Check this out-

Bike Calculator

Useful calculators for estimating your speed on a bicycle velocity from various parameters.

bikecalculator.com

Will do exactly what you ask and lots more. Good entertainment.

 

You can just work out the gravitational potential energy (work done moving it a given height) as it a) won't change based on velocity and b) assuming constant velocity the kinetic energy will be very small, so it's a reasonable estimate

E=mgh
= 2kg * 9.81ms^-2 * 1524m
G.P.E = 29.9KJ ()

If you wanted to be specific you'd have to add the kinetic energy (work done accelerating it to 5mph), which will be relatively very small...
E = 1/2MV^2
= 0.5*2*(2.24^2)
= 5J
So 29,905J work done, and your power would be 2.76W (29,905/10800)

 

Thank you both, really helpful replies.

2.76 W is a very small price to pay for having enough water; it puts things into perspective.

 

Nice! I love the question and the analysis especially since it helps to put 'real world questions' into perspective. It makes me wonder whether or not it would be worth the effort to try to lose another 5 pounds before next year's race season. I could just spend a bit more time training to increase my FTP by a few watts....

 

Work on both numerator and denominator.

 

N+1

 

Speedo ♾️

 

 

Hi. Not sure what you're going for, but an added concern to me is that if you're over-weight, you tend to need more water. (So,unfortunately I carry a lot of water.) Your body has to cool more mass.

 

Two litters of water is a lot. If you need it to finish the ride take it. And let’s say it is 10 watts extra for round numbers.

I am 77 kilos. I have a 4wpk ftp. So if I take a 10 watt penalty it’s a 3% penalty. Not a big deal less than sales tax.

Now let’s say I have a 2.5wpk ftp. That 10 watt penalty is just under 5%. Still not a huge deal.

If you are a smaller rider the penalty is a greater %. And over longer periods of time even 5% adds up to being much slower. But dehydration will make you really slow. From riding road bikes if it’s moderate temperatures you should be drinking one bottle/24 oz and hour to maintain. You lose other stuff also like salt. Another thing is are you starting the ride hydrated or already behind? What you eat plays into it also. So many variables


Sent from my iPhone using Tapatalk

 

If you are carrying the weight on your back there is also the effect of the extra weight pushing down on your butt/ seat interface. I have noticed less chafing and a more comfortable experience on my rear end since i transferred water, tools, tube etc from my back to my bike. Not to mention less back sweat with no pack.

 

I understand that you were asking about work, but a consequence of carrying 2L of water on your back is that your center of gravity is higher, and that water sloshes around. It can throw off your balance if you're riding aggressively and can make you lose control.

 

Isn't it a differential equation since your loosing weight as you sweat it off. Like a propulsion solution to a rocket where the weight decreases as fuel is burned.

 

I am interested in understanding the consequences for carrying extra weight on a climb, specifically how much work it requires to carry an extra two liters of water. For example, if I were to carry water weighing 2 kg up a 15 mile ride climbing 5,000 ft at a pace of 5 mph?

Google says a kWh is equal to 102 kg x meters / seconds. Is it correct then that carrying 2 kilos of water up 1,524 vertical meters in 3 hours (10,800 seconds) equals 28.8 kWh? Seems high that I would have to expend an additional 9.6 watts to maintain the same pace? Am I doing something wrong? Thank you for the help.

Try carrying a wiggling 30lb toddler who constantly grabs the handle bars and nearly wrecks you. 2 kilos of water is no big deal.

 

The results of the calculations makes me wonder if obsessing over a small amount of bike weight reduction is worth the financial cost for most people. Obviously, a heavy bike is harder to control, but it does allow the bike/rider combination to have a lower Cg, although it makes better brakes a requirement if the rider wants to maintain control well.

The comments about water sloshing and possibly upsetting the balance makes me wonder who decided that a tandem MTB would be a good idea.

 

The results of the calculations makes me wonder if obsessing over a small amount of bike weight reduction is worth the financial cost for most people.

Fewer people obsess over bike weight these days than they used to.

 

Now..... how much less energy are you going to have if you don't take the water and dehydrate?

Can someone please calculate energy reduction due to dehydration?

Then you need to minus energy reduction from additional energy used and determine which outcome is best.

 

Now..... how much less energy are you going to have if you don't take the water and dehydrate?

Can someone please calculate energy reduction due to dehydration?

Then you need to minus energy reduction from additional energy used and determine which outcome is best.

From personal experience, I can say that becoming dehydrated sucks and really saps strength & endurance. I found out the hard way hiking into and out of the Grand Canyon- there were times near the ends of the hikes when I had the strength to walk about 10-15 steps before I had to rest. I knew I would need plenty of water, so I carried extra bottles to fill at the watering stations, but that wasn't enough. Fortunately, it wasn't excessively hot. I should have made sure to replenish my electrolytes.

 

It is not for me a question of intentionally dehydrating myself to save carrying weight, but if I am doing a longer ride than usual, or going when it is hotter, then there is the nagging question whether it is worth the extra watts to carry more water. One one hand I have hauled two liters to the top of a mountain and then back to the car without touching it, which seemed like a waste; but I have also skipped the extra water and been MURDERED by the heat and dehydration.

2.75 watts is not a big deal for me. And it is a nice luxury to be able to drink as much as I desire without having to ration.

 

It is not for me a question of intentionally dehydrating myself to save carrying weight, but if I am doing a longer ride than usual, or going when it is hotter, then there is the nagging question whether it is worth the extra watts to carry more water. One one hand I have hauled two liters to the top of a mountain and then back to the car without touching it, which seemed like a waste; but I have also skipped the extra water and been MURDERED by the heat and dehydration.

2.75 watts is not a big deal for me. And it is a nice luxury to be able to drink as much as I desire without having to ration.

I don't like hauling around more water than I need either. If I'm in a new area that's unfamiliar to me, or if I'm riding on a really hot day, I might bring extra water but for my usual local rides I typically bring one bottle (and rarely drink all of it). One measure that I take is to bring water purification tablets like backpackers use. They weigh virtually nothing and take up minimal space, but I have them for backup in case I need to refill my water bottle. This tactic assumes you have a water source so it might not apply to where you live. I live in Oregon so we have streams all over the place from which I can grab more water. Just an idea.

When you become dehydrated the blood thickens and is less effective in supporting the muscles being used. How much water is actually needed though varies more than people realize and the suggested minimums are ridiculously high.

Some experts recommend a gallon of water per day and hauling around 8 lbs of water is a problem of bulk more than weight. Recent studies have shown that the amount of water consumed has little measurable impact on kidney function for anyone.

I got chastised by my daughter a couple of years ago for not drinking as much as "they" recommend. I replied that I haven't died from dehydration yet, so...

 

When you become dehydrated the blood thickens and is less effective in supporting the muscles being used. How much water is actually needed though varies more than people realize and the suggested minimums are ridiculously high.

Some experts recommend a gallon of water per day and hauling around 8 lbs of water is a problem of bulk more than weight. Recent studies have shown that the amount of water consumed has little measurable impact on kidney function for anyone.

 

I'm terrible at math but I can cut and paste.
One pound of excess body weight takes two watts to get up a hill, or three kilograms of fat takes an extra three seconds per kilometer on a climb. Meaning that if you have ten pounds to lose you could climb 7-10% faster. Those gains would take much longer if your focus was strictly on increasing your power output.

 

If I get an ebike / emtb will I need to carry less water?

 

Meanwhile...Tinker Juarez straps a backpack of rocks on his back and rides 13,000 ft. of elevation.

 

I don't like hauling ME up hills- how is he doing that?

 

Isn't there an app for that?