Miradaman

Gonna be wrapping the handlebars on my old Trek. How clean do the bars need to be? There's 30+ years of old adhesive on them that's hard to get off. I scrubbed with GooGone and steel wool and got 90% off but there's still some thin patches here and there. Does this make a difference?

Moe Zhoost

It probably will not make a feel-able difference. I've wrapped bars that had a lot of hard residue, but I've also cleaned bars first. It really depended on how I felt on the day that I did it (OCD or meh). At a minimum, scrape off any loose stuff.

sdmc530

I have sever OCD and when I re-wrap bars I am all in making them CLEAN. Here is my procedure.
1. remove old tape and pick off what I can
2. get a butane torch and burn off very carefully what left.
3. Use acetone/alcohol like solution to get all the residue off.
4. clean with whatever
5. new tape

I am sure I overdue this and its defiantly not necessary but I do this and I am at ease.
Wife says I am nuts, probably am

Iride01 

It might depend on what you wrap them with. If you use a very thin handlebar tape you might feel the roughness underneath. If you use a tape that depends on it's adhesive, then as a general rule, adhesive doesn't adhere well to adhesives.

However most handlebar wraps that I've used recently wouldn't have a problem with how clean the bars are before wrapped. It's what makes you feel good.

Le Mechanic

It depends a lot on what type wrap you're using as the others have said. If you're going full retro with some super thin cotton tape, those clumps will likely show through. Most modern handlebar wrap is pretty thick and it shouldn't be an issue at all. With all that being said, doing a quality wrap job is something a lot of DIY bike mechanics struggle with, many not even realizing it. I made a Youtube tutorial video about a year ago with some tips, tricks, and hacks that may be useful.

Miradaman

Thanks much to all for everyone's advice. Gave the handlebars one final scrub and even though some old adhesive still remained it was thin enough to be barely noticeable to the touch. Went ahead and wrapped the bars. Turned out OK for my first attempt. Not the best but certainly not the worst.