Chr0m0ly 

I’ve been digging around the Vintage Trek sight and noticed the Reynolds 531 used had an 8-5-8 top tube and a 10-7-10 down tube.
How does that change the dynamics when compared to the matching 9-6-9 top and down tubes used by Tange and Columbus and others?

T-Mar

Reynolds 531 was available in multiple gauges and builders could mix and match. Incorporating a heavier a gauge down tube generally stiffens up the BB (bottom bracket) region and decrease lateral flex for more efficient power transfer, especially when paired with heavier gauge chain stays. Using a lighter gauge top tube would offset the weight penalty of a heavier gauge down tube and add some compliance at the expense of some lose in torsional rigidity.

Bottom bracket stiffness became a topic of concern for many designers in the mid 1980s with improving road conditions. A lot of Italian builders had long employed an SL tubeset with SP gauge down tube and chain stays for heavier and/or more powerful riders. Bianchi's Superset frame designs used this same concept of heavier gauge down tube and chain stays, starting in 1984. Columbus officially addressed the situation by developing SLX ( and SPX), whereby helical ridges in the BB end of the down tube, seat tube and chain stays, increased BB stiffness with a minimal increase in weight. Japanese manufacturers such as Ishiwata responded with triple butted tubing, having thicker butts at the BB end to increase BB stiffness. Miyata would eventually go one step further by adding stiffening splines to the ends of their triple butted tubing.

Wildwood 

Without answering directly the 531 tube part, there are other factors - geometry, stays, fork - that complicate an objective answer.

SLX Merckx CorsaExtra 61cm versus SLX labeled DeRosa Pro 60cm of similar vintage +/- 1 year
Merckx rides like a cloud, DeRosa rides like a stage race bike.
DeRosa reportedly used SP as downtube, maybe just larger frames, combined with 'tuning' the fork by frame size.
The road feel difference (when using the same wheelset) is significant, but the geometry also varies.

edit: 80 Mondia Special (531SL) rides more 'lively' than '82 Holdsworth (db 531 main tubes) but that's not really an apples to apples comparison.

Chr0m0ly 

So it’s a fine tuning of the design aspect of using a larger diameter down tube than top tube, that makes sense. You need to counteract the twisting between the pull of the handlebar and the push on the crank arm.

And of course, every tubing manufacturer had their own proprietary (read “marketable”) way of working the same desire for BB stiffness.

I'd love to find a frame designed "pre-improving road conditions" for slogging through Chicago's always-under-construction infrastructure. (Or you know, just fit bigger tires)

T-Mar

It's a case of thicker/heavier gauge tubing, not larger diameter. Larger diameter tubes will also be stiffer but that came slightly later, with Masi's Volumetrica being the notable early adopter, circa 1984. When road designers took the cue of TIG welding and fillet brazing from the ATB designers, it opened the door to varying combinations of tube shapes and diameters, in order to more selectively increase stiffness and strength in certain areas and directions.

Edit: I neglected to mention one earlier version of tube shaping that could be used to increase stiffness with standard lugs. Some manufacturers would crimp longitudinal flutes into the tubes. Perhaps the most prominent practitioner of this technique was Colnago.

Chr0m0ly 

I thought standard vintage frames had OD 25.4 top tubes with OD 26.8 down and seat tubes?

T-Mar

Standard diameter imperial frames used 25,4mm (1") top tubes with 28.6mm (1-1/8") seat and down tubes. The easiest and most common method to increase stiffness in the BB region while employing standard diameter imperial tubing, is to employ a heavier gauge (i.e. thicker wall) down tube and seat chain stays.

verktyg 

Hesitant to question one of the most knowledgeable BF members but you mean heavier gauge chain stays not seat stays don't you?

Lateral stiffness across the bottom bracket to reduce side to side flex is one of the only areas on a frame where stiffness can be advantageous. Heavier gauge wall thickness down tubes and chain stays is an easy fix for the problem.

