last tri in 83,
Much of your “pain” most likely has to do with pacing. This is very common for experienced as well as novice long distance riders.
There is a very real tendency to ride too hard or fast in the beginning only to discover this in the last half of the ride. This is where the suffering begins for those who have fallen victim to these urges to go fast or hard too early. These rides can often be termed “death” rides after they are over.
One feels great at the beginning and starts by riding fast. Over the course of the ride, as one begins to tire and as the effects of riding fast (too fast) in the beginning take their toll, one slows down over the remainder of the ride or works even harder to “keep” up with everyone else. This only compounds the problem and causes the “death” spiral. Ultimately, one can usually review the riding time for each quarter of the ride and see clearly how it progressively declined for each successive quarter of the ride.
What may help you more than anything else, is starting a little easier and keeping a lid on the urge to go faster when you know you can. You need to try and restrain yourself like this for the first quarter of your distance. This period will allow you and everyone else to get loosened up and comfortable with the pace and effort. Remember, its going to be a long day in the saddle. Its not a race, but a ride.
As the next quarter begins, if you desire, ease the pace up modestly making sure no one is working too hard. Remember, you still have a long way to go.
On the third quarter, if you are still feeling great, you may wish to simply continue at your current pace or to inch up the pace some more. This is okay, but the operative word here is inch up the pace, not jump up the pace.
Now you have reached the last quarter and you feel good and there is gas in the tank. You are ready to bring it home fast and hard if you feel like it and you will still feel great when you reach the end as well as later in the day and on into tomorrow.
So here is your pacing formula, 1st quarter easy, 2nd quarter moderate, 3rd quarter strong, last quarter fast if you like. After the ride, you will feel great! Now mind you, this all presupposes that you are mindful of nutrition and hydration. Ride smart and enjoy rather than carelessly/foolishly and suffer.
Plan your ride and ride your plan.
I hope this can help. Good luck.