Unbalanced wheels - why?

Acceleration when rotating is something like v^2/r, so if you go 60mph instead of 30, then you have
4X the force. Also, I'd venture to guess that perhaps car tires are more compliant in relation to
the wheel's weight so that they can hop more when out of balance.

Patrick said:

I've probably had at least a half dozen pairs of wheels over the years, and each and every pair
has been "unbalanced" (in the sense that car wheels are balanced/unbalanced). I'm talking about
quality wheelsets built by experienced builders - nothing factory made or wildly non-traditional.
I assume it just doesn't make much difference, as long as they're round & true (which they always
are). But I'm curious *why* it doesn't make a difference. I can really feel them bob up & down
sharply when I give them the old hand-spin. I would think that should translate into some handling
problems, but it doesn't. Physics explanation, anyone?

--
Lincoln Ross NOTE ADDRESS CHANGE: [email hidden]

Bicycle wheels are not balanced by the small extra weights as the car wheels are balanced. Thus, the
small unbalancies due to the valve holes, spoke reflectors, speedmeter magnet, inner tube or the
tyre or whatsoever remain there. But the loads on the wheel are quite different, wether the wheel is
rotating freely in the air without touching the ground, or when supported by both the bearing and
the ground, and also with part of the rider's weight dampening the vibrations.

Antti

Patrick wrote in message <[email hidden]>...

Quoted message said:

I've probably had at least a half dozen pairs of wheels over the years, and each and every pair has
been "unbalanced" (in the sense that car wheels are balanced/unbalanced). I'm talking about quality
wheelsets built by experienced builders - nothing factory made or wildly non-traditional. I assume
it just doesn't make much difference, as long as they're round & true (which they always are). But
I'm curious *why* it doesn't make a difference. I can really feel them bob up & down sharply when I
give them the old hand-spin. I would think that should translate into some handling problems, but
it doesn't. Physics explanation, anyone?

Not a detailed answer, but it's probably just a function of the mass of the wheel and the speed of
rotation. Cars have a LOT more of both. It does make a difference in the amount of vibration you can
feel on a fast descent, but typically not enough of a difference to translate into a handling
"problem".

SB

"Patrick" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I've probably had at least a half dozen pairs of wheels over the years, and each and every pair
has been "unbalanced" (in the sense that car wheels are balanced/unbalanced). I'm talking about
quality wheelsets built by experienced builders - nothing factory made or wildly non-traditional.
I assume it just doesn't make much difference, as long as they're round & true (which they always
are). But I'm curious *why* it doesn't make a difference. I can really feel them bob up & down
sharply when I give them the old hand-spin. I would think that should translate into some handling
problems, but it doesn't. Physics explanation, anyone?

Antti said:

Bicycle wheels are not balanced by the small extra weights as the car wheels are balanced. Thus,
the small unbalancies due to the valve holes, spoke reflectors, speedmeter magnet, inner tube or
the tyre or whatsoever remain there.

I found that the balance of my front wheel was greatly improved by adding a second speddometer
magnet. I also managed to maintain a much faster pace for twice the distance, so it seems that
balance is indeed very important.

--

David L. Johnson

__o | Arguing with an engineer is like mud wrestling with a pig... You _`\(,_ | soon find out the
pig likes it! (_)/ (_) |

"Antti" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

Bicycle wheels are not balanced by the small extra weights as the car

wheels

Quoted message said:

are balanced. Thus, the small unbalancies due to the valve holes, spoke reflectors, speedmeter
magnet, inner tube or the tyre or whatsoever remain there. But the loads on the wheel are quite
different, wether the wheel is rotating freely in the air without touching the ground, or when
supported

by

Quoted message said:

both the bearing and the ground, and also with part of the rider's weight dampening the
vibrations.

Antti

Patrick wrote in message <[email hidden]>...

Quoted message said:

I've probably had at least a half dozen pairs of wheels over the years, and each and every pair
has been "unbalanced" (in the sense that car wheels are balanced/unbalanced). I'm talking about
quality wheelsets built by experienced builders - nothing factory made or wildly non-traditional.
I assume it just doesn't make much difference, as long as they're round & true (which they always
are). But I'm curious *why* it doesn't make a difference. I can really feel them bob up & down
sharply when I give them the old hand-spin. I would think that should translate into some
handling problems, but it doesn't. Physics explanation, anyone?

I like Antti's explanation. You can choose the location of spoke reflectors, speedometer magnet, and
other items to mitigate the imbalance situation. I suppose that you could also put lighter or
heavier nipples at the appropriate balance points on the wheel since there are alloy nipples, 12 and
16 mm nipples, etc. However, I would not make the nipple compromise for the purpose of achieving
balance. David Ornee, Western Springs, IL

With three magnets you could have gone even further and faster...

"David L. Johnson >" <David L. Johnson <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I found that the balance of my front wheel was greatly improved by adding a second speddometer
magnet. I also managed to maintain a much faster pace for twice the distance, so it seems that
balance is indeed very important.

"Patrick" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I've probably had at least a half dozen pairs of wheels over the years, and each and every pair
has been "unbalanced" (in the sense that car wheels are balanced/unbalanced). I'm talking about
quality wheelsets built by experienced builders - nothing factory made or wildly non-traditional.
I assume it just doesn't make much difference, as long as they're round & true (which they always
are). But I'm curious *why* it doesn't make a difference. I can really feel them bob up & down
sharply when I give them the old hand-spin. I would think that should translate into some handling
problems, but it doesn't. Physics explanation, anyone?

Because spinning the wheel and noticing that one spot always ends down, while true, is just not
significant. A variance of, say, a gram is enough to initiate that effect but lost in the noise of a
complete bike/rider system.

Try a large spoke reflector on a light wheel. Spin the wheel with the bike in midair, even held in a
sturdy stand, and it will bounce all over hell. When you ride the bike, even that much "imbalance"
is hardly noticeable.

So "balance" your wheels if it makes you feel better but don't claim any great advantage from it.
--
Andrew Muzi yellowjersey.orgyellowjersey.orgOpen ↗ Open every day since 1 April 1971

Patrick Most riders average speed is under 25 mph which keeps the wheel rpm low enough that a small
imbalance in the wheel is hardly felt. What causes the imbalance is the insert at the seam where the
rim is assembled. A large imbalance can cause handling problems at higher speeds. My average speed
in races often excedes 30 mph ( streamlined recumbents ) and have done 100 kilometers at an average
of 35 mph. At these speeds a wheel imbalance is noticable and a source of fatigue. My method to
balance the wheels is to hang the wheel horizonal and look for the low side by eye against an
acurrate level. Just as a "rule of thumb" most wheels are balanced with about 4 inches of solder on
the valve stem side. For spoked wheels, wind it around the nipple. Or place it under the rim tape on
the inside. For further details your welcome to call. Steve "Speedy" Delaire 707 591 0915

Patrick said:

I've probably had at least a half dozen pairs of wheels over the years, and each and every pair
has been "unbalanced" (in the sense that car wheels are balanced/unbalanced). I'm talking about
quality wheelsets built by experienced builders - nothing factory made or wildly non-traditional.
I assume it just doesn't make much difference, as long as they're round & true (which they always
are). But I'm curious *why* it doesn't make a difference. I can really feel them bob up & down
sharply when I give them the old hand-spin. I would think that should translate into some handling
problems, but it doesn't. Physics explanation, anyone?

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