A 58t Front Chainring Will NOT Make Me Faster on the Downhills

I'm changing my front triple (55/39/30) to a double (58/42).

In doing so I'm stepping smack into the middle of the mistaken conclusion of many that I'm doing so in order to exceed my current 54 mph max downhill speed. 

First, I can exceed the 54 mph max downhill speed already without changing my gearing.   Just don't use the brakes. 

What with the long, steep and straight descents out my way I spin out in my 55/11 combination at around 42 mph (that's about 111 rpm).  The difference between the 42 mph and 54 mph is solely due to a) angle of descent, b) minimal to zero crosswinds, c) good road quality. 

Second, a 58/11 combination will see me spinning out at around 46 - 54 mph.   

So why am I making the switch?

Short answer: because on the initial ascents and initial descents I will be able to apply power longer (maintain and accelerate speed) before I spin out. 

As it is with the 55t, when the conditions allow it, I spin out and am `stuck' at that speed,  having to `coast' down or up to the next ascent/descent.  I'm just a sack of flower on two wheels restrained by the limits of my pedal rpms. 

Why don't I `pedal faster?'  Because increased rpms generate instability, esp. if conditions are not just perfect. 

Explanation. 

On long, 4%+ descents, many casual/recreational cyclists can exceed 54 mph simply by not applying the brakes.  Especially if that casual cyclist has `ballast.'  (Ask a pro cyclist weighing 120 lbs how difficult it is to achieve and maintain descending speeds). 

I have kept my descending speed `down' to 54 mph simply because it is unneeded risk injected into a race by going faster.  Any extra distance gained by that added speed is lost very quickly at the next turn, when you have to slow down because of a pack of cyclists blocking the road ahead, or because of road conditions. 

When I am capable of consistently maintaining high speed (without spinning out) on initial ascents and initial descents (i.e., achieving `'54 mph' sooner and staying there longer) I accumulate additional distance over my competitors.  I get fast faster and stay fast longer because I can continue to apply power to the pedals at a manageable rpm. 

Example #1:

A cyclist will pass me (doing 58-60 mph) on a roller.  He then begins ascending the next hill/roller.  As gravity slows him down he applies power until he either reaches his power-to-weight maximum or he has to downshift. 

As I begin ascending that next hill/roller my 58t big ring allows me to apply power longer without spinning out, passing the other cyclist at a good rate of speed, adding cumulative distance that will be very difficult for the other cyclist to recover.  (Note: I have a very strong power to weight ratio; much better, longer, than most cyclists).

Example #2: 

I and another cyclist will be racing neck and neck as we reach the next descent.  As we both accelerate down the descent he will reach his `spinout' threshold (i.e., when he has to stop applying power and simply coasts) sooner.  Because I have a bigger (58t) front ring I will be able to apply power longer without spinning out.

Caveat:

There are many cyclists who are both capable and willing to pedal at a faster cadence, higher rpm, than me.  All things being equal, then, the advantage of my 58t ring will be reduced.