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On my touring bike, about a year ago, I upgraded my tires from the low-end stock ones to better lighter ones. The weight gain was 205g per tire so 410g on the whole bike, plus a few grams on the tubes that were smaller ergo lighter since I reduced my section.

This made a huge difference in the reactivity, and the overall velocity of the bike.

Now for my racing bike, I intend to replace the wheels from the heavy stock ones to higher end ones. In addition to features such as stiffness and so, the new wheelset will be 410g lighter and I will gain a few more grams with a cassette change.

So weight-wise, the gain is very similar, will the feel be similar as last year? since this weight gain is also done on moving weight

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The short answer is that weight loss is probably not responsible for the improved the performance you noticed: bicycles.stackexchange.com/questions/7133/… –  James Bradbury Jan 6 at 12:09
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410 grams is a little less than one pound, not really enough to notice unless you're a small rider on a lightweight bike. What does make a big difference is switching to tires with a relatively smooth tread and supple construction (though possibly with higher pressure), as this greatly reduces rolling resistance. –  Daniel R Hicks Jan 6 at 12:52
    
I would say that lighter wheels will have less of an affect as lighter tires. When you put on lighter tires, the weight reduction is all at the circumference of the tire so has the largest effect on acceleration, but since some of the wheel's weight reduction comes from a lighter hub and lighter spokes, it will have a smaller effect. Though I doubt that the 400g reduction has much of a real-world effect at all. –  Johnny Jan 6 at 22:21
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4 Answers 4

This word is key to understanding what weight loss mostly helps with

"reactivity"

I think what you really getting at is that the bike accelerates faster. Humans are very low power engines so any change in weight can produce noticeable changes in acceleration. But they don't produce that much change in overall speed. You get to your top speed faster, but that's about it.

For "just riding around" this may or may not be important. For racing and riding in a group where you are making constant accelerations to stay with the pack, it can make a huge difference. This why racers obsess about weight for climbing/racing bikes, but focus more on aerodynamics for TT bikes. The primary limiting factor on total overall speed is aerodynamics, not bike weight.

There is some advantage to reducing "rotational" weight, but it's not that big if you crunch the numbers.

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Depending on your ability level this might be noticeable or it might not. Pro racers are often able to tell when as little as 100g is added somewhere on the bike (or geometry changes by .5 degrees for example).

With switching wheels the weight loss is felt in a couple different ways:

  • Overall weight On a bike that only weighs, let's say, 28 lbs (12,700g) a loss of .9 lbs (410g) is about 3% savings. If your bike weighed 100lbs it'd only be about 1%, so the impact of general weight savings is dependent on light the bike is already.

  • Rotational weight Heavier wheels are harder to spin up and slow down faster. Reducing that weight will reduce these effects. However, this comes mostly from the weight at the edge of the wheel (tires, tubes, rims), so if the weight savings are coming from a lighter hub, it will be less noticeable.

As usual, these all depend on the specifics of the wheel, the bike, and the rider and how all three interact. If your looking at dropping whole pounds by switching equipment I'd do it, but if it's just to save 50g, then it's probably not worth it.

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It should be noted that weight on the wheel circumference has exactly twice the effect as weight on the frame in terms of acceleration/deceleration, and exactly the same effect as weight the frame in terms of climbing effort. In general, weight anywhere has negligible effect on rolling resistance for a road bike (until the weight becomes a substantial fraction of rider weight). –  Daniel R Hicks Jan 6 at 15:42
    
You need to compute percentage gain based on the weight of both bike and rider. 1lb is much more significant for a 120lb rider than a 200lb rider. –  Fred the Magic Wonder Dog Jan 6 at 15:47
    
@DanielRHicks your right about the effects, but I think the OP was asking more about the effect of a weight change from the tires and wheels than the rolling resistance change of the tires compared to the rims. And Fred, I'm pointing out the general effect since we cannot assume all riders weigh the same. –  Aaron Jan 6 at 17:09
    
I was referring to rolling resistance due to added weight. The four resistances a cyclist is concerned with are rolling resistance, climbing resistance, acceleration resistance, and wind resistance. To about 2 decimal places weight only affects climbing and (to a much lesser degree) acceleration. –  Daniel R Hicks Jan 6 at 17:49
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Dropping wheel weight is the most significant place to gain performance. When upgrading my bicycles, I always purchase lighter/stronger wheels before upgrading any of the drivetrain components.

I do this because it requires a substantially greater amount of force to overcome the mass spread through the crossection of your rim/tire.

In fact, the governing equation for an infinitely thin ring (incredible approximation here) moment of inertia is

I = mr^2

where m is the mass of the ring and r is the radius.

To compute the energy, it can be substituted into the energy equation:

E = 1/2 m r^2 omega^2 where

omega is the d(theta)/d(t) term (angular velocity).

Since the mass of the wheel has a moment arm represented as the square of the radius, it has an exponential effect on the amount of energy required to change it's momentum, whereas static weight (frame/component weight) has a much less significant effect on the amount of force required to accelerate it.

So, yes, you will notice a big improvement in acceleration if you upgrade the wheels, same as your commuter bicycle.

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Don't think exponential is the right word here. –  A.E. Drew Jan 7 at 16:32
    
As has been shown elsewhere, an ounce of weight on the circumference of a wheel has exactly twice the effect on acceleration as an ounce of weight on the frame (and exactly the same effect as weight on the frame for climbing, etc). While perhaps this might be considered "significant", I have to feel is falls well short of "substantially greater". –  Daniel R Hicks Jan 7 at 17:05
    
@A.E.Drew Exponential is the correct word. Moment of inertia is a function of the square of the radius. Squaring is an exponent of 2. –  Tyler Jandreau Jan 8 at 14:03
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"Moment of inertia is a function of the square of the radius." But on a bicycle wheel, angular acceleration is inversely proportional to the radius. (And, contrary to what you believe, the term "exponential" does not apply to a simple squaring, but applies to a repeated application of a multiplier, where the number of applications is one axis.) –  Daniel R Hicks Jan 8 at 16:41
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Sigh. When you convert linear acceleration into angular acceleration you divide by radius. And despite your attempt to muddle it, the term "exponential" is not used, in either mathematics or general discourse, the way you want to use it. –  Daniel R Hicks Jan 8 at 17:36
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Ok, with lighter tires you might accelerate noticeably faster but you will also decelerate faster when you stop pedaling. This is because of the inertia of the spinning wheel. (inertia = mass X velocity)

If you follow close behind an all carbon race bike you notice that it jumps forward with every pedal stroke whereas a steel framed bike with heavier wheels is much smoother in its motion. This is because the increased inertia of the heavier wheels and frame carry the bike and rider through the uneven pulses of power created by the pedals.

If you cycle on the flats there is minimal gain from lightweight gear. Slightly slower acceleration to get up to speed but once you are there it requires the same energy to stay there (given identical aerodynamics and rolling resistance).

However if you are in the hills you have to lift that extra weight up to the top making a significant reduction in efficiency. (You lose much of that potential energy surfeit going back down the hill due to wind resistance and braking etc.)

Then why does that carbon race bike feel so fast on the flats? Probably because you just spent $5,000 on it!

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"Accelerate noticeably faster" is highly questionable. –  Daniel R Hicks Feb 10 at 19:47
    
See my last paragraph! It's mostly a question of perspective. –  user19614 Feb 10 at 19:49
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