We all know that tire pressure should be set based on the total system weight (e.g. bike+ride+accessories+anything else). Yet tech editors everywhere constantly ask riders and mechanics for tire pressure.
I understand that asking a rider their weight is socially unacceptable and I’m aware of the risks of eating disorders in cyclists. For this reason, I would not suggest that tech editors ask riders their weight. My proposal is the following:
Let’s start talking tire pressures in pressure/weight. For instance psi/100kg (yes I can handle the mixed imperial and metric units) or maybe better kPa/kg.
E.g. my system weight is 108kg and I inflate my 2.8” MTB tires to 15p.s.i., giving a pressure of 15*100/108= 13.9 (p.s.i./100kg).
I know it’s a little bit of work to calculate. But when I find out a rider on a video is running Xpsi, I’m left estimating their weight, which I can at best estimate +/-10%. So if I wanted to try their tire pressure adjusted for me, I can only estimate it that accurately. And if you’re asking on a podcast and I’ve never seen the rider, then you may as well just not ask at all!
Normalizing pressure to total load makes good sense. One could build a useful data set of pressures for different tire sizes and conditions that should work for any rider or load. And as you said, it would be easy to transfer someone else’s pressure preferences for your own use.
From the point of view of putting tyre pressure into some form of context, it seems sensible. Unfortunately it wouldn’t be too difficult to extrapolate the riders weight from the bar/kg system weight (within a margin). Not same as asking them what their weight is directly, but end result would be the same.
Weight doesn’t have that big an impact on tire pressure, at least according to online tire pressure tools (we’ll have to wait for more of Ronan’s PHD thesis).
Try out the Silca or SRAM guides and keep changing the weight. Tire size has a much bigger impact than system (or rider) weight.
I like the idea of normalizing pressure but it’s a complicated calculation that’s not linear. A rider with a system weight half the example you gave would not be running 7.5psi. I have no idea what the right comparison would be though.
Tire pressure is a personal thing. As such I kind of don’t listen to who is running what PSI because that’s their setup. For example, I tend to run way lower PSI than others across all disciplines. As a result, if you tried to calc my weight based on that, you’d come in way low. I’ll wager folks like Pidcock, WVA, MVdP all may be the same way; great bike handlers avoid flats. Others may need a lot more in order to not pinch flat.
The entire “Asking a persons weight” thing is modern BS. We can all just look at a person and tell if they are overweight. Especially if they’re in Lycra. I mean, we can all just look in the mirror and know if we’re overweight or not. People who are overweight know it, and but they may not know how to properly loose weight. Avoiding that conversation isn’t really helping them. Certainly avoiding the conversation has not helped millions of children who are now on the road to obesity.
As for tire pressure - I agree. It’s totally a personal thing, based on needs - Comfort vs RR vs Surface.
The whole “you’re overweight so you need to do something” thing is uninformed at best. It ignores all of the factors that might influence a person’s weight and reduces a person’s weight to a binary condition: not overweight is good while overweight is bad. Sorry, it doesn’t work that way, and more importantly it’s no one else’s business. Fortunately, doctors have access to a person’s medical records and can thus make informed decisions about a patient’s health along with that patient. Internet commenters? Not so much.
I think this goes further and should also include tire width.
I‘m a big guy, think of Walscheid or Ganna.
Each spring cycling media discusses the right tire width for roubaix and it makes me furious that there is a supposed optimum for 90kg guys like Ganna and small riders like Pauline Ferrand-Prévot.
I want to see the graph that matches system weight with tire width. And then we can discuss tire pressure.