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  1. #1
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    New question here. Aren't heavy wheels sometimes a good thing?

    Most of the time, fat-bike riders and builders are looking to lighten their wheels: with drilled-out, single-walled, rims and 120tpi tires. For climbing and quick handling, this makes sense. But, under some conditions, doesn't a little extra rolling inertia come in handy? Like riding through snow, perhaps?

    Curious, Dave.

  2. #2
    will rant for food
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    I don't think you're crazy for thinking that.
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  3. #3
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    I do, you have to create inertia before you can use it.

  4. #4
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    For me personally in the summer considering my physical abilities and size (fat and not super fit), where I ride (Minnesota) and the speed I ride (medium fast) I find a fat bike with 3.7 inch tires is the fastest and most efficient use of my energy over an entire ride. I also think what is true is different for everyone. Little skinny racer on tight climbing course would likely be fastest on a 26 inch wheel. My personal order of speed on my bikes from fastest to slowest is 3.7 inch tire fat bike, 29r, Moonlander with100mm rim and the big tires and then 26 inch mtb bike. I think a big part of why 29r wheels are faster for some people has a lot more to do with the weight of the wheel helping it roll better rather than the size alone allowing it to roll better. Even if a 29 and 26 inch wheels weigh the same pushing that weight way out there on a 29r makes it ride like a heavier wheel which I find benefits me.
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  5. #5
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    Quote Originally Posted by Hogdog View Post
    I do, you have to create inertia before you can use it.
    For some of us, overcoming the inertia of our own bodies is much more of a challenge than that of a heavier wheel.

    I always laugh when I see guys creaming themselves over the latest lightweight do-dad that they're planning to drop big bucks on to shave a gram or two when they're rolling with bellies that are barely contained by their jersey.

    I'm a clyde and ride my old school Large Marge wheels. Yeah, it'd be nice to shave some weight there, but would probably be better served by losing a few pounds off myself before losing anything off the bike. I can spin the LMs up quick enough and can climb well enough with them because I have the size and strength to do so. Would lighter wheels help me ride better/faster? Probably, but I go back to the rider issue - until I get down under 240 I don't see the point in losing weight on the bike.

  6. #6
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    Quote Originally Posted by BluNosDav View Post
    Most of the time, fat-bike riders and builders are looking to lighten their wheels: with drilled-out, single-walled, rims and 120tpi tires. For climbing and quick handling, this makes sense. But, under some conditions, doesn't a little extra rolling inertia come in handy? Like riding through snow, perhaps?

    Curious, Dave.
    Given that light for a fatbike wheel is still heavy in the MTB world I don't see any benefit to having a heavier fatbike wheel given the current constraints in technology.

    I've never been riding through sand or snow and wished for more weight in the wheels.

    The issue with lightweight and fatbike wheels is that the tires/tubes are reaching the point where there are durability penalties for going lighter and lighter.

    What's more important to me is having tires that have the lowest rolling resistance and that still meet my other needs. Slow rolling tires suck energy from you with every pedal stroke and that's no fun on a long ride.

    Of course you have to balance low RR with getting the traction you need and adequate durability.
    Safe riding,

    Vik
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  7. #7
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    I'd rather ride a sub 30 lb fat bike compared to a 40+ beast of course, but I agree, no need to go too crazy with it.
    Biggest difference I've found is the tires themselves. Sure is easier to roll a hudu than a nate yah know?

    But overall wheel weight, it's just a different type of riding. Once the heavy fatties are up to speed, they pull you through corners & speed up down hill.
    Switching to skinny tires for a bike trip couple years ago, I was way more tired when i wasn't used to how quickly the skinny tires would lose momentum. (on the same trails)
    Riding.....

  8. #8
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    I don't think any extra weight on a bike, rotating or otherwise will ever make anyone faster overall over the course of a ride, race, or whatever. There may be some short climbs, or rough sections that the additional momentum will keep you from losing speed as quickly, but this will be more than made up for when having to brake earlier, and accelerate more slowly when necessary.

    Now, if the extra weight is giving you something else in return, like traction, or shock absorption, it may help you go faster, so heavier can be better, but not on it's own.

