Unless I missed it being mentioned, that chart was for Michelin Pro4 or Pro3 tires. Michelin used to include it with their tire packaging. Unless your tires have the same TPI, I wouldn't use it for other brands. Even so, I think it's a bit high. I'm 205 lbs and ride my Michelins at 105 front and 110 rear on "standard" width rims. I reduce that based on the rim width. I'm way too damn lazy to figure the correct pressure based on weight and volume, so I just guess. For my Flo 60's, I use 95 front and 100 rear.

hah

edited to add, I still ride 23mm tires.

What pressure were you using last week?

So do people think this chart is intended to convey recommended pressure for minimizing rolling resistance (making some assumptions about road smoothness) or minimal pressure to avoid pinch-flatting or something else? Because it seems to me it could be conveying a variety of things.

It's for general use (basically RR). It's well above where you'd typically be for pinch flat protection.

The upper cutoffs are not based on engineering, but based on the lawyers. In theory the diagonal lines should continue on well above 116psi.

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ECMGN Therapy Silicon Valley:
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The HED Jet+ rims have a wider than normal internal width which increases the measured width of the tire when mounted. The 22mm Attack measures closer to 25mm wide when mounted on a Jet+. Adjust your pressure accordingly. I'm about the same weight as you and run a 22mm Attack up front at 85psi. I'd run the Force at 80psi. If in doubt, contact HED.

The pressure recommendation is based more on tire air volume than mounted width.

80 psi on an 22mm tire at 175lbs is likely to roll slowly and have high pinch flat risk.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

The old Force is 24mm and is nearly 27mm when mounted on a Jet+ rim.

Can one generalize about pinch flat risk across rim widths, i.e. are there logical reasons why the same tire at the same PSI (or is it casing tension I should be holding constant, or perhaps PSI and casing tension stay proportional for a given tire size mounted on varying width rims?), on a narrower or wider rim, would be more or less pinch flat resistant?

All else being equal, the wider rim has a greater risk since less deflection is needed to pinch the tube.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

If the wider rim means the tire is at greater risk, do you need higher casing tension (PSI) to compensate? Seems backwards, no?

I switched to 25's this spring, and have been running 95psi rear and 90psi front since. Zero flats, and seems just as fast.

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I'm closer to the feathered end of the spear than the point.

Believe it or not this isn't always the case. I'll try to find the diagram but often a wider rim makes the tire taller. It's counter-intuitive but you can replicate the phenomenon with a loose tire.

Ah, found it:

Looking at the 25mm tire on the 19 and 25mm rims in that diagram, the width of the casing certainly looks larger on the 25mm rim. They should be equal since the tire does not stretch.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Yeah...I've always pointed out that some of those outlines in that pic look mis-labeled.

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http://bikeblather.blogspot.com/

If you give me your "all up" mass (bike+rider+equipment), plus the MEASURED width of the tires as mounted on the rims (at a pressure near what you might run), then I can throw it into the calculator I reverse-engineered from the Frank Berto "15% drop" chart recommendation. I'll typically use it, along with an assumption of front/rear weight bias to come up with a starting point for the rear pressure.

Unlike Berto though, I don't assume the F/R weight balance is "static" since it seems to result in under-inflated front tires, especially under braking and turning, so after figuring out the rear pressure, I usually only drop the front by ~5 psi...but again, the output is just a ballpark starting point.

So, for example, a tire that measures 28mm across when inflated, with a 50kg rear wheel load will call for a pressure of 83 psi from the calculator. I'd probably just make it easy and run 85psi in the rear, and put 80 in the front (assuming same tires and rims F/R).

Just let me know...

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http://bikeblather.blogspot.com/

So I was one of those who started buying 25s when I saw the charts and there was no mention of MEASURED width. Happy enough with 25s on what I consider to be rough roads.

After reading the responses, it looks like I could be going back to 23 Conti 4000s on my FLO 30s and get better performance with less pinch flat risk. Bike and rider weight 160-170lbs. Yes/No?

The tire doesn't stretch. It's a geometric quirk that's tough to describe. Think of it this way: you have a fixed length of tire to form two shapes: a circle and an oval. You'd form the circle by having the beads super close to each other. The oval-ish shape is formed by spreading the beads apart. At a certain point the beads will be wide enough that the tire casing forms a half-circle. Anywhere between those two points the bead curtails the shape of a circle resulting, from a tire height perspective, in an partial oval.

If you have a few different rims at home you can replicate HED's chart above yourself.