Tire Pressure calculator Comparison and Accuracy
 

I tried the Silca Tire Pressure Calculator then compared it to a couple of others. It gave me the lowest pressure compared to the others. Does any body have experience with these and use them.

I also use the SRAM calculator, which for me gives very similar results. They have slightly different parameter choices, for example Silca uses measured tyre width, while SRAM uses spec width and internal rim width. Silca has more choices of road surface. Both should give you a good starting point if you input your parameters accurately.

I haven't used any others, but when I switched over to 32mm tires, the Silca calculator gave me a lower pressure than what I had been running, I adjusted pressure accordingly, felt like an improvement in ride to me.

Never used the Silca calculator before. It recommended 60ish, I've been running 52ish based on the Rene Herse calculator and will continue with that.

I like the rene herse calculator personally https://www.renehersecycles.com/tire...re-calculator/

it is a bit simpler.

I just ran both for a 32mm tubed tire at 260. Silca said 67 lbs vs rene herse saying 67 to 82, so they are somewhat aligned

I use the silca one and it's pretty close to what I normally do. Which is 28mm gatorskins measured at 25= 85-90 psi or so at my 225lbs. 23mm measured at 95-100psi. Was a similar ballpark to what I was running before.

I don’t bother with charts anymore. There’s too much variation between tires.

When I try a new-to-me model of tire I go out through the neighborhood and do a bunny hop session and let out rear tire air incrementally till I hit rim on landings, then I go home and add 15psi and set the front tire to 7-10psi under that. It’s usually perfect for one day. I’ll go 10psi over whatever those one-day pressures are if I’m wanting to ride five days without pumping.

I pump up my tire to a target pressure, measured using the gauge on my floor pump (> 15 years old, I've no idea how accurate the gauge is), and based on past experience with the particular tire I'm running, and also dependent on my ride (slow/fast, good roads/not-so-great roads, wet roads/dry roads, etc.). So, for a "fast" (for me) ride on decent roads that may be a little wet, just as an example, I might target 65-ish psi in my 32mm tires (rear), and a couple of psi lower for the front. Probably a little below 65 psi, actually, I'd just eyeball it as I got close to 65 and stop pumping when it felt right.
Then I pinch the tires between my finger and thumb, look up at the ceiling for a couple of seconds, and maybe add a little air or let a little out depending on my gut feel.
Then I ride.
Takes about a minute for both tires. Maybe two, if I haven't ridden in a few days and the tires are low.
After my ride, if the feel was overly harsh or overly squishy, then I keep that in mind for next time. Or, maybe I forget and make the same mistake again, but eventually the feedback influences the actions resulting from the pinch test (which is really the gold standard - the gauge just tells me when I'm getting close).

I used the Silca one and found it to work for me. But no two riders, road conditions, etc., are identical. The guides are just that-a guide, and a good place to start. A little up, or down from the recommended pressure might work a bit better, trial and error to get what works best.

I regard their outputs as a suggested starting point. The Silca one is perfectly adequate in my experience. Then I keep riding and lowering the pressure until I don’t like it and take up just enough that I do.

Otto

Are you expecting them to know exactly what pressure you must run in your tires?

Just consider it and any other sites recommendation a good starting point that might be right or might not. Then you can adjust up or down as you prefer. Base your tire pressure on what matters to you. Perhaps the performance data you record over a dozen or so rides at a particular pressure compared to any different pressure you used for another dozen rides. Or just your personal preference for the feel it gives your legs or how you perceive the comfort of your ride or the way you feel the road handling characteristics through your bicycle.

That was a silly website.

It recommended my pressure be about 20 psi less than I normally use on my road bike.

Calculators like Silca and SRAM all clearly state that they are intended as a starting point from which to fine tune your setup as required. But I haven't yet found any reason to deviate from their recommendations. If they didn't exist I think I would end up running pressures too high, especially with wider road tyres. The drop in pressure with increasing rim and tyre width is surprisingly high. More than most people would probably guess.

