Wire size for 28.5
Do you have the Owner's Manual? Believe it is in there. You can search the Archives for "wire size" and 28.5 to see an item about forestay size. It is 1/4" for the 1 x 19 wire. So the backstay would almost certainly also be 1/4". Typically the shrouds(side stays) are one size smaller or 7/32" in this case. But measuring is still the best way. I'll see my friend's 28.5 tomorrow if I can just remember my mic.