Have no idea what kind of riding you are doing averaging that speed. Can only benchmark, but for your typical ride of 1-1.5 hours, I would typically only need to hydrate. If longer stuff, the rule I use is electrolytes every 30 minutes, carbs every hour. I've used gels as my carbs, and previously I've used Skratch, but I now prefer Liquid IV.
One other poster touched on this, but I think what you are doing the weeks prior to is going to be every bit as, maybe even more, important. Start taking potassium and magnesium supplements. Do it well ahead of time, magnesium can upset some people's digestive system. Also carry something for cramping, I've had Base Salts take me from having to be pulled out of the water (long swim) to being fine in a few seconds (literally).
All that said, my endurance racing stuff is limited to swimming, not riding - so hopefully if it does not translate, someone will call BS on my post. And I tend to be faster and be able to hold a higher heart rate than most people, so I was more prone to cramping than most, but also less reliant on refueling than most. For longer recreational rides with peers, say 2.5 hours, I've been fine with just a few liters of water (more for MTB, less for gravel and road), and a 200-ish calorie bar with a mix of simple and complex carbs. But, getting your salt levels up well in advance of your event is not going to hurt you, and may be a bit help, so I'd still do it.
