, and how much the tire will deform even on a perfectly-smooth surface - depend not only on PSI but also on rider weight. A heavier rider can afford a higher pressure without getting bumped around by surface irregularities, and also needs a higher pressure in order to keep the tire from being flattened too much against the ground.

If lower pressures persistently felt slower, I'd probably use too-high pressures even knowing that they're slower. Lower pressures can "feel slow" initially, but you get used to them.

I remember the first ride I took on the 2.1" Rat Trap Pass ELs on my gravel bike. Between the smoothness of the ride and their strange deep road hum, initially I felt like the speedometer was reading high. That sensation was gone by the end of the ride, and now that same low road hum "sounds fast" to me.

Thanks - that's really helpful

Hey Josh, I just mass read all of your blogs on tire pressure lol. So thanks for all that info!

In the section on aerodynamics you talk about the 105% rule. I currently run Profile Design 58/Twenty Four wheels (24.5 width) with 25mm tires. Am I drawing the right conclusion in that I should switch back to the 23mm tires with this wheel set?

Same boat here... I would think it has to do with the actual tire width and not the stated size... and I don't have any way of measuring the actual size of my tires but they are the Conti GP4000sii that is so ubiquitous

I also just downloaded the TyreWiz app and for my weight and tire size and it puts me at 72/75psi and the HED chart (I don't have HED wheels) says 67psi!! I've run around 80 in training some but have recently settled on 85psi in races. Should I go down to 75?

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Triathlonpal.com
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one thing I notice from my N=1 kind of riding around with people is that non-supple tires seem to roll very slowly. Something like the older armadillo, or bontrager hard case or refuse or other heavy duty stiff winter tires seem to roll really slowly, not sure why that is. The gatorskin is a little better, as it has sort of a flexy sidewall, kind of.

The beefy protection layers that those tires are made from tend to be stiff, and take a lot of energy to deform. And when they spring back at the tail end of the contact patch, they're not very lively about it, and not much of that energy is returned to your forward motion. This is what's meant when people talk about a tire suffering from high "hysteresis loss."

You can reduce the high hysteresis losses by pumping such tires to a very high pressure, so that they don't deform much in the first place. But then they don't work very well as a suspension system! So they're slow no matter what.

Thank you for the info, very insightful.
I have a couple of somewhat related questions:
- can old pumps start lying about pressure. I have a 15+ years old one and thinking about upgrade
- are there pumps that lock into a disk hole without connectors? I've searched on forum and found only one adapter from slica that costs like it was made from metal taken from a returned lunar module.

That's about what I do. My suggestion is to experiment on your own and over time, draw your own conclusions about what works for you. I like to run around 110psi on my 25mm tires, not higher than 115psi. So I'll pump em to around 115 within 24-48h before race and I'm good to go.

I have never had to bother with pumping up tyres on raceday morning.

Here is my over time analysis of tire pressure. Bigger the tire the lower the psi. Correct answer it depends and it is complicated by factors. Bigger rider means usually more pressure. I read a lot of cyclocross riders roll 18-22 lbs pressure. If you weigh over 220lbs you are rolling on the rims with that psi. Trust me. My rule of thumb for my 210-220lb body weight is pretty much.
23 mm tires 110ish psi
25 mm tires 90 ish psi
28 mm tires 80ish
32mm tires 65ish
35 mm tires 40ish
38 mm tires just under 40
42 mm tires 35 ish

Those are road and hard pack or rougher gravel numbers I start out with.
mtb 2.25 inch usually I run 30-35ish.

Cross on high end tubulars 30-35ish depending on how hard packed the course is. I don't even own 23mm any more. Even my track tires are 25s that are not that easy to find. 90% of my riding on the road is on 28-32mm. I don't feel the drag on those tires but 35-38mm I can feel the drag and 42s feel like pushing rubber on a road ride.

We can argue tire pressures till the cows come home but for my weight and riding level those numbers work for me. If you weigh 50 kg less than me let some air out. When I first started riding in the late 60s for time trials we used to pump up Conti tires to 180psi. Felt very fast but boy did you bounce around a lot on tires that hard. They felt fast as hell, but probably weren't. Playing around with psi is interesting, but can use more brain power than you really need to use. Over thinking seems to be becoming an obsession for some folks.

"Bigger the tire the lower the volume. "


Huh?

I also use the tirewiz app. It is pretty spot on from my fatbike to roadbike.

So i run about 70psi for tires that measure 25-26mm. I am 130lbs. I will push a little higher (80psi) for smooth roads or a smooth climb, but otherwise our roads are bad enough, that lower is better.

Josh (silca) once said, lower your pressures to that bouncy point, then go above that. What feels smooth is generally fastest. But yrmv based on the tarmac quality.

Bigger the tire volume the lower the psi it should have stated. sorry