This confirms what I have been believing for a while. Most everyone tells me "it is all dehydration, take some salt tabs" etc. I picked up cycling 2 years ago. I've been averaging now 3-4 rides a week, around 120-170mi per week. I had plenty of opportunities to test the dehydration theory. It might have contributed some, but none of the level that it made a major difference. First months of cycling I would start cramping at the 25mi mark. Half year I would reach 30-35mi. One year and I extended my rides to 40miles. Today I can complete 60-100mi without cramping. My hydration hasn't changed at all, but my endurance after 2yrs of training did and cramping is happening at much higher levels of exertion.
The only one contribution I haven't tried is fueling. I very rarely carb load (unless we count all the beer/margarita carbs, which are plenty

) and I never eat while I ride. So now I am going to use this ride to test how much impact fueling has on cramping. I don't believe it will have a major impact but hope I could push a bit further without cramping.
Carb loading started yesterday, 500gr of carbs a day (potato, pasta, oatmeal, rice). No meat (vegetarian) and removed most fat. Aiming for 3L a day for hydration. Going with this till Friday. Pre-ride I will do candy to top off. Still need to figure out fueling while riding situation, I have never done it.
This is the first large group ride for me and it will be a mental challenge. I am used to ride with faster riders and always end up overexerting myself. I am betting this has a high likelihood of happening too. My personal reference is a ride to Portola, 60mi 2,600ft loop that I can complete in 3hr 35min moving time. This saturday ride is 68mi 3,000ft (?) and I know adrenaline will kick in and might get a bit too excited and try to beat that Portola pace. Best case I can push it a bit further and end up with a massive grin in my face. Worst case, cramps kick in around 3hr mark and I blow the ride. We'll see.
Now to finish this disgusting oatmeal bowl