Tradeoffs…

[DismalScientist]

It also depends on where the weight is. Weight on rotating parts (i.e. wheels) is takes more energy to accelerate than weight on the frames, although there is more of a freewheel effect at speed with heavier wheels.

It also matters whether your brake pads are rubbing.:p

[TwoWheelsDC]

Most of the info on the interaction between weight/tires/grade/power is pretty easily found…for instance: http://bikecalculator.com/veloUS.html. I think things get pretty complicated when you move into the real world though, as you have to compensate for rider size/proportions, position, bike aerodynamics, drivetrain losses, etc, so getting precise calculations will always be problematic.

If my understanding of physics is correct, weight isn’t an issue when it comes to maintaining speed (on a level surface)…it only affects acceleration/deceleration. And the funny thing with skinny tires is that they are more aerodynamic, but have higher rolling resistance, so my understanding is that they are only beneficial at relatively high speeds. Not totally germane to your question, but kinda fun to think about.

[rcannon100]

@TwoWheelsDC 52873 wrote:

And the funny thing with skinny tires is that they are more aerodynamic, but have higher rolling resistance, so my understanding is that they are only beneficial at relatively high speeds.

You lie!!!

Oh wait, you dont!

Wider tires roll faster than narrower ones: Riders have argued for years that narrower tires – especially on the road – roll faster and are more efficient than wider ones when in fact, the opposite is true. According to Wheel Energy, the key to reducing rolling resistance is minimizing the energy lost to casing deformation, not minimizing how much tread is in contact with the ground. All other factors being equal, wider casings exhibit less ‘bulge’ as a percentage of their cross-section and also have a shorter section of deflected sidewall.

This is interesting:

I’m so confused now.

[dasgeh]

@TwoWheelsDC 52873 wrote:

Most of the info on the interaction between weight/tires/grade/power is pretty easily found…for instance: http://bikecalculator.com/veloUS.html. I think things get pretty complicated when you move into the real world though, as you have to compensate for rider size/proportions, position, bike aerodynamics, drivetrain losses, etc, so getting precise calculations will always be problematic.

If my understanding of physics is correct, weight isn’t an issue when it comes to maintaining speed (on a level surface)…it only affects acceleration/deceleration. And the funny thing with skinny tires is that they are more aerodynamic, but have higher rolling resistance, so my understanding is that they are only beneficial at relatively high speeds. Not totally germane to your question, but kinda fun to think about.

Ah, yes… HS physics is vaguely coming back now… Maybe some easy rule of thumb, similar to MPG for cars? Like how long my commute would take with bike set up X v. bike set up Y. (or more seriously, I bet you could model an “average” rider, and an “average” city (lots of stops) v. path (fewer stops) route and have a time for that average rider to ride that route. Obviously, that won’t be the time it takes most people to ride most routes, but it would provide a comparison and an idea of the tradeoff when buying that yummy looking dutch bike that’s on ridiculous sale at REI v. a speedy road bike.

[lordofthemark]

@dasgeh 52892 wrote:

Ah, yes… HS physics is vaguely coming back now… Maybe some easy rule of thumb, similar to MPG for cars? Like how long my commute would take with bike set up X v. bike set up Y. (or more seriously, I bet you could model an “average” rider, and an “average” city (lots of stops) v. path (fewer stops) route and have a time for that average rider to ride that route. Obviously, that won’t be the time it takes most people to ride most routes, but it would provide a comparison and an idea of the tradeoff when buying that yummy looking dutch bike that’s on ridiculous sale at REI v. a speedy road bike.

very interesting calculator.

Seems like going to the non-MTB tires, and losing a few pounds of my person, will do most of what I’m looking for. And increasing my wattage !!

[rcannon100]

There is a newer version of the calculator than the one linked.

Fiddling with the numbers, while weight is a variable, it is a weak variable (at least at 0 grade). What is the strong variable? Wind resistance…. the positions of your hands on the bar. Having your hands in the drops, or in aeros, makes a big difference over the more upright hands on top of flats.

So if I lose 10 lbs, I will only go 0.5 mph faster. Cool! Keep eating the ice cream sundays!

[mstone]

@dasgeh 52868 wrote:

In all this talk of “what bike to get”, there’s often an issue of tradeoffs between speed and weight, rider position and tire size (I feel like I’m missing one). Does anyone know of a scientific comparison of those issues? E.g. all else equal, 10 additional lbs on the bike requires 20% more effort to go the same speed. Or going from skinny to fat tires requires 10% more effort to go the same speed, all else equal.

Does that make sense? I want to suggest my brother-in-law, who’s studying aerospace engineering, do this as a project, but if it’s already out there…

There’s not any real good general data of that sort. Many of the old rules of thumb have been disproven by experimentation, but setting up reliable experiments is hard/expensive and there are too many variables to get compare data across disciplines. Someone spending $10k in a wind tunnel with a road bike isn’t likely to run the same tests on an MTB and a Walmart bike just for science, but that leaves open the question of how those bikes actually compare. E.g:

@TwoWheelsDC 52873 wrote:

If my understanding of physics is correct, weight isn’t an issue when it comes to maintaining speed (on a level surface)…it only affects acceleration/deceleration. And the funny thing with skinny tires is that they are more aerodynamic, but have higher rolling resistance, so my understanding is that they are only beneficial at relatively high speeds. Not totally germane to your question, but kinda fun to think about.

Bicycle Quarterly did a bunch of tire testing and shook things up with claims about tire size vs rolling resistance. The trouble is, most of the testing defined “skinny” and “wide” as something like 19 and 25 mm (IIRC; may have been a little wider on the top end, but nowhere near MTB sizes). There’s likely a point of diminishing returns, but I don’t know where that point is. Probably sometime before you start mounting SUV tires on your bike. The bigger tire is also going to be a lot heavier, the pressures will start getting real low, and in the real world you don’t find really supple high-quality 2.5″ tires, so you’ll be comparing apples and oranges. (A lot of other factors can make the width advantage disappear: a 23mm cotton tubular will outroll a 25mm armadillo.) I’m sure they’d love to test more tires, but they just don’t have the time/money to test every tire on the market. And they’d get bored. I’ve also seen some numbers on the acceleration issue, and the math suggests that the affect is pretty limited. It may be significant in being able to stay with a pack in a race, but over the long term it doesn’t matter. Except…if it feels faster, you may ride better. It’s really, really hard to separate the physics from the brain–and double blind bike studies are darn near impossible.

[Rod Smith]

My silver bike goes faster than my green bike. I have 28s on both so it must be the color.

[ebubar]

I’m reminded of a popular physics joke:

A farmer goes to a physicist to solve a problem he is having with his cow. The physicist comes back a week later and says, “I’ve solved your problem! First, assume the cow is a sphere in a vacuum…”

Basically, physics in the real world is pretty complex and we typically work in ideals. Quantifying all these variables with extreme accuracy would be pretty tricky, if not impossible.

[fuzzy]

@Rod Smith 52937 wrote:

My silver bike goes faster than my green bike. I have 28s on both so it must be the color.

I think its state of mind.

[Author]

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