Bicycle assesment

I haven't rode with a speedometer in 5 years. I needed to install one for mileage. Since I have to extend my long rides, I need to be able to measure my distances. However I can now see my speeds. What I saw was not impressive. It was blowing pretty hard. I think these were the windiest conditions I have experianced ever on a bike. I hope that Hawaii will not blow harder. Anyway, I averaged 17. I think with my forecasted training, I can only improve. Lets say I don't improve, it is windy and because of the hills, I slow to 16mph. That puts me at 112/16 = 7 hours. That still leaves about 10 hours for a marathon and swim. 112/17 = 6:35. I was able to avg nearly 20mph for my only other Ironman.