TallRider

In the past decade, I've wondered why off-center rims haven't become more popular for rear wheels. For people unfamiliar, OC rims have the spoke holes off-center, to minimize the effective dishing of the wheels, and have less difference in tension between drive-side and non-drive-side spokes. This allows a wheel that is less likely to have fatigue failure of non-drive-side spokes, or drive-side spokes pulling through the rim because tension is too high. OC rims seem to be similar weight to their symmetrical counterparts (some, like Velocity Aerohead, are lighter).

Possible reasons why these haven't become more popular:
* I've heard there may be trademark or patent royalties involved
* bike companies like to just order more of the same part. Witness most bikes using equal spoke count for front and rear wheels for decades, even though front wheels are under far less stress than rear.
* consumers don't like the asymmetrical look of off-center rims
* consumers don't care about the practical value of off-center rims
* there are technical concerns that limit the value of off-center rims (e.g., asymmetry makes them a bit less aerodynamic)
* the dish and spoke tension problem they are solving is fairly minor

Here's a visual of how OC rims affect dish, and gives you an idea of the asymmetrical shape:

OCR Rim_.jpg

Andrew R Stewart 

Two different stocking and manufacturing specs for what's otherwise the same situation. When you pay the bills you get to decide this. Andy

dabac

For the huge majority of riders who don't pop rear spokes often enough to be genuinely troubled by it, OC rims offer an improvement that doesn't provide any actual ride advantage.
Sometimes there's no difference in use between "good enough" and "better".

pdlamb

I suspect this has a grain of truth in it, although possibly not how dabac meant it.


Some huge fraction of bicycles bought are ridden for a season, put away, and never used again. Call it 90% are ridden 500 miles or less. Any rim with halfway decent spokes and machine build will last that long. OC rims are going to be more expensive to fabricate, source, stock (double your rim SKUs), and build with, just because somebody's got to turn them right way 'round if they're flipped. Of the 10% of bikes that are ridden further, some fraction (call it half) are ridden with no load and light riders. Since it's cheaper and just as good for maybe 95% of all bikes made, they're all made with centered rims. Inertia takes over for problem wheels. How many of us who have had problems with wheels started the replacement process with, "here's what it had when it was new, I want another one just like it?"

davidad

At a 2.5mm offset the NDS tension is 68% and at 0 offset it is 57% on a 700 series road wheel. Doesn't seem like enough to make a big difference.

FBinNY 

IMO - it's more about marketing than anything else. The benefits are too difficult to explain and so don't command a premium. So since the bike company can't expect a commercial benefit form OC rims, they don't see it as worth the bother.

Also, the issue isn't that bad, and it's certainly not smart to discuss issues of rear wheel dish when trying to sell bikes.

As a practical matter, I've been building trouble free wheels for decades, and I'm most definitely not the only one.

dbg

All of my bikes use OC rear rims (except for the IGHs). I liked the idea and definitely notice a difference when building wheels. I do it for longevity but have no clue if it helps anything.

nfmisso

An alternative is to use different diameter spokes on the DS and NDS. For example 2.0/1.7/2.0 on the DS and 1.8/1.5/1.8 on the NDS; with a standard rim result in very near equal tensile stress in all the spokes - and a very robust wheel.

FBinNY 

I've been doing that for 30+ years, but even without doing so, it's easy enough to get good service life as long as you don't use overly stout spokes.

As for any benefit, my feeling is that as long as a wheel lasts until killed by a pothole or crash or the brake track wears through, any longer fatigue life is meaningless.

fietsbob

cost.. people want to pay less, even bike forum writers..

so getting 10,000+ rims and using them for both wheels helps the bottom line..

OP wants to pony up the cost of a hand-built wheel for themselves, is welcome to do So.


...

Shimagnolo

After a friend told me about them, I tried one on my next build, and I am sold on them.
All 3 of my road bikes have either Velocity Synergy O/C or Aerohead O/C on the rear, (built by myself).
IIRC, on the one with Campy 10s, the NDS tension difference was 44% of DS with symmetric rim, vs 66% with O/C rim

TallRider

This is helpful. It sounds like the main reasons are
a) manufacturers want to minimize sku count, so build wheels with same rim front and rear: same spoke count and same dimension
b) the dish/tension problem to be solved is really fairly minimal with a well-built wheel

I'm 200# and built 32-spoke wheels (Sun M13II) 10 years ago for my main bike, and after many thousands of miles the wheel has stayed true, despite using the same butted spokes on drive-side and non-drive-side. (I should have gone for differential with stiffer spokes on drive-side).

