InTheRain

I have a few wheelsets:

1. Mavic A-319, 36 spokes, shimano LX hubs
2. Shimono Ultegra 6600 (wheels & hubs), 20R/16F spokes
3. Mavic Open Pro, Ultegra hubs, 28 spokes

The Mavic A-319's are on a touring bike. The Ultegra 6600 are on a 17 lb carbon fiber road bike. Open Pros are a spare set of wheels.

I have never broken a spoke or had the wheels go out of true in 3 years of riding. Most of the road conditions that I ride on I would rate as good to excellent. I am a heavy rider (225 lbs) and I thought that I would have problems by now with the low-spoke count wheels. The salesperson at the LBS did not have any concerns with the low-spoke wheels and said to me that he expected that they would be every bit as strong and durable as the 28-spoke Open Pros.

What do you think? Are the Ultegra wheels just as strong/durable as the Open Pros? I know that the A-319's are the strongest of the bunch just by the sheer weight, number of spokes, and design of the rims. I've always been under the impression that the number of spokes was the most significant factor in determining the strength of a wheel (assuming that the quality of the build is constant.) Am I wrong? And I'm talking about reasonable quality wheels... not the type you would get on a department store bike.

Should I be worried at all about the 20R/16F spoke count wheels? They have been fine for this long.

oldschoolsgoose

I am not familiar with the type of wheels you have, I do different type of riding. The spoke lacing pattern, has a factor in strength. Radially laced, mainly looks, 3 or 4 laced are what I use, but again I do different riding.

dabac

First off you need to be a bit more specific about what you mean with "strong". Is it durability or lateral rigidity? These two characteristics can end up in conflict.

And, as always for assembled units, there is no single component that alone determines the strength/durability of the finished product.
There's a balance between rim rigidity, the spoke tension the rim can take before collapsing into a taco, the spoke tension the rim can take before the nipples pulling through, the spoke tension the hub/rim configuration will allow for DS/DNS, the stretchiness of the spokes and so on.
One of the few things that just about never is an issue is the sheer tensile strenght of the spoke.

Durability is mainly about keeping the spokes tight, but not at the cost of collapsing or breaking the rim.
A wheel with a high spoke count but a radially soft rim can be less durable than a wheel with a low spoke count but a radially very rigid rim.
A wheel with a high spoke count but a radially soft rim and butted spokes will be more durable than the same rim laced with regular spokes.
a wheel with a radially very rigid rim can have good durability even with regular spokes.

Main issue with low spoke count wheels tends to be that if you pop a spoke they tend to go more out of true than their multi-spoked counterparts. For my 32-spoke commuter losing one is pretty much a non-issue in terms of rideability.
On a secondary note it does put more stress particularly on the nipple/rim interface, which has to be designed accordingly.

blamp28

Dabac said it well. The only thing I would add is that an assumption that build quality is consistant can only be made if you know the builder's record for this. I never assume a wheel is well built and always check for balanced and adaquate tension. These two factors are the most important as far as the "build quality" component if we were to assume equivalent components. I realise you probably know this but it is not at all uncommon to assume a consisten level of build quality where it may be lacking. A lighter rider can get away with such an assumption and is not as likely to ever know the diference. As a heavy rider myself, I have found a real value in getting my wheels as close to perfect as I can.

AEO

higher build quality required for wheels with fewer spokes.
or conversely, you can get away with a poorer build quality when using a wheel with more spokes and a lighter load.
If the wheel with higher spoke count is loaded up enough, be it heavier rider or more rugged terrain, it can easily show signs of poor build quality.

davidad

How many miles have you put on the Ultegra wheels? At your weight I would say that you are lucky not to have some problems.
I don't like the rear freehub. The axle support is niboard on the drive side. It is worse that a freewheel hub.

Dan Burkhart 

Shimano puts no weight limit on any of their wheels, regardless of spoke count.

MrCjolsen

I broke a spoke on a 36 sp wheel, and didn't even know until I put it on the stand for a periodic truing.

bikejack

The Rims.

The bike hangs off the rim via the spokes.

I've had less trouble with strong rimmed low spoke count wheels than light rimmed 32-36 wheels.

Kimmo

Has Shimano ditched their superior freehub design?

Why on Earth would they do that?