Is it the chainline?
 

http://i98.photobucket.com/albums/l2...Me-OffRoad.jpg

Why is this bike faster and more efficient than all my other bikes? Mine is singlespeed and the chainline is straight as hell. Is that the secret? Or is it the slick tires? Or the relatively light weight (17lbs)?

Granted, my other bikes aren't $1000 road bikes, but I feel that the efficiency of my little bike is due to the perfect chainline. In any case I wanted to see what you guys thought. Detailed specs here:
http://www.pacific-cycles.com/bikeca...cat=3&rnum=888

You are riding a fixed-folder with a touring package on a dirt trail wearing full road kit.



I am at a loss for words re: efficency.

wheel size. that's a lot of weight you're shaving with such small wheels.

You are my hero.

It's not fixed, it's singlespeed (although the freewheel is in the front). Also, that's not me in the pic. I don't use a touring package, I don't wear kit, and I don't ride in the dirt. I just thought it was a good pic of the bike.

I was thinking that, but the bike is only 17 pounds....light for a folder, but just on the low side of average by full size standards.

Oh, and I forgot one other thing, maybe it's because the frame fits me well?

ahh but now we enter the world of rolling weight vs. overall mass.

rolling mass has a completely different inertia. it's ridiculous how much more efficient losing 50 grams from the wheels can make your ride feel as opposed to 50 from the frame or a non-rotating part.

That thing needs a suspension fork and seatpost badly.

Don't forget the radius. It is far easier to rotationally accelerate a wheel that has a 2" radius versus a 13.5" radius (27/2).:D

Weight has nothing to do with efficiency.

Carry on.

Well, the practical difference between rotating mass vs nonrotating mass is a bit dubious. It's been discussed ad nauseum in the folder forum and my conclusion is that it's very hard to say how much of a difference it actually makes.

Certainly in terms of acceleration a pound off the wheel is worth two pounds off the frame, but the armchair physicists will argue until they're blue in the face that weight makes no difference what-so-ever (rotating or not). However, they are clearly wrong as the "weight doesn't matter" argument applies to carrying furniture just as well as it does bicycles...and we all know that weight does matter when it comes to carrying furniture. The key, of course, is in the physiological losses. Those are what determine just how much more efficient losing rotating mass is compared to non-rotating, but I haven't seen much discussion of those.

Yeah, but the effect is exactly canceled by the fact that the smaller wheels must rotate faster to achieve the same bike speed.

On the contrary. Don't confuse the gross energy with the net energy. Newton's laws may be conservative, but muscles are certainly not. All that body heat generated when cycling is lost energy...and which do you think will work up a greater sweat, riding a light bike or a heavy bike?

Carrying furniture != riding bike. I believe the point was that weight doesn't influence efficiency if you're getting extra momentum for your extra effort. A big boy on a bike is harder to stop than a little one. For the furniture, that extra momentum ain't helping you since it's working in the wrong direction (i.e. down via gravity). Still, I agree muscles don't provide equal returns at certain loads.

PS: And you're not my hero now that it's not you in the photo. Sorry.

Yes, carrying furniture != riding a bike, but neither does riding a bike equal riding an electric bike.

Muscles are complex things. Obviously if you assume that all the energy used by the muscles goes into the momentum of the bike (minus frictional losses) then you will get no loss of efficiency, but that is assuming the conclusion (since we know that newton's laws are conservative from the get go). Carrying furniture is just an extreme example of the fact that all the energy used by the muscles does not get turned into mechanical energy such as momentum (in fact, unless the furniture is going up stairs then none of the energy gets converted into mechanical energy).

The real point is that if your body is getting hot, tired, sweaty, then there is a loss of efficiency, which must be accounted for. In the case of carrying furniture the loss is as high as 100%. Who knows what it is in the case of cycling. However, considering the fact that I sweat at least as much when cycling as I do when carrying furniture I bet it's probably the dominant source of inefficiency and I bet it somehow depends on the weight of the bike.