Work (as most accurately measured in watts, but MPH will do) is work; 20 MPH is 20 MPH—wind, hills, resistance, and other factors aside— and it doesn’t matter if you’re doing it by mashing a big gear at 70 RPM or spinning a higher one at 110 RPM. I read somewhere that Lance Armstrong’s average cadence was about 110, and someone, I forget who, was quoted as saying that if Jan Ullrich had won more TdFs than everyone would be mashing big gears at low RPMs. You go with what works best for you.

That said, the generally accepted ideal running cadence is 180 RPM (90 RPM per foot) and if you are mashing a big gear somewhere below 90 RPM for multiple hours it is going to be more difficult to adjust to the optimum running cadence than if you’d been cranking out 90 or more RPM on the bike. Mashers will often downshift several miles out from T2 and start spinning in order to get that quick turnover feeling going in their legs. As in all things, there is a happy medium somewhere in the middle, you just have to find it, and/or (sometimes) create it.

As for big vs. small chain ring, I don’t understand why that would make a difference as the gearing in the middle of your cassette tends to overlap a little no matter what chain ring you are in. I have a 12/23 cassette and if I am riding the small chain ring on the 16 tooth cog, it is nearly (but not quite) identical to riding the 21 tooth cog in the big chain ring; and the 19 tooth cog in the big chain ring is identical to the 14 tooth cog in the small chain ring. But then again, I’m not a coach (http://www.cyclesportcoaching.com/Files/CUTraining10.pdf)

If one of your weaknesses is cycling in low resistance, high cadence spinning, you should do more of it!!! The more you do it the better you will improve your pedal stroke efficiency.

There is a school of thought that your cycling cadence, should equal your running cadence. From a nervous system perspective/neuromuscular junction activity level, having the same frequency of stimulus during both activities makes you feel "fresher". Try it! Do some bike work at a low cadence, then go run. Then do some bike work at a high cadence, and go for a run.

Off season I train at 95+, racing season around 90, for a race I'm right around 88-90. I do low cadence work as well. Big gears, big efforts @ 55-60.

Having the ability to do both, is an important aspect of your training, it will incorporate more muscle groups into the pedaling motions.

Lower cadence can also cause more frequent power spikes, due to terrain differences. Power spike destroy run splits.

Not much to really add here. Both VJ and Tao pretty much summed it up. I personally try to stay between 85-95 RPM. Any slower and as VJ says your more prone to power spikes and use more leg power to crank the arms. Any faster and I'm not using enough optimal power + I'm bouncing around all over the place. I range between 85-95 because my run cadence is 88. Cycling at 85-95 for 2-5 hours (70.3 or 140.6) has my legs on auto pilot for a good portion of the run before fatigue ever enters the equation.

Again, it all gets back to "history". You are wired to push big gears, at low cadence (typical skier profile). Big muscles are highly active during contractions. My wife has/had the same problem, it takes time, but it will come around.

Race what u train.
Sounds like u almost want to train one way and told to race another.
Sounds like receipe for disaster

I think everyone is different. I did a small ring workout yesterday, and finished about 10 minutes slower than the same workout from 2 days earlier. I find it difficult to keep 85+ cadence, and the legs burn when i pedal that fast. Joints are uncomfortable by the end of the ride as well. But on a positive note, running might be a possibility. I could tell that when I am in the small ring, and pedaling fast, I do not have to play with my gearing as much. Slight increases in resistance from hills and wind are mitigated by the fact that I was pedaling fast, and I didn't have to work quite as hard or gear down in order to get through the rough spot.
Theoretically, there are a couple different ways to go faster that I can think of off the top of my head. 1. Pedal faster. - if you are pedaling sub 90, probably the easiest way to coach an increase in speed, (unless you are a fatty, in which case, see #3)
2. Mash harder - probably would require additional muscle mass which would also increase weight
3. lose weight - less weight to push, unless you are skinny and you would have to lose muscle to get there.
4. get more aero - $$$ -

[quote=hamlet_cat]One of my weaknesses in cycling is low resistance, high cadence spinning. I find my legs fatigue quickly and it just doesn't feel efficient. So this year I have been adding some of these intervals into my training. However, I don't really know why ... My coach's response was this: "you should race in the lower gear because your legs will be fresher for the run." [/quote]

That's surprising. Usually a higher-cadence is less taxing on the legs; it's more work from a cardiovascular perspective, but it is supposed to "save your legs" for the run. However, now that I think about it and recall from your previous posts, you've described yourself as a small 5'3". I'd suspect that from a power-to-weight ratio perspective, it probably isn't that hard for you to move yourself along in the big chain ring (i.e., you don't need to use the small chain/high cadence). For most/many cyclists, especially larger males, higher cadence/low(er) resistance is still good advice. But if I recall from your skiing posts, aren't you around 100lbs/45kg? If so, at that size, you could go start-to-finish in the larger front chain ring with a 12X27 rear and have all options you'd ever need.