Classtime 

Do you have a regularly ridden go fast club ride or training bike with a lower and longer stem compared to your dedicated long distance bike? I'm very likely overthinking this but:

Is there any downside to doing most of my training rides of 100-130 miles on my regular road bike and then some training and a SR series on my Rando Bike with a stem 2-3 cm. shorter and 2-3 cm taller? I feel good with my standard road fit for long rides (100-130m) and used it on my 200ks and on a 300k a few years ago no problem. Raising the bars 3cm will shorten the reach some while using the same stem length. So I guess another way to ask my question is, "Do you lower the stem on your long distance bike when you do some shorter faster rides?"

unterhausen

I tried a 2 cm shorter stem and felt cramped. I think more people raise their stems. I'm not sure it helps comfort and slows me down, so I don't do it. Best to combat the causes of pain, i.e., do pushups and shoulder strengthening exercises.
I feel like the changes you propose are too radical. I suggest getting a riser stem and trying that first.

pdlamb

I wouldn't try changing bike fit this drastically for a single ride. If you think you want the bars closer or higher, change the stem now and see how it works in ordinary riding. If it's OK, keep it. Otherwise, change it back. Ride a long ride with what you know works.

79pmooney

I used to vary my stem height (always same quill stem and mo more than a cm change at a time) in my racing days. I started the season with the stem up around 1 1/2 cm. It gradually came down as the season went on. For criteriums when I was in form, it got slammed. Up about a cm for 4 hour races.

Now I do not race and have several bikes. I keep the reach roughly the same on all. (Fix gears get the position rotated forward, seat forward, stem longer and lower for the same reach and back/thigh angle but a more aero position for the inevitable slogs upwind in too high a gear.)

Classtime 

This bike will be set up for rides of 200, 300, 400, and 600k. Ordinary riding I can do on most any set up. What I try to do is keep all my bikes the same within 5mm with 5 cm drop.
So higher bars is what most LONG riders prefer and not necessarily shorter horizontal reach?

unterhausen

Some people probably change things and never tell anyone, so we can't know what they are doing. But putting in an extra spacer or two is all I ever hear of anyone doing. People have extra stems sitting around, you might be able to get one cheap in the classifieds here.

Classtime 

Thanks. I periodically obsess over fit and contemplating a 600k has me at it again. My intended randonneuse has got a quill stem with plenty of height adjustment.

Tourist in MSN

As I age, my stem moves up slightly. I think my stems are about 10 to 20 mm higher over the past decade. During that time my Dr records probably say that I have gotten about an inch shorter. I am 68. I try to setup my rando bike, road bike and touring bikes to the same fit.

Carbonfiberboy 

I ride my single with the slammed stem and proper reach no matter how long or short the ride is. On long rides, one thing I really don't want is to make them any harder, so I ride my fast bike. I do fitness work off the bike so things like my arms, shoulders, and back don't get more tired than my legs.

jbithaca

This might help you determine changes before you spend any money. Stem Comparison Tool | yojimg.net