All other things being equal (tire width, inflation), why not run slicks off road? Obvious answer is that the knobs "grip" the trail. But is this really true? Seems more like gravity + contact patch is what's gripping, and the knobs provide minimal benefit except in certain specific circumstances.
Is there any evidence to support using knobby tires on a mountain bike?
Yeah, try it for yourself; rail a gravel corner fast on knobby tires and then try to do it on slicks. Assuming you're going fast enough you can feel the bike begin to slide while on slicks while the knobby tires will have more bite. It's pretty pronounced especially when you start to dig in the with your weight on the outside pedal; try to do that on slick or bald tires and the bike cannot hold an angle for too long or it will just slide under you.
Another thing to try would be damp trails, slicks will do no favours there especially if there's any sort of technical climbing.
You can use slicks off road (I do it every day on my commute), you just need to take down the speed on corners as you can easily exceed the limits of the tires.
There is a noticeable difference between my Bonty connection trails, and my IRC Mythos II's.
I went up a hill with the IRC's and didn't spin much... changed treads due to wear concerns from riding road so much lately, and I spun the whole way up..
so if there is a difference between two low end treaded tires....
You can imagine the HUGE difference between slicks and knobbs.
Like on trucks, Had a buddy who had a chevy diesel pickup, but he had all season tires on it... When he came to pull us out of the mud, all he did was spin. Called in his friend, with 35'' swampers, to come pull us both out, and he bit in and was able to get enough grip to yank us out...
Just a related topic, sort of: What's best for sugarsand, tread-wise? I've been thinking of bringing a spare wheelset to the jersey pines with some schwalbe marathon pluses, just to see if it hooks up in sand better (like, a beach cruiser effect) or if I'll end up dead. Having the spare wheelset with the usual nevegals in the trunk will be nice, after my experiment fails.
for the sand, you mean, Ed? I run nominal 29x2.55" WTB weirwolf LTs in the pines, and they're not noticeably better than the 2.1" nevegals. The weird old-timers i've spoken to, who are obsessive about the pines, they're saying too much tread sucks, but they're scared of slicks. (So am i, but I'm also follhardy.) They figured 29" would save them from the sugardemons, but my experience hasn't supported that belief. (Been a few years since i talked to these guys.) The volume seems like it could help, though.
Once Deer Tick season is over, I'm going to hit Mt.Misery with my whole quiver of rubber. Wish me luck
All other things being equal (tire width, inflation), why not run slicks off road? Obvious answer is that the knobs "grip" the trail. But is this really true?
Yes, it is really true.
For example, I have some Bontrager Jones ACX tires that hook up pretty well for me on sandy stretches of trail that I deal with, especially on the sandy climbs. By contrast, I have to take extreme care with weight distribution to avoid spinning out when riding those same trails with slicks. (And sometimes I spin out anyway).
There is one particularly steep downhill coming into town where I live -- on an ATV trail -- on which I can lose both front and rear traction when running slicks. When I come in that way on my commuter bike, I have to be very careful how I brake to module my speed, and at how I approach the turns. The difference between tread and no-tread on that one hill is night-and-day.
Tread helps in loose sand. It helps in mud. It helps on damp ground. It helps on soft ground.
It is true though, that you can ride many trails with slicks. You just have to ensure that you with within the abilities of whatever tires you are riding.