Join Date: Jul 2006
Location: Toronto (again) Ontario, Canada
Bikes: Norco Bushpilot (out of commission), Raleigh Delta
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Originally Posted by CPFITNESS
So what will happen if a 230 pounder rides a bike with 36 spoke single walled rims? Lets assume they are properly tensioned. Is this asking for trouble or can we assume they will at the very least be safe?
Contrary to popular belief, cycling stuff that is okay at 199.9999 lbs doesn't just immediately explode in failure at 200.0001 lbs, having said that, if you go back over the last 3 years of wheel threads you will find that a few rims keep getting recommended over and over. For those solidly in clyde territory, it's best to select one of those rims, which are all double wall, BTW rather then picking something else that may not work. If your buying a bicycle which comes with 36 spoke wheels and single wall rims, then you don't need to immediately replace them, but you need to watch them for common issues. Once a week or every 100 miles or so (whichever comes first), you need to wipe the dirt off the rims and carefully check for problems.
The most common failure for rims is cracking around spoke holes, this is most often found in cheap rims where the spoke holes are punched out and not then reinforced, then this is combined with high spoke tension. The punching process weakens the metal slightly around each hole, and the high tension then causes it to start pull the spoke through the rim, the first stage of pull through is to crack. Cheap rims that are low spoke count are most vulnerable to this, because they get the highest spoke tension. Higher quality rims have the holes drilled out, the drill is kept cool with lubricating oil and it doesn't weaken the metal around the hole. The ideal is a rim that is drilled and then a reinforcing ring is put around each spoke hole.
Double wall rims, have a reinforcing piece (sometimes more then one) that ties the sides of the rim together, this keeps the sides from splaying out (the rim effectively gets wider), if it splays out far enough the tire can blow off, although you should get cracking at the sidewall or brake rub long before it gets to that point. Because of the reinforcement, double wall rims are far less likely to splay out then single wall rims. Splaying is far more likely to be caused by someone putting insanely high pressure in the tires and keeping the tires at that pressure, so it puts constant force on the rim, then a heavier rider. For example 150PSI in a rim rated for 100PSI max.
The only other issue is when the spoke tension is not monitored and gets low enough that the rim is allowed to bend out of true to the degree that spoke tension can't pull it back into round, the only way to fix this to replace the rim.