how much a diff is 300grams in wheelsets

Discussion in 'Cycling Equipment' started by jrstang473, Apr 2, 2005.

  1. jrstang473

    jrstang473 New Member

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    Im thinking os switching out my bontrager race lite wheels for a set of am 420's or some mavic ssc sl's.My race lite's are around 1750 grams and the wheels mentioned are 1500grams and below.What im trying to ponder is if i will be able to see or feel a diffrence in riding between the wheels mentioned above and the ones i already have. I weigh 160lbs and my bike is at 16.2 lbs now.I hasve alot of big hills in my area that i try to ride up alot.
     
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  2. Adam-from-SLO

    Adam-from-SLO New Member

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    Think about this:

    1 pound of wheel weight REDUCTION (so... 465 grams.. I believe) , is equivilent to shaving off 5 pounds of total bike weight(ie. frame/ compontents, saddle/ etc.).

    Its all about the wheels ;)
     
  3. 53-11

    53-11 New Member

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    This is completely false. Where do you get your info?

    That whole rotational weight thing is load of BS. maybe it matters a little when turning, but not acceleration. (your legs feel a lot of different forces when accelerating- body weight/total bike weight/rolling resistance/total aerodynamic drag) Relatively speaking just reducing weight at the wheel is a drop in the bucket. (reducing weight at the wheel isn't any more effective than reducing weight elsewhere)

    Difference between Ksyrium Elites and SSC SL (200 gram difference) is very slight. The only way you'd be able to measure is with a stop watch over a fairly large distance.

    So much hype regarding wheels.
     
  4. Adam-from-SLO

    Adam-from-SLO New Member

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    Its a free country, believe what you want to believe. Try riding some heavy wheels(wire beaded tires, 25C + heavier rims + 32 or 36 14g. spokes / brass nipples ), maybe a tire liner, etc. .......... then go to a lighter tire/ kevlar bead , alloy nips, butted spokes 28F, 32R , lighter rims , ................. and you will notice a chunk of difference.
     
  5. 53-11

    53-11 New Member

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    if you are speaking strictly weight as in comparing something like a Kysrium Elite wheel to a Kyrium SSC SL (both have same no. spokes/same aerodynamics). The 200 gram weight difference between those is only noticeable during a long race and with a stop watch.

    Analytical cycling.com ....go plug in your own numbers if you don't believe me.
     
  6. smartie

    smartie New Member

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    Weight and effect is dependant upon where the weight is being shaved from. 200 grams being removed from the rim area will have the effect of giving greater acceleration due to the whirling mass of the wheel.The bike would tend to also decelerate quicker as well as the momentum of the wheels is also less.

    The same weight being removed from the hub would not have anywhere the same effect and would be like removing weight from the frame.

    This is exactly the same as lightening the flywheel in a car to give better response.

    How much you will notice the difference i don't know, but at the top end i suppose every 0.1 second saved in accelerating out of a corner adds up to a huge amount in something like a TT, not so much in a peleton.
     
  7. 53-11

    53-11 New Member

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    I used to believe this, but it's not true.


    You cannot compare a bicycle rim to a car's flywheel anyway.

    Flywheel is connected to a clutch, no clutch on a bike.
     
  8. smartie

    smartie New Member

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    It's all a matter of torque. The further out the centre of mass the greater the effort required to move that mass as per the equation:

    Torque = Force x Distance.

    Therefore the further out the mass, the greater the torque required to accelerate the wheels with all else being equal (Gear ratio, crank length etc.)

    The reverse is also true of braking in that the brakes will have a harder time stopping a wheel that is heavier due to its greater whirling mass.

    Try it one day by using an old tube, filling it with water and spinning it, you will notice it is harder to get it up to speed and once there will require greater braking effort to stop it.
     
  9. jitteringjr

    jitteringjr New Member

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    I have heard the 5 pounds for 1 pound thing myself, but I have never seen proof one way or another, so I don't know what to belive. Anyone have proof?
     
