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Oh man, I've been driving an RV across the country for a friend for the last 3 days and totally missed this tire pressure party!!

For s5100e.. the calculator does have a pinch flat predictor.. this is run by an energy equation that take tire spring rate and radial height and then compares compression energy to rider mass/velocity. Early versions of the calculator had an 'average speed' entered as a velocity number, but since the energy calculation is taking 'average' velocity and then assuming a velocity distribution based on that number, people were always tripping the warning by saying they rode at 'average speed' of 25mph..

As for the rest of it, the problem with impedance is that it really encompasses 3 components, 2 rider related and 1 tire related:
1. High vertical accelerations make for extra high Crr numbers, so to Tom's broomstick analogy, normal Crr is the difference between energy put into the tire to make the contact patch vs energy given back by the tire as it returns to shape. But in the impedance realm, the vertical forces can be so high that the tire is off the ground when it gives back that energy..so if you high speed a tire hitting a broom stick, you see this massive compression against the tire both vertically and diagonally against the direction of motion, followed by the tire going 'airborne' over the other side of the broomstick and the tire regaining shape before hitting the ground.. so NONE of the energy is going back.
2. Rider contact points: different riders will have different contact point hysteresis and different stiffnesses of bike will affect this as well. Ride the Carrefour de l'Arbre 1 time and your hands will be hot and blistered.. this is hysteresis
3. Rider body composition hysteresis. This is perhaps the biggest question using our data.. nearly all of our data comes from world class athletes and even the non pros on our list are guys/gals with some serious fitness and palmares. This is important if you think about hysteresis as damping.. the more fit you are the lower your body damping coefficient will be. To a 180lb person who is 2% body fat will have lower damping than a 180lb person who is 20% body fat, so in theory this should likely move the break point lower for higher hysteresis people and higher for lower hysteresis people... and looking at the athletes on our list, they are by and large about the lowest hysteresis people you could find!!

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joshatsilca wrote:
3. Rider body composition hysteresis. This is perhaps the biggest question using our data.. nearly all of our data comes from world class athletes and even the non pros on our list are guys/gals with some serious fitness and palmares. This is important if you think about hysteresis as damping.. the more fit you are the lower your body damping coefficient will be. To a 180lb person who is 2% body fat will have lower damping than a 180lb person who is 20% body fat, so in theory this should likely move the break point lower for higher hysteresis people and higher for lower hysteresis people... and looking at the athletes on our list, they are by and large about the lowest hysteresis people you could find!!
I wonder about that. If we're talking about something as high-frequency as paved road irregularities, is the rider's body actually a responsive enough part of the system that rebounded energy would be meaningfully biased toward returning as forward motion? I wouldn't be surprised if a lower-hysteresis body just means that the energy bounces around longer before being dissipated.
Hi Josh, thank you for chiming in. The whole discussion of body composition and contact point hysteresis is very cool latter probably ripe fit innovation to mitigate!

Wondering about the case with the broomstick. In the case where the wheel hits the broomstick, tire doesnâ€™t fully compress and the bike is lifted up & over the stick (launched in air or not). When the wheel hits the broomstick there is a diagonal vector at the point of contact the vertical component of that diagonal vector is the force available for lifting the bike up and over... but there is a horizontal component to that vector pointing straight backwards, opposing forward motion. This will impart an Impulse (F.dt) on the bike.. basically bike and earth exchange some momentum and bike slows down..

a) is there something wrong with this thinking?
b) do you account for this type of â€ścollisionâ€ť type of interaction in your impedance thinking, modelling?
Hi Josh, I am not certain why when I pull the SPPC up I no longer see the pinch flat side bar when I enter the pro version. As for speed I was referring to a speed range or average, not an absolute number assuming a fast group ride is a range depending upon what is fast???? my fast is not real fast and so it is a bit hard to relate those numbers. So what I mean is have both the text as well as the intended speed range. But i note that say between recreational and fast group is only 1.5 psi front and 1 psi rear so if I assume the slower then I am still on the correct side of the breakpoint.

For the Rider hysteresis maybe add in BMI? ;-)

Thanks for the calculator I swear by it even though I am not certain I interpret it all correctly I typically look at what the result is an how sensitive it is to the areas I am uncertain in.
Did some more testing this weekend on more typical road surface and wider range of pressures... not lining up with Silca calculator at all actually.. actually getting that 20-25psi diff... want to do that do one more set of testing.. just to make sure...

found some more advice on crunching data here:
http://www.floataero.com/...esting-scenarios.pdf
Got a bit busy...

Three trial... getting better at doing these I think...

I have gone back to thinking the Silca calculator reads high 15-20psi for riders of my weight ~60kg/72kg (bike+rider)

Some of my observations/conclustion:
1. on very smooth pavement ~80ish psi tested lowest Crr, but the difference in Watts between 60-80 was less that a Watt.. imho 60psi would be the better practical choice given 1) comfort & fatigue 2) likelihood of mixed road texture over totality of ride meaning that over the ride a lower pressure would be better performing 3) almost no performance penalty for going to lower pressure... ~80psi is what silca recommends
2. on textured pavement with some cracks 60psi (vs ~80ish psi to 73psi as predicted by Silca calculator) seemed to be the better choice over two trials..
3. I observed a bowl shaped curve, but did not observe the steep, marked impedance increase as seen in other's analysis.. still improving my process at getting better data.. so work in progress... I have pretty low BMI so could some of this effect be much lower for me??

Last edited by: doctorSpoc: Sep 21, 20 19:42

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