We have a tandem Terra Trike that we bought used last fall, ( it is such a pretty red,) it had about 1000 miles on it, we put 300 on it before winter. It has the original ties it came with, which I think are Schwalb marathon tires. The tread on the tires looks quite worn, we are new to this trike stuff, not sure how to judge when the tires need to be replaced. I'm not sure what the tread on new marathons looks like so it's hard to compare them to new ones. I know they didn't do very well on our gravel road, especially if the road had just been graded, it was hard to get good traction going up hill. We ride about 1/2 mile on gravel before we get to a paved road. It doesn't seem to me that tires with only 1300 miles on them should need to be replaced so soon. How do I know when to replace the inner tubes? DH is blind, so if we get a flat on the trail , it's up to me to fix it. ( trying to avoid that since it is something I still need to learn.) Any suggestions are appreciated.