lol

i got a bit of 2" wide wood, measured the rim diameter 18.5" (but they 17"s????)
cut the wood to 18.5" then, as the rim is 17" i measured in 3/4" from each end to give me a 17" long bit, put a nail in one end, marked off several 3.5mm bits as i got a spreadsheet that says for a 17" rim ever 7mm or so is 1 degree. tied a bit of wire to nail, and a heavy nut on other end, held it flat against rim, and noted the mark where the wire passed.

both sides were about 11mm, which is 1.5 degrees negative on the spreadsheet.

thats how i done it lol