Ultegra R8000 crank spacer Does the Hollowtech II Ultegra R8000 crankset need to use spacers?
I just converted my bike from Praxis to Shimano (finally I have the whole groupset!). I had to replace the BB and cranks (duh) for this upgrade, I bought both brand new. Neither came with any spacers, I've installed the cranks and there was some rub on the front derailleur and the crank arm, which I've alleviated by turning in the front derailleur limit screw however it's awfully close.
Reading online there seems to be a lot of conflicting advice, this post says I need 3 spacers (2R, 1L), same with this post. Others say this crankset needs no spacers (3rd comment). My old Praxis cranks were wider and did have a single spacer on the drive side so maybe I should add one to the new setup.
But the question then is how many do I add, what size do I buy, where do I buy from. I've found 2 vendors (Amazon, eBay) that sell 2.5mm spacers for 68mm bb (my bb is 68mm), is that right? do they need to be Hollowtech II spacers? will any old one do?
Is the bike safe to ride without the spacers? it's going into the shop in a week to have the threaded brake reservoir screw removed &amp; replaced + new front caliper so I will only be riding it on the trainer this week, should I sack my training off for a week to wait for spacers to arrive and fit before putting any miles on it? I've done a test ride and the bike is riding well, alot smoother than the praxis (probably because those bearings where knackered) and all gears appear to be indexed and performing as i'd expect.
Shimano hollowtech comes in various sizes. The links you posted was for a mountain bike. Mountain bike crank spindles are for 73mm frames, so they need spaces for 68mm frames. 

Shimano road crank spindles are for 68mm frames. A BSA (normal British threaded) bottom bracket, doesn't need any spacers, you just thread the cups on and then put the cranks in. 

I suggest you watch a tutorial on how to put on a bb and crankset and make sure you follow the manufacturers torque and grease recommendations. When in doubt, get a local bike shop to fit it or take in some food and drink for them and ask them to have a quick look so double check your work. 

Also, Shimano have excellent online document on which have all of this information and more. I think your BB and crank should have come with instructions on all of this, unless they've stopped physically including.