AtlPirate

I recently changed/upgraded my mtn tires from 1.95 to 2.1, and a little more knobby tread. However i took it out this weekend and it was a whole new feeling bike. It felt super sluggish, li8ke driving a tank, Now i know that my wheels are a tiny bit bent but neither rub on brakes. Is this new feeling just cause of bigger tire? or is there something wrong?

John Wilke

More rotating mass, more rotating intertia?

John Wilke
Milwaukee

grolby

Most likely the knobbier tread gives the wheel more rolling resistance. There's no way that you're going to notice any significant difference in the bike's speed or sluggishness simply by adding a slightly bigger tire. Rotating weight is the big bogeyman of cycling - it means a lot less than the tire tread and pressure. It will effect acceleration and climbing anyway, not sluggishness. A 40 pound bicycle and a 15 pound bicycle will be equally easy to maintain at 20 MPH, all other factors such as aerodynamics and friction from drivetrain and parts being equal. Slap some knobbier tires on the 15lb unobtanium bike, and it's going to feel slower than the 40lber, due to the increased rolling resistance. It'll accelerate faster and climb more easily, but that's it. I would put my money on increased rolling resistance because of the knobbier tread on your new tires. If they run at a lower pressure than the old ones, that may be a contributing factor as well (though this is not an easy matter to quantify)

Also, a nitpick - inertia doesn't rotate, seeing as inertia is a property of objects with mass, not a physical object itself.

Sluggo

Moment of inertia = mass times lever arm. Weight on the outside of a wheel (like a tire) does indeed matter more than weight on other places on the bike for acceleration (but not for steady speed or climbing).

grolby

Which I didn't claim was untrue. I would still argue that it is far overrated in terms of its impact on performance, but that's neither here nor there. All I said was that inertia is a property of moving (in this case, rotating) objects, and is not a 'thing' that would rotate, itself, the point being that "more rotating inertia" is a meaningless phrase. That was itself not particularly germane to the question at hand, which was "what's slowing my bike down?" My answer was "your tread pattern is likely causing more rolling resistance, and hence more friction for you to fight against in order to keep moving at a steady speed." Do you wish to propose that the moment of inertia at his tires is what's responsible? Because if so, I happen to disagree, but we can fight over it if you want . Pistols at dawn, sir!

Sluggo

If AtlPirate went from a relatively light 1.95 to a relatively heavy 2.1, it could make the bike feel "sluggish" just because of the tire weight.

As the challengee, sir, I believe it is my privilege to suggest the weapons and location. Espresso at 2 PM (I get pretty sleepy about then)!

supcom

Bigger wider knobbies give you more traction, not more top speed.

phantomcow2

yea, the beefier tires come with side effects.
I really noticed it last week when i stuck on knobbies for the first time in a few months because of the snow. What a difference it makes in traction! What a difference it makes in how much slower it is!

AtlPirate

ok well that pretty much answered it. Yeah traction with them is now awesome, just acclerates slower....but its all good.

Avalanche325

When putting on a brand new knobby tire, even the exact same type, it feels like you are dragging an anchor around for a few rides. There is a good reason that cross country racers use semi slicks.

Also, going to a wider tire is putting more rubber on the ground. You will get more rolling resistance there too.

The good sides are that you should be able to carve the turns better, climb loose and rocky hills better, and float over sand better.