I’ve heard that getting the right tyre pressure can make a big difference to your TT time, but online calculators I’ve found give me wildly different results. Is the reality that you just have to experiment to find what works best for yourself?
For rider weight 72kg, decent road surface and 700x25 tyres, the results I got were:
Hmmm, I am about your same weight and got pressures about 70-75 on Silca (not looking at my sheet). The last time I ran my numbers a couple of years ago, the weight in Silca included the bike and accessories. Maybe that is where the difference is at?
Thanks, I tried running the Silca one with higher weight and that just made the suggested pressures even higher!
There is something wrong with the silca calculator for me too - pressures too high and it actually says to use higher pressure for tubless than is does for butyl tubes - I wouldnt trust that one at the moment.
So the other two look more realistic? They are at least fairly consistent.
Silca’s calculator seems the odd one out. When I tried it and compared it to the various other ones, Silca’s would be a tad higher, but not nearly that much. Given your weight and tire width, SRAM’s suggestions seem similar to what I used to run on my previous road bike (when I ran 25s).
Depending on the road surface’s roughness, I’d adjust the pressure a bit, though.
I would go with SRAM as it uses internal rim width as a factor, the other ones don’t. 19 mm or 25 mm internal width makes a big difference in internal volume of the tire and therefore als the ideal pressure
IDK. I look at SRAM, Enve, Silca, and Vitorria. I kinda like Vitorria’s. All of them show somewhat higher pressures than I end up using. I’ll start with their recommendation, then try lower pressures until I run into some issue, then go back up from there.
Silca addresses this in a different way by asking for the measured width of the tire as opposed to the stated width. As you say, for any given tire the measured width (and volume) are going to vary quite a bit dependent on internal rim.
I’ve been using the Wolf Tooth app and not been disappointed.
From what I have heard from others and they have discussed on GCN a few times, is that Silca’s calculator is built to suggest the “fastest” pressure based on what you enter. It is not ‘most comfortable’ or ‘best traction’ or anything that really should matter to most people, it is purely saying if the fastest pressure for this tire is X - and usually that means it suggests a much higher value than people actually want.
As others have said, I have tried a bunch of these and they all are usually higher than I would actually use in the real world. Also agree with webdev above, the Wolf Tooth app is pretty good and it can read the current temperature from your phone and adjusts pressure based on that. You can save multiple bikes in there and not have to re-enter all the details every time.
Silca pressures are too high.
I like the Wolf Tooth app the most as I keep my bike indoors and it accounts for inflation and riding temperatures, surprising the difference that makes when its 6 degrees outside I don’t fully understand the physics but it says to put about 4 psi extra in, so the tyres are quite firm when you set off but perfect 5 mins later. I select the smooth pavement setting, gives me 64/66 psi on 30s at 92 kg system weight.
I also like the Vittoria one gives me similar readings on the balanced or supple setting.
I just tried the WolfTooth app and it does look good. It’s only a couple of psi higher than I ride for both gravel and mtb.
I played with the various calculators and didn’t find them of any use. All of them are WAY too high for me.