A Tandem on a century with any form of hill is not an easy bike to ride. I know- I used to do one every year and my years training was evolved around this one ride. It's that training that you have to get right. My ride was In june so from February I was down the gym twice a week. From April it was extra evening rides aswell taking a hilly 30 mile route that we used as our marker for our our fitness. When we got to doing the 30 miles in 2 1/2 hours- then we were fit.-normally about a month before the main event.

But hills at the end of the ride are killers. Our ride had the worst 3 in the last 20 miles. Only a 1 mile stretch at a time but first came the constant 15%- Then the rutted trail broken 15% with 18% just at the end---Then the killer of 12 to 22% over broken bricks and Scree. I have seen grown 20 year olds crying as they pushed their solo bikes up these hills. Mainly because of the Muscle strains and Blood oozing from scratches from the number of "Offs" they have had on the ride.

So if you want to do Hilly centurys this early in the season- Start training earlier. It will still hurt but possibly not quite as much.