Rolling Resistance, Weight, and Tire Placement
I read a lot about rolling resistance. I also read a fair amount about tire weight, and next in frequency would be tire placement front or rear. From my personal experience I very much notice differences in tire weight, particularly on the rear. I've formed my own opinion, possibly just flat out wrong, that rolling resistance would only be noticeable on smoother, flatter trails where they would require more work to keep rolling. That assumption has lead me to believe that you wouldn't notice rolling resistance differences while climbing. I also have an assumption that the effects of rolling resistance and tire weight are much less noticeable when the tire is mounted up front. Help me understand and distinguish the differences here, and dispel any myths in my assumptions.
Flat, smooth trails are the least of my rolling resistance concerns ;-).
Rolling resistance is the energy lost by deforming the tire to the surface it's riding on. Any surface leaves a 'dent' in the tire that moves around its circumfence. Just picture the earth rolling around the tire, not the tire moving on the earth. Not sure if you know what I mean (not a native English speaker here...), but hey, I'm trying. It's like you continuously ride into a speed bump.
The energy needed to overcome that dent moving around the tire, is rolling resistance. On flat, smooth ground, the dent is not deep and long. On proper bumpy MTB stuff, you guessed it, the dents are short and deep.
I like my tires to deform with ease to what is under them. This is determined by tire width, tread, suppleness of the casing and pressure. The tires have to float over rough stuff, also, or perhaps more importantly, on climbs. A stiff tire or a very supple tire can mean the difference between floating over roots or rocks, or stalling on them.
In short: You do notice rolling resistance on climbs! See for yourself and try to do a rough (but not loose) surface, steep climb on a thin, hard casing tire with 40psi in it and then with a wide, supple tire on 20psi.
On soft soil, it's not only the tire that deforms, but the soil as well. This is where you need really low tire pressure, because you need to create the optimum balance between putting the dent in your tire and putting a dent in the earth.
It's kind of old, but I still think this test is one of the best resources about what influences rolling resistance: Mountain Bike Tyre Rolling Resitance
Rolling resistance is huge, and the first thing you're going to notice... especially climbing.
try a nevegal stick e 2.1. Its 650g and it'll be slower than a 800g UST xc tire.
We can go through the math if you want but rolling resistance is most noticeable around 10mph. With a 10 percent differance in rolling resistance which is about the differance between mountain bike tires and 700c tires 10 mph on the higher resistance tire will get you 10.5 mph on the lower resistance tire.
"Dish is illogical." Spoke of Vulcan.
looking forwards to the math on this one
Originally Posted by zerodish
Yeah, math that takes into account the affect of roots, rocks, soil conditions, etc.