# Singlespeed & Fixed Gear - Does the front wheel count as rotational weight?

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.

05-04-05, 12:41 AM
Since your power does not go directly into the front wheel does it help acceleration as much, if any, if the front wheel is light? Just wondering since I just re-laced my front wheel with longer spokes using 3-cross instead of radial lacing. (I know the actual difference is just a few grams, but I'm curious anyway.)

Oh and I guess it's sort of fixie related because I put my spoke cards in the front wheel. :D

Dutchy
05-04-05, 12:52 AM
I'm not a scientist but I would guess that the front wheel is just as important as the back wheel. Considering both wheels spin at exactly the same speed this would mean that both wheels would affect acceleration equally.

CHEERS.

Mark

andygates
05-04-05, 05:00 AM
It spins. You have to accelerate it, just not directly. It still has rotational inertia, and yeah, a light front wheel and a light front tyre really improve your acceleration, deceleration and jump. It counts.

stevo
05-04-05, 07:26 AM
"Considering both wheels spin at exactly the same speed this would mean that both wheels would affect acceleration equally."

assuming, of course, you have identically sized/inflated tires and ride in a straight line.

Martyr
05-04-05, 07:47 AM
"Considering both wheels spin at exactly the same speed this would mean that both wheels would affect acceleration equally."

assuming, of course, you have identically sized/inflated tires and ride in a straight line.

yeah, well your pennyfarthing is a whole different kettle of fish.
in all other respects though, it was a pretty fair assumption dont you think?

stevo
05-04-05, 07:54 AM

yes, i believe your assumption is fair.

powers2b
05-04-05, 07:55 AM
Relative to the road surface the bottom of your wheel is stationary at all times.
The axle is traveling at the speed indicated on your bike computer and the top of your wheel is traveling at twice the speed indicated on your computer.

That ought to cook your noodle

Enjoy

Martyr
05-04-05, 08:00 AM

yes, i believe your assumption is fair.

hehe.
i tell you. once you've tried pneumatic tyres you'll never go back. they're a revolution you know.

captsven
05-04-05, 08:07 AM
Since your power does not go directly into the front wheel does it help acceleration as much, if any, if the front wheel is light? Just wondering since I just re-laced my front wheel with longer spokes using 3-cross instead of radial lacing. (I know the actual difference is just a few grams, but I'm curious anyway.)

Oh and I guess it's sort of fixie related because I put my spoke cards in the front wheel.
Changing spoke length would be negligible.

If you change to a lighter rim, tire, tube and Al nipples, the change could be huge. The area of the bike where weight savings vs. money spent (to achieve greater acceleration) gives you the best value is the outer wheel area. Of course the down side of a light wheel is durability and reliability.

I do not know what a "spoke card" is? Is it a card that rubs against the spokes to create that clicking noise? If that is the case, that would be a significant source of friction and would slow you down. The friction from the spoke card would be greater, by far, than having a slightly heavier wheel from longer spokes. It's like having a brake pad rub constantly.

Martyr
05-04-05, 08:10 AM
Relative to the road surface the bottom of your wheel is stationary at all times.
The axle is traveling at the speed indicated on your bike computer and the top of your wheel is traveling at twice the speed indicated on your computer.

That ought to cook your noodle

Enjoy

noodles nearly done.

i believe that only the centre of the axle will travel at the speed indicated on the computer.
and:
the top of the wheel only travels 2* the speed of the computer when the bottom of the wheel is not stationary relative to the road surface... is that right, or is it time for me to go to bed??

marty

stevo
05-04-05, 08:34 AM
"The axle is traveling at the speed indicated on your bike computer"

Since I dont have a bike computer, does that mean my axle is not travelling? I guess I'm not anyway since the the bottom of my wheel is stationary.

but seriously, if someone changes the rolling circumf. setting in the computer to a larger value, would that make him go faster?

powers2b
05-04-05, 08:37 AM
noodles nearly done.

i believe that only the centre of the axle will travel at the speed indicated on the computer.
and:
the top of the wheel only travels 2* the speed of the computer when the bottom of the wheel is not stationary relative to the road surface... is that right, or is it time for me to go to bed??

marty

Since the axle is not spinning the whole thing and everythig it is attached to (you and the bike) travels at the speed indicated on the computer.
When the bottom of the wheel is 'not' stationary relative to the road surface you are skidding.

nightey night

Enjoy

05-04-05, 08:37 AM
i believe that only the centre of the axle will travel at the speed indicated on the computer.

unless you have some different kind of hub, the axle (which might more properly be called a spindle) does not rotate; hence the entire axle travels at the same speed. on a flat surface, in a straight line of course.

following what captsven said, spokes would contribute very little to rotational inertia compared with rim/tire/nipples; that is, the stuff furthest from the center of rotation. spokes contribute to drag, although i don't know if there's a difference between radial versus 3-cross in this regard.

just curious, blasty, what made you decide to switch from radial to 3-cross?

bostontrevor
05-04-05, 09:15 AM
Yes, there's rotational inertia to the front wheel. It's a rotating system so by definition it has rotational inertia. The question in my mind is, is the energy necessary to change its rotation separate from the energy necessary to change its lateral motion?

I suppose it is given that a bike on the stand still requires energy bleed off (through braking or some other friction) to stop the wheel. In the usual case, I suspect that the rotational inertia would be hugely dominated by the intertia of the entire bike-rider system.

05-04-05, 09:16 AM
unless you have some different kind of hub, the axle (which might more properly be called a spindle) does not rotate; hence the entire axle travels at the same speed. on a flat surface, in a straight line of course.

following what captsven said, spokes would contribute very little to rotational inertia compared with rim/tire/nipples; that is, the stuff furthest from the center of rotation. spokes contribute to drag, although i don't know if there's a difference between radial versus 3-cross in this regard.

just curious, blasty, what made you decide to switch from radial to 3-cross?

For some reason, the difference between the front and rear lacings didn't settle well with me. I bought the wheels used so I didn't have much say to begin with. It did give me a chance to try my hand a wheel building. Now there isn't anything on a bike I can't fix myself.

Regarding the idea of weight counting more at the rim, yes I do agree that makes a difference in the rear wheel where your leg energy is directly accelerating that rotational weight. However, wouldn't the front wheel be more like "static"(?) weight much like a handlebar or saddle. Example, taking 200 grams off the rear wheel makes a noticeable contribution to the feeling of quick acceleration versus taking 200 grams off the saddle (and I conjecture, the front wheel).

05-04-05, 09:19 AM
Yes, there's rotational inertia to the front wheel. It's a rotating system so by definition it has rotational inertia. The question in my mind is, is the energy necessary to change it's rotation separate from the energy necessary to change it's lateral motion?

I suppose it is given that a bike on the stand still requires energy bleed off (through braking or some other friction) to stop the wheel. In the usual case, I suspect that the rotational inertia would be hugely dominated by the intertia of the entire bike-rider system.

Ahh, good point.

isotopesope
05-04-05, 09:21 AM
my axle stays stationary, and the hub rotates around it... i don't know what sort of wheels you weirdos are using.

Martyr
05-04-05, 04:42 PM
Since the axle is not spinning the whole thing and everythig it is attached to (you and the bike) travels at the speed indicated on the computer.
When the bottom of the wheel is 'not' stationary relative to the road surface you are skidding.

nightey night

Enjoy

like half cooked noodles: DOH!

i have had my sleep, and realise that that was probably the stupidest thought i have had for a while.

cheers

marty