I recently got a new FS XC bike. The bars are 800mm wide, which is about five times wider than the ones on my 2008 26" FS bike, which has a long stem.

I am not what you would call an Enduro Bro.

Although I have owned mountain bikes since about 1992, I don't really feel like a competent mountain biker.

My instinct is to saw off about 50 to 100mm from each side of the bar, because my wrists hurt, but I also am reluctant to change stuff that would degrade a new bike with "Down Country" modern geometry. (The bike is a Cervelo ZFS-5, which is essentially a Pon clone of the SC Blur, trail version.)

How do I determine how wide the bars "should" be. (The distance from the nose of my saddle to the outer hand position is the same now as that from my saddle nose to the hoods on my drop bar all-road bike, which is custom-fitted, which maybe suggests I should leave it alone.)

Id probably ride em for a couple months see how you like em.

Ive settled on 740 in the desert, and 700 on tight forest trails

one thing to consider if you have a carbon bar

many carbon bars have a minimum recommended width … and some of those carbon bars have an insert or more material (increased wall thickness) at the ends

decades ago off road motorcyclists would find the ideal bar length by measuring spread of the hands when doing pushups … not sure if that is still a thing

years ago mtb bars were too narrow - now I see many that look too wide … ridiculously wide … but that’s just my opinion

I did see the recommendation for pushup stance width. However, I am far too weak to do a pushup.

The best advice I've had is to have the bar length just wide enough to have your elbows slightly bent when everything else feels comfortable. Probably ride a few times as suggested above and if you feel uncomfortable, slide the grips in 10 - 15mm and try again, then shorten if necessary. I wouldn't go below 700mm though.

Ride it for a little while before breaking out the hacksaw. If you do decide to trim the length, you may find that you will need to go with a longer stem.

Santa Cruz is also owned by PON now, they own a lot of stuff and do a lot of stuff well beyond just bikes and VW importing. Their bike portion of the business is huge for them in terms of importance but like a tiny little sliver of actual business despite is being so huge.

Go for some rides and get a feel. Then after some rides if needing to, maybe chop 5mm off every few rides until satisfied. I am sort of the same, coming from old stuff the bars were comically narrow and the stems comically long but after having so 780mm bars (uncut) it is excellent like so nice. It took a little adjustment but I was never really a huge enough mountain biker to have a memory but it certainly worked out well. I would also highly beyond highly recommend Ergon grips of any kind those are the best. I have the GS1s on my mountain bike and they are the best. If I wanted closer to round probably the GA2s would be the choice or GXRs for a pure round.

Give it some time. Also, if your grips and bar allow it you can run the brakes/shifter inbound with the grip and see how a "short" bar feels before you chop it. I ride bikes from 600mm(1987) to 780mm(2010-2016) bars.

This^^^

If your grips can’t slide inboard, get a set that are open on the end that can.

Big changes in width feel really off at first, but over the years, every time I’d go 20-30mm wider (total width) it felt a little
better. Went from 580mm bars in the 90s to 775mm around 2015 on my Trail bike and now the 750 on my fat bike feels a little narrow.

I took a few rides on a bike with 800mm bars and it feels OK, but not any better, so I am sticking with 770-780.

A lot depends on how much you want your elbows bent. My “neutral” riding position on the MTB has a lot of bend in my elbows (that is intentional) so wide bars feel very good.

~720mm is my sweet spot. 800 mm is just too wide unless you have ape arms.

Coming from the old school when 580mm was common, going to 640mm was a big change. I did trails and singletrack on the 640mm for a while and never felt lacking, but the modern 700mm+ bars had me curious. So when I built a flatbar road bike I went with 740mm because that's what the fixie kids ran, and it felt too wide to split lanes or ride in the city in general. So for commuting and flatbar gravel, I went down to 640mm which feels right to me. Now, I've got a set of 800mm bars on the hardtail and I'm mixed on it - it feels absurd riding on the road but it's natural on the trails, though I'm more nervous when passing others (hikers, other cyclists) or riding narrow singletrack. FWIW on my road bikes I run 42-44cm bars. I think at the end of the day, there's probably a wide tolerable range and your body will just get used to whatever width bar you choose.

