dougmc

No, not weird.

Though I would think that even if the frame did absorb a significant amount of energy, it wouldn't be noticed. Suppose you're a 150 watt cyclist, and your frame is absorbing 10% of that -- which would be massive. 15 watts of heat -- about half of a small soldering iron. The heat would likely be generated in a small part of your frame, but being metal, it would be conducted out to the rest of the frame pretty easily. But you're riding, so there's a 15 mph wind or so cooling this frame. And it's basically just bare metal, with no insulation (paint doesn't really count.) I don't think the frame would get hot at all -- at most, it would be a few degrees warmer than the air around it.

But I do think your friend is right, that most of the energy is returned. And really, they don't flex that much. I'd expect any losses to frame flexing to be under 1%.

safariofthemind

He explained it as being akin to a spring - it moves, but the energy is stored and released. Only a small amount becomes heat. That sort of makes sense.

Steely Dan

if fatter, lower pressure tires are really faster than narrower, higher pressure tires, then why hasn't anyone slapped some 70 PSI 35s on a race bike and cleaned up on the professional circuit yet?

just from my experiences with my own bikes, i'm way, WAY, WAY faster on my road bike with 135 PSI 23s than i am on my hybrid with 80 PSI 35s. i know that not all of the other variables are equal in that equation, but the speed/effort difference is significant, and i know a big part of it is the tires.

chasm54

Fatter tyres have less rolling resistance. That doesn't mean they're necessarily faster. They are heavier and, more importantly, less aerodynamic. So the faster you go, the greater the advantage of running a narrower tyre because it cuts through the air better.

garage sale GT

The roughness of the road is a huge factor. When the road vibrates the bike excessively, that power comes out of your pedaling.

MMACH 5

The difference between fat and narrow tires is just conditioning, all in my mind or simply a marketing agenda? Oh please.

There are, and have been how many professional cycling teams, coaches, trainers and riders? And they've been doing this for how long? Do you really think they would sacrifice speed, which in turn would likely cost them victories, simply for marketing? Their whole goal is to win races. They don't care what looks cool. They only care about speed and efficiency. I promise you they have tried every which way from Sunday to make their bikes faster and if a fatter tire was more efficient, they'd be using it.

safariofthemind

Racing conditions are not the same as touring conditions. Loaded, at typical cruising speeds the tires will behave differently than what you see racing. A lot of trade offs are made to gain lighter weight so they climb better, for example. It's not a simple apples to apples comparison.

fietsbob

Vintage Bike quarterly, apparently goes on and on about rolling efficiency of high quality supple wider tires in 650B
and 700C, we are talking 32 wide or there abouts, and compares narrow 23 wide
high pressure, clincher/wire bead tires..

But you will note the Pros still race on 23mm ish hand made sew-up tires,
that 700c resemble,
unless the sponsors pay their contract with the stipulation to ride the sponsor's stuff...

fast is about the work the rider puts on the pedals, efficiency is about the hardware.

Steely Dan

ahhhh, that might make more sense. the Jan Heine and Mark Vande Kamp study that brianoglivie posted about didn't make a distinction about how the tire was being used (or at least brian didn't mention anything about that), so his post came off as a de facto blanket statement that wider, lower pressure tires will ALWAYS roll with greater efficiency than narrower, higher pressure tires, which runs 180 degrees opposite of my experience of riding bikes with various width/pressure tires (along with the entire history of competitive road cycling), but then i've never done any loaded touring so the advantages in efficiency that a wider, lower pressure tire might afford in that situation wouldn't be something that i would have ever experienced before.

either way, when i commute on my road bike with 135 PSI 23s. i rarely, and i mean RARELY get passed by other cyclists along my route (several times a season at most). and yet when i ride my hybrid with its 80 PSI 35s, i am routinely passed up by roadies. the engine is exactly the same in both situations, the bikes themselves are indeed a bit different, but the difference in speed is so great that i have absolutely zero inclination to switch out the rubino pros on my road bike for something fatter and spongier.

also, i'm getting some 100 PSI 25s for my hybrid, so when i slap them on it'll be interesting to see if i can pull some more speed out of my old girl with some narrower, higher pressure tires.

BarracksSi

I can imagine the energy being stored and released, but I don't imagine it releasing in any useful direction.

BarracksSi

Think there'll still be a speed difference due to riding position?

Steely Dan

oh yeah, i would strongly suspect that my road bike will always be significantly faster than my hybrid for a variety of reasons, but i do expect that my old hybrid will run faster after i switch out the 35s for the new 25s i'm getting. either way, it will be an interesting way for me to personally find out if there's any truth at all to this idea that fatter, softer tires roll faster than skinnier, harder tires.

TassR700

At slow speeds rolling resistance makes up a higher percentage of the force needed to move the bike. As speed increases, wind resistance becomes the dominant force to overcome. Narrower tires have less wind resistance so as speed increases, the rolling resistance advantage gets marginalized by the wind resistance increase. Throw in the difference in wind resistance from riding position between a road bike and a hybrid, and the rolling resistance difference disappears.