Moving to Narrower Road Bar - Need to Adjust Stem Length?

I’m looking at swapping out my current handlebar and stem (42cm, 110mm) and looking to switch to an integrated aerobar/stem combo. I’ve got an Emonda and the new Bontrager Aeolus RSL VR-C that is coming on the new Emonda looks like a great option.
It would also help me clean things up on my bike as I have a Di2 junction box sitting under my stem at the moment.

https://www.trekbikes.com/us/en_US/us/en_US/equipment/cycling-components/bike-handlebars-accessories/bike-handlebars/road-bike-handlebars/bontrager-aeolus-rsl-vr-c-handlebar-/-stem/p/601217/

Given the move to an aero bar, I was thinking of also going slightly narrower than the 42cm I’m currently using, perhaps down to 40cm. Would that necessitate any adjustment in stem length or should the small difference in width not have that great an impact?

Maybe, but you need to make sure you check the Bar Reach value and compare that within the equation.

Stem length change to bar width change is more common in MTB, since the bars are double the width and the impact of our arms at that angle is rather large. For road, the arms are more close to parallel, so a width change has less overall impact on Reach to the bars. I tend to think you may not need much stem length change unless you are making a large shift in bar width (assuming bar reach is identical).

Thanks Chad. I’ve been using a Bontrager XXX VR-C roadbar in 42cm. From what I can see it is 100mm reach on both this bar and the integrated RSL. Is this correct in your eyes?

  • That has 100mm Reach, 124mm Drop.

Seems to match between the two bars, so unless you feel cramped on the 42cm bars, I think the same stem length should work fine on the new ones.

Actually I’m wrong. The 42cm XXX VR-C road bar is only 85mm reach (I went outside and checked my bar…), so a shorter stem length might be needed with the RSL being 100mm reach.

Perhaps a 10 mm shorter length to compensate?

Yeah, at 15mm difference in reach (new being longer), I think 10mm shorter stem makes sense, along with the narrower spacing, should work well.

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i went 44 to 40 a few years ago and no issues; i’d start with same and see how you like it.

ps you’re gonna love it!

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