Here's one of many ways to think about tires. A point of view not often expressed. Maybe it'll make sense to you, or maybe you'll think it's all hogwash (which it isn't).
Tread for Roads On dry asphalt, the road embeds itself into the tire, so you'll get the best traction with a slick, which increases the contact patch with the road.
Once the road is damp or wet, some kind of tread helps. This violates some tire-grip theories out there, but I quit riding pure slicks in the winter when I started scratching out on steep climbs, and slipping around corners. Tread helps in the wet, but you don't need a lot of it, just some. That's why the Roll-y Pol-y and Ruffy Tuffy and Jack Brown have the tread they do. Half smooth, half slight tread, and it seems to work.
(When you ride on a wet road, just watch it around corners. No crash due to slipping is ever the tire's fault. Even if somebody made an oil-impregnated tire that oozed oil constantly as part of the Plan, it's still your job to figure out what you can and can't do on the tire.)
Treads for Trails On dry trails, tread increases traction by increasing contact area as the tread digs in to the dirt. You can buy tires for every kind of soil imaginable, but it's better to ride a moderate knobby and learn how much to trust it in a variety of conditions, than to ride a different tire for every type of soil, never learning any tire's capabilities really well, and then blaming a crash or washout on the tread pattern, or your tire choice for that day. It's your job to learn what the tire can't do, and then don't do it.
In parallel worlds, there are fisherman who changes flies every ten casts and think the secret is getting the right pattern; and photographers who keeps buying new cameras in search of better photos.
Every year there are new tread patterns, but the chance are you have one---or at most two---types of soil in your neck of the woods.
For deep, loose and leafy trails, ride big knobs; for dense hardpack, ride shallow knobs or negative (inverse) treads. And if you find yourself with the "wrong" tire for the conditions, work with what you've got, and consider that people used to ride everywhere on solid rubber tires on hi-wheeler bikes.
Treads for mud Ride as skinny and as slick as you can. If in dry conditions you'd ride a 2-inch knobby, in the mud try a 1.5-inch not-so-nobby. Small or shallow knobs, maybe The key is to maximize the air space between the tire and frame, so the tire won't jam up as quickly; and to minimize mudpacking and make de-clogging easy. A knobby tread gloms onto muck and doesn't let go, so the tread ends up buried in the mud, anyway.
Tread directionalismismism doesn't make THAT much difference, and sometimes none When the tire has a forward and backward direction, there is usually an arrow somewhere on the side indicating forward (it may not say "front" or "forward", but it's not pointing backward). In the case of road tires, the idea is that water enters the tire from the center of the tread (the part that contacts the road), and channels or grooves radiating outward from center are the exit chutes.
It may work better in theory than real life, or maybe it works some in real life, but it doesn't work obviously fantastically in real life. If you mount a tire backwards, you probably won't notice the difference. At least your tires don't end up hydroplaning.
Trail tires are often directional, and the theory is more complicated than it is with road tires. There are even some "front-only" and "rear-only" tires, and it used to be a thing to ride a Front Model X and a Rear Model X; but it also used to be a thing to ride the rear tire backward, for greater traction up and down hills.
The tires don't say much about this, but I think it's probably a case, partly at least, that tire makers know you tend to ride conservatively, and if directionalism, or frontalism and rearalism gives you the confidence to ride a hair less conservatively, you'll still be riding within the traction limits of the tires, but now the tires will get the credit. It's sort of like telling your 5-year old wearing the flotation vest that it's safe to gingerly plop off the end of the low-board in the deep end. (Nobody ever overestimate's a tire's tractionability right off the bat.)
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Tire width-to-Rim width fit-ups, and tire stability during turns There's a good trend these days toward wider racing rims, and kind of toward wider rims in general. I think it started a few years ago with downhill mtn bike rims, and is trickling around to all other kinds, re-estabilishing sanity in rim widths that existed up to about 1980.
The worst combination is this: skinny rim, fat tire, low pressure, fantastic traction, high speed, sharp turn. The tire grips the road, but there's so much distance between the road and the rim, and so much leverage working against the rim, and the tire is so soft, that the tire tread stays put on the road and the tire bead stays put in the rim, but there's a big ol' soft wobbly tire between them, sort of like holding a Slinky closed between two hands, then shifting your hands around relative to one another. (I think "Slinky Factor" could be the name for this.)
The SF is less noticeable on pumped hard than on pumped soft tires, and on low-traction trails, and at lower speeds.
In non-racing wheels with 38 to 50+ mm tires and 23mm wide rims and such, even though the ratio of tire width to rim width is high, a few extra psi stops the wallow. Maybe it should be "Wallow Factor".)
Both DT and now Velocity have introduced 23mm wide racing rims, about 4mm wider than the normal 19mm or so. DT's original claim is that it created a smoother and more aerodynamic joint between rim and tire, with both now being close to the same width. Velocity also says it makes the tire more stable on the rim (addressing the Wallowing Slinky Factor). At racing tire pressures it can't be THAT noticeable, if at all, but the theory is sound.
I like the unintended effect of making the rim more suitable to fatter road tires.
