The Pro Version is now out. Just got the email and playing around with it now. Definitely nice guide to pavement quality.
Edit: after playing around with it it seems like the pressure guides are even a bit higher than the previous version.
The gravel pressures are a lot higher in this pro version. i personally feel like the original aligns more with my previous experience, but YMMV
Rob,
What settings are you seeing as quite different? I just ran a handful of gravel scenarios in both calculators side by side and am getting nearly identical numbers? So in the original we had ‘coarse gravel’ which was in between Cat3 and Cat4 gravel on the new calculator and mild gravel which was sort of between cobbles and cat3 gravel in the nw calculator. The underlying algorithm is the same between them, we are just trying to refine the way that the surface roughness is defined by the user.
If you haven’t tripped it up yet, there is also a pretty slick pinch flat predictor running in the background based on rider velocity and impact energy that will let you know if your optimal pressure is getting too close to, or beyond the danger zone for your weight/surface/speed.
The Pro Version is now out. Just got the email and playing around with it now. Definitely nice guide to pavement quality.
Edit: after playing around with it it seems like the pressure guides are even a bit higher than the previous version.
The gravel pressures are a lot higher in this pro version. i personally feel like the original aligns more with my previous experience, but YMMV
“Mountain bike” recommendations are quite low
I guess it could have just been my original interpretation of the surface conditions. I was looking at coarse gravel before, which gave me 32.6f psi and 34 rear for 39mm tires at 185lb system weight. That’s right on the high end of what I’ve found to be comfortable on most normalish gravel roads.
I was then looking at cat 3 gravel in the pro system, but now I realize that’s not really an apples to apples comparison. The calculator is 2.5 psi higher. But cat 4 is pretty similar to what the other one said for coarse gravel. So I was wrong in saying the pro was way higher… I was just using it incorrectly.
To me 35/36.5 sounds a little high for a tire that wide on roads that look like the cat 3 photo. But, a little high is safer than slicing a tire with your rim on a hard hit…so probably not horrible advice.
The Pro Version is now out. Just got the email and playing around with it now. Definitely nice guide to pavement quality.
Edit: after playing around with it it seems like the pressure guides are even a bit higher than the previous version.
The gravel pressures are a lot higher in this pro version. i personally feel like the original aligns more with my previous experience, but YMMV
“Mountain bike” recommendations are quite low
For several years I’ve been running around 20 front/25 rear, the recommended pressure I got was 22 rear/20.5 front. And that’s with me being a Clydesdale, on 26"x2.2" tires. So at least for me the results seem reasonable…
Josh, I still fear that this version doesn’t make it clear enough that you need to actually measure the width of the tire for this to work. Most complaints I have seen about the calculator seem like they come from people who maybe are just reading the sidewall of the tire.
This was my thought (at least since so many appear to be saying they need to inflate way more based on this calculator, which strikes me as unlikely). When I did my calculations, I was about where I expected to be—maybe need to adjust a little and I’ve definitely been trending downward the last few years with info published before this ever came out.
And, even with this calculator, I thought (aerocoach?) came to the conclusion that the penalty for being too high is far worse than the penalty for being too low.
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And, even with this calculator, I thought (aerocoach?) came to the conclusion that the penalty for being too high is far worse than the penalty for being too low.
That was the Silca blog (and probably Aerocoach somewhere along the way
Right. The key is that this calculator gives optimal pressure for a single set of conditions. If you have some bad pavement, drop the psi. If you want to be more comfortable at a very small penalty, drop the psi. Basically there is no reason to ever go higher than what this calculator tells you to do, and there is often very little reason not to go a bit lower.
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And, even with this calculator, I thought (aerocoach?) came to the conclusion that the penalty for being too high is far worse than the penalty for being too low.
That was the Silca blog (and probably Aerocoach somewhere along the way
Or me…I’ve only been saying it on here (ST) periodically for the last 12 years or so 
https://forum.slowtwitch.com/forum/?post=1744801#p1744801
“On the pressure, from what I’ve seen, from a Crr standpoint, it’s FAR better to “err” on the side of slightly too little pressure than too much. Once you hit the “breakpoint” pressure (where the tire stiffens up so much that too much energy is transmitted through them) the “resistance to forward motion” of the whole bike rises pretty dramatically.”
When in doubt, if it was a good idea, it was probably Tom A. Good rule to follow.
Basically there is no reason to ever go higher than what this calculator tells you to do, and there is often very little reason not to go a bit lower.
Indeed, assuming you input the correct information into the calculator
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Total system weight… Is this bike plus rider?
Plus nutrition, plus atmospheric pressure, plus the weight of your conscience on race day.
(I’m assuming)…plus anything else you strap to bike or yourself, including fluids, helmet, shoes, etc.
That’s what I thought. Just making sure the rider was included
so, is everyone using a micrometer to measure tire width? I didn’t realize I needed one in my tool kit. I imagine there is going to be a run on Amazon. Anybody have one they like?
as Josh mentioned the GP4000s with nominal 23mm actually measure at 29mm… so probably worth checking, if going to use the calculator…
I like this one,
https://www.garrettwade.com/...ass-calipers-gp.html
inexpensive with a nice retro-grouch look and feel.
Mine used mostly for measuring fishing rod and reel bits and pieces, carpentry etc. Works fine for non-critical applications. If actually engineering the digital ones are better.
The calculator we’ve all been waiting for!
Link doesn’t work although I submitted my info.
your browser or ad-blocker is removing the info… turn off all adblockers and try again.
or try a browser without protection, like the vanilla Microsoft Edge.
So sorry, the original link was going to the old calculator and not the new one. I’ve updated all links to go to the proper place.
Please let me know what feedback you have.
https://info.silca.cc/silca-professional-pressure-calculator
We also did a video covering a bit of the math/science, data set and other rationale behind the tool.
Would love any and all ST feedback!
Josh
I ran the calculator and did some field testing.
https://strava.app.link/Atot2wpjZ5
Worked great for me!
The worn pavement suggested pressures proved fastest in what was pretty good looking chip seal.
I was blown away by how high the suggested pressures was for me, as I was running significantly lower.
Thanks for sharing a great tool!