I'm with Patrick on the tire mattering a lot. I ride more the utility/brick side of tires than he does (and consequently have developed a habit of leaning towards higher inflations rather than lower), and the optimum balance between 'feels slow' and 'starts bouncing' can deviate notably from Jan's calculation and the graph that Steve showed. Curiously, I keep all three of my bikes between 45-60 PSI (45-50 front, 60-ish rear). Except they're all three different total (bike+me+stuff) weights, tire widths, and tire types. My 3-spd roadster with its 35mm Delta Cruisers works out a a bit low per the formula but I like the comfort more over the speed at that inflation on that bike, inflated per the suggestion I think I can feel every pebble bounce me. My road-ish Centurion 650b conversion with its 38mm Soma New Xpress tires is a bit high but not by a lot. The real outlier is my Clem with its 50mm Schwalbe Mondials, which are drastically higher inflated at 45/60 than the formula would suggest, but any lower than that and I can actually feel the increased rolling resistance over my seven mile commute. Like I left my brake on, or about the same feeling as using my bottle dynamo on the 3-spd. It's notable. If I tried to ride those down as low as 30-40PSI like suggested I'd feel like I was stuck in the mud. At 60 front and 70 rear they start getting that 'baseball' bouncy effect.
I always start with the formula's suggestion and then try 5-10 PSI over and 5-10 PSI under and tweak where I actually leave it for any given tire based on where it felt slugglish and where it felt bouncey. On Tuesday, May 5, 2020 at 10:48:41 AM UTC-4, Patrick Moore wrote: > > Wait: Leah weighs *less* than 170? Boy Steve, you blew that one. > > Back to tire pressure: I recall how as a boy I first saw "Inflate to 70 > psi" on the side of my cheap 27 X 1.25" gumwalls, and after pumping them to > more or less that (probably per gas station gauge), how fast the bike felt, > and nope, it wasn't due to vibations, which has *never* been an indicator > of speed for me; it's always been ease, or perceived ease of pedaling, > along with a feeling of smoothness; ie bikes feel faster on smooth roads > than bumpy ones, all else equal. > > But the question of pressure relates to tire quality too. Cheap tires > really do go, or at least feel, faster when hard -- try riding a $15 > Walmart 2" knobby at 35 psi! Pump it to 50 and it's much better. OTOH, I've > let really supple tires deflate potentially disastrous levels -- > 30-something psi on a 28 mm Elk Pass (I do weigh 50 lb less than 220) -- > and didn't notice that they were low until I started bouncing in the > saddle. Once I got a rear puncture and didn't notice it until someone > behind me noticed the flat profile and said, "Puncture!" She then asked, > "Didn't you notice it?" -- very surprised that such sagging hadn't caused > massive drag. But not, the Elk Pass feels normally fast even at pressures > way below appropriate. > > With the Big Ones, just as supple, I've not noticed mid-teens in the back > until sidewall flop in a corner almost causes me to wipe out. > > So there is a huge difference in the effect of air pressure on rolling > resistance when comparing top quality and cheap quality tires. > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/rbw-owners-bunch/27227c2f-6bcb-48fa-b1aa-b1129342d34a%40googlegroups.com.
