I would agree that indented rims with recessed spoke holes are the strongest, however I would say that they are only necessary for certain applications when it comes to motorized bicycles, and in most cases I would say that they are over kill. Steel bicycle rims with heavy gauge spokes and strong hubs will be sufficient for many riders average daily use. In the case of the OP, it might be worthwhile for him to look into, since it seems that none of the other suggestions that have been given have satisfied him. Those type of rims are heavy due to their construction and I would also imagine they are relatively expensive to manufacture, thus expensive to buy. This is another example of an expensive solution that is unnecessary for the average hobbyists. Racers and others who are building heavy duty bikes or riding in extreme conditions may want to consider such a rim. Though mags are another option that are stronger than most spoked wheels, and I would recommend a mag wheel before a solid steel one, due to weight concerns and the mag wheel most likely being less expensive. For example, I am pushing about 4 horses and 3.5 ft/lbs of torque. I have chosen to build my own wheels, using a 130mm dirtbike drum in front and a 90mm moped drum in rear, both laced to 24" steel bicycle rims with 11g spokes. I am quite confident that for my application, these wheels will be strong enough. They are a bit on the hefty side, but not too heavy for the engine's power and since I am gearing the pedal side as low as possible, I believe that I should be able to pedal them easily enough when necessary. They are still lighter than a motorcycle rim, yet strong enough with the 11g spokes for my application. They are also 24" rims, so the spokes are shorter, making them even stronger yet. A friend of mine had a worksman steel front wheel with 10g spokes and a 90mm drum in front, and he rode quite hard over bumps a lot. After two years, that rim was still arrow straight even with the abuse he put it through. My personal advice to the op is to build his own wheels, as he can choose the rim and hub, and is likely to save money over purchasing a built wheel of the caliper he requires. Its exactly why I chose to build my own, not to mention better brakes, better axles, better bearings, better stronger components overall really, than any built bicycle wheel currently available.