Last year I switched from knobbies to slicks, and it was a revelation. Smooth, quiet ride, feeling like you are on rails, etc.

Recently, I've been exploring unpaved roads and rural tracks, in addition to my regular street commute. The 1.5" slick tires have performed very nicely on my 26" bike. I've learned to shift my weight from the front to rear as the ground demands it, to avoid front-wheel slipping or to preserve traction on the back. Basically I practically never get uncontrolled skidding anymore. The only times where I've wanted a bit more traction is with very muddy/soft ground, or with very loose and big gravel going uphill.

So my question is, just when does one "need" to switch to knobby tires? I still have my old tires lying around, and I guess the anxiety comes from seeing them gathering dust.

(Maybe I should just get off my lazy bum and switch them, and give them a try...)

i have my old cyclocross tires that came on my bike I put them on when I rode the Great Allegheny Passage this year. they were a little wider 28 vs 30 and had tread. People I was supposed to ride with said that I would want something with tread if it rained. It did not rain at all in 4 days of riding. Poured for 8+ hours on the drive home but not while I was riding. I commuted a lot on those before I put the michelin citys i have on it now. I have ridden a gravel trail with the city tires and they do okay. Just have to remember to not push it as hard.

so all that to say try it you might like them. It really is up to you and there is no wrong answer unless you put no tires on the wheel

The knobs really help in mud, but I find that wide slicks work fine on gravel and dry dirt. I also rode the GAP and C&O Canal trails this summer on 32 mm road tires, Panaracer Paselas, which have a little bit of tread. They were fine on the GAP, which is all gravel, except for the steeper downhill portion from the Eastern Continental Divide to Cumberland, MD. The Paselas were a little sketchy in spots where the gravel was thick, but I'm not sure treads would have helped much. However, the C&O had a lot of muddy spots and some CX tires with more tread would have definitely helped there. If I ride the C&O again, my bike will have CX tires.

I'd say you've answered your own question right there:

When slicks stop gripping it's time to get some tread, although depending on conditions you may be able to use a file tread or a hybrid tread with a center rib like the new Clement USH.

you might also consider BMX style tires. I have these on my MTB and enjoy speed and soft ground traction. these are MAXXIS Holy Rollers https://www.biketiresdirect.com/prod...roller-26-tire

Check Sheldon Brown. The surface your riding on is the tread, not the soft rubber tires

I can recall two times commuting when my slicks momentarily slipped. Once in the mud and grass I was forced to ride through due to flooding, and another time in fresh snow. This is so infrequent, it is hardly worth even mentioning. If your commute involves mountain biking, or climbing or descending steep hills in mud, yes to knobbies, otherwise, no. For snow, I use winter tires which are lightly treaded with carbide studs.

Thanks for the replies, everyone. The Sheldon Brown page on tire tread is certainly interesting.

I'd say the point where it matters is the point where you need cornering traction. For a commute on a dirt road I'm not feeling any lack but if I were to take it on the single track parallel to the dirt road I'd rather have the knobs.

Also remember that different knobs really do different things. There's a spectrum of wet to dry and packed to loose and you need to read between the lines on the marketing bumf to pick the tire for the dirt.

Mondays.

I would rather switch bikes than tires.

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