MASHing vs Spinning

Sure...Mash away.  Makes it easier for me to catch you on the run :P

In all honesty, you have to do what works best for you...But keep in mind that you do have a long run ahead of you and you may need some of the muscle that you mashed out on the ride. (coming from someone with skinny little legs who is jealous)

I don't know if this will be the same for you; my legs are not that large.

I found that if I stand up on hills much or do very much mashing I suffer on the run.  If I stay seated and always try to spin up the cadence my running legs are there for me when I need them.

I think everyone has a natural cadence which is the best to maintain.  I've tried spinning and mashing to see what works best for my run (which is horrible regardless of bike cadence) but for me a slightly lower cadence (80-85) works better in terms of my run being closer to a non-triathlon run time.  For reference, I am heavy and have large legs for an endurance athlete (ex-hockey player).

The idea that you have massive legs and that you should be mashing presumes that you are in the same gear or within a fixed gear ratio compared to a smaller competitor. Fact of the matter is that you are not using fixed gears. Because of this...you could be spinning at 90 RPM in a lower gear than someone next to you spinning at 90 RPM. What does this mean? It means that the size of your legs has nothing to with whether you mash or spin. Both riders are spinning at 90 RPM, however, one rider is producing more watts.

GREAT way to explain it.

You will find your natural cadence...just ride lots and it will come to you.

I went through a time a coach worked on increasing my cadence and if I did TTs often my cadence was 100-110. Worked with another coach who had me do low cadence work.

Guess what when no focus on cadence I've gone back to what I started with before coaches had me do different cadence work. Last couple years I don't really pay attention to my cadence just observe it from time to time.

I do know if I have same power output with various cadence the higher cadence option with same power will have higher HR, lower cadence same power lower HR often 15 rpm may lower HR 10-15 BPM.

I have large legs.

People have called my calves "cows."

The young guys at the LBS wonder if i have to have my jans custom made.

My racing cadence is 100-105rpm.

Just my n=1 to contradict yours.

The large legs don't change much for endurance riding. They don't seem to hurt/help that much. 

Higher cadence tends to work better for long distance riding. Without a powermeter and TT tests, it may not be apparent, but once you start doing tests showing the effects of mashing at 60-70rpm where you legs burn out before your cardio, you'll be surprised at the better overall speed you'll hold, particularly for distance requiring over an hour of riding.

Your big legs will certainly help a LOT for road cycling accelerations, sprints, and short distance racing including sprint triathlons. Your top speed will be better because of your large legs. I have ok but not top-level cardio, but genetically have had large legs which with zero weight training enabled me to leg press over 1000 lbs despite a bodyweight of 140-150ish. While I can still never hang with the top cyclists overall due to the endurance issue, I surprised a bunch of active Cat1 cyclists on a very short hillclimb in the beginning of a group ride where it's known to be a sprint to the top - immediately after the climb they were asking what team I rode for. (Which was very embarassing as I knew that the moment we had a hill that took >45 sec to climb, I'd be off the back of their pack.)

My big legs haven't really helped or hindered on those longer rides like I mentioned, but it does become less of an issue to even think of my top speed, whereas I commonly see guys with smaller legs asking if doing more leg presses will help (nope).

I think cadence is overemphasized, but there is a transition point of higher vs lower overall returns that can be found with testing for a particular distance. I don't think I'm too dissimilar from many in that I get higher avg TT speeds in a <20 minute TT by relying more on my leg strength at low cadence, whereas this approach totally fails me at 60+ mins. It's not a huge gap, but it's pretty obvious what went wrong when you look at the power curve dropoff post-workout on long workouts where I try to mash my way through it. 

Most of the top roadie TTers use a pretty high cadence in their TT races as well, excepting for the very steep sections. Doesn't mean it works for everyone of course, but I do think there's truth it the risk of more lactic acid to the legs if you start out with a very low cadence. 

60 is still pretty low - watch videos of most pro TTs from start to finish and they're going pretty fast. Again, not that that's the definitive way to go for everyone, but when a majority of guys are going 90+ at all distances, it suggests there's something to it. Chris Carmichael (Lance's coach) also makes a big point about training to spin at 90s, which is definitely debated, but 60s is pretty low for nonhill situations. I'm pretty sure Jordan Rapp isn't even in the mid 70s himself despite his 'lower' cadence.

Nope. Pro major-Tour cyclists average around 90 on the flats. There's significant representation in the spectrum (on flats) from about 80-100 for individuals' average cadence. Same holds true even if you look at the top-top pro cyclists.

This is even less true for pro triathletes, who tend to have lower average cadences than pro cyclists.

What brigby1 said about Jordan is pretty true of most top pro triathletes. To be fair, data showing that top pro triathletes' cadences average low 80s isn't on flats alone, but that actually doesn't change the fact that pro triathletes tend to have lower average cadences than pro cyclists.

I think the take-away lesson from all of that, as well as most of the posts here, is that people do have a wide range of sweet spots with regard to cadence.

I'm going both from my own testing and according to coach Chris Carmichael's philosophies. They're not ironclad and certainly debateable, but it's very clear by my own personal testing, whereas I learned through testing that my typical race strategy of going out at a lower cadence (probably a holdover from extensive hill work) led to a slightly higher speed for trials

I've watched a  good number of youtube TTs as well and am pretty impressed with how fast the guys spin out of the gate. I used to think upper 90s was brisk, but it's not uncommon for the pros, to be 100+ right out the getgo. 

I'm also fairly certain that my leg strength helps me a lot in not only road race sprints but also with sprint-distance racing. I'm not saying everyone should go out and lift weights -I totally agree that going out and riding more, with harder intervals, is the way to go, whereas weights are of minimal benefit in cycling. However, for guys with strong legs such as myself who don't need to lift weights to maintain that sort of sterngth, if your aerobic component isn't too far off, you can put up some good numbers not only in sprints but in shorter races. It's possible I'm just 'more gifted' at cycling than running, but for sure, my leg strength is the obvious difference in my case, as my running results despite running up to 100 mpw aren't suggestive of any particular special gifts.

Again, I don't think it's a magic formula for going faster, and I do think most of it is attributable to better pacing, but there are some pretty respected proponents (Chris Carmichael and L.A. being the main ones) who try and strive for higher 90+ cadence.

Sounds like we're exactly on the same page, then. 80-110 is exactly what I'd expect. 60s is low, and even 70s seems pretty low for an typical overall cadence in a tri bike leg. I also agree training can acclimate you to higher cadences. 

I don't think Carmicheal's idea of higher cadence is just marketing fluff - it's in pretty much every cycling book he's written, regardless of what Lance is involved with. Whether you buy into his philosophies is a different story, and he's definitely not the be-all-end-all, but I'm not coming up with this out of the blue, and he's definitely one of the most respected cycling coaches on the planet.