spare_wheel

depends on the tire, the route, and the commuter.

bobbyl1966

Thank you for your answer. I have one real weird problems with my road bike wheels. I put new rim tape but is move the rim tape and do hole in the innertube. that happens without i ride the bike is do that when i put air in the tire. I do like use the max psi

Jaywalk3r

Incorrect.

spare_wheel

Incorrect

Jaywalk3r

It's already been shown. Look upthread.

mikeybikes

I think this is the second this month, what with the clipless thread finally dying down.

trailmix

Maybe if they keep repeating the same points from the last 20 identical threads, someone will magically change their opinion.

noglider 

I was just thinking the same. Thanks for noting it. Oy!

cyccommute 

You can do your own research. Wheel Testers from Finland have done the studies on the rolling resistance gains and that's where the value for the rolling resistance come from. There are numerous sources of graphs for the energy required to overcome drag at various speed. You can do your own math...but probably won't.

cyccommute 

A 25mm tire is still a skinny tire. The studies done on wider tires haven't been on going from a 23mm to a 35mm tire but, rather, in going from a 23mm to a 25mm or 28mm tire. And I don't think you'll find anyone saying that a heavier tire is faster. That's usually a caveat when every going to a wider tire is recommended for reduced rolling resistance.

Weight is always a factor in every vehicle we monkeys use to move down the road. Bicycles aren't the only vehicle that has seen radical weight reduction. Cars, motorcycles, and large trucks have all seen significant reductions in weight in recent years. Even airplanes. Getting the weight up to speed is only part of the problem.

Newton's Laws of Motion say that an object in motion will stay in motion unless operated on by an outside force. Moving through the air is that outside force. In fact, you are the outside force if you look at the action from the standpoint of an air molecule. You, as the cyclist, may not be accelerating but you are accelerating each and every air molecule you slam into. The acceleration of each molecule acts as a drain on the larger body's (your) momentum and you have to make up that drain by putting more energy into the system to maintain your speed. The more weight you have on the bike, the more you have to shove into the air and the harder you have to work. Rolling resistance of a 35mm or 42mm or 50mm may be lower than a 23mm tire but the weight of each of those is significantly higher which translates to more energy required to move it down the road.

Not at all. I'm not talking about trying to get the bike 2 feet off the ground but just getting it over a pothole or up a curb. Any bike can be hopped up or down a curb or over a pothole.

cyccommute 

I bunny hop with my saddle in a normal position all the time. The height of the saddles in that video are for demostration purposes. He's trying to get a lot of air so he's got his saddle down but the technique is the same with the saddle high.

I have, by the way, miss judged a high speed hop up a curb with tires closer to 50mm and put a nice deep curb shaped V in a wheel. I didn't stop hopping up curbs but I'm much more careful about doing it since replacing a wheel isn't that cheap. Just slamming potholes or curbs is hard on your pocketbook.

turky lurkey

I'm not sure about this. The drag force acting against the bike and the rider doesn't increase as the weight of the bike and rider increases. In fact it seems like the effect of wind resistance should be less for for a heavier bike, therefore have less of a slowing effect as a heavier bike and rider will be exerting a greater force against the air molecules than a lighter alternative (the mass of the air molecules is not affected). According to Newton's law the heavier object should have more of a tendency to maintain the same rate of motion than a lighter object, given the same force opposing the two objects. Of course the greater cross-sectional area of a fatter tire will tend to cause the bike to slow down.

Isn't this the same reason heavier cyclists can travel downhill faster? Acceleration due to gravity is the same no matter what the mass is. The forces exerted by the cyclists however are not the same, a heavier cyclist exerts a greater force against the air molecules and is slowed less by them.

cobrabyte

"do your own research"

translation: "I couldn't possibly provide sources, because all the crap I'm writing is created in my own insane mind."

Walter S

"do me"

translation: <bleep>

DunderXIII

Exactly, an object that moves keeps moving forever unless it has an external force (drag). Its also harder to accelerate a heavier object to a given speed. Because cyclists are always slowed down by drag we must always 'accelerate' to keep a given speed (that's why we pedal). So heavier is harder.. because of drag.. not because it "displaces more air" (that's a question of volume) but because its harder to 'accelerate'.

mikeybikes

C'mon guys, where are your free body diagrams?

spare_wheel

And yet...you feel the need to comment and post helpful smilie GIFs....

Andy_K 

No!!!!

When accelerating a massive body from rest, the force needed for accelerating is proportional to the mass being moved. When applying force to a moving body to counteract a resisting force and maintain constant velocity the force required is exactly equal to the resisting force. Unless the resisting for is dependent on mass (which air resistance is not) then force needed to maintain constant speed is also independent of mass. Air resistance is determined (mostly) by frontal cross-sectional area, and so we big fellows on upright bikes do still bear a bigger burden than are slender brethren riding in a nice tucked position, but it's not because of weight.

DunderXIII

I stand corrected And the 'air resistance' needed to slow down an object is also proportional to weight, so heavier counters air resistance better.

I think it has to do with 'where' the weight is on the wheel (ie: you need to make the wheel turn, so you're playing against gravity?). Not that I haven't done any research on that part but I'll take a look. <-- nevermind

mikeybikes

And yet...you feel the need to comment on my need to comment and post helpful smilie GIFs....

Andy_K 

You should really pick a side and jump in to the pointless debate. It's fun.

mikeybikes

At the risk of having someone pointing out mistakes and making me feel stupid, here's my FBD:



Fp is the force exerted against the road surface as a result of pedaling, that's all your muscles.

I don't know enough about the various drag forces though to make a call on how mass affects it. I purposely left the force of drag vague. If the force of drag was negligible (which we know it isn't), more force would be required from pedaling in order to achieve the same rate of acceleration if there's more mass involved.

There you guys go. Work off of that.

mikeybikes

That is such an oversimplification. There are too many things left out and aren't accounted for.

Andy_K 

Nice!



I believe this is the assigned text for this course: Bicycling Science: David Gordon Wilson: 9780262731546: Amazon.com: Books

mikeybikes

I have to admit, it took me much longer to make that FBD than it should have. I haven't done those in years. Also, I spent way too much time trying to decide if it was sin, cos, or tan... I was positive it was cos, then I realized I had shifted the axes...

Maybe I'll pick that book up for some light bed time reading.