Also a really strong rider, say a sprinter can appreciate increased rigidity in the head tube area to reduce torsional flex that shows up mostly in the side to side motion of the bars at maximum output.

My first all Campy bike was a 60cm 1971 Gitane Super Corsa that I got new for $150. It had an extremely light frame and was so flexy across the bottom bracket that it ghost shifted every time I sprinted or climbed a hill. I was quite a masher back then which didn't help matters.

There were several possibilities:

1. The frame could have been made of one of the supper light Reynolds 531 tube sets with 0.5mm x 0.3mm wall thickness main tubes. It could happen... Back then bike manufacturers used whatever tubes they had handy.

2, The seat tube was brazed in upside down with the butted end at the top. It happened more often that most people realize during the bike boom.

3. They used a seat tube for the down tube and/or # 2, the main tubes were light gauge Reynold 531, say like 0.8mm x 0.5mm wall thickness.

After few months I found someone who wanted the frame and I traded it for a new 57cm Super Corsa frame. It was made with the standard 1.0mm x 0.7mm main tubes used in most Reynolds 531 production frames. That solved the ghost shifting problem.

To address the OPs question, many custom builders used tubing with wall thickness they thought best met the needs of the customer, regardless of the tubing brand.

All of the common tubing alloy steel tubing had the same strength so frequently the choice came down to the cost of the tubes! Later in the 1980's when the super alloy high strength steel tubes came out, they allowed for lighter frames because the wall thickness was thinner.

I'm currently putting together a new Ed Litton frame that I recently bought from him. He built it while back using a mix of Columbus SL and Tange Prestige tubing. It 's my size and I like the colors. Can't wait to ride it when the weather clears a little.



verktyg

T-Mar

Yes, I meant chain stays, not seat stays, thank-you. I don't know why I did this. At least all the stay references in my earlier post are correct. I'll go back and correct it.

Like yourself, I was a relatively big and strong rider, with sprinting being my forté. I never liked French frames. They were too flexy for me. The French did like lighter gauge gauge tubing. They were the only ones who used 531SL to any great extent. They also tended to design with slacker angles and slightly longer wheelbases. While all this will contribute to more flex, I've always considered the main culprit to be the metric standard tubing. Everything else being equal, the smaller diameter seat and down tubes will have a lower value for the section modulus and be less stiff. I calculated the differences for the various gauges of Reynolds 531 at one time and believe it came out to about 12-15%. The slightly larger diameter metric top tube should provide more torsional stiffness and better directional stability but it never quite seemed to make up for the deficiencies in the down tube and I found the steering could be a bit unpredictable when pushed hard.

Of course, there are a lot of riders who adore vintage French frames and their characteristics but they didn't suit my taste. This caused some friction with the owner of the LBS that I managed. He sponsored a local race and wanted me to compete on one of the store's brands, preferably a Peugeot or Gitane, which were our two best sellers at the time. However, I never competed on a store bicycle, let alone a French one.

T-Mar

I neglected to mention how much I like the Ed Litton. It certainly doesn't hurt that the livery is reminiscent of a mid-1980s Team Miyata. Nice choice. Enjoy!

