urbanknight

Yeah, but for an extra 20 grams, it's worth it to me to just cross both sides of the rear wheel. I understand why crossing is almost unnecessary on the front, though.

waterrockets 

10-4

FormerBMX'er

Who said anything about weight savings? I've built 2X and Radial non-drive rear wheels.

Phantoj

Or a pushing force. Well, not really pushing, but a relieving of the tension on the forward-pointing spokes, so it's the same effect as pushing. Sort of the same idea as the bike "standing" on its bottom spokes.

BTW - no braking torque with rim brakes - that's why front wheels on rim-braked bikes can be full radial.

urbanknight

I was just quoting the average weight savings gained by radial lacing (about 10g per side on a 32h wheel). My only statement was that for such little benefit, I'd rather be safe and have both sides of a rear wheel crossed. Haven't broken a spoke yet. Not that I'm saying there's anything wrong with radial lacing either side of a rear wheel, just that I feel safer with them crossed.

edit: My logic is that the hubs is fairly firmly planted to its place in the frame, so the non-drive side gets some of the torque as well. No proof, just what makes me feel better, that's all.

roadfix

My very first wheel build, years ago, was a radially laced front wheel, simply because it was a no-brainer...

urbanknight

Yep, can't say I ever messed up the lacing pattern on a radial laced wheel.

waterrockets 

I'm pretty sure I could screw that up...

Pico

Rims brakes don't apply any significant torque on the hub. It's not even possible because the hub is on bearings so it is free to turn if any torque is applied (well it will take some torque to spin the hub and bearings, but it's only a tiny amount). The torque the brake applies at the rim is cancelled out by the force the ground is exerting on the tire so there is no net torque. The net result is a force on the axle, which is what slows the bike down.

Disc brakes are a different story, they apply torque at the hub so they do require radial lacing.

Wil Davis

?

- Wil

vpiuva

I've screwed up the radial side of a half-radial rear

urbanknight

Disc is on one side only, so it applies all the force to that side only. Mucho torque.

Eh, that's forgiveable. 10 Hail Hincapies and 3 Our Lances.

Chad's Colnago

Another benefit of radial lacing is it's quite easy, and fast to lace up.

Ligero

The length difference between 2x radial is usually around 6 to 7mm. So if you have 28 spokes laced 2x and switch to radial you took off a about 168mm of spoke. A Dt revolution will weigh about 5 grams including a alloy nipple in a 290mm length, so by taking off 168mm you removed a little over half of one spoke or about 2.5 to 3 grams. That is for the whole wheel not per side.

Reynolds 

But the disc is attached to the hub, which has spokes on both sides.

Phantoj

Same as a drive wheel, really. How much is transmitted over to the other side is dependant on the stiffness of the hub in torsion (pretty stiff!) and the stiffness of the other side spokes.

steaktaco

ah! just built up (or, rather, rebuilt) my fsa rd600s and I was wondering why the non-drive tension was so high compared to drive-side... I was skeptical but even though I still don't understand at least I know it's normal. thanks.

btw ot q does anyone think the middle (third) flange needs to have the highest tension? I kinda just winged it and the drive side ended up with the most tension.

urbanknight

The cassette is also attached to the hub, but it still experiences torque because it's on one side.

waterrockets 

Well, the tangential spokes approach the rim at a shallower angle, while the radial spokes approach the rim at a steeper angle.

Here's a chicken scratch I did a while back to illustrate. The red drive side spokes are 3x, while the green drive side spokes are radial. If you look at where they leave the hub flange, you can see why the green ones have a steeper approach angle. Of course this illustration is really exaggerated with the short spokes, but its easier to see that way. My illustration wheel also gets a little help from the radial side being head-in, so the spokes depart the outside of the flange. If you go radial non-drive, go heads out to give those spokes less of an advantage (raise their tension):

urbanknight

I did find an error in my calculations (I forgot to cut DT's weight for 64 spokes in half to make a 32h wheel, so my outcome was doubled) but my calculations still used different variables than you. I calculated this for a 32h 3 cross vs. radial wheel, in which case the difference in spoke length is about 12mm. 12mm times 32 spokes is about 384mm, which is equal to about 1.3 spokes. I also calculated it for DT Competition (a much more frequently used spoke) which comes in at about 6-7g per spoke according to DT's website. That comes to 8-9 grams per wheel.

Either way, it shows that it's an insignificant weight savings.