Aching back

[vickster]

Right at the base of my spine, along the same area as where the elastic from your boxers sits.
I don't think there is one specific thing that does it as in my last comment I can't avoid hills where I live but whether it's steep hills or just your average gradients I get it regardless.
As for time, maybe only 15 minutes after, nothing bad but during the cycle it can get to a good 7-8/10

My money would be on tightness or inflammation around your SIJ, super common in cyclists, or if hurts when sitting possibly coccyx

Physio, chiropractor or osteopath depending on your choice of practitioner should be able to help, if it's really a 7-8 pain wise, get checked sooner rather than later, that's v severe

 

[Kajjal]

Right at the base of my spine, along the same area as where the elastic from your boxers sits.
I don't think there is one specific thing that does it as in my last comment I can't avoid hills where I live but whether it's steep hills or just your average gradients I get it regardless.
As for time, maybe only 15 minutes after, nothing bad but during the cycle it can get to a good 7-8/10

I would go to your GP to see what is happening. If nothing major it could be as simple as your bike setup, since it only happens after 20 miles of cycling.

I once put my back into spasm and bike riding was recommended. The first up hill nearly finished me off with lower back pain but after that it losened off and was fine. A relative of mine with lower back pain with a different cause was told under no circumstances to ride a bike and to do palates plus walking which works for them. Best to be sure.

 

[Mrs M]

Osteopath would be my first choice .
Hope you find some relief.