Do you often ask for advice so you can ridicule it for disagreeing with what you want to do? Have you met Larry?

I am not sensitive enough to feel subtle differences, nor do I ride so consistently that marginal gains in speed will manifest themselves, so I just go with a pressure in the ballpark of their recommendations.

OTOH, last week I wanted to try 32mm tires, but I didn't want to pay $50-$80/tire to get 32mm GP5Ks to replace the 28mm GP5Ks on that bike, so instead I got 32mm Vittoria Corsa G2.0s, because Bike Closet has them for $35 each. I swapped them in, pumped them up to 70/75 (roughly Silca's recommendation) and went for my usual Sunday 59 mile ride. They were comfy, yes. Not necessarily that much comfier than the 28s at 80/85. But they were definitely SLOWER. I ended up with about 0.4 mph slower average speed over that route than my all time average for it.

Then I looked up the rolling resistance for GP5Ks and Corsa G2s on bicyclerollingresistance.com, and the Corsas have a 4w disadvantage. So I went to Bike Calculator and played with the power, and sure enough, that 8w disadvantage (2 tires) yields 0.4 mph slower speed.

So, in the end, I executed a poorly controlled experiment and learned nothing. :(

There could be many valid reasons for that, but their data is derived from real world pro testing.

Maybe you're running suboptimal tire pressure.

Same for me. Ride comfort is easy to judge subjectively, but rolling resistance much less so. The Silca recommended pressures always give me a comfortably acceptable ride and I just trust that they are in the right ballpark for speed.

My thoughts:

1, Tire pressure actually is a pretty big deal (and free!)
2. Actual tire pressure is very hard to measure. Even gauges change over time.
3. Don't forget that tire pressure rises with temperature - enough PSI to be noticeable, but not like 10
4. The online calculators should better indicate which inputs are the most and least critical
5. The online calculators should output charts that you can play with
6. The online calculators should output test ideas that you can run yourself to see if your times line up with their predictions.

Seems to me that you learned quite a bit:

• bicyclerollingresistance provides actionable tire data
• Bike Calculator quite accurately matches the real world

Hence the arguments.
​​​​​​A good one won't drift much, and can be calibrated.
​​​​​​Not enough to even worry about it.
​​​​​​'Inputs'? What are we talking about?
​​​​​​What should these charts illustrate?
Testing requires a very controlled environment and rigorous procedures that few (or no) recreational cyclists can muster; hence the calculators.

Possibly, but the thing is, my Superpower as a Scientist has been my consistent ability to come up with hypotheses which completely and elegantly explain observations, but which, when tested, turn out to be completely wrong. So, I've learned never to fall in love with my hypotheses.

BTW, one interesting thing is, using the Silca calculator, you need to specify a measured width. On these rims, my "28mm" GP5Ks measure 29mm, whereas my "32mm" Corsas measure 30mm.
https://cimg6.ibsrv.net/gimg/bikefor...567a58185c.gif

Nothing prevents you from incrementally changing variables and plotting the results yourself.

This is one advantage of riding the same route repeatedly - I have a lot of observations of how fast I am usually going at a given spot on the route for a given RPE and/or HR. So, for example, when I rolling along one stretch where I'd normally be going between 17 and 19 on the GP5Ks, on the Corsas it was more like 16-17. Similar for max coasting speeds on downhills, like the one where I spin up to 30 mph before the crosswalk and then coast. I usually can get up to about 35.5 - 36, whereas with the Corsas it was 34.5-35. In fact I was surprised that my average speed wasn't a lot slower.

Their purpose is to provide a suggested optimum pressure for a specific rider, tyre, rim, road combination. If you are thinking of changing one of those input parameters (eg wider rims or different tyres) then it is easy to see what effect it will have on the recommended pressure.

Some calculators, like Silca also provide slightly different recommendations for recreational comfort vs performance/racing etc