Stem length reduction equals more power?

[Xplora]

Hey champs,

Had my fastest ride in ever to work (45 minutes in 20.5 kms) after swapping the 115mm stem to a 90mm stem. Fresh legs, sure, but could the extra stretching be robbing me of that much power? I honestly didn't feel that quick, but I noticed I was pushing a gear or two higher than normal without much extra effort. I was definitely not pushing hard on the downhills because I'm not totally confident in my allen key skills and the stem or headset having an off day can ruin your year at 40kph in trraffic.

Anyways, could the stem really make that much difference? Back and neck felt better than normal as well, not straining anymore

[Nobody]

Find out what the wind direction and speed was that day if possible. May tell you more...

Eg:
http://www.seabreeze.com.au/graphs/nsw.asp

[sogood]

Fresh legs and traffic light sync can make big differences.

Otherwise the fit can definitely affect one's comfort and power production. But I doubt this completely applies in your situation.

[high_tea]

I agree that commute times aren't a great metric. Not demonstrably slower and more comfortable sounds like a win to me, though.

[Xplora]

4-5knots behind me wouldn't make up that much speed, but I don't check the wind speed most days

Over the distance there really isn't that much difference in the lights, I normally have to stop at a couple lights but it's not a major part of the trip. Just pure kms and hills slowing me down

[trailgumby]

Shorter stem will speed up steering response and place you in a slightly more upright riding position. This will be slightly less aero, but may be overcompensated for by better comfort allowing you to put out more power for longer.

The only way to tell for sure is to fit your bike to a power meter equipped trainer, get warmed up and see if the difference makes any change to wattage.

[Nobody]

4-5knots behind me wouldn't make up that much speed, but I don't check the wind speed most days

Over the distance there really isn't that much difference in the lights, I normally have to stop at a couple lights but it's not a major part of the trip. Just pure kms and hills slowing me down

If you want to know for sure, keep swapping the stem and do alternate testing.

[Rich-Ti]

Shorter stem will speed up steering response and place you in a slightly more upright riding position. This will be slightly less aero, but may be overcompensated for by better comfort allowing you to put out more power for longer.

Exactly.

Closing up the hip angle (i.e. using the longer stem) could be making you less efficient, despite actually being more aero. It all depends on the individual, your flexibility, limb lengths etc as to what works for one and doesn't for another, but it certainly sounds like opening up your hip angle (which the shorter stem will have achieved by making you sit more upright) may well suit you better.

[Xplora]

Just an update, I've actually noticed that the main benefit is less tired shoulders and neck, more than anything else. Confirms that I need my hoods angle changed because that is the main contributor to my hand stress it seems. Noticing it is much more comfortable in the drops as well, but I'm going to drop the bars an inch soon so maybe that will change LOL more aero, must be better

[trailgumby]

Take it easy for the first couple of weeks, that's a big change. Your body needs time to adapt.

[toolonglegs]

What happens then if one day you do a hard hour in the drops... Then next day you do a hard 1 hour climb on the tops... 10 cm different hand position.
IMO if 15 mm makes that big a difference you were probably stretched out too much. BUT arms and shoulders need conditioning as well... Too many variables with out a power meter or a long climb to test on. Commute times mean nothing... What if you had a rest and came back fitter after all?. 4 or 5 km tailwind would make an enormous difference etc.