I chose the lightest rims I could afford coz that’s what I’ve been doing on this build. It has a dynamo and will have big fenders so I’ve been saving weight where I can. It’ll have 28mm tires minimum. It’ll get ridden on nasty roads and some gravel, but mostly pretty chill bike lanes. It will get ridden about 5 hours a week 30 km at a time in whatever nasty ass weather there is until I have time for more riding. If I want to go proper adventure riding and need big tires, it already has the DT 650b wheel set.
I bet if I ask nicely I can swap them for AR36 or 46.
keep the ultralites, you’re small enough (you said 60kg?) and keep an eye on your tire pressure. Getting spoke tension right might be a slightly sticky wicket compared to monster aero rims, but again, not a showstopper, just a bit more work.
If you do switch though, the AR36 feels like a normal alloy rim when spinning up from a stop. doesn’t feel as whooshy as a 56mm rim, but it’s a decent tradeoff.
the hed jets have a pretty good reputation. alloy rim with carbon fairing. not the lightest alloy wheelset available, but decent and good aerodynamics.
of course, you cant hang your bike from a hook so might rule these out for anyone storing their bikes this way.
I’m sure I’m fine on those rims. I’m exactly the use case, and I’m not worried about the build. The first rims I ever built where TB14s so I’m sure I’ll be fine.
I’m only dithering about the watts I’ll save on my commute, which is pretty silly. I also have to lug this thing up several flights of stairs, so weight is an actual consideration.
I got tied up in a long conference call last night and could not respond. I figured somewhere the internet has argued this point, much like a helicopter on a turntable or an airplane on a treadmill. This post on StackExchange does it better than I could have. I was going show how integrating the deformity over the entire radius of the toroid has the same surface area and volume. This math is much simpler.
For giggles, I did an experiment in my garage with my 50 psi gauge. On a 700x40c tire, I tried 45 psi, 15 psi, and 5 psi with the gauge hooked up and mounted the bike. In all cases, the needle did not move from me getting on the bike. When I bounced, the needle bounced, but not more than a quarter psi. I would blame that on using an analog gauge.
Ok, what do you mean by “the same”? The link you sent calculated a 0.03% reduction in volume. Which is not very much, but it’s only “the same” for loose definitions of “same”
(caveat - I think this is true, it makes sense to me, but I just thought of it so consider this thinking out loud) Another way to think about pressure is that the added weight of a rider is spread out over the entire surface area of the tires, not just the contact patch. The combined surface area of two 29x2 tire-esque torii is 2210 in^2, so supporting a 220 lb rider would add ~.1 psi. I would expect the deformation at the road to reduce the volume of the tire a very small amount (see yonderboy’s link for a mathematical approximation), and the stretch of the tire to allow the volume to increase a very very small amount, with a net reduction in tire volume
this is very helpful, thanks to everyone who took me on a physics learning journey! i’d always assumed that i was compressing the tires significantly, but it seems it’s not the case!
now, to pump my 20x2.2 Marathons to 80 psi and absolutely haul ass on my longjohn
Can you show me this in an equation? I don’t understand and I really want to. Based on how I calculated it, the pressure change should be 0.1psi for a fully inflated tire of this size, regardless of original pressure. The catch is that for a 10 psi tire that’s a 1% change, and for a 100 psi tire that’s a 0.1% change.
Again, I know I’m being a Heath about this and that this is not quantitatively or qualitatively measurable for anyone without lab equipment
Based on the molar mass of 16g of CO2 and a 26x2.1 tire volume (from here):
27.726 psi unmolested (calculator)
27.734 psi with a 0.03% reduction of volume (calculator)
I just used the calculator to shortcut all the inputs, but it’s doing P = nRT / V in the background. The first link goes through all the math in detail.
this dumb thing probably wouldn’t get my chainrings any further outboard than the stock gxp spider right? going full dither to make these bikingreen rings work better…