Originally Posted by DirtPedalerB
I would think the diameter is around the same if not exactly the same. A heavier tire will take more energy to spin up to speed and I'm sure most 2.25 tires weigh more than most 1.85 ties. Also the wide tires will have bigger contact patch which adds more friction again increasing preceived weight. Wheel weight is the most important to the response of the bike, body and frame mass can't really be changed as a variable when we are discussing changing between tires. So I say he will feel like he is riding a slug .. especially if he goes with a more knobby tread pattern than he has allready. But I seriously doubt they fit.
A carpenter ant weighs more than a mound ant. Which one takes more effort to pick up?
Indy tires are wider than Nascar tires. Which car is faster?
These facts have nothing to do with the questions that are asked. And they are exactly the same as the things you are saying. I can take two ball bearings from the same line on the same day and I GUARANTEE that their mass is not the same. The reason is simple, the statement makes no sense because there is no parameters on what equality means. An engineer will define a precision with with equality can be assessed. But real objects that exist in the real world cannot be measured EXACTLY so we must define thresholds for the sake of making conversations meaningfull.
You say that it will take "more energy". You have failed to define what levels of energy is relevant and perceptable. You say wider tires are "slower" because there is "more friction". But had you looked at your physics more carefully you would have discovered that the frictional force is the mass times the coefficient of friction (
Ff=mµ). And the coefficient of friction for a material is independent of surface areas since the increased surface area decreases pressure. Did you know that the low pressures that racers so desperately seek in their tires also increases the surface area?
Like I said before, increasing the wheel diameter (the tire is the outermost portion of the wheel) changes the effective gearing ratio. This is probably explains the "sluggishness" you perceive. This is no different than the "sluggishness" you feel when shifting from 7th to 8th gear. Put a 2.5" tire on your rim and you will still be able to push it with your pinky. Just imagine how relevant such a mass is to the largest muscle groups in your body in and around your hips and thighs?
As an afterthought, I am well aware of changes of moment in inertia as the mass in a rotating body increases in radius. I am trying to convince you that it is pretty much irrelevant unless you are a serious endurance racer.
In general for off road, wider tires are often better as they more easily conform to terrain. The benefit of this is two fold. First, you get increased traction as more of the tire is actually in contact with the trail and you are more likely to be in contact with a surface that will hold. Second, the yielding nature of the pneumatic tire is beneficial as deflect from irregular trail features. The alternative is bouncing the bike up and down. That bouncing is no good. It is a translation of perfectly useful forward kinetic energy into heat energy from flexing the tires. When one conserves kinetic energy, we are not so blindly eager generate it with promises of lesser inertia moments that have never been calculated with reference to the overall inertia of rider mass plus non-rotating bike mass plus rotating mass to determine whether it's even remotely relevant.