My riding buddy and I hack out a lot of the world’s problems while we are on the road. Here is one we need clarification on:
Weight of the rider
Weight of bike and wheels
Weight of the wheels
Which of these is most important to minimize for speed and efficiency on the bike?
I’m not sure I am asking the right question. Is it useful to spend thousands reducing your bike 2 pounds when the rider could drop 10 for free and gain efficiency? I guess I will ignore aero for now. WHat gives you the most boost for the buck?
did the math on wheel weight and argues that, assuming that TOTAL BIKE WEIGHT is equal, having more of that weight being in the wheels is actually FASTER
So if your BIKE + wheels = 20lbs, the more of that weight you have in the wheels, the faster you will go. He did the math for inclines too, still faster.
That said, I’ve seen on the innertubes somewhere a field test where they added 5lbs of water to a bike in various ways. once to the frame, and once inside the tires to change the wheel weight. The inside the tires test was the slowest.
But was that because of wheel weight or the way that affected rolling resistance?
Going a constant speed down a road, uphill, downhill, flat land mass is mass is mass. Lose it from yourself first and then lose it from your bike. All of this assumes that aero is constant and speed is constant. If you are doing a lot of acceleration then mass of the wheels will have more effect in how fast you can accelerate than any other mass.
I think you have hit the nail on the head here, even though the math may indicate an advantage to heavier wheels, he notes that it is tiny.
I think no special concern need to be placed on wheels for removing weight unless you are a sprinter or having to accelerate a lot.
Going a constant speed down a road, uphill, downhill, flat land mass is mass is mass. Lose it from yourself first and then lose it from your bike. All of this assumes that aero is constant and speed is constant. If you are doing a lot of acceleration then mass of the wheels will have more effect in how fast you can accelerate than any other mass.
My riding buddy and I hack out a lot of the world’s problems while we are on the road. Here is one we need clarification on:
Weight of the rider
Weight of bike and wheels
Weight of the wheels
Which of these is most important to minimize for speed and efficiency on the bike?
I’m not sure I am asking the right question. Is it useful to spend thousands reducing your bike 2 pounds when the rider could drop 10 for free and gain efficiency? I guess I will ignore aero for now. WHat gives you the most boost for the buck?
The only weight that has any significant affect is the weight of the rider. More weight to be lost there and it helps with performance (better heat loss ability with greater surface area to volume ratio and less internal friction to overcome moving the parts around, and less rolling resistance, edit, and also smaller frontal area most likely). If losing weight on the bike makes it more flexible it can actually slow the rider down substantially through increased power transmission losses.
All signs point to the rider. Assuming that you cut the same amount of weight from any of the three, the greatest impact on efficiency lies with the rider. Reason is that lack of perfect riding form causes lateral motion of the bike, thus reducing the energy contributed to forward motion. The heavier the rider, the greater the displacement (laterally) of the c.g. Reduce the weight of the rider, and you will reduce lateral motion caused by shifting weight. Think of how the bike rolls when you start mashing the pedals. Besides, cutting 20 pounds from a rider is handily cheaper than cutting a few hundred grams from the bike, components, or wheels.
The difference in weight between the lightest bike money can buy and my P2C is less than the weight I can lose off my body. Seems to me that you go for the low hanging fruit first and lose weight off the rider first and then worry about the bike.
If I were already at my best race weight then I’d worry about the bike. But I expect that for the majority this isn’t the case.
“If losing weight on the bike makes it more flexible it can actually slow the rider down substantially through increased power transmission losses”
I can’t believe I’m going to open this can of worms, but here goes…
…lets see some evidence to back this up. I mean, where, exactly, is the transmission “loss” going? If you’re right, Why weren’t all those Vitus frames from the 80’s glowing cherry red at the top of the mtn. stages?
If the losses are flex-induced, that’s going to be expressed as heat… how much heat is going to be produced by “substantial” losses?
From the math I’ve seen on this, I think it’s probably a hell of a lot more accurate to say “flexible bikes feel like they should have substantially higher transmission losses…”
“If losing weight on the bike makes it more flexible it can actually slow the rider down substantially through increased power transmission losses”
I can’t believe I’m going to open this can of worms, but here goes…
…lets see some evidence to back this up. I mean, where, exactly, is the transmission “loss” going? If you’re right, Why weren’t all those Vitus frames from the 80’s glowing cherry red at the top of the mtn. stages?
If the losses are flex-induced, that’s going to be expressed as heat… how much heat is going to be produced by “substantial” losses?
From the math I’ve seen on this, I think it’s probably a hell of a lot more accurate to say “flexible bikes feel like they should have substantially higher transmission losses…”
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flex loss is going to heat (all losses end up going to heat). Bend any piece of metal back and forth and you can feel the heat. The amount of loss would depend upon the materials and the degree and frequency of the flex, but it is going to be there and slow the bike down from what the rider should otherwise be doing. It wouldn’t take much loss to overcome the tiny benefit saving a few grams on the bike gives one. Once one has done that then I would call it “substantial” since the reason for doing the weight loss has been effectively negated and is now counter-productive.
By way of example I just went to analytic cycling and using their base numbers, except making the road flat I get 11.23 m/s for 250 watts with a bike rider combination weight of 75 kg. I had to lower the weight a full kg to get the speed up to 11.24 m/s. I then, lowered the power to 249 watts (edit, weight still 74 kg) and found that lowered the speed to 11.22 m/s. A tiny loss of power transmission efficiency has a huge loss on speed whereas a large drop in weight has a negligible effect on speed.
bike weight will have the same effect as rider weight
dropping grams from a bike may cost $$, where as dropping grams from rider weight (take a piss before your ride) is free.
you may be able to ride around on a 10000$ bike that weighs 14lbs, but wouldnt it just be easier to have a 2k bike and lose a little weight?
as long as you arent losing power- drop fat, not muscle mass- then your efficiency gain is free.
as far as the water in the wheels… water is a liquid. its viscous. its just gonna swish around in the tire, of course you’ll lose efficiency, its like internal drag. if the weight was fixed- say an equivalent amount of lead shot… glued inside the rim- then you’d see real results
its like the age old question- which rolls farther… the disc, the hoop, or the ball?
Bike weight is by far the most important. I mean what kind of a sicko asks people to pick him up at the coffee shop to show them how light he is and therefore the superior cyclist? sheesh.
Bike weight is by far the most important. I mean what kind of a sicko asks people to pick him up at the coffee shop to show them how light he is and therefore the superior cyclist? sheesh.
While the OP asked for engineering input I think you hit the nail on the head as to what goes into purchasing decisions. It is all about psychology and bragging rights.
Which of these is most important to minimize for speed and efficiency on the bike?
reducing the weight of the rider can have the additional benefit of increasing VO2. VO2 is a formula, the divisor is weight.
VO2max scales with about a 2/3 power of mass, a 60kg athlete with a VO2max of 80 compared to an equally trained elite athelete who weighs 100kg would be expected to have a VO2max of 68
climbers are small, so are marathoners.
On the flats, when gravity is not a factor, then wind resistance is paramount. For people mass increases with the cube of height, while surface area only increases with a square (and less in a TT aero position). the advantage of mass - power generating mass - can overcome the small increase in frontal area (drag).