in Group Rides, Bike Trips, and Events

I dunno if this is the place to bring this up since I dunno if there are any road bike forums or other discussions for Mad area non MTB trails..

Anyhoo I am thinking of doing my first century (100 mi.) ride using the GD trail from C. Grove to Waukesha and back.

I did 60mi. on it a couple weeks ago. My longest ride this year and I plan to ride 70 - 80 mi this week.
Is that a good idea? To build up to it?
If there is any helpful advice for making a century ride as easy as possible or to help this rider so that he can do it from those who have, or any words of encouragement, please share.

I ride more west, south and northwest but this applies to all the longer rides I do.

Be mindful of wind direction and speed. It can make a big difference when you're out for a long ride. Comfort stuff is important. I can sit on Zoic liners I think they call "carbon" longer than any other shorts I have I believe is because they are thinner which might see counterintuitive. If you are going on a mostly unpaved route or bumpy route how supple your tires are adds up.

For food I carry some sports food bars but like to make a sandwich or two, bring fresh and dried fruit. Eating more normal or whole foods works better for me on long days and after the rides. Some like the Nuun (I think) tablets with caffeine. I'll tend to buy a caffeine beverage at a stop.

Rail trail riding can be blessing and curse for me. I can get hand and foot numb issues and more body pain on simple pathways more than rides with more climbs and turns. Quite often I do routes that combine the rail trails with other ridding or make loops instead of out and back. If you have a Ride With GPS account you can search out lots of century routes and build your own routes. Google Maps with bike routes selected helps make routes too. The "Gravel Map" site also helps me with routes.

For the wind direction and speed topic and going east, remember there is rail trail that goes south through Jefferson, Ft. Atkinson and Janesville. That could help you stay off of roads and cut headwinds.

If you are not aware of the club already, I suggest you check out The Bombay Bicycle Club. They have been around for a very long time and sponsor a host of local road rides. A link to their webpage is below:

https://bombaybicycle.org

A century is a huge milestone. Go for it!

I would agree that it’s preferable to ride the route in loop rather that out & back, and would suggest heading west, maybe towards Mt. Horeb and New Glarus with a mix of backroads and trail. The roads out there are sparsely traveled and the drivers are typically accustomed to seeing cyclists so they are pretty courteous. There’s also great food/drink options in both towns.

An out & back on the Glacial Drumlin would be so flat that you’ll never need to change your cadence or get out of the saddle. That can end up making your hands and butt pretty sore since you’re not changing positions enough to relieve any pressure points.

Lots of good advice. My 2 cents worth. Most importantly is nutrition. Make a point of stopping and eating something every 25 - 30 miles. You may not feel like you need it early on but it will sneak up on you later in the ride and will be harder to recover.
Second thing I would suggest is to quit riding the Glacial Drumlin out a little farther each time for training. By time you do the whole century you are going to be bored with the trail. Try riding the military ridge all the way to Dodgeville and back for a change of scenery if you want to stick with rail trails to avoid road traffic. That should be about 70 miles out and back depending o exactly where you start. Bonus points, there are about 8 miles of double track in Gov dodge that they allow bikes on. I do it on my gravel bike, guess it depends on what type of bike you are riding.
Another mostly rail trail ride with some road is to take Military ridge to Mt Horeb, roads to New Glarus the sugar river, ride that to Monticello and then back in to madison on the badger trail. I beleive that loop is about 65 miles.
Good luck