Been riding with a moderately fast recreational group on my old 25 lb. ten speed with steel frame that I converted to a 14 speed. Could consistently stay at the front of the pack, could outclimb everybody. Then I went and bought a new 30 speed, alum/carbon frame,ultegra components throughout, 18 lbs. weight. The only thing entry level is the wheelset, Shimano WH-R500. On the new bike I am really having trouble keeping up, especially on hills. The new bike is smaller, 50cm with 700X23c wheels as opposed to 54cm with 27"wheels, crank length is the same as the old bike. The new bike is smoother, lighter, shifts better, but it's slower and it's tearin' me up to drop a grand on a bike that I can beat with my 25 year old ten speed. I don't know anything about geometry or much about bikes in general. Any ideas?

Once one is used to riding a specific bicycle setup, even minor changes can effect a large performance alteration. In some cases, not only will performance be decreased, but overuse injuries may crop up quickly.

If you were comfortable (and fast) on your old bicycle, ideally the new bike will be set up in a similar manner. Some specific measurements to look for are:

1) Saddle setback from bottom bracket. If you have the same saddle on both bikes, this is easy. Drop a plumb bob from the nose of the saddle and measure the distance between this line and the bottom bracket axle. If you are using different saddles, you will have to figure out where your pelvis contacts the saddle and measure from that point.

2) Saddle height. Again, this is simple with the same saddle. Measure from the center of the bottom bracket to the top of the saddle (or to a saddle rail). If different saddles are used, you again will have to figure out where you sit on the saddle to determine actual height. Some people will suggest using a straight edge across the top of the saddle to help make this measurement.

3) Total length of top tube and stem. Measure from a standard point on the seat (note how to do this from the previous two points) to the center of the bars along the stem.

4) Drop between seat and bars. Measure from the floor to the top of the seat and to the top of the bars. Subtract.

These four measurements are by no means the only way to adjust the bikes to have similar feel. Differences in tube angles, bottom bracket height, wheels, tires, etc. may mean that the two bikes still ride differently, also. However, it should be a good starting basis to return to your previous ergonomics.

It could be just an adaption period, give it a little time, but obviously you'd want your new setup to match your old one. Also check your crank arm length.

SS

Going from a 54 to a 50 frame, you are on a much shorter top tube -- this is going to push you to a very modern competative posture, as opposed to the (probably) much more stretched out and traditional "french" posture of your old bike. And that is going to completely change the mechanics of your body.

Check out this great link on bike fitting:
http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

Note the styles of fit. Measure your body. Check out the measurements on your old bike. Check the sizes on the new bike.

Your old bike was almost certainly what they call the "French Fit" -- a more upright and stretched out style (a style I also tend to prefer, being an old fart). So it may be you have just wed yourself to too small a frame for the style you have adapted to over 25 years! If this is the case, try a larger frame. Set it up to the French style. Feel the difference. If you have been riding for 25 years, you are probably not going to be flexible enough to adapt to a fully modern "competitive" posture -- this is a posture for 25 year old guys, not guys who have been riding 25 years!