Your best bet is to purchase a very accurate gauge that you can remove from a tire with minimal air loss. Then, do your own repeated tests to see how much pressure loss you cause by taking a reading. Take a few readings back-to-back with out pumping. Then, compare your first measurement to the last and divide by the number of readings you took minus 1. That will give you your average pressure loss by simply taking a reading. Then, inflate to your target plus your expected loss.

Also, you will need to do some repeated pressure loss tests, because you will not pump the tires immediately before riding, and you will lose pressure during the ride. So, estimate how long you will have between pumping your tires and the middle of the bike ride (that way, you will average your target pressure). If you pump up 1 hour before the start of an HIM, that will net to about 2.5 hours of air loss time to target PSI. So, do some tests where you pump up your tires, wait 2.5 hours, and take a 2nd reading to determine how much pressure you lose per hour.

Realistically, you probably will not get closer than 2 PSI to your target. Most very good gauges may be ±2% - ±3%, which means that they may be off by 2 to 3 PSI from actual. Your best case is probably ±1%, if that even exists, which would be about 1 PSI off.

What is the sensitivity of that spreadsheet? In other words, if your weight changes by a couple lbs. or your front/rear balance changes by 1%, how much does the PSI change? If the PSI swings a lot based on small changes in the input variables, then precision may not be that critical. So, getting within 1-2 PSI may be as good as you need to be, since your input variables could be off by more than the precision of a high-quality gauge.

That are good questions. Each percent of is not very critical, but the less accuracy for each factor makes you more off target. I have measured my front/rear balance, and I have a small scale with me on travel to get the most accurate race weight.

Any recommended high quality gauge that works with a disc wheel?

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I bought an AccuGage PR100BX because those are highly regarded and easy to read. And, it is easy to get a read with little air loss on a disc wheel. Mine is ANSI Commercial Grade B rated, which means ±3% from 0-30 PSI, ±2% from 30-60 PSI, and ±3% from 60 to 100 PSI. In practices, it is more accurate than that, but I do not know how much more.

In your case, I would shop for a high-quality digital gauge with a small head to work well on a disc. Accutire claims ±0.05 PSI accuracy (0.06% at 90 PSI). But, I am not sure if they have a good product compatible with Presta that would also fit in a disc. The Blackburn Honest claims about ±1 PSI accuracy. There was a thread here somewhere about good gauges for disc wheels, but I cannot find it.

Pump it up to 90psi and call it good.

Quarc TyreWiz

Yep!

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I disagree with the claim of ±0.05 PSI. 1% is good, .1% pressure measurement is at least $1K. I know of only a few labs that can calibrate a .06% gauge

±1 PSI is realistic

https://www.alliedelec.com/...e8b863f1bb5c2fdf.pdf

At what stage in the race do you want the tyre to hit that 84.2 psi?.
Taking into account altitude changes, tires warming up, air leakage etc.

We've dealt with all of this for the last 2 years developing SuperPista Digital. We worked with Wika on the PCB and sensor and are using a custom curve fit to try and balance accuracy at the low and high end as digital sensors have some inherent non-linearity. Team Bora has been using this tech in the field with solid results and nearly zero gauge drift over thousands of inflations.

We were able to achieve slightly better than 1% between 10 and 100psi with the gauge drifting to 2% at 200psi

There is some extreme nonlinearity of price with accuracy and precision of these components as has been pointed out here. We do a 4 pressure calibration of the pumps using 0.5% gauges from Ashcroft that cost $500+ and every month calibrate those gauges with another fixture using a 0.05% gauge costing well over $1000. Gauges are an area that really defines the old maxim of 'you get what you pay for'

SPDigital has a HIRO chuck that works in most all disc wheels as well as a thread in Schrader chuck that can take a disc adapter if you have an original Zipp or lightweight disc with the super small hole.

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Thanks for the tips. It looks great, but how much does it weigh? consider making a travel version?

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I guess it depends but I believe in general that we will try to hit 84,2 psi in average. So if the pressure loss is 4 psi across the race I will start at 86,2.

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How are you going to get 0.2psi accuracy?

Or......own an air compressor and change out the included regulator/gauge for a nicer and more accurate unit.

Then, just set the outlet regulator to your desired tire pressure. Done. Perfect.

I have an SKS Digital Gauge and an Accu Gage for gravel. The SKS bleeds more air out than the Accu Gage, but it is still pretty handy. The SKS works with schraeder and presta valves. The Accugauge works with one or the other. The Accu Gage I have is 60psi max and uses a presta valve. Great for gravel, CX, and MTB, but obviously won't work for road. They make higher pressure gauges, but then it will be more difficult to dial in exact pressure. Plus, I don't think either of my gauges would work on a disc wheel.

Another option is one of the handheld craftsman inflators. They are harder to find now, but Summit still has them for a good price. They have a digital pressure gauge built in. I don't know how accurate it is compared to the SKS or Accugage, but they are SUPER handy. The stock pump head isn't great, but you can easily remove it and install any other pump head. I'd probably just install one of the Silca Schraeder chucks and then you can thread on a silca crack pipe or any other silca head. It's great for traveling via car or in checked luggage. I don't know if you can take it in a carry-on.


https://www.summitracing.com/parts/shc-911586

You do realize your tire pressure will change as you are riding? Also, road conditions will change, sometimes a lot. It seems a bit silly to be worried about such precision for an application with considerable variation :-)
It would take a pretty impressive spread sheet to factor in road temp, air temperature, internal tire pressure, road conditions, over the entire course profile on a specific day.... And even if it could, the algorithm would spit out a very precise number based on a huge amount of subjective data with subjective priorities, ie a number that is probably at best +/- 10% of actual ideal pressure! (Whatever that is)
If you are really concerned about optimized riding performance, don’t obsess over a couple psi, pick a tire that has the least change in characteristics over a range of pressures. That is one of the most overlooked, and best attributes of the Continental 4000s. Much less performance change over a range of pressures.

There sure is a lot of variations. Why is that an argument for adding another one not knowing if your pressure is 80 or 90 psi to start with? I never understood that kind of reasoning.

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The argument isn't 80 vs. 90. It's 88-92 PSI.

Also, the argument is that the estimate of tire pressure is a gross estimate. There are large variations in road surface, temperature, tire characteristics, pressure loss over time, etc. Because the model used by the calculator generates numbers with a precision of 0.1 PSI (or whatever) does not mean it predicts the optimal real-world tire pressure to 0.1 PSI. There's going to be a significant variance. The precision of the model gives a false sense of predictive accuracy. It just, hopefully, puts you on the correct ring of the dart board.

As others have said, here, just go to whatever the model says to within 2-3 PSI with a decent pump. Any error vs. the model has just as much chance of accidentally falling closer to the true optimal real-world value as it does falling farther from it. If you want increased peace of mind or you want to start your own spreadsheet for your own testing, get the Silca pump.

Somthing that I think would be interesting is to look at is if a certain contact patch area is most effective for a tyre, as this could be a way of establishing a base tyre pressure from various weights/ front to rear balance.

At a minimum of 105kg of bike and rider for me, I’m thinking some reasonably wide tyres are going to be wanted at 90 psi...