wheel balancing?

[jimmyhackers]

im not talking about spoke adjustment here persay. unless i am unknowlngly

more about offsetting an unbalanced wheel with weights as your would a motorbike or car wheel.

i get that at normal pushbike speeds and unbalanced wheel is virtually unoticable. but at 20-30mph+ even a gram out of balence could exert about 3kg (i think if google/memory serves me well) in unbalanced force.

my wheel alignment/spokes seem bang on. however with the bike suspended in the air i can feel the rear wants to move around a bit at high rpm likes its unbalanced. im thinking its something to do with the valves/weight offesetting things.

do halford balance wheels with weights? can they balance e-bike hub wheels?

thanks in advance
jim

 

[KTM Bike Industries UK]

20-30mph is normal speeds for push bikes for a lot of people.

You really don't need to worry.

 

[Gringo]

Your over thinking a problem that isn't there, if as you say " even a gram out of balance could exert 3kg at speed" what about everyone who has a speed pickup fitted onto a spoke ? my one is At least 10+ grams and I've hit the heady heights of 47mph without issue. I'm hoping to join the 50+ this year ( if I find a steep enough hill LOL )
If your experiencing any wobble or undulation as speed, it's most likley to be your rim out of true, not out of balance.

 

[jimmyhackers]

sorry if i wasnt clear. i was talking about the possibility rather than the reasons not to bother.

im not noticing any unblance under riding conditions so your answers are expected. its only when as i said its losely hung up from my ceiling without me on it to weigh it down and steady it it wobbles. granted the hub in this configuration should be traveling a lot faster than normal riding conditions. but its still out of balance.

shame is the home brew method of letting it sit in a level stand etc doesnt work as my bearings seem pretty dam sticky (ill ask about this in another thread)

http://dnr.louisiana.gov/assets/TAD/education/ECEP/auto/d/d.htm

thats the website (i know its for cars) it says an ounce (23g) goign at 60mph with exerts 7.73pounds (3506g) of wasted force per revolution.

not quite sure how that equates out at my top speed of 30mph. Probably a lot less. but its still a loss, and im trying to explore (see my other weird threads ) how many ways there are to cut them down.

when i "modified" my first car. my emphasis wasnt on more power. it was on lightweighting, handling, braking, mpg then power came a lot later in the cars life.

what my plan is (nearly any mans to some degree) to put a jet turbine "modded hub" in a shopping trolley "my bike". i find how i differ to most other people is that i want the shopping trolley ready, tested and overengineered for the possible power beforehand.

my plans is now a 48-96v hybrid/switcher thingy which means im going to be going possibly a lot faster than the stock 30mph so being out of balance may effect me in the future hence asking.

 

[morsmana]

1 if you are concerned with 'losses' friction is the number one by far. Pure wasted energy dissipated as heat. Your 'sticky bearings' will be like having a brake applied continuously. Could be wrong viscosity grease, too much of the wrong sort, misaligned when installed etc. This has to be fixed first.
2. A bike wheel can be considered to be a single disk. Car wheels are treated as two of more disks because of their width. The out of balance force is the out of balance mass times its radius times the square of the rotational speed. This is why you must balance statically first, then dynamically, and why the effect of out of balance is so speed sensitive. Your force at 30 is 25% of the force at 60. Look at a bike wheel - all the mass is at the outer edge. You could add a tiny mass to balance it first, but dynamic balance will be due to variation in tyre mass distribution. If you're that serious you could rotate the tyre to reduce the effect.....life and get one comes to mind!!

 

[morsmana]

Ps tyres do a brilliant job of absorbing any out of balance force!

 

[Deleted member 4366]

The forces on an out of balance bicycle wheel are not enough to bother anyone at 30 mph. If it still bothers you, you can easily balance it yourself by removing the brake so that the wheel can turn freely. The heavy side will hang downwards, so add a bit of weight to the spokè the opposite side until it balances. Use solder as a weight. Wrap a bit around the outer end of the spoke

 

[trex]

...
i get that at normal pushbike speeds and unbalanced wheel is virtually unoticable. but at 20-30mph+ even a gram out of balence could exert about 3kg (i think if google/memory serves me well) in unbalanced force.
...
jim

you are correct about the effect of unbalanced wheels at high speed.
The centrifugal force is calculated by this formula:
F = mass (in kg) * radius (in metre) * (square of angular speed in rad/sec)

for 1 gram on a 26" rim going at 30 mph (spinning at 400 rpm), F = 0.001kg * 0.3M * (400 * PI * 2 radians ^ 2 /60sec) = 0.53 Newton

You need about 10gr-20gr of unbalanced weight for it to become noticeable at 30mph. Of course the effect increases with the square of your speed, it won't be long before this force lifts your wheel off the ground.