Cycling related IT band syndrome

This is likely to be caused by one or both of the following... foot stability / pronation or poor engagement / use of glutes.

If you are beyond your twenties, I'd suggest that it will at least be partially caused by poor glute engagement. 

Go see a physio to understand what is happening and look at a long term plan.

An interim solution would be to foam roll - assuming the injury is not too acute - whilst at the same time, making an effort to stretch your hip flexors and glutes. 

Alongside this, work in some remedial exercises, such as squats, one-leg step ups (really focusing on form), glute raises, clam raises and similar, that focus on the activation of the glutes. You'll probably want to do some other core engagement exercises prior to those glute exercises to ensure you get the most from working your butt. 

But... if it is glute related, doing the above will make a tangible difference in a surprisingly short period of time. 

However, if it doesn't solve, or ease symptoms quickly, then its more likely to be foot related, so seek help around that. At least you've still got a fitter arse at the end of it either way!

I had this issue over about 6 months last year. It coincided with upping my milage and also the intensity of rides. Pain starting on the outside of the knee and gradually extending all the way up the outside of the thigh to the hip. The first hour or so on the bike would be fine then pain would generally get worse over the course of a ride (would notice it sooner when riding at higher intensity). It was never enough to stop me riding completely but was certainly uncomfortable and the pain would get worse after riding, it was particularly noticable when climbing or decending stairs.

Post ride foam rolling and stretching definitely helped also using "K-tape" when riding + ibuprofen before long/hilly rides helped me keep going for longer. It eventually dissapeared and has not re-occurred, I still keep up the stretching and foam rolling.

Foam rolling helped instantly reduce pain after rides but I think streching had the biggest impact.

Yes.  Cured with a few rounds of Sports Massage, a bike fit and post ride IT band stretches as part of warm down.

They still get tight after a big ride but not painful.

I did get it in my mid-twenties from running, stupidly tried to 'push through' and it eventually got so sore I couldn't walk... but even after it got this bad it eventually went after three or four months and didn't return, I was actually able to cycle without much pain at all but cut back on this too. I mostly swam and did strength exercises. 

I found there isn't really much you can do beyond not doing the activity that's causing it and a bit of ice to ease pain and inflammation. The advice I got from a physio was to avoid foam rolling if your IT is injured but there's not really a consensus on this as far as I know. If it's cycling that's causing it I'd just stop until it stops, it's really frustrating but the only way in my experience! Hope this helps.