Originally Posted by
BCRider
It's from looking at the loading geometry of the spokes. I'd have to draw up some charts to show you but it comes down to the torque multiplication due to the angles involved. A tangental load is running near 90 from the axle to the hub hole and then to the spoke. A radial wheel is running a zero angle that under torque is going to flex to a measurable but small angle. The leverage angles the torque is working with are acting to multiply the resulting tension load on the spokes to many more times what they are required to endure with a tangential setup. Also since the radial angle is zero (as for inline) the multiplying factor is infinite at first and only comes down as the hub torques around within the lacing patter to produce a small tangential angle and the spoke takes up that extra load.
NO! The wind-up and angle is CAUSED by the torque from the hub, it doesn't GENERATE the torque or the increase in tension. What happens is a dynamic sequence:
1. torque is applied to hub
2. hub winds up
3. flange pulls on spokes
4. spokes increase in tension... up to the point where they even out the torque
What happens is ALL hubs will wind-up until the increase in tension equals the applied torque. The exact
amount of wind-up then depends upon the tangential-angle of the spokes coming out of the flange and their tension. So lacings with exactly 90-degree spokes relative to flange will have the least amount of wind-up. On large-flange hubs, this can be 3x, and on small-flange hubs, 4x. Lower crosses like 3x, 2x, 1x, will result in
more wind-up for the
exact same increase in spoke-tension. It's the torque that causes the wind-up and tension-increase. But that tension-increase is the same in all cases and comes from the force applied at the pedals.
Originally Posted by
BCRider
So even if the spokes CAN handle the locads of a pure radial laced rear wheel there is going to be some windup and release in the all radial system rather than a crisp and far more flex free link in the tangential setup between the hub and the tire contact patch.
Basically if you lace up your drive side radially then you're setting up a situation where the torque has a lot stronger leverage ratio and the spokes are going to see a tensile buildup many times more than they would in a regular tangential arrangement. How much? I'm not sure without doing some serious head scratching and would need some numbers to play with. But I have no doubt that it would be very significant.
Here's a good start:
1.
250 lbs = 114kg = maximum total-force on pedals for Olympic level track-racer (use 1/2 that for most arm-chair racers here)
2.
170mm = 0.170m = crank-length
3. 114kg * 0.170m =
19.38kgm torque at bottom-bracket
4.
0.288 ratio = 52x15t = gearing used for 100% all-out sprint
5. 0.288 * 19.38kgm =
5.58kgm = torque at rear-hub
6.
38mm = 0.038m= diameter of rear-hub
7. 5.58kgm / 0.038m =
147kg =
total pulling force on spokes at hub
Note that this force on the spokes at the hub is the same regardless of the lacing. That's because the force at the hub comes from the force at the pedals, through the crank, through the gearing, to the flange. Now, let's look at how this total force is distributed amongst the spokes:
32-HOLE 4x/3x/2x
32h /2 =
16 = number of pulling spokes
147kg/16 =
9.19kg = extra tension added to each pulling spoke
120kgf = initial tension
9.19/120 =
7.7% = increase in tension on each pulling spoke from Olympic-class sprinter at maximum-exertion
32-HOLE 0x RADIAL
32h /1 =
32 = number of pulling spokes
147kg/32 =
4.59kg = extra tension added to each pulling spoke
120kgf = initial tension
4.59/120 =
3.83% = increase in tension on each pulling spoke from Olympic-class sprinter at maximum-exertion
The thing with radial is that ALL of the spokes becomes pulling-spokes on a rear wheel. What we're talking about here is torsional rigidity. That is, the relative rotation of the hub relative to the rim when any amount of torque is applied to the rear-hub. It doesn't have anything to do with wheel-strength, stiffness or durability. It does have an impact on the "feel" of a rear-wheel when you torque on it. But if you're smooth and have an even pedaling-style (like a track-sprinter), you won't even notice that the rear-wheel is radial or crossed. Gee, I wonder how I know this...
Originally Posted by
dabac
So everyone is saying, and I don't deny the theory. But given the extreme rarity of people actually building and riding radials all we actually can say is "bad in theory". Unless tested or properly calculated we don't really know if current materials would actually let us get away with it. What we do know, because it happens with some regularity, is that it's possible to rip a hub flange apart with too high spoke tensions in a radial.
Exactly, that's the only issue we're really talking about here is hub-durability with radial-lacing. You really do want to get a hub with lots of meat on the flange to handle the outward-pull of radial-lacing. And if you want stiff wheels, you want radial-lacing. Check out the stiffness wheels here:
Damon Rinard - wheel-stiffness test data. Notice the effect of heads-in vs. heads-out radial-orientation on wheel-stiffness.