I’m building up my first Mtb. To keep the cost down I’m cannibalising by old bad boy for selected parts. At the moment it’s got an on one Mtb stem with a 25.4 funn riser. As I’m a novice I won’t be doing anything too radical in terms of riding so wondered if there is any issue with not having an oversize bar? Assume benefits for oversize are stiffness in more extreme conditions?

it’s fine

I have 25.4mm bars on my bikes. I’ve not found it a limiting factor so far.

Assume benefits for oversize are stiffness in more extreme conditions?

Not really no. (Maybe in those 800mm bars.)

Good quality stems are getting harder to find for 25.4. Which is a pain.

I’m fairly happy with my 25.4 set-up, but recently wanted to try something different. The problem is finding 25.4 bars particularly in the larger width. There’s just far fewer options, which is a pain.

You can use a shim to fit an OS stem and 25.4 bars.

Main reason to ‘go big’ is that oversize bars make it look like you’re much better at shredding the gnar.

I’ve got both fitted to different bikes. Can’t feel any difference when riding, tbh.

Just miss a step and get the new 35mm stuff (although I thunk it might actually be 34.9) It’s 30% faster you know.

Just kidding by the way. One inch stuff is fine

As above, nothing wrong with 25.4 bars and stems. I very recently upgraded to 31.8 for no better reason than I needed a new bar and stem at the same time (those that came on my bike were much too high rise for my personal taste) and it made sense to move to 31.8 as they are far more widely available than 25.4 these days.

If the 25.4 kit you have is in serviceable condition, then it will be fine.