jPrichard10 

The Trek catalog shows some big changes in the 720 from year to year, but the one I can't seem to wrap my head around is the tubing. The 82 says it's built with Reynolds 531, 83 says 531C, 84 says 531ST main tubes and 531C rear triangle and 85 says 531C.

My confusion here is that 531ST is of course a heavier duty tubeset than "vanilla" 531, but I was under the impression that 531C was a lighter version (thinner walls? Short butt lengths?) than 531. As a fully loaded tourer, 531ST makes sense, but it seems that the 531C version would be quite noodley under a full pannier load?

Am I missing something about this? Was the 1983 version intended to actually be 531CS, or did the 531C mean something different than the 531C that all the super light race frames had?

And lastly, was the 82 720 specced with a heavier duty version of 531 than, say a 713 or other Trek 531 frame?

Obviously some questions for John Thompson, but if anyone else knows they can chime in too!

abdon 

Are you asking from a practical standpoint or just to satisfy a curiosity?

From a practical standpoint you would be splitting hairs something fierce. Frame stiffness matters most to racing, so unless you plan on racing a touring bike...

It is a bit of a noodle but that comes more from the looooong geometry than anything else. What I love about the derided noodlelyness is that the bike feels the best fully loaded while my other bikes start riding like crap after 40 pounds or so.

It is a truck, not a sports car. It is like complaining that an F150 doesn't corner as well as a Porsche

pwert

My '83 has been working great for 41 years for Triathalons and Sunday afternoon rides in the country. Leave the metalurgy to the experts and enjoy the ride.

jPrichard10 

Definitely more for curiosity. I prefer a noodlier ride, but I figured that an unloaded 720 would be quite stiff.

sd5782 

I would bet not stiff at all unloaded on that 82. I have an 83 700 in full 531 with the 531C sticker. Very pleasant and compliant ride. I have kept my eye out for a 720 thinking how it would just be even more compliant with the stretched out wheelbase. My thinking was “floaty”.

abdon 

You could not make a bike that long stiff even if you wanted to. And again; _touring_ bike; the fatter tires they sport would soak up the stiffness they don't have. As a steel frame they have the typical steel bounciness you expect and would want for the task at hand.

I seriously doubt anybody could tell the difference between the two frames and if by a miracle you could, up the tire size 2 millimeters and it will feel even more bouncy than the other.

rhm

+1. From 1983 to 1999 or so I had two bikes: a 1974 Raleigh Professional, and a 1982 Trek 720. I thought it would be interesting to see how they compared. But I never could tell any difference in the ride. I'm afraid I just don't weigh enough, or ride hard enough, to make either frame noodly. Or maybe I'm just not a very sensitive guy.

abdon 

That's not something a bike necessarily becomes when loaded.

When I was touring and bike commuting my main bikes were the trek 720 and a '71 Paramount. Overloading the paramount made it handle worse and worse, even feeling twitchy. The more weight I loaded on the 720 the more stable it felt.

By far it is a factor of the geometry not the particular steel. On the trek the longer wheelbase, relaxed angles, and generous fork trail makes it a way more stable platform for carrying weight. From there racks are designed to distribute the load better and it accept fatter tires for suspension and road contact

Chr0m0ly 

It's just marketing.
If you look at the butting specs it's all .8 .5. .8 Top Tube, 1.0 .7 1.0 Down Tube and .8 .5 Seat Tube, whether it's 531 531c or 531ST
You can check the first pages of the catalogs for tje butting specs on Vintage Trek dot com

bikingshearer 

I mostly agree, and certainly agree that a well-designed touring bike really comes into its own with a full load on board. My one quibble is that I think you do want a pretty stiff bottom bracket area on a loaded tourer. The long wheelbase (and especially long chainstays) are a must and that means a bit of give and less quick handling, which is okay because on a loaded tourer, straight line stability is very much your friend. (A full day of trying to keep criterium geometry on the straight and narrow? No thank you.) But that kind of flex is one thing, Flex coming from a noodley BB is something else.

abdon 

If this is a particular concern of yours there was a single year where the trek 620 had the exact same geometry than the 720. The difference between the two frames is that in the 720 both triangles are made of the lighter steel, the rear triangle of the 620 used the thicker/heavier/stiffer steel.

I have overloaded my 720 and it just rides beautifully.

RiddleOfSteel

Resident owner of a 1982 720 in the largest 25.5" size. 200 lb rider. This frame/bike is superb. Frame/fork/headset weight is 3,180g, which is a lot lighter than my '85 620 (same size and 47cm chain stays) which came in at 3,530g +/-. Both have excellent out-of-saddle response, but the 720 requires less tire to be as comfortable as the 620 (or conversely, the 620 needs more air volume to take the edge off bad roads than the 720). I have my '82 715 frameset that weighs 20g less than the 720 despite 3.5cm shorter chain stays. They both ride very similarly. I would think that all 720s would have a similarly beautiful ride and weigh within a few grams for a given size. The lugs on an '83 are the same as '82, and '85 720s are mostly '84s with '85 graphics (per production charts).

I'm not a loaded tourer/commuter kind of guy, and sure my 720 would probably be fine, but it is the best riding bike I've owned and is so as a bike, no racks, fenders or load. Dead stable tracking, beautiful turning, sublime out-of-saddle manners (which is important to me in judging the character and eagerness of a bike/frame), and as fast or faster than any race frames I own.

I look for '83s as I like the colors a lot plus the canti look is just cool. I think the most telling would be for frameset weights to be ascertained for a set size and compared. If they're super close, then it's probably going to be really good. Well, if A=B=C=D, A being 1982. Find any 720 and enjoy it, that is my best advice, because it will be easy to do!

Road Fan

Interesting! When I decided to send my Woodrup out for painting, I thought it would be nice to compare it with a 720! I finally found a 720 in my size, but it needs an alignment. So, still on hold!

nlerner

My understanding is that Reynolds started using the 531C designation in the early 80s when they introduced a couple of other variations, including 531P and 531 ST. In other words, 531C isn’t a lighter tube set, just “regular” 531 newly designated.