Basic Tire Anatomy "Casing" is the entire, woven or overlaid base of material, the foundation of every bike tire. The tread goes on top of the casing, and the uncovered sides are the sidewalls. The sidewalls have at least a UV-resistant coating on them, and sometimes extra material that's not actually tread.
Sidewalls come in three basic types:
Skinwall, the lightest in color and often in weight, too. The least durable, but durable enough for all but the slashiest conditions. More vulnerable to sun damage than the other styles, so not the preferred sidewalls for Tucson.
Gumwall, the heaviest kind and not much seen anymore on new bikes. Before about the mid-'70s most low-to-midpriced ten speeds had gumwall tires, but they'd disappeard from midpriced bikes by the late '70s. Now sometimes you see them as replacement tires in Cheapy Big Box stores, and in Japanese bike shows where the winner will always be the bike that looks like a brand new French bike from the early '50s, gumwalls and all.
Blackwalls can be light or heavy, but all things equal, the black rubbery coating on the sidewall makes the tire more cut- and sun-resistant. They're kind of dark, mean-looking tires and give any bike a bit of Goth-look, but practically they are the most practical, and if I can come to accept them, anybody can.
Now and then there's a belt, an extra layer of rubber, nylon, kevlar, or something else between the casing and tread, to stop thorns.
Sidewall suppleness and speed Supple casings (and therefore, sidewalls) are said to soften the ride, but they aren't as effective in that way as lower tire pressure. If a bare tire has a supple casing, but is so skinny that you have to inflate it to 100 psi just to protect the rim, you lose the benefit of its supple casing. It may behave a lot like a stiffer tire at 90psi.
I'm not convinced that tires with supple sidewalls are faster than stiff ones, because I can't see how that can be. But the notion that they are faster certainly is prevalent, and I may be wrong about this. People smarter than I am say supple sidewalls make a tire deform over bumps more, to roll through the bump faster, and I can see that. What I can't see---my deficit---is how lowering tire pressure to compensate for stiffer casing wouldn't have the same effect.
Faster or not, I still like high quality, but thicker, stiffer casings, even reinforced casings. A good, thicker casing-which tends to be stiffer- ages better and lasts longer than a thin one. It stays safer longer, and I'm ten times more concerned about safety than rolling resistance. Rolling resistance plays a minor roll, and I'd say an insignificant one, in recreational riding. It just has no bearing on anything for me. For me, for me. Don't let my inability to understand that get in the way of your---anything.
The other, final thing I like about stiffer sidewalls is a small thing until you need it: When you're riding on a dead-flat tire because you haven't got a tube, a stiffer casing is easier to ride on, it protects the rim more, and it suffers less damage, because the rim isn't grinding it into the ground.
This next comment will get me branded Wacko Forever, but it has some merit, and yes, I believe it. Heavy tires impart a quality to the ride that one can come to prefer. Heavies don't accelerate from stoplights all that well, but that's mostly a leg thing, and come on -- how important is a superfast acceleration downtown?
Once the heavy tire is rolling, though, it tends to plow through and over things that would upset lighter tires, and the bike just feels kind of dreamy. That's a lousy description. We have some 950g tires on one of our demo bikes here, and without exception, customers who ride that bike love it, and 90 percent comment on the ride quality. We don't say, "It's da heavy tars," but they have a lot to do with it.
At some point heavy is toooooo heavy; but if all you get out of this is the idea that maybe you shouldn't wrestle with 300g verses 400g, or 500g vs 600g, then---that's good.
Presta valves, not Schrader Prestas are the skinny, metal threaded two-stage valves you see on most decent bikes and all good ones. Schraders are the kind car tires have. Prestas are easier to pump and hold air better. You can adapt a presta valve to a Schrader pump, but not the other way around, so go presta and be done with it. If your rim has the bigger Schrader holes, get hole-adapters to fit presta valves, or tape the skinnier presta valves to fatten them up to fit the big Schrader hole.
Beads that fold and beads that don't Tire beads can be Kevlar or steel wires. Kevlar beads usually cost about $10 more, save between 60 and 90g per tire (up to about 3oz) make the tire floppy off the rim, and easy to fold. If you normally ride around with a spare tire in your bag or are fanatical about weight, folding is the way to go.
But folding tires are fussier to mount, and more likely to come off the rim if you have the misfortune to have to ride home on a dead-flat tire. In the end, the pros and cons are small, so ride whatever.
But don't think you can't fold a non-folding tire, because you can (just not as small), and here's how: (If you can't download the pdf, just read the notes below). And here's how in a video.
0. Begin with an unfolded tire. This one is wire/steel bead, the hardest kind to fold, but still easy.
1. Squeeze it to form a fig.8, with loops leaning away from you.
2. Fold top loop down to the mid-point of the bottom loop. Hold on so it doesn't spring open.
3. Fold the left loop over (in front of, toward you) the right loop, and shove the right loop behind the left one, so you're stuck with two loops on top that look like one, and the one below.
4. Fold the top loops forward and down, behind the lower loop. Tape or zip-tie or tie them somehow so they don't spring open, and that's it.