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Old Skool
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Discussion Starter · #1 ·
I understand the theory behind rear rims with the spoke holes drilled off-center (OC). My questions are as follows:
  1. How much difference do these really make in reducing the dish of the wheel / increasing its strength?
  2. Why are these not recommended more often in threads concerning “bullet proof” wheels? People seem to recommend Deep Vs instead.
  3. Velocity makes the Aerohead OC. What other OC rims are available?
I am desperately trying to catch up on equipment advances after ten plus years out of the sport. Therefore, this question is meant more a discussion prompt than a call for specific advice regarding a specific wheel build. Thank you in advance for your input.
 

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wheelbuilder
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2,220 Posts
Stogaguy said:
I understand the theory behind rear rims with the spoke holes drilled off-center (OC). My questions are as follows:
  1. How much difference do these really make in reducing the dish of the wheel / increasing its strength?
  2. Why are these not recommended more often in threads concerning “bullet proof” wheels? People seem to recommend Deep Vs instead.
  3. Velocity makes the Aerohead OC. What other OC rims are available?
I am desperately trying to catch up on equipment advances after ten plus years out of the sport. Therefore, this question is meant more a discussion prompt than a call for specific advice regarding a specific wheel build. Thank you in advance for your input.
Other OC rims available.

Alex Crostini
Velocity Synergy
Other rims are parts of prebuilt wheels like the Hyperons, some Bontragers, some Ritchies and more.

The concept does work. On average, the tension is raised by 20-30%. It can always be an option for a heavier rider looking for suitable rims. The mains advantage Deep V rims have is the increased aerodynamic performance. On flast and rolling terrain the Deep V rims will be a little faster than shallower rims. Deep V rims (and similar) should be considered by more "light" riders.

When considering shallow, offset rims like the Aeroheads for a heavy rider, use 32 or 36 spokes in the front and 36 spokes in the back wheel. Increasing the spoke count and using lighter gauge spokes is always a better option than fewer heavier spokes.

-Eric
 

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A wheelist
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This doesn't answer the original question but here's what happened to my 4-yr old offset rims - Bonty Mustang ASYM mountain bike rims to be exact. This happened at almost every spoke hole. The sideways split was right along the inside support rib (could be seen in a hacksawed cross-section only) as the rib probably caused a stress-riser. No more OSB rims for me!

I think OSB rims are a solution looking for a problem. How many times do dished wheels fail because of their dish?
 

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Mike T. said:
This doesn't answer the original question but here's what happened to my 4-yr old offset rims - Bonty Mustang ASYM mountain bike rims to be exact. This happened at almost every spoke hole. The sideways split was right along the inside support rib (could be seen in a hacksawed cross-section only) as the rib probably caused a stress-riser. No more OSB rims for me!

I think OSB rims are a solution looking for a problem. How many times do dished wheels fail because of their dish?
You're making a pretty large assumption, here, that it was the fact that the rim had offset spoke holes that caused the failure. That, unfortunately is not in evidence, nor is there any reason to believe that is the case.
 

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wheelbuilder
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Mike T. said:
I think OSB rims are a solution looking for a problem. How many times do dished wheels fail because of their dish?
Wheels don't fail because of their dish. The reduced dish of an offset rear rim adds to the lateral stability of the wheel. It is not the most important part of making a good wheel, but it does have a positive effect.

-Eric
 

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alienator said:
You're making a pretty large assumption, here, that it was the fact that the rim had offset spoke holes that caused the failure. That, unfortunately is not in evidence, nor is there any reason to believe that is the case.
No other rims that I have ever seen (other than OSB) have an internal radial rib*. These cracks (about 20 out of the 32 spoke holes) were right along the edge of the rib. I've seen many perpendicular rim cracks (radiating from spoke holes) but never a radial crack. I'm sticking with my assumption. I ran my pics and assumtions past a ME and he agreed with my theory.

*I don't know for sure that all OSB rims have internal radial ribs.
 

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wheelbuilder
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2,220 Posts
Mike T. said:
No other rims that I have ever seen (other than OSB) have an internal radial rib*. These cracks (about 20 out of the 32 spoke holes) were right along the edge of the rib. I've seen many perpendicular rim cracks (radiating from spoke holes) but never a radial crack. I'm sticking with my assumption. I ran my pics and assumtions past a ME and he agreed with my theory.

*I don't know for sure that all OSB rims have internal radial ribs.
All OSB rims do not have the internal rib. The most common (Velocity Aerohead OC) does not. WTB has an internal rib in their non offset rim so the technology is not limited to offset rims.

-Eric
 

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Dishing and resistance to lateral loads

ergott said:
Wheels don't fail because of their dish. The reduced dish of an offset rear rim adds to the lateral stability of the wheel.
But don't wheels fail due to lack of lateral stability? Dishing decreases wheel strength to lateral loads from the right. A dished wheel is more likely to taco than a non-dished wheel.

If you compare an MTB hub with road hub, with few exceptions you'll see that they have the same distance between flanges - the difference is that the MTB hub has longer axle stub on the left side, moving both flanges laterally to the right to decrease dish. This better balances wheel strength to lateral loads from either direction (i.e. it trades off some of the strength to loads from the left to increase strength to loads from the right).
 

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Unsupported spans of spoke bed

alienator said:
You're making a pretty large assumption, here, that it was the fact that the rim had offset spoke holes that caused the failure. That, unfortunately is not in evidence, nor is there any reason to believe that is the case.
I don't think its that large an assumption. The Mustang rim has a relatively wide, flat spoke bed. Moving the spoke holes to the left increases the width of the unsupported spoke bed to the right of the eyelet, increasing the bending stress between the eyelet and the sidewall, and this is exactly where the cracking can be seen in the photo.

Many other OCR rims are V-shaped, where the sidewall angles in a more direct line to the spoke hole, so there is less bending stress experiened in the sidewall. As mentioned, still other OCR rims have a rib connecting the wider span of spoke bed to the outer rim wall, also decreasing the bending stresses.

The large bending stresses generated from spoke tension on wide, flat spoke beds is what generated the need for spoke washers, eyelets and sockets (double eyelets), to better distribute spoke loads and decrease localized bending stresses. Forming the rim into a V-shape, so that spoke loads are more directly tranferred to the sidewalls also decreases bending stresses. Simply moving an eyelet sideways in the spoke bed, without reinforcing or increasing support of the widened span of spoke bed, may indeed increase the likelihood of cracking the spoke bed.
 
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