Disc hub lacing - optimum pattern?

mfhor said:

Hi y'all:

I've just opened the boxes on the first pair of Shimano ISO disc mount hubs that I've ever intended to build up (all previous experience was on OEM versions of these, or Centrelock, or other manufacturers) and I notice they have a little lacing diagram of the top right hand corner of the instruction sheet giving the lacing pattern.

2 questions:

Is it worth using an OCR or similar to offset the dish on the FRONT wheel? I intend to use one on the rear.

The diagram shows the outside spokes LEADING on the front, so they take the braking force windup. Ok, I understand that. It also shows, and here's the rub, that the DRIVE (right) side should use outside trailing spokes, but the braking side (left) should use INSIDE trailing, leading to a lacing pattern I gave up years ago, i.e., non-mirror image.

Any thoughts, or should I look at the faq?

M "confused" H

Yes, on the use of OCR for front disc wheel. Are you planning to use Velocity Synergy? (I just finished a wheel using Velocity Synergy and Sapim spokes.... and it went together better than any wheel I have ever built... out of over 650 wheels so far.)
Yes, you should follow the spoke pattern diagrams for optimum results. However, I don't think using mirror image pattern would harm the stabilility and reliability of the wheel or any of it's components. It would be interesiting to ask the engineer behind the pattern what he or she was trying to accomplish.

For some reason it is hard to find detailed information on just which way the bends should face on a disc wheel.

Conventional (non-disc) wheel building says the bends should face inwards on the trailing spokes for a rear wheel. Reason being, when forward torque is applied the hub, the trailing spokes are transferring the hub torque to the rim, which will slightly straighten the trailing spoke where it crosses the leading spoke, and will actually pull the spokes towards the center of the wheel.

Does not make a difference which way the bends are facing on a non disc front wheel, as there is no torque being transferred from the hub to the rim.

This theory changes for disc hubs however, since braking forces apply a greater amount of torque then pedaling forces do (it takes way less time to decelerate a wheel then it does to accelerate it). You want the spokes to pull towards the center of the wheel when you are applying the greatest amount of stress, so for lacing disc wheels, leading spokes should be bend inwards.

Reversing the bend pattern from the left to right sides of a wheel will actually change the dish of the rim slightly when force is applied. In your example, when the disc brakes are applied, the leading spokes on the disc side (which are bends out) will pull the spokes away from the center of the rim (to the rider’s left). The non disc side (which are bends in) will pull the spokes towards the center of the rim (also to the rider’s left), which may result in the rim being pulled slightly to the left when the brakes are applied. Would the rim be pulled to the left very far? No. It would barely be noticeable, but why introduce any negative elements to your wheel when there is no noticeable gain in performance?

Another small argument to running the leading spokes bends inwards is in the event that the chain is derailled inwards too far and falls between the cassette and the spokes. The chain acts as a mini-buzzsaw on the spokes, and I am thinking if the chain is going to saw through some of the spokes of my rear wheel, I would rather it saw through the spokes that are responsible for acceleration, rather then sawing through the spokes that are responsible for stopping my bike. Yes, this is unlikely for anyone that has the skill to set up a rear derailleur correctly, but derailleurs have been known to bend during a wipe out...

Cheers,
Juba

daveornee said:

Yes, on the use of OCR for front disc wheel. Are you planning to use Velocity Synergy? (I just finished a wheel using Velocity Synergy and Sapim spokes.... and it went together better than any wheel I have ever built... out of over 650 wheels so far.)
Yes, you should follow the spoke pattern diagrams for optimum results. However, I don't think using mirror image pattern would harm the stabilility and reliability of the wheel or any of it's components. It would be interesiting to ask the engineer behind the pattern what he or she was trying to accomplish.

Ta for your reply. I'm going to use Ritchey OCR Pro Disc (friends with the local Aussie rep) and DT Competition. Funny, in Oz, Velocity suffers from the cringe we have about anything that's not imported - i.e., not good enough. 🙁 I wanted a disc specific rim, and have nothing against Velocity in general, have had good experience with their Razor and have resurrected quite a few cheap wheels with their budget rims mid-tour (Great Victorian Bike Ride, etc.) for overweight or over-powerful customers.

Ah Shimano. The inscrutable wisdom of the Orient. I'll swallow my pride and do it like they say, I think.

M "easily swayed" H