After plugging in my info to all three of these calculators, I get basically the same result - within 1 lb psi. SRAM’s loses points with me for only listing 650 and 700 as wheel size values (boo!). On Oct 7, 2023, at 2:23 PM, Ted W <ted.l.w...@gmail.com> wrote:
Thanks for the link, Brian. I’m adding that to the collection of bookmarks under “bicycle related calculators. It’s so funny how they’re all so different given very similar information. It just goes to show you how subjective ride feel can be and how many factors have an effect.
I’ve linked the other two calculators below for the curious:
Silca calculator:
SRAM calculator:
Between all of these, Silca has always proven most reliable… but again, it’s highly subjective. I do like that there are additional parameters you can tweak on theirs, though. Jan’s seems a little too cookie cutter.
I think I’ve run probably 5 sets of Rene Herse tires over the years; both with tubes and tubeless. I’ve actually found that I’ve had good luck referring to Jan’s tire pressure recommendations using his calculator, found here: Like I said, I’ve used this and it’s worked pretty well for me, especially because I like to ride my bikes loaded down with gear. I also appreciate the meticulous, scientific approach that Jan takes to cycling. It’s not for everyone, but I kinda like it.
This is very interesting. I use the extralight Naches Pass at 30-35 and 35-40 f/r depending on load, and I feel no flop or sidewall collapse; not until pressures drop below 20 psi. The NPs do feel more staid, less nimble in turn-in than the 28 mm Elk Pass, this on the same bikes, but not at all squirrelly. They do make those "rubbing" sounds a bit, though.
I wonder if front-end geometry has a lot to do with it? I've used the Naches Passes on road customs with, possibly, steeper, more agressive geometry than those ridden by the OPs; one of the bikes was Grant designed and the other is a geometrical and dimensional near-clone of a Grant design.
Or rider weight? I'm 170-175, but then I often carry heavy-ish loads on the bike in question.
What does feel a bit squirmy, not squirrelly, is the Soma Supple Vitesse SL 48s, even at a relatively hard 25 psi; it's as if the rubber is somehow soft and needs to harden. The tire makes "eraser on plastic" sounds when turning; but far from feeling squirrelly these tires (labeled 48, measure 51 on 35 mm OW rims) have transformed the handling of the Matthews #1 into the much more Riv-Road-like handling I wanted compared to the vagueness in turns of the ultralight 60 mm Big Ones. "
felt like the front just flipped over on itself"
That's a good description for what mine feels like. I also notice they get really loud on sharp turns/curves when the tire is inflated to the psi that causes the bad handling. The front tire doesn't do that when it's aired up very hard, but that largely negates the benefit of having a fat, supple tire. I could run Big Apples at a much lower pressure and get the cushion effect without the squirrely front end handling, but they are just so heavy and both had a wobble in them, from the day I got them. Not the first Schwalbe tires I've owned that wobbled, so I'm wary of the entire brand, now.
That squirrelly feeling is another thing I noticed with the Naches Pass on my Surly. It was actually the cause of a crash I had on that bike. Front end got all squirrelly on me mid corner and it felt like the front just flipped over on itself... I always attributed it to having stretched out the fit on a too-small frame (I’m 6’1” and bought a 54cm Long Haul Trucker to be able to have it in 26” wheels) and the us having shifted my center of gravity too far off the where the frame intended but having now heard a couple people here mention the feeling on the same slick tires, I’m wondering if it’s not the tires on more “touring” geometry frames, that pneumatic vs geometric trail thing that was mentioned earlier. Very interesting indeed!
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