bike wheels question

depends on the frame size.  if it's on the smaller end, maybe not.

The main problem will be the brake mounting locations. With 2 different size wheels, there may not be enough adjustment in the brake pads to allow them to work on rims that the bike was not designed for.

Max

depends on how tall you are as well, I am only 5'6" and I ride 700 .

I guess that is not much help but there you go.

Roy

No expert here but for what is worth above average (5'9"+) should use 700c. Smaller stature persons could use smaller 650c for a slight gain in weight and rotational inertia but since they are not as popular as the 700c size, sometimes tires and tubes are harder to come by, etc. Bikes like Kestrel automatically maximize the "right" tire size for the frame size. Some tri bikes even use a small 650c up front and the larger 700c in back to "rake" the bike to get some wind economy and really get you down in a tri position. But then if you want to carry spares you need both sizes? I thought a frame is usually one size or the other. Looking at my bike, the brakes would have to have a huge reach (5cm?) to fit a smaller 650c wheel? To swith the front I would need to change the forks. Thus, NOT really interchagable. But that is my bike, maybe some out their could switch?

Also, I would stay away from tubulars (sew-ups) until you are more experienced racer (higher expense and maintenance). Thus, make sure you get "clinchers", the standard tube and tire setup. Also most decent bikes now are set-up with Presta valves, they are much skinnier and higher pressure than the tradition shroeder valves on most bikes, so you need a newer pump.

Goodluck. Lee

No, the frame is contructed for one or the other, but not both. My frame was originally only available for 650c so I had to have it custom built for 700c. You'll have to decide on wheel size before getting a particular bike/frame.

Cheers,
Scott