I'm particularly interested in OC rims for building up really old 122mm-spaced frame with modern gearing range. I've spread dropouts from 126mm to 130mm, but am less comfortable with going from 122 to 130. Going with an OC rim and thicker spokes on the drive-side would allow me to use 126mm rear spacing with an 8/9/10-speed drivetrain without having a weak rear wheel.

Bill Kapaun

Obviously your wheels are "good enough". I've got 50 lbs. on you and built up the same rims 4 years ago with a lighter spoke on the NDS. Time will tell.

On spreading the dropouts-
Once you spread past about 6mm, the dropouts aren't very parallel. I was "eating" DS cones and think that might be the reason??? I think it actually put a bend in the axle when clamped.

Facanh

I think most Fulcrum rims are asymmetrical even the Fulcrum 7 and the wheelset costs around 150-180 bucks. DT Swiss makes a few asymmetrical rims too and i'm sure there are a few more I don't know about.

bradtx

Tallrider, IIRC the asymmetrical rear rims were designed to allow rear wheel dish to be closer to that of a 7S hub on 8S+ hubs. At the time there was concern by some that the amount of dish required to fit the wider free hub may result is a markedly weaker wheel. This concern has been largely erased and was done so fairly quickly, resulting in so few OC rims now available.

That written, I like the concept and I have an asymmetrical rim on my mountain bike and a new touring bike wheel set will be built with an asymmetrical rear rim.

Brad

Ronno6

Being another tall person (and girthier than I used to be,) I have several bikes with OC rimmed rear wheels.
I have used Ritchey Aero OC, in road bike applications; Velocity Synergy OC, Bontrager Fairlane OC on
touring wheels, and am preparing to build a set of wheels with Velocity A23 OC rear rim.
Whenever possible I have paired these OC rims with Ritchey Zero system hubs for wheels with almost NO dish, or at least they would have almost no dish if I didn't tinker further.
Most of my rides, road and touring, are older Cannondales with 126mm rear dropout spacing.
I KNOW that there are many who just cram a 130mm rear hub into their older 'Dale frames, and all is good, but I choose not to do that.
So, removal of 4mm of NDS spacer and redishing the wheel 2mm to the DS takes care of things.
So, the OC rims and Ritchey hubs really help.
I only wish I could find those hubs in 36°. Supposedly used on Jamis Aurora touring bikes for a couple of years, but I have never found any.... In those instances I use Shimano Ultegra hubs, which have a 5mm NDS spacer.

HillRider

I think this is the real answer. I have rear wheels with well over 35,000 miles of hills and rough roads and have never broken a rear spoke in over 30 years since I got my first wheels laced with DT or Wheelsmith spokes.

The OC rim solves a nearly non-existant problem for most riders and introduces manufacturing and inventory problems of its own. And, yes, good enough is really good enough.

TallRider

The main reason I'm thinking about an OC rear rim now is wanting to use a 122mm-spaced frame with 126mm-spaced hub with a modern freehub. Massive amount of dishing. I don't want to spread the dropouts too far (as Bill Kapaun mentions), and I'm basically doing the modern freehub-in-126mm-spacing as bradtx describes.

I agree with HillRider and others that for most riders and most situations (including myself) this is not an issue.

jimincalif

My bike came with Shimano RS10 wheels with an OC rear rim. The OC may or may not help, but the wheel has other issues.

Broke one NDS spoke after about 3,500 miles. Broke another about 250 miles later. I weigh between 205 and 210# and the wheel has just 20 spokes. They are pretty beefy spokes, even the nipples are oversized and need a non-standard spoke wrench. Both spokes broke right where they enter the nipple.

The problem appears to be the rim holds the nipple vertical, so the spoke bends out slightly where it exits the nipple and fatigues there.

Shimano doesn't make these spokes anymore. I've looked at getting other straight pull spokes and rebuilding it, but by the time I'm done it will be $70. Doesn't seem worth it as I will still have a 20 spoke wheel.