Physics of crankflips, hicktriples ect...(Torque) 125's vs 137's


From what I have read since I started unicycling, 125s flip faster than 137s (or shorter cranks flips faster than longer cranks). Why would 125s flip faster? I’m no maths wizard but I was told at AUS Uninats that you could get more torque out of 137s.

I looked at this video later on to see what torque actually is. It is a little confusing as I haven’t learnt about all this vector stuff.

What I have gathered from it is that the distance vector (length from the pivot point) X newtons (force) is the amount of torque. The more torque, the faster the wheel spins right? Below I drew up a diagram of a 137mm moment crank with mathematical symbols and calculations.\

Torque = Force (how hard the cranks are kicked/flipped) X Distance (length of the cranks). In the diagram the distance is 117mm and lets say the force is 10. So the torque here is…

10 (force) X 117 (distance) = 1170

The torque is 1170.

If we were using a 125mm crank…

10 (force) X 105 (distance) = 1050

The torque is 1050.

The 137mm crank has more torque meaning it will flip faster, but if we put this rule into a real life perspective, would we be able to apply the same amount of force to different crank lengths?
If we can than 137s flip faster. If not then…?


Just because have more torque, does not mean you can spin faster. The 125’s can theoretically spin the WHEEL faster because the distance the pedals have to rotate. The smaller the circumfrance ofthe pedal “circle” (I don’t know what else to call it =P) the less distance the pedals have to travel. So for example, say you have to push 125’s down 10cm to execute the crank flip. The circumference of their circle is only 30 cm. But on 137’s you still only push down 10cm, but the circumfrance of what the needed distance of rotation has now increased. So the PEDALS them selves may be moving AT&T the Sam speed, but the wheel does not.

P.S. I’m sorry if this first make any sense but this is how I see it =P

more torque = more linear velocity. But the velocity of flip is angular velocity that is equal to linear velocity/radius. So, with longer cranks more torque but more radius.

. . . I see a lot of people getting velocity and acceleration mixed up

the more torque you have, the more ACCELERATION you have. . . NOT velocity!!!

and because there is no resistance other than momentum (and bearing friction, but if that’s a problem, crank size is the least of your worries) when you jump off the ground, the acceleration doesn’t matter so much as the maximum velocity you can spin the wheel with the cranks.

the smaller the crank, the faster you can spin them, less distance to travel as mentioned earlier.

obviously there are limits, make the cranks too small, oh lets say 65mm freestyle cranks, and yea, you may have trouble getting the cranks up to speed before you take your feet off

. . . also I feel as though a piece of my life has just been stripped away from my very soul . . . . go ride and stop worrying about it.

You know that with crank sizes, the distance refers to the center to center distance between the pedal and hub interface, right?

torque is what you want when climbing hills. that is what makes ling cranks good.
smaller cranks have less mass, thus less force is required to push them one revolution.

which is the effective distance the force is applied at.
more torque can be applied at a distance of 137mm, say 100 lbs of force=137 lb x mm , 125mm cranks would output 125 lb X mm

but that doesnćt really matter with 125 mm cranks, the comfortability level of the rider is generally higher and more force can be applied to the seathandle to counteract a greater amount of force at the pedals. the effectiveness of a crankflip also depends greatly on the amount of weight at distance (per say) from the axle, 137 mm cranks weigh more.

125mm cranks are harder to land tricks on too. especially tricks where the wheel is moving, or jumps in general. 11 sets are very hard to land on 125 compared to 137s in my experience.

anywhere you see force vector in all of those fancy physics language, just delete Vector from your mind. it is a general personćs common sense if it SEEMS like it would make it spin faster, it probably does, if it SEEMS to make it spin SLOWER it probably does.

EDIT ‘’’ I am a civil engineering student (senior) and I bet if you searched for moment it would be easier to come up with a good understanding of the torque concept, it is the same thing. moment is what all my engineering classes call torque

I wasn’t arguing against that. But the first post has the effective distances adjusted for the distance from the end of the crank, which isn’t necessary.

Do your legs have accelerometers in them?

Does your brain do physics calculations while you ride?

How will your riding change based on this knowledge?

Keep in mind that you’re analyzing but one component of a very complex system (rider + unicycle)… and the formulas we’re seeing are simple approximations of that component. Without doing an error analysis, the numbers you’re seeing here are meaningless.

The best advice was posted by juggleaddict… just ride.

YES. my legs have acceleroscopes in them (they can detect but not measure acceleration)

YES. i think about physics constantly so it doesnt really stop when im riding.

NO, you don’t.

He asked if you do calculations while riding.

Longer cranks weigh more plus the pedals are further away from the axle, both increasing the wheel’s inertia, and therefore harder for it to change speed. IMO the increased leverage more than compensates for this, for starting the flip. Since the longer cranks have more Q-factor they cause the wheel to wobble more @ higher RPM’s.

Shorter cranks have less Q-factor but their shorter distance conversly gives the wheel less inertia, each making the wheel spin slower and faster respectively. Again IMO the Q-factor has the greater effect of the two and w/ this set-up the wheel would spin @ a higher RPM.

Overal: longer cranks might make it easier to learn one flip, but I bet doubles, tripples, etc. would be easier w/ shorter cranks, but then there’s skobro’s point that they’re harder to land on.

Edit: at some point the ease of starting a flip would be more valuable than the speed of the wheel. ie 100’s might be harder than 125’s which whould be easier than 150’s (or maybee even 137’s).

ok well i will restate that i do think about and do small calculations in my head while i ride. and by acceleroscope i mean that my legs can sense acceleration. for example if i were to swing my leg really fast i would feel, or sense, the acceleration. which is what an acceleroscope does

Oh, my. I read through all of this and just hope that we can all at least agree that, regardless of the length, force, torque, and units, the magnitude is always 768.

And there is Harper for the win. If there is anything in this thread that makes sense, it is 768.