Besides the living in a non-nudist world, folks like me (blonde or redheads) burn easily so have to use high SPF lotion to protect our skin. This sometimes results in fewer tan lines. This is evidenced by a certain someone in my non-landed group always ribbing me that I am so pale!!! ;)
Theres far, far more to nudism that laying in the sun. In fact I hate laying in the sun. Its massively boring. Any tan I get is incidental to whatever I happen to be doing. Ill wager most nudists arent sun worshipers, and dont care a lot about tans one way or the other.
Not all nudists are interested in getting a tan. I for one do not spend any more time in the sun than I have to and passed up WBNR rides the last two years because it was too hot and sunny. All of us live in a textile world and are required to wear some clothing from time to time. For me it is daily. I can't work in my yard while nude so depending on the weather I will be completely covered except face and hands to just a pair of very short shorts.
Do the Chicago ride, its an evening ride.
I'd suggest asking those people you think have tan lines. One of my early concerns were the nasty red lines left by tight or badly fitted lingerie which is a more dramatic disguring of the female body. When I asked one particular lady about her own marks, she admitted she should have better fitting underclothes and we spent a very comfortable couple of hours in similar discussions. Ask the right people and you'll have the better answer. I happen to avoid burning with a mixture of massage and tanning oils, plus some insect repellant which I apply regularly. This is often sensual and results in my penis being swollen. If anyone asks, I tell them what it is and most people are keen to try something out for themselves or be educated in protective matters which they should but don't always have experience of.