    Maybe you could take the flywheel effect to an extreme, and use it to store energy from braking with a gear system to spin up a separate flywheel mounted next to the wheel, then use that to accelerate.

  9. #9
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    Quote Originally Posted by autodoctor911 View Post
    I don't think any extra weight on a bike, rotating or otherwise will ever make anyone faster overall over the course of a ride, race, or whatever. There may be some short climbs, or rough sections that the additional momentum will keep you from losing speed as quickly, but this will be more than made up for when having to brake earlier, and accelerate more slowly when necessary.

    Now, if the extra weight is giving you something else in return, like traction, or shock absorption, it may help you go faster, so heavier can be better, but not on it's own.

    Maybe you could take the flywheel effect to an extreme, and use it to store energy from braking with a gear system to spin up a separate flywheel mounted next to the wheel, then use that to accelerate.
    I agree with the above.

    I will also add that people overstimate the amount of inertia you actually gain with heavy wheels.
    If you hit a rock, the total energy of you plus the bike is what will get you over the rock, and the wheels are a small fraction of that energy.

    For example, a 90 kg guy on a 10 kg bike going 15 meters/second (about 10 mph).

    Total energy = 1/2MV^2
    = 11250 KgM^2/sec^2 = 11250 joules

    so what about rotational energy of the wheel? Well, the total energy of the wheel is the sum of translational and rotational energy, and works out to be,
    E=MV^2 (ask me to derive this and I will!)
    so the total energy of the rotating wheel is twice that of a non-rotating wheel translating at the same speed.

    For a 2 kg wheel
    E = 450 joules
    compared to the total energy of 11250 joules, it is 4% of your total energy. The rotational energy is half of that, but there are 2 wheels.

    So the rock you hit doesn't see much difference whether you have heavy wheels or not. But if you want more inertia, you can fill up your backpack with lead wieghts. Clearly, inertia is not the goal you should be striving for.

  10. #10
    gran jefe
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    in you were in a competition where you were riding off the top of a 100foot cliff, and the winner was the person to land farthest from the bottom of the cliff, then heavy tires would help. outside of that, i don't see any benefit. trying to spool up the especially heavy wheels of my beast isn't gratifying in any way. now, gyroscopic forces so large you can feel them, that is kind of fun...

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    Thanx for all the opinions guys. Makes this all more interesting.

    Two other heavy rolling (non-bike) examples to ponder:

    #1 - I once had a pick-up truck that got 17mpg running around town, and 20mpg on the highway during long trips. I always kept close track of my milage. Then one day, I was hauling some really heavy steel equipment on a long trip. My truck was propably overloaded weight-wise, but, everything fit inside the bed, so there was no extra wind-drag. I got over 23mpg on that trip! It was gently rolling terrain (not mountainous) and the momentum of all that steel, just kept carrying my truck along, with my speed hardly varying at all. More weight was more better, and my truck's engine didn't have to work as hard throughout the trip, except for the initial acceleration getting it up to highway speed.

    #2 - I used to own a farm tractor (John Deere), and a small farm. Sometimes, when working through some muddy areas, it would lose traction and the wheels would spin-out. My fellow farmers told me to fill the tires about 90% full of water (and some anti-freeze for winter). They did this through the valve stems, when the stems were up high at the 12 o'clock position, so about 10% of the tire at the top, still had air. Now, we're talking several hundreds of pounds of added water weight, maybe even thousands of pounds on their large dually tractors. I asked them about all the extra engine power (and diesel fuel) it was gonna take to roll all this water back & forth across the fields. They just laughed and said that the water doesn't rotate at all. The wheel just revolves around, and the water keeps slipping along inside the circle, as if it's in an endless tunnel. Sure enough, I never noticed any additional fuel usage, never had to run the diesel at any higher RPM, and my tractor quit slipping in the muddy areas. Go figure?

    Don't know how these 2 examples translate over to fat-bikes? But, it all involved changing weight, on wheels, without using more energy.

    Thanx, Dave.

  12. #12
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    I've always felt like heavier wheels could provide me an advantage during races... so long as they were on the other guy's bike!

