LeoZ

I'm planning to buy some AMClassic 350s just had one question I was hoping someone could answer preferably a physicist...

Does having lighter wheels mean you equally sacrifice rotational-inertia of heavier wheels for equally greater acceleration of a lighter wheels?

Obviously the lighter you are the greater the acceleration ...F=ma...but on the same token can you say that heavier you are, the more inertia & momentum and thus less affected by resistance forces...i.e more easy to maintain constant speed?

More to the point, does being light mean you gain faster acceleration equally as you lose the ability of the ease to maintain constant speed?

I'm only 63kg ~ 140lbs
Help me!!!

531Aussie

did you see the inertia/stiffness/aero study?

https://www.rouesartisanales.com/article-4934445.html

merlinextraligh

If you're riding on dead flat terrain, and only have to accellerate once, and then never change speed, put two great big flywheels on your bike. (hence the guy who used a weighted disc for an hour record on the track.) Otherwise lighter wheels equal faster.

kirbyx

When you are accelerating, you will do be doing work to do two things;
1. Increase the linear speed of you, the bike, its wheels, everything.
2. Increase the angular speed of your wheels.
You will have to do more work if the linear mass (measured in kg) of your bike is greater...
You will have to do more work if the angular mass (measured in kg.m^2) of your wheels is greater.

Hmmm.... angular mass;
Imagine that you have two wheels that are exactly 1 kg each, ignoring spokes.
Wheel A has a hub of 0.25 kg and a rim and tire of 0.75 kg. -->greater angular mass
Wheel B has a hub of 0.75 kg and a rim and tire of 0.25 kg. --> less angular mass
Wheel A will take considerably more work to accelerate than wheel B.

Assuming that you are riding on level ground on a smooth pavement, the size and shape of two bikes are identical, and the area of contact between the road and tire are identical, then the linear mass and angular mass of the bike is as near as dammit irrelevant once one has constant speed. For greater acceleration (speeding up and slowing down), have a light bike and wheels with light rims and tires.

Note... there is almost zero aero advantage to gained from bladed spokes.

More (from interview with MIT cycling team in Bicycling mag)...
WHAT'S YOUR SECRET TO TTT SUCCESS?

Ariel Herrmann, M.S., '06: We've realized that the team time trial isn't about power; it's about efficiency. In a 15- to 20-minute race, it's hard to increase power output by 5 percent, but increasing efficiency by 10 percent isn't that difficult.

THE WIND TUNNEL GIVES YOU A BIT OF AN ADVANTAGE OVER YOUR COMPETITORS.

Cote: Well, it's not like we hang out there at night figuring out whose sideburns have less drag. It's not so much using the wind tunnel as it is being able to understand and apply the information we get. We've learned that your bike accounts for only 15 to 25 percent of your overall drag; 75 percent of how fast you go is determined by how your body gets in the way of the air. But there's a push and pull between aerodynamics and power-output efficiency. We look at the biomechanics and the power output, and then we say, "Okay, that looks good aerodynamically, but you can hold it for about 30 seconds and we need 30 minutes."

ANY OTHER TRICKS OF THE TRADE YOU'D CARE TO SHARE?

Cote: Most people don't realize that a nonaero helmet creates four times the drag of a nonaero wheelset. So you can spend two thousand dollars on a wheelset, or spend two hundred on a helmet and be faster. How you put your race number on matters more than having an aero wheel; today, we glued on our numbers to get them to fit flatter. Then there's water bottle placement: On a round-tubed frame, having a bottle on your seat tube is more aerodynamic than not having one at all, and it's much more aero than putting it on the down tube. And wearing gloves in a time trial will slow you down more than using a nonaero front wheel.

donrhummy

I would assume that the difference is not just weight but also aero (and as mentioned above stiffness). So if you had a super-light wheel that wasn't super aero and a super-aero but heavier wheel, on flat ground you might end up doing the same work over a long distance.

rruff

No, having lighter weight wheels will help your acceleration (and deceleration) very slightly, and will *not* inhibit your ability maintain speed. Inertia doesn't enter into it when you get to a steady state. For maintaining speed the W/CdA ratio dominates... power divided by drag. So, if you want to maximize speed you want to minimize aero drag... and the lightest rims are not usually the most aero.

I'm not a physicist... but I am an engineer.

bbattle

To answer your questions, yes.