My chainguard broke on my bike the other week. I thought I could ride without one however the pair of pants that I wear have been getting caught up momentarily in the teeth of the chainring and now a small tear has started which has encouraged me to replace the chainguard.

I am riding a 2007 Trek 7200 hybrid with its stock Shimano TX-71, 28/38/48 crankset. I have looked online and it seems that selection for chainguards for a 48t chainring is very slim and most of them are 104bcd. If I measured the correct bcd on my crankset following Sheldon Brown's instructions then I have a 169-170bcd which says to me the 104s will not come close to fitting. Maybe I am measuring something wrong?

Is there a chainguard replacement that can be purchased for this size or is it best to purchase a new crankset (preferably with chainguard) with a more standard BCD? I have mostly been looking at aluminum options so that I will not have to worry about breaking another chainguard in the future.

I appreciate any help - I love biking and have been commuting exclusively by bike for nearly 5 years but my knowledge about components and such is virtually zero.