Kuromori

For some reason Trek also insists 531c had a 1/7/1 DT. Reynolds 531 has pretty much always recommended a thinner top tube than downtube, but part of that may simply date back to the early days when they established their standard of 9/6/9 DT and 8/5(0.56)/8 TT. The TT is almost a 8/9 scaled down DT, and the wall to diameter ratio is around 1:45. However, Reynolds embraced this idea on most of their tubesets even when the top tube wasn't a scaled down downtube. The idea is to give greater rigidity between the HT/DT/BB, to give a more planted feel. This is something generally appreciated by stronger riders on larger frames, who tend to impart higher forces due to size, and frames tend to be less stiff because of size. Reynolds generally preferred a happy medium when it came to stiffness, but used the 8/5/8 and 1/7/1 pairing for 531ST(special tourist) to help solve handing issues with touring loads. Among bike designers, it's generally understood that a stiffer DT helps with responsive and precise handling (and some BB stiffness, but those concerned with BB stiffness also stiffened up the rear triangle), at least if the tube is thin enough to cause problems. The top tube is considered a safer place to shave weight, and also associated with "good" flex, although too thin a tube has been associated with proneness to shimmy. Good luck finding a consensus on exactly what mechanisms this works by except that is solves bad flex, but the idea is that the DT is associated with "good" stiffness, and the TT associated with "good" flex. It's a design trend that's still evident today. It's something a large rider on a large frame will notice more, but for people that don't have frame flex issues, it becomes increasingly difficult to determine what changes in feel are compared to geometry, subtle differences in fit, and tires etc.

Now if bike designers were serious about controlling flex on a standard size lugged downtube, they'd specify a straight gauge down tube because of the way springs with different K in series work. In fact, I believe Frank Brilando, chief engineer for Paramount, did this on larger frames, but he also had an obsession with stiffness, and Schwinn had their Schwinn reputation to live up to, so he specified thicker than normal tubes and standard top tubes were even thicker than their 1/7/1 top tubes at 1.2/8/1.2, intentionally stiffer than normal, and notably different from what was being supplied to many other American frame builders

Basically, it can help people with frame flex issues, but less likely to negatively affect liveliness, feel, weight, good flex, fairy magic and unicorn dust etc than using thicker tubes everywhere.

There were also Cantiflex tubes, an early attempt to stick oversize tubes into standard lugs.

If Daniel Rebour is a trusted source, then 0.3mm (which I'm pretty sure is actually 0.38mm given the way Reynolds does things and the fact that Rebour states the butts are 0.7mm thick and not 0.6mm) was special and rather uncommon and difficult to obtain. A flipped seat tube should be easily detectable by measuring the seatpost, and I wouldn't be surprised if the frame failed in short order. The bottom of the seat tube is a very common point of failure and a high stress area. The BB tries to bend the ST, instead of twisting like it does the DT, or twisting and compressing as it does to the CS. Also if Rebour is to be trusted, French 5/10 (0.56) tubes were 7/10 in the butts, and the French also apparently didn't follow the convention of regularly putting a thicker downtube in place. Apparently, in the French framebuilding world according to Rebour, Dupieux was running a very different operation in France, not just using metric diameters, but also stocking different standard gauges than what seemed to be recommended for the Anglophone world, and what was standard in France was apparently different than elsewhere.

drpaddle

Following on your mention of crimping tubes for stiffness, here is a photo of an old Express Werk German track bike that passed through my hands a few years ago. Note the crimped chainstays. More photos of the bike at: https://photos.app.goo.gl/fCvpo3uGaj4gATMq1.


Express Werk track bike with crimped chainstays

Chr0m0ly 

Thank you for the post!
My initial question about vintage Treks specifically was referring to my ‘83 720 in size 24” comparing to my ‘79 514 24”.
I took the 720 on a camping trip and it felt like the steering tube would flex back and forth when I had the bike loaded up. I hope it was from my overloading the rear panniers and not using front low riders, but I haven’t had a chance to experiment with different weighting concentrations.
Looking back through the catalogs I had to wonder if the 8 5 8 top tube might have played a factor, as the flex seemed to center at about the first brake cable guide on the top tube.
The feeling was that when I initiated a turn, to the left for instance, the bike wanted to go straight, and the front would go left, the top and down tube would flex slightly to right, and then it would all spring back into alignment as the turn continued.
I had moved all the heavy stuff to a handle bar bag, and I think that combo of overloaded rear rack, and heavy, high front load is the culprit, but like I said I need to try front low riders to make sure.

I wondered if either my ‘79 514 or ‘84 520, both having the same tube butting of 9 6 9 in the top and down tubes might have handled my poorly thought out load distribution better.