    Seriously though, I could imagine instances when the increased gyroscopic stability of heavier wheels would allow you to hold a line better and avoid braking or scrubbing more speed in turns. I just think that benefit is so rare an occurrence (on x-country rides) compared to all the times you would be hindered by slowly bringing heavier wheels up to any speed that my first sentence holds true.

    It also seems like any benefit from heavier wheels would more commonly exist in downhill situations where maintaining the ideal line might allow you to maintain speed and the effort to bring wheels up to high speed is easier with the gravity assist. Indeed downhill racers don't seem overly concerned about wheel weight (or total bike weight).

  13. #13
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    Quote Originally Posted by Bill in Houston View Post
    in you were in a competition where you were riding off the top of a 100foot cliff, and the winner was the person to land farthest from the bottom of the cliff, then heavy tires would help. outside of that, i don't see any benefit. trying to spool up the especially heavy wheels of my beast isn't gratifying in any way. now, gyroscopic forces so large you can feel them, that is kind of fun...
    Show me the math.

    The bike that's going to land the farthest from the bottom of the cliff will be the one that's going the fastest when it becomes airborne. Assuming that the aerodynamics between the bikes is the same.
    Riding Fat and still just as fast as I never was.

  14. #14
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    The "feeling" most people cling to (and parrot) is that "heavier rotating mass kills acceleration". This is generally not true at all for big heavy cars, although it can be true. Most things we fret about make no appreciable difference in the grand scheme of things.

    Rotating Mass, Available Horsepower, and Acceleration
    Quote Originally Posted by BluNosDav View Post
    Most of the time, fat-bike riders and builders are looking to lighten their wheels: with drilled-out, single-walled, rims and 120tpi tires. For climbing and quick handling, this makes sense. But, under some conditions, doesn't a little extra rolling inertia come in handy? Like riding through snow, perhaps?

    Curious, Dave.
    I gotta agree with you Dave ... There will always be a condition where rolling inertia can be used to advantage.

    And there will always be an argument for and against the condition

  15. #15
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    Quote Originally Posted by BluNosDav View Post
    Thanx for all the opinions guys. Makes this all more interesting.

    Two other heavy rolling (non-bike) examples to ponder:

    #1 - I once had a pick-up truck that got 17mpg running around town, and 20mpg on the highway during long trips. I always kept close track of my milage. Then one day, I was hauling some really heavy steel equipment on a long trip. My truck was propably overloaded weight-wise, but, everything fit inside the bed, so there was no extra wind-drag. I got over 23mpg on that trip! It was gently rolling terrain (not mountainous) and the momentum of all that steel, just kept carrying my truck along, with my speed hardly varying at all. More weight was more better, and my truck's engine didn't have to work as hard throughout the trip, except for the initial acceleration getting it up to highway speed.

    #2 - I used to own a farm tractor (John Deere), and a small farm. Sometimes, when working through some muddy areas, it would lose traction and the wheels would spin-out. My fellow farmers told me to fill the tires about 90% full of water (and some anti-freeze for winter). They did this through the valve stems, when the stems were up high at the 12 o'clock position, so about 10% of the tire at the top, still had air. Now, we're talking several hundreds of pounds of added water weight, maybe even thousands of pounds on their large dually tractors. I asked them about all the extra engine power (and diesel fuel) it was gonna take to roll all this water back & forth across the fields. They just laughed and said that the water doesn't rotate at all. The wheel just revolves around, and the water keeps slipping along inside the circle, as if it's in an endless tunnel. Sure enough, I never noticed any additional fuel usage, never had to run the diesel at any higher RPM, and my tractor quit slipping in the muddy areas. Go figure?

    Don't know how these 2 examples translate over to fat-bikes? But, it all involved changing weight, on wheels, without using more energy.

    Thanx, Dave.
    In example 1, I have to say that there is no way a loaded truck gets better mileage than an empty one, despite your observation. Moving mass takes energy. Imagine running up and down some hills while pushing an empty shopping cart. Now load the cart with bricks. Is your running going to be harder or easier?

    Example 2 - it would take more energy if you had to spin the water, and its true you don't, but you are still moving the water when you move the tractor which also takes energy. Loss of traction on the other hand is a loss of energy also, so there is a trade off.

  16. #16
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    Theoretically, an empty truck and a full truck rolling down a hill will go the same speed and get to the bottom at the same time. If they then continue to roll up a hill on the other side, they will reach the same height. But after they slow down it will take more energy to keep the loaded truck moving.

  17. #17
    gran jefe
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    The truck full of steel got better mileage because it's ride height was lower, which improved the aerodynamics. Also the steel filled some portion of the bed, which also improves the aerodynamics. There's also quite a body of literature on "pulse-and-glide", which is what you were doing going up and down the hills.

    Quote Originally Posted by crashtestdummy View Post
    Show me the math.
    No. I assumed that the extra weight was in the form of a hang-glider attached to the top of the bike. a-HA! If you can shoot someone down by changing the assumptions, then so can I!

  18. #18
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    The math is simple:

    Energy = work = force x distance. More mass =, more force = more energy needed.

  19. #19
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    This is an interesting thread because I was wondering the same thing the other day.

    Basically the Physics I know is contrary to my perception when I switched from my fatbike to an ordinary 26" bike. The heavy fatbike felt smoother and easier to pedal up a moderate grade, yet it should not be so in theory. There's obviously other factors involved.
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  20. #20
    will rant for food
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    Well - the story I seem to recall is from mikesee, the application being riding in deep snow (yo: he would know). If I recall right, he found himself in a situation where riding through successive snow drifts got progressively easier (easier being an extremely relative term here), and noticed that his rims had acquired snow buildup.

    Like a flywheel.

    I don't know. It sort of makes sense. Are lighter bits better 80% or whatever% of the time? Yeah probably. But there are other times where maybe it isn't so critical.

    Feel free anyone (Mike particularly) to correct the gaps in my memory.
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  21. #21
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    If you are going to roll down a hill and bash through a snow drift, then yeah, you want your bike to be heavy. But if you have to pedal it up to speed and bash through it, you use more energy to get the heavy bike up to speed. Then, when the heavier and lighter bikes are both up to the same speed, the heavier bike goes through the snow drift more easily, but the energy you feel you have saved through the drift was used before you hit the drift. Overall, on a heavier bike, you will use more energy.

  22. #22
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    Quote Originally Posted by smilinsteve View Post
    Theoretically, an empty truck and a full truck rolling down a hill will go the same speed and get to the bottom at the same time. If they then continue to roll up a hill on the other side, they will reach the same height.
    Nope.. Theoretically full truck rolls faster. More gravitational pull against the same windage. Higher speed at the bottom and the full truck ends up higher up the next hill. After that point the lighter one rules. So in the end it depends if you live on top of the hill or not..

  23. #23
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    Quote Originally Posted by TeddyTS View Post
    Nope.. Theoretically full truck rolls faster. More gravitational pull against the same windage. Higher speed at the bottom and the full truck ends up higher up the next hill. After that point the lighter one rules. So in the end it depends if you live on top of the hill or not..
    Nope.. grab a pencil and a large bolt (different weight, about the same aerodynamics) drop them from the same height see which one hits the floor first?
    Report back with your findings. You can't get "more gravitational pull", it is constant.

  24. #24
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    Quote Originally Posted by temporoad View Post
    Nope.. grab a pencil and a large bolt (different weight, about the same aerodynamics) drop them from the same height see which one hits the floor first?
    Report back with your findings. You can't get "more gravitational pull", it is constant.

  25. #25
    gran jefe
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    Quote Originally Posted by TeddyTS View Post
    Nope.. Theoretically full truck rolls faster. More gravitational pull against the same windage. Higher speed at the bottom and the full truck ends up higher up the next hill. After that point the lighter one rules. So in the end it depends if you live on top of the hill or not..
    Yeah, this is true, but isn't what anyone else was talking about. My car with 1000 lbs of feathers in it will roll down a hill a lot faster than a cardboard box on wheels the same size and shape as my car, and will roll farther up the next hill. You used incorrect verbiage that people will argue with, but you are right.

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