  10. 53-11

    53-11 New Member

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    I found this article http://www.biketechreview.com/archive/wheel_theory.htm

    "How can it be that wheel inertial forces are nearly insignificant, when the advertisements say that inertia is so important? Quite simply, inertial forces are a function of acceleration. In bike racing this peak acceleration is about .1 to .2 g’s and is generally only seen when beginning from an initial velocity of 0 (see criterium race data in Appendix D ). Furthermore, the 0.3kg/0.66lb difference in wheels, even if this mass is out at the rim, is so small compared to your body mass that the differences in wheel inertia will be unperceivable"


    If you think about weight at the rim might be consequential to turning though (small degree). Take a wheel in your hand a spin it.....now turn it (you'll feel some resistance).

    It has no extra effect on acceleration or climbing than any other source of weight. 1 lb off the wheels= 1lb off the frame= 1lb off the rider.
     
  11. 53-11

    53-11 New Member

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    You are not just accelerating your wheels, you are accelerating your body and your bike too.

    Not only that, while you are accelerating you are also trying to overcome air resistance and rolling resistance.

    There are a lot of forces that your muscles are feeling....it's not all your wheels. (aerodynamics of wheels is another topic we are speaking strictly weight here)
     
  12. alienator

    alienator Well-Known Member

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    I suppose you'll find comfort in the Flat Earth Society. You obviously don't have a grasp of physics. Try to follow along.....a bodies moment of inertia, I, is defined as I=sum[(r^2)*m], where r is the radius at a given point and m is the mass at that point. You have to sum over all the points and their radii in the body. Whether you understand what a moment of inertia is or not, you should be able to see that if the mass is located near the center of say, a wheel (i.e. r is small), then the moment will be very small since it changes with the square of r. If r is cut in half, I is reduced by a fourth. If the mass is near the rim, then the moment will be very large, especially compared to a wheel with it's mass located mostly near the axle (r~0).

    Now hold on, Skippy: angular momentum, L, is defined as L=I*omega, where omega is the angular frequency of the wheel (number of rotations per a given unit of time). If you're paying any attention at all, you'll immediately notice that if I (that moment thing again) is small, the angular momentum will be small.

    Here comes the part where you have to pay attention: changing momentum causes a force.....or if you want to say the converse you can: a force causes a change in momentum. Both are true. "So what?" you say. This what a force is just an acceleration applied to a mass. Gee... so if your on your bike and you want to accelerate, you have to change the angular momentum of your wheels. If you've got wheels w/ a lot of weight in the rims (I is relatively large) you gots to put more oomph in them to get them to accelerate at the same rate as wheels with weight concentrated near the axle.

    What you believe, in this case, or what you used to believe really doesn't matter. The physics is the same. It doesn't matter whether your talking about bicycle wheels, flywheels in race cars, or a flywheel on the ISS. It's all the same damned thing. FWIW, the only difference in terms of physics between a flywheel (something designed to store energy) and a bicycle wheel is that the flywheel has a much larger moment of inertia, I.
     
  13. smartie

    smartie New Member

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    Thank god yo saved me the time of calculating the both mass and Moments of Inertia for differing wheel masses.

    The article is extremely good in determining how much effect there is in lowering the mass of your wheels.

    And to put the article in laymans terms, the following benefits are found.

    50% lower overall wheel mass = 0.33% less power required

    50% lower overall wheel MOI (weight position) = 0.035% less power required

    It is a marginal benefit however not the ZERO benefit as stated.

    By this article, i would spend my money on improving the aerodynamics of the wheels as they 2.4% benefit for a 50% improvement as stated.

    The benefit you would feel is totally dependant on your wheels starting point (i.e. really heavy wheel/tyre combo). The guys at the top end of pro cycling would be using all they can to gain that 0.035% advantage. Put into perspective that 0.035% is equal to about 0.175 seconds over 5 seconds of constant acceleration.
     
  14. 53-11

    53-11 New Member

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    The upshot is the inertia of the rim is so small as to insignificant. The are much greater forces involved than the measly inertia of a lightweight bicycle rim.
     
