I have used Café press to make a couple of shirts in the past they aren't bad,
They are a bit $$$ and you don't own the rights to any design you submit.
but if you have a favourite picture of your bike it comes out very nice
It may seem like that, but it's not. There are hundreds of Harley-Davidson shirts out there, to be found online, at flea markets and bike shops alike. There are very few Triumph, let alone Rocket 3 shirts out there, just trying fill the gap. When was the last time you found an original Triumph shirt in XXL or XXXL. And hey, if you never buy a shirt, no sweat. And if you do, great. I hope you enjoy it!