It took me a long time to get used to the modern 780-800 bars I'm not convinced they're better but I'm used to them now

I didn't read any other previous replies. That said....unless you are 6ft 10in, 800mm bars on an XC bike is not typical. I was just watching some YouTube videos regarding handlebar rise and a couple of those referenced bar width. I high recommend you search there and watch a few. you will quickly see that bar width from 1990s bikes are irrelevant to modern bike geometry. I think the videos provide much more information than written descriptions, procedures, and recommendations.Bar is based on your own physiology and preferences for your riding.
Nope, I am not going to even state my own bar widths which vary on my two bikes.


here is one video to start you off... Joy of Bike - MOUNTAIN BIKE HANDLEBAR FORMULA | The Body to Bar ratio

Some of the best $$$ I've spent on a bike has been a "bike fit". As we get older, all sorts of things degrade and proper fit becomes more important. One of the things I found is the proper fit greatly reduced carpal tunnel related numbness in my hands.

When descending rough stuff do you ever struggle to keep the wheel pointed where you want? This is the sort of thing wide bars are helpful with and the reason why you see them so commonly on the enduro end of things. For XC and light trail (aka downcountry) riding, though, I bet this won't be an issue. My MTB has 110/130 travel and a 68 deg HTA - I ride Blues and some Blacks on it, but I'm not blasting through rock gardens at warp speed and don't need piles of steering leverage. 720mm is plenty for me.

Road or mountain?

Since my custom road bike is exactly fitted to me, do you know of any way to transfer that information from road to mountain bike setup? For example, does road reach and stack have any straightforward re-interpretation? Front-center? Saddle nose to stem/bar interface?

I had the fit done on my primary road bike.

To port over the fit, measure everything on the road bike that affects the fit (seat tube, seat post extension, crank length (add those together), top tube, stem length, distance from front of seat to center of handlebars, front axle center to center of stem.

Then try and duplicate that on the MTB. However, on the MTB you'll have a very different stance, whether you have a dropper seat post, etc., you will probably want some differences. I don't ride a MTB any longer, so I can't really give you specifics.

If you google "bicycle reach and reach+" you should find some help on this.

Thanks. I think I have done much of that (above), at least to first approximation, but will spend some more time with this shortly.

I very much appreciate everyone's advice. I just want to make sure I don't saw off too much too soon, so I am still in the experimental stages.

tl;dw:

height in cm x 4.4 = max bar width in mm

(771 mm for me)

That conventional wisdom was abandoned a while ago. The only thing that is transferable anymore is the bb-to-saddle distance (adjusted for crank length where applicable). New MTB geo (and approach to fit) has changed radically from the days when it took cues from Road.

Interesting. I’m 5’10” and that gives me 782mm which is pretty much what I like to use.

The guy in the video (Lee McCormack) is a proponent of the idea that what really matters for mountain bike fit is the angle he calls RAAD in the figure below:




https://ridelogic.bike

The saddle height, position, etc doesn't even enter into the calculation. (Enduro Bros don't sit.)

Lee has his fans and detractors in the MTB community.

I think it's mostly a matter of personal preference and what terrain you're riding. Despite having fairly broad shoulders, I don't particularly like really wide bars. For me, 780mm is my happy spot for my enduro bike and <730 for XC.

As you may remember, I've got the corporate cousin of your bike ('24 SC Blur TR.) I ended up at 730 on it...although I could see going even narrower on the right terrain. As it is right now, I'm able to run a very aero position for XC racing, without compromising my abilities in the technical sections. For what it's worth, I'm still running the stubby little stem that came on it.

I'm 6'1" on an XL Supercaliber. The bars started at 720, I cut them down to 700, and still naturally find my hands a cm or so in from the ends. I clipped a tree and crashed this past weekend, which makes me consider shortening them again.

Edit - just sanded them down to a shade over 690.