  15. alienator

    alienator Well-Known Member

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    Accelerations don't have to be large to have noticeable effects. As for the quote, there is no empirical basis for such assertions. The human body is quite adept at sensing small forces or changes in forces. You should not accept everything you read on the internet as truth. Try reading some textbooks to learn facts about physics.
     
  16. 53-11

    53-11 New Member

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    Placebo effect is strong. ( although no doubt in a race the effects will noticeable.....seconds in race are noticeable)

    Even if you could reduce weight at the rim by a drastic 25% (not easy at all.....in fact to accomplish that would most likely involve switching to a tubular set-up). How does that impact the grand scheme of things? Very little.


    Resistance to acceleration at high speed is more a by-product of air resistance than wheel inertia.

    Wheel inertia has it's place.....but it's tiny.

    See I'm not doubting that wheel inertia exists, but the effect is very small.
     
  17. 53-11

    53-11 New Member

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    One more last question-

    If you look at most of the lightweight aftrermarket wheels in the 1500 gram range, how much lighter are they in the rim than a typical run of the mill 1800-1900 gram set?

    Answer: Rim usually weighs about the same. In fact the Kysrium SSC SL rim (440-460 grams) weighs more than a Open pro (420 grams) found on a heavier wheelset. Most of the weight savings of 1500 gram boutique wheels (Ksyrium SSC SL and AC 420's) are had by using microhubs etc. (not by saving weight at the rim)

    Wow.....what's weight lost in the hub going to do me?

    So much for the gains of a 300 gram lighter wheelset? Unless the weight savings are in the rim I'd don't even get the wheel inertia reduction (which is very small anyway )
     
  18. smartie

    smartie New Member

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    You can play with your placebo effect, Issac Newton played with physics and here so are we.

    Using 53-11's own research, your intended wheels are 14.2857% lighter than those you originally had (1750-1500 grams) and averaging it across both the front and rear wheel, and just for 53-11's sake we will forget about the wheel inertia gains for now as we do not know where the weight has been taken from and will assume it all comes from both skewer pins.

    Now the power you need to exert is the equation:

    P=W/t

    P = Power
    W = Work (your effort)
    t = Time

    We also know that a 50% lessening in weight gives 0.33% improvement in Power.

    So by our relationship of 14.2857% weight saving you would would have a 0.094% power benefit.

    Therefore to retain the same speed you can pedal with 0.094% less effort. Converselt you can exery the same effort and get to your destination 0.094% quicker.

    Q.E.D.
     
  19. 53-11

    53-11 New Member

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    We did the math over at BikeForums.net using Analyticalcycling.com's calculator. I forgot what the guy plugged in for watts etc, but the increase in speed of a SSC SL wheelset vs the identical aerodynamic, but heavier Elite was something like .00017 mph on flat ground and .005 mph faster in a climb (not sure what % grade he used)

    Not as fast as people think, but in a race the SSC SLs would be worth it.

    The SSC SL vs Elite comparison is valid for weight becasuse they are the same wheel with same aerodynamics but one is made with lighter materials and is therefore 200+ grams lighter.

    BTW, below is a picture of Pettachi's Dogma. Notice he has Mavic Cosmic Carbone wheels. Do you know how much those wheels weigh?

    Answer: His wheels over 2000 grams. LOL....he doesn't have any problems accelerating to 40 mph with these either.

    Aerodynamics of wheels matter more for acceleration and sprinting.
     
  20. smartie

    smartie New Member

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    What both our results show is that there is very little benefit in changing wheels purely for a weight gain unless you are going to a huge differential as per from a wheel made of lead to Carbon fibre (unless of course beating another competitor by 0.1 second is your goal as per the Olympic Pursuit).

    At this level, feel and comfort in pushing hard are probably the keys to your ultimate speed and having an "off" day would have more effect on your times than a few grams off your wheels (or any other part of your bike)

    You will also find quality of bearings, grease, tyre grippiness, pressures, road surface, and a myriad of other influences would also come in to play. But let's not go there.
     
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