Q: I have an old steel bike that I would love to do a modern drivetrain on. Do you have any recommendations? I was thinking Shimano Di2, maybe Dura-Ace, but Ultegra for sure.
My first thought is wondering if you’ve thought this all the way through. On a sheer cost/benefit analysis, is spending upwards of $3000 to upgrade your old bike versus putting the money into a new bike worth it? Personally speaking, I love Shimano Di2, but if history tells us anything, there should be a newer version coming out soon. So, if Shimano is your choice, you might want to hold out a bit longer to either buy the new stuff or get the old stuff at a discounted price.
On the flip side, I think SRAM eTap AXS might be a better choice, because it is wireless and the batteries are mounted on the derailleur. This means on an old steel bike you would just have brake cables that most likely run externally.
In my opinion, while not the most fiscally responsible, it could still be the makings of a clean build and a great balance of classic and modern. If you want to go crazier still, throw on some deep carbon wheels and Cane Creek eeBrakes for a bit more flair. I had a bike a few years ago like this and have